Analysis, quantitative

Quantitative l3C NMR is desirable in two situations. First, in structural determinations, it is clearly useful to 

There are four reasons that broadband-decoupled nC spectra are usually not susceptible to quantitative analysis. 

Section 5.1) varies among the nC nuclei, and the signal intensities vary accordingly. 

The number of data points used to record the peak may not be sufficient to record the proper shape and area of the peak. 

The pulse consists of a central frequency (1 ) of maximum amplitude with frequencies of decreasing amplitude on both sides. Peaks resulting from these different pulse amplitudes vary in amplitude. 

To enable quantitative measurements to be made, the analyst requires the ability to determine the areas or heights of the detector responses of analyte(s) and any internal standard that may be present and then, from these figures, to derive the amount(s) of analyte(s) present in the unknown sample. The software provided with the mass spectrometer allows this to be done with a high degree of automation if the analyst so desires. 

As stated previously, the advantage of the mass spectrometer is that mass can be used as a discriminating feature and this may allow quantitative measurements to be made on unresolved components. 

The data considered above have been derived from a TIC trace, i.e. have been acquired from full scanning, but the same methodology is used for analysing 

Why is the sensitivity obtained when using reconstructed ion chromatograms (RICs) for quantitation less than that achieved when employing selected-ion monitoring (SIM) to monitor the same ions  

To answer this question, we must consider the ways in which the data are acquired. An RIC is generated, post-acquisition, from consecutive full scans in which a small amount of time is spent monitoring each ion, as discussed above. The data produced in a SIM experiment are generated by monitoring only a small number of ions, thus taking advantage of the increased time spent monitoring each ion. 

Qualitative analysis NMR is one of the most powerful methods available for determining the structure of molecules. It identifies the number and type of protons and carbon atoms in organic molecules, for example, distinguishes among aromatic, aliphatic, alcohols, and aldehydes. Most importantly, it also reveals the positions of the nuclei in the molecule relative to each other. For example, NMR will distinguish between CH3—CHj—CHjOH and CH3—CHOH CH3. It does not provide the MW of the compound. NMR is also applied to compounds containing heteroatoms such as sulfur, nitrogen, fluorine, phosphorus, and silicon. 

Quantitative analysis NMR is useful at % concentration levels, but trace levels (ppm) are becoming attainable with reasonable accuracy. 

Quantitative analysis IR is used routinely for the quantitative analysis of organic compounds, particularly at % concentration levels. It is used for liquid, solid, and gaseous samples. The related field of Raman spectroscopy complements IR. 

Qualitative analysis UV absorption can be used for identifying functional groups and the structures of molecules containing unsaturated bonds (it electrons), such as 

It does not indicate MW or give useful information on saturated bonds (a bonds). NMR and IR have almost entirely replaced UV absorption spectroscopy for organic compound identification. 

Quantitative analysis in the infrared region is based on considerations similar to those applied routinely in visible and ultraviolet spectrophotometry, namely, application of the Beer-Lambert law. The law states that at a given wavelength of light 

The Beer-Lambert law states that the absorbance, 4 is a linear function of the concentration of the absorbing substance, and there are many cases where this relationship holds true. An example is given in Figs. 4.1 and 4.2. However, linearity is not always observed. For cases in which a plot of absorbance versus concentration is not linear as a result of the association or dissociation of the sample, or interaction of the sample with the solvent, correction can be made by use of a calibration curve based on an experimental plot over the nonlinear region. Corrections can also be made by a change of solvent to reduce the association, dissociation, or interaction. Deviations from the law can also be caused by other factors, but use of the spectrometer under the proper operating conditions will frequently resolve such difficulties. 

In the case of gases proper adjustment of gas pressures will eliminate deviations due to a phenomenon known as pressure broadening, in which there are changes in the apparent absorbance values. 

The method of quantitative analysis which uses an internal standard has been referred to earlier in Chapter 3. Although this method has been used mainly for solid samples, Beyermann (1967) has determined the protein content of diluted aqueous solutions of a variety of proteins. He used the film from an evaporated solution and measured the intensity of the peptide band at 1538 cm and compared it to a thiocyanate band at 2041 cm Protein quantities larger than 5 fig were measured with a standard deviation of 15 %. 

The differential method is often used to analyze mixtures containing several substances. It requires that one match the absorbance of the sample against the reference in a double-beam spectrophotometer. If the mixture contains two or more substances that absorb at the same frequency, one can determine what part of the absorbance is due to any single component by preparing a reference containing all the components in the correct proportion except the one being studied. The preparation of several mixtures and references allows one to make a calibration chart of intensity versus concentration (Rao, 1963 Potts, 1963 Alpert et al., 1970), which is then applicable to the multicomponent system. 

Quantitative analysis of tanning products (raw materials and extracts) requires firstly rational sampling and then suitable preparation of the sample and solution, and includes mainly determinations of the total soluble matters, the tannins and non-tannins, water and insoluble substances.1 Other determinations sometimes made are those of the ash, sugar and sulphurous anhydride, and in industrial practice the specific gravity and colour of the solutions are often measured. 

The principal methods for the quantitative analysis of tanning materials are given below. 

Sampling—The samples for analysis should be taken from at least 5% of the casks, bags, baskets, lumps, etc., comprising the bulk, the following points being observed  

1 For these determinations and for the preliminary operations mentioned, the directions laid down by the International Association of Leather Trades Chemists are officially adopted in Europe. These specify also that the results should always represent the mean of two distinct and concordant analyses. The official methods used in America are those of the Association of Official Agricultural Chemists of the United States and of the American Leather Chemists Association and differ in some details from the European methods (see Allen s Commercial Organic Analysis, 1911, 4th edit., Vol. V, pp. 76 et seq.). 

If the extracts are partly dry and partly moist, the whole sample is weighed, allowed to dry completely at the ordinary temperature, powdered and again weighed, the loss of weight (moisture) being allowed for in the calculations. 

Quantitative analysis of a sample is essentially performed by determining its absorbance and comparing this with the infrared absorptivity a or the molar absorptivity e (see Table 7.2 and Sec. 7.3) of pure compounds. 

errors incurred in quantitative analysis by the infrared method include error in measurement of the 100% line, deviations from the Beer-Lambert law, error in the zero line and error in the measurement of %T. The effect of deviations from the Beer-Lambert law is such that one should try to work at values of %T greater than 407o for the most accurate results. 

If a double-beam spectrometer is used to analyze a multicomponent mixture, then it is possible to eliminate the spectrum of one or more of the components by putting the same amount of the component in the reference beam. In principle, one may cancel the spectrum of each component separately and successively, making it possible to analyze the mixture without overlapping bands. In practice, this is usually limited to three or fewer components. This procedure is useful if small amounts of impurities are to be determined. 

A danger in this approach is that strong absorbance in the reference beam can cause loss of servo power in the instrument and the production of erroneous spectra as the instrument tries to take the ratio of two very small signals. 

The analysis of a mixture by directly comparing a known with an unknown sample in a double-beam spectrophotometer is called differential analysis. When two or 

Quantitative phase analysis is used to determine the concentration of various phases that are present in a mixture after the identity of every phase has been established. Overall, the task may be quite complicated since several critical requirements and conditions should be met in order to achieve satisfactory accuracy of the analysis. 

Proper alignment, and especially calibration of the diffractometer are very important. Calibration should be performed by examining one or several different mixtures arranged from carefully prepared and well characterized materials. In general, any of the many available standard 

In addition to instrumental factors, specimen preparation and properties introduce several key features that may have a detrimental influence on the accuracy of quantitative phase analysis. Sample-related factors cannot be avoided completely, but their effects should be minimized as much as possible and/or accounted for in all calculations. The main problems in quantitative analysis, borne by the nature and form of the employed sample are as follows  

Several different methods of the quantitative analysis have been developed and extensively tested. They may be grouped into several broad categories, and the most commonly used approaches are described below. 

The absorption-diffraction method employs a standard intensity (7°m/) from a pure phase and the intensity of the same Bragg peak (/ ) observed in the mixture. The phase concentration in a mixture can be calculated by using King s equation  

As discussed in [1], precise quantitative results will be obtained when a stable isotope dilution assay (SIDA) is performed. In this procedure, stable isoto-pomers of the analytes are used as internal standards. Consequently, the major effort in the development of SIDA is the synthesis of the labelled standards since most of them are not commercially available. 

The majority of the more than 100 odorants (reviewed in [1]) synthesised for use as internal standards are labelled with deuterium. However, during the quantification procedure some deuterated odorants might undergo deuterium-protium exchange, which would falsify the results. Examples are 4-hydroxy-2,5-dimethyl-3(2H)-furanone (furaneol) [68, 69] and 3-hydroxy-4,5-dimethyl-2(5H)-furanone (sotolon) [70], which are consequently labelled with 

The precision of SIDA has been checked in model experiments [22]. Although after cleanup the yields of some analytes were lower than 10 %, the results of quantification were correct as the internal standards showed equal losses. 

As an example, the problem concerns quantitative determination of glucose in soft drink. The content can be expected to be in the 5gl range. The three procedures are as follows  

Content = internal standard amount x amount ratio = lOx 0.4 = 4gl 1 

The external standard method is the simplest one and should therefore only be used for simple analytical problems. The injection must be performed with good reproducibility thus it is recommended that the complete loop filling method be used (see Section 4.6). With multiple-point calibration it is not recommended to inject different volumes from a reference stock solution (e.g., 10, 20, 30, 40 and 50 pi) because it is well possible that neither accuracy nor precision of these injections are high enough. It is better to prepare a number of calibration solutions with different concentrations and to inject equal volumes of them (with complete loop filling or with exactly the same procedure as is used also for the sample). 

In the case of internal standard calibration this is not necessary and small variations in injection volume cease to be important. If sample preparation is complicated or demanding, the internal standard approach is strongly recommended. In this case the standard is added before the first preparation step has begun. The choice of a suitable internal standard may not be easy. It must be a pure, clearly defined compound with similar properties with respect to sample preparation, chromatographic separation and detection to the compound(s) of interest. If possible it should be eluted in a chromatogram gap and not at the very beginning or end. Examples can be found in Figs 11.2, 13.1, 13.2 and 21.4. 

Standard addition is elegant if the sample amount is not limited. It allows calibration of the analysis under realistic conditions, i.e. not with a standard 

This example will illustrate the quantitative analysis of aspirin (acetylsalicylic acid), phenacetin and caffeine in a mixture. The structures of these three are shown in Fig. 4.4a. 

Analgesic tablets often contain aspirin and caffeine, and we will eventually use the results for the quantitative analysis of a commercial tablet. 

These three are no problem to separate, they have been done on a variety of stationary phases, for instance ion exchange or reverse phase bonded silica. We will simply use a recipe, taken from the 

The obvious choice for detection is by uv absorbance. Fig. 4.4b shows the uv absorption spectra (from 300-225 nm) of the three compounds, made up in the mobile phase. 

Peak areas on the chromatogram were measured with an integrator. The integrator prints out the retention time for each peak, together with a number that is proportional to the peak area. 

Although it is necessary to mn a quantitative analysis at a signal-to-noise ratio of better than 10 (Section 6.1) an S/N ratio of 3 can be adequate for qualitative evaluation. 

The detector signal is much more dependent on specific compound properties in liquid chromatography than it is in gas chromatography. For example, the UV signal is a function of the molar absorptivity, which varies between 0 and 10 0001 mol cm depending on the compound used. The molar absorptivity and absorbance maximum also vary between homologues. Hence at least one calibration chromatogram must be obtained for each quantitative analysis.  

DIN 32633 Chemical analysis -Methods of standard addition - Procedure evaluation, Beuth, Berlin, 1998. 

The following sections deal with the quantitative analysis of the differential microstructural characteristics. 

Manipulated Inputs. Before delving into a detailed quantitative analysis, we need to identify the manipulated variables for these three different types of processes. As pointed out by Luyben, it is important to maintain stoichiometric balance for neat reactive distillation. Al-Arfaj and Luyben chose to use one of the feedrates. In this chapter the feed ratio is used as one manipulated variable. In addition to holding the stoichiometric balance, we need to control two product compositions using two manipulated variables. However, for reactions such asA + B C + D, if the conversion is properly maintained and the product flowrates are equally distributed, one-end composition control will do a fairly good job. 

Following Al-Arfaj and Luyben, for the type I flowsheet of MeAc production we chose to control the bottoms composition using vapor boilup while fixing the reflux ratio. 

Similar to the type II flowsheet, a decanter is used for the type III flowsheet to separate the water from the overhead condensate and therefore composition control is not necessary. The organic phase is totally refluxed back to the column. However, the bottoms acetate composition is controlled by changing the reboiler duty. Note that all of the control structures mentioned in this section use temperature control. In summary, the manipulated variables are 

Type I feed ratio and reboiler duty (fixed reflux ratio) 

Infrared spectroscopy can be used for quantitative as well as for qualitative analysis, although it does not have the quantitative accuracy of some other analytical techniques—e.g., gas chromatography. In most cases, however, it will do as well as or better than the desired performance on the required quantitative analysis, and frequently it is the only feasible way of doing the job. 

There are two approaches to quantitative analysis that can be used one where there are only a few samples and it is doubtful if any more of this type will be received the other where there is a series of samples which will arrive over an extended period of time. The method of attacking the problem is very different for each. The following sections of this chapter will outline ways in which these analyses can be accomplished and briefly discuss the various problems involved. 

As IR spectroscopy is a secondary method of analysis, the development of quantitative analysis methods requires calibration with a set of standards of known composition, prepared gravimetrically or analysed by a primary chemical method, to establish the relationship between IR band intensities and the compositional variable(s) of interest. Once a calibration has been developed, it can then be used for the prediction of unknowns, provided two general conditions are met i) the spectra of the unknowns are recorded under the same conditions as employed in the calibration step (i.e., same instrumental parameters, identical means of sample handling, etc.) and ii) the composition of the calibration standards is representative of that of the unknowns. 

An advantage that PTR-MS and the other techniques discussed in this chapter have over conventional analytical methods is that they are real-time techniques and can provide an immediate analysis of a sample. In PTR-MS for a reaction between HjO and an analyte M in an air sample, we have 

The reaction is a pseudo first-order reaction as [M] [HjO even when [M] is at trace levels in a sample. The rate equation may be ejqrressed as 

If it is assumed that only a small fraction of [H30 q is removed, then 

Substituting (8.42) into (8.41) and taking the first term of the Taylor expansion gives 

However, although PTR-MS is loosely based on estabhshed measurements of proton transfer rate coefficients these cannot be applied directly as an absolute method for quantification of an analyte because of the presence of the electric field in the drift mbe. For exothermic proton transfer, a reaction rate coefficient of 2 X 10 cm s is often used in PTR-MS to estimate trace analyte concentrations. However, the rate coefficients for proton transfer have been measured under thermal conditions (e.g., SIFT) and vary between 1 x 10 and 8 x 10 cm s. It is therefore necessary to resort to calibration proceditres using permeation mbes or calibrated mixtures of analytes at the operational field strength of the instrument to determine the absolute analyte concentration in a sample. 

The following discussion deals with the various steps necessary to develop a procedure for the quantitative analysis [1] of a compound. It is assumed that the chromatographic conditions for the separation of this compound have been set 

A quantitative analysis may be subdivided into the following individual steps  

Chemical analysis starts with the sampling procedure, which is aimed at obtaining a sample that represents the bulk composition. To ensure sample quality, only samples with a known and documented origin should be analyzed. For every single sample, it must be possible to reconstruct 

Depending on the purpose of the analysis, the origin of the sample, and the analytical method being used, regulations and directives are already in effect and standard procedures have been written up that describe and regulate sampling as well as the storage and preservation of samples [2-12]. The common practice 

Handbook of Ion Chromatography, Fourth EditioiL Joachim Weiss. 

Sample preparation Separation Detection Signal processing 

Handbook of Ion Chromatography, Third, Completely Revised and Enlarged Edition. Joachim Weiss Copyright 2004 WILEY-VCH Veriag GmbH Co. KGaA, Weinheim ISBN 3-527-28701-9 

Each of these techniques offers varying degrees of accuracy and precision so, it is important to understand their strengths and weaknesses to know which one will best meet the data quality objectives of the analysis. Let us look at each of these in greater detail. 

As in other more mature trace element techniques such as AA and ICP-OES, quantitative analysis in ICP-MS is the fundamental tool used to determine analyte concentrations in unknown samples. In this mode of operation, the instrument is calibrated by measuring the intensity for all elements of interest in a number of known calibration standards that represent a range of concentrations likely to be encountered in your unknown samples. When the full range of calibration standards and blank have been run, the software creates a calibration curve of the measured intensity versus concentration for each element in the standard solutions. Once calibration data are acquired, the unknown samples are analyzed by plotting the intensity of the elements of interest against the respective calibration curves. The software then calculates the concentrations for the analytes in the unknown samples. 

This type of calibration is often called external standardization and is usually used when there is very little difference between the matrix components in the standards and the samples. However, when it is difficult to closely match the matrix 

Practical Guide to ICP-MS A Tutorial for Beginners, Second Edition 

Infrared spectroscopy as a quantitative analytic tool varies widely from one laboratory to another, but high-resolution grating instruments considerably increase the scope and reliability of quantitative infrared analysis, which is 

The baseline method of quantitative analysis involves selecting an absorption band of the substance under analysis that does not fall too close to the bands of other matrix components. The value of the incident radiant energy Pq is obtained by drawing a straight line tangent to the spectral absorption curve at the position of the sample s absorption band. The transmittance P is measured at the point of maximum absorption. The value of log P(/P) is then plotted against eoncentration. 

Many possible errors are eliminated by the baseline method because the same cell is used for all determinations, all measurements are made at points on the spectrum sharply defined by the spectrum itself, so there is no dependence on wavelength settings. Using such ratios eliminates changes in instrument sensitivity, source intensity, or changes in adjustment of the optic system. 

The precision of absorbance measurements and the possibilities of storage and re-treatment of the spectra have favoured quantitative analysis by infrared. The method is widely used for the facility with which the absorption bands of a particular compound can be located even in a mixture and because efficient methods of statistical analysis are available for the near IR. However, the development of reliable ETIR instrumentation and strong computerized data-processing capabilities have greatly improved the performance of quantitative IR work. Thus, 

In the early ages of FTIR, some analysts considered that double beam dispersive instruments were preferable for quantitative analysis as they are the only ones to compare the intensities transmitted by the two pathways (of reference and sample) at the same instant. 

For solid samples dispersed in a KBr disc the thickness of which cannot be measured with precision, a compound is introduced as an internal standard (calcium carbonate, naphthalene, sodium nitrite), in an equal quantity to all of the standards as well as to the sample. 

For liquid and solutions, the absorbance measurements are carried out in cells of short optical path I to minimize absorption by the solvent, of which none are really transparent in this spectral domain. The uncertainty in the value of / is linked to the softness of the material used for the construction of cell windows. This means the periodic calibration of their optical path. 

The absorption bands in the near-IR originate from harmonics or combinations of the fundamental vibrations present in the mid-IR. 

We often want to know not only the identity of chemical elements but also their concentrations in a specimen. Thus, quantitative elemental analysis is often required. The concentrations of elements must relate to their peak intensities in the spectrum, similar to the relationship between weight fractions of crystalline phases and their peak intensities in the XRD spectrum. Chemical compositions should be calculated by comparing the ratios of integrated peak intensities among elements in the specimen. In general, the weight fraction (C) of an element in relation to the relative intensities of its peaks (Ir) is mainly affected by the instrument factor (K), and the matrix factor of specimen (M). 

The instrument factor K includes conditions of primary sources, the geometrical arrangement of specimen respect to radiation and detection, and detector characteristics. The matrix factor refers to the interactions among the elements in the specimen. 

There are three main matrix effects in XRF primary absorption, secondary absorption and secondary fluorescence. Primary absorption refers to the radiation that is absorbed on the beam s path to reach the atoms to be excited. Secondary absorption refers to absorption of fluorescent radiation from atoms that occur along its path inside the specimen to the detector. Secondary fluorescence refers to the fluorescent radiation from the atoms which are excited by the fluorescent radiation of atoms with a higher atomic number in the same specimen. This phenomenon is possible when energy of the primary fluorescent radiation from heavier atoms is sufficient to excite secondary fluorescence from lighter atoms in the specimen. The absorption effects reduce the intensity of characteristic X-ray lines in spectrum, while secondary fluorescence increases the intensity of lighter elements. The matrix factors of EDS analysis in an electron microscope (EM) are described later in Section 6.8. 

Specimen preparation conditions may also affect the relation between intensity and concentration, such as chemical homogeneity. For accurate quantitative analysis, either a standard sample of pure elements to be analyzed or a sample with similar composition to that of the specimen is needed to determine factors M and K in Equation 6.6 precisely. 

The following sections will briefly introduce the methods of quantitative analysis by XRF and EDS in EM, separately. There are differences in the factors affecting the analysis because EDS in EM uses an electron beam rather than X-rays as the primary source. 

Whenever possible, samples should be dissolved in the mobile phase to provide longest column life and maximum precision in quantitative analysis. The sample solvent must not have stronger eluting properties than the mobile phase, since this will result in wider peaks, and possibly in peak distortion. 

Samples of biological origin must be deproteinized before injection since, otherwise, proteins will precipitate on top of the column resulting in rapid destruction of the column. Precipitation of proteins may in most cases be accomplished by simple methods, e.g., addition of methanol, acetonitrile or whichever modifier is used in the chromatographic system, followed by removal of the precipitated proteins by centrifugation. Using this simple technique serum or urine samples can be injected without further purification onto columns in reversed phase systems. 

In biochemical analysis a reversed phase chromatographic system will often be the best choice, since such a system allows for the direct analysis of biological samples. If at all possible isocratic elution should be used, since isocratic systems are more stable than gradient elution systems, and give better reproducibility in quantitative analysis. Furthermore the necessity of solvent purity is not as strict in isocratic elution as in gradient elution, and less expensive equipment is needed. 

In many cases, however, the sample composition makes it necessary to use gradient elution in order to elute all compounds of interest within a reasonable time and with sufficient resolution. In gradient elution it is important to use very pure solvents since, otherwise, impurities from the solvents may accumulate on top of the column as the gradient runs with low solvent strength, to be eluted as interfering peaks as the solvent strength is increased. 

For reproducible retention times the gradient must be run in a reproducible fashion. The best way to accomplish this is to use a fixed delay between each gradient run. This does not necessarily mean that the column is in equilibrium with the mobile phase at the start of the run, and thus the chosen delay must be strictly adhered to. Another possibility is to ensure that the column is at equilibrium before each run, but this may often require a very long delay, perhaps hours, between each run. In order to obtain a reasonable throughput a short, fixed delay should thus be chosen. 

Properly controlling the different steps of the production process requires knowledge of the API concentration throughout the process (from the raw materials to the end product). The characteristics of the NIR spectrum require the use of multivariate calibration techniques in order to establish a quantitative relationship between the spectrum and the chemical (composition) and/or physical parameters (particle size, viscosity and density). 

Calibration is the process by which a mathematical model relating the response of the analytical instrument (a spectrophotometer in this case) to specific quantities of the samples is constructed. This can be done by using algorithms (usually based on least squares regression) capable of establishing an appropriate mathematical relation such as single absorbance vs. concentration (univariate calibration) or spectra vs. concentration (multivariate calibration). 

The calibration methods most frequently used to relate the property to be measured to the analytical signals acquired in NIR spectroscopy are MLR,59 60 principal component regression (PCR)61 and partial least-squares regression (PLSR).61 Most of the earliest quantitative applications of NIR spectroscopy were based on MLR because spectra were then recorded on filter instruments, which afforded measurements at a relatively small number of discrete wavelengths only. However, applications involving PCR and PLSR 

Quantitative infrared spectroscopy suffers certain disadvantages when compared with other analytical techniques and thus it tends to be confined to specialist applications. However, there are certain applications where it is used because it is cheaper or faster. The technique is often used for the analysis of one component of a mixture, particularly when the compounds in the mixture are alike chemically or haye very similar physical properties, e.g. structural isomers. In these cases, analysis by using ultraviolet/visible spectroscopy is difficult because the spectra of the components will be almost identical Chromatographic analysis may be of limited use because the separation of isomers, for example, is difficult to achieve. The infrared spectra of isomers are usually quite different in the fingerprint region. Another advantage of the infrared technique is that it is non-destructive and requires only a relatively small amount of sample. 

In this present chapter we will look at how infrared spectroscopy can be used for quantitative analysis. First, we will examine the various ways in which an infrared spectrum can be manipulated for analysis. We will also see how the Beer-Lambert law can be applied to the analysis of samples containing a number of different components. 

CNSL used in polymerisation with formaldehyde as for example in friction dusts may not require elaborate analysis. Nevertheless interest in the industrial chemical uses of phenolic lipids has led to a study of quantitative methods of analysis by a variety of chromatographic methods. For cashew phenols these were first based on GLC. Thus the (15 3), (15 2), (15 1) and (15 0) constituents of methyl anacardate, cardol and cardanol have been separated by GLC on PEGA columns (ref.206), the free phenols (anacardic acid as methyl anacardate) by GLC on SE30 (ref207) and the hydrogenated anf fully methylated phenols on Dexsil and PEGA columns (ref.208). A further number of stationary phases have been investigated 

Analytical chemistry deals with the determination of composition of materials—that is, the analysis of materials. The materials that one might analyze include air, water, food, hair, body fluids, pharmaceutical preparations, and so forth. The analysis of materials is divided into quahtative and quantitative analysis. Qualitative analysis involves the identification of substances or species present in a material. For instance, you might determine that a sample of water contains lead(II) ion. Quantitative anaiysis, which we will discuss in the last sections of this chapter, involves the determination of the amount of a substance or species present in a material. In a quantitative analysis, you might determine that the amount of lead(II) ion in a sample of water is 0.067 mg/L. 

A fundamental feature of the spectrophotometric analysis is that the absorbance is an additive function. The Lambert-Beer law states that absorbance is proportional to the number or molecules that absorb the radiation at each wavelength, and this principle is valid even for different absorbing species. This means that the absorbance of a mixture at a given wavelength is equal to the sum of the absorbance of each component of the sample at that wavelength and this is at the bases of all quantitative spectrophotometric methods. Very importantly, this is no longer the case when two or more of the present species interact or react with one another. 

The quantitative spectroscopic analysis methods can be divided in three classes that will be separately discussed hereafter. 

In the absence of interfering effects one would expect that the intensity of a fluorescent line from element A in the sample would be directly proportional to the atomic fraction of A present. But interfering effects do exist they are not trivial and the fluorescent intensity can depart widely from proportionality to the amount present. Examples are shown in Fig. 15-8 for three binary mixtures containing iron. These curves demonstrate that the fluorescent intensity from a given element depends markedly on the other element or elements present. 

Matrix absorption. As the composition of the sample changes, so does its absorption coefficient. As a result there are changes both in the absorption of the 

Enhancement (multiple excitation). If the primary radiation causes element B in the specimen to emit its characteristic radiation, of wavelength Ag, and if Ag is less than A. then fluorescent K radiation from A will be excited not only by the incident beam but also by fluorescent radiation from B. (This effect is evident in the Fe-Ni curve of Fig. 15-8. Ni Ka radiation can excite Fe Ka radiation, and the result is that the observed intensity of the Fe Ka radiation from an Fe-Ni alloy is closer to that for an Fe-Al alloy of the same iron content than one would expect from a simple comparison of the absorption coefficients of the two alloys. In the case of an Fe-Ag alloy, the observed Fe Ka intensity is much lower, even though Ag Ka can excite Fe Ka, because of the very large absorption in the specimen.) 

These effects so complicate the calculation of fluorescent intensities that quantitative analysis is usually performed on an empirical basis, i.e., by the use of standard samples of known composition. These samples need not cover the 0-100 percent range, as in Fig. 15-8, but only quite limited ranges, because the greatest use of fluorescent analysis is in control work, where a great many samples of approximately the same composition have to be analyzed to see if their composition falls within specified limits. Standard samples of known composition, established by wet chemical analysis, may be purchased from the National Bureau of Standards [15,2] or from various commerical sources [15.3]. 

Three methods are used for quantitative analysis calibration curves, empirical coefficients, and fundamental parameters. 

The intensity /k, (2 a) of a spectral emission line, i. e. the radiative recombination of an electron of a species A from a higher energy level k to the lower level i, is characteristic of a sputtered element or molecule A and is calculated by use of the equation  

Similar to other sputter-based techniques, a sensitivity factor can be determined  

Taking atomic sputtering into account the proportion of the particles emitted as molecules is negligible and the partial sputtering yield for element A in sputter equilibrium can be determined by use of  

Taking into account that E -a = f the bulk concentration of element A is given by  

If relative sensitivity factors are used, reference measurement of standard samples is not necessary. The ratio of two different elemental concentrations in one sample is given by  

The analyses which follow are arranged in the order in which they would be applied to a newly discovered substance, the estimation of the elements present and molecular weight deter-minations(f.e., determination of empirical and molecular formulae respectively) coming first, then the estimation of particular groups in the molecule, and finally the estimation of special classes of organic compounds. It should be noted, however, that this systematic order differs considerably from the order of experimental difficulty of the individual analyses. Consequently many of the later macro-analyses, such as the estimation of hydroxyl groups, acetyl groups, urea, etc. may well be undertaken by elementary students, while the earlier analyses, such as estimation of elements present in the molecule, should be reserved for more senior students. 

Principle. A known weight of the substance is heated with fuming nitric acid and silver nitrate in a sealed tube. The organic material is thus oxidised to carbon dioxide and water, whilst the halogen is converted quantitatively into the corresponding silver halide. The latter js subsequently washed out of the tube, filtered and weighed. 

The method is general for all organic halogen compounds and is the standard method for almost all such compounds, except of course 

Meanwhile, the organic compound can be prepared for analysis whilst the sealed end C (Fig. 72) of the Carius tube has been cooling dow n. For this purpose, thoroughly clean and dry a small tube, which is about 6 cm. long and 8-10 mm. w ide. Weigh it carefully, supporting it on the balance pan either by means of a small stand of aluminium foil, or by a short section of a perforated rubber stopper (Fig. 73 (A) and (B) respectively) alternatively the tube may be placed in a small beaker on the balance pan, or suspended above the pan by a small hooked wire girdle. 

Place in the tube sufficient organic compound to give subsequently about 0-3 g. of the silver halide, and weigh again. Now allow the small tube to slide carefully down the inclined Carius tube until it finally adopts the position shown in D (Fig. 72). If the compound readily loses halogen in the presence of nitric fumes, the Carius tube should first be rotated in an oblique position to wet the tube for about 10 cm. from the bottom the small tube, if cautiously inserted into the Carius tube, will now come to rest when it first reaches the wet portion of the tube and will thus be held above the main bulk of the acid until the tube is sealed. 

For a homogeneous binary sample using reference samples in the same instrument  

Not all samples consist of binary mixtures, and difficulties exist with the extension of the matrix factor approach to multi-component systems. 

If the composition of the outermost layer is different from that of the bulk (for example, as a result of surface or grain boundary segregation), a different approach has to be made. For example, if a partial overlayer of element A of fractional coverage 9a covers a substrate of element B, the spectrum contains three contributions that from the overlayer, that from the exposed part of the substrate, and that from the covered part of the substrate. 

A monolayer matrix factor QAB can be defined such that  

0 is the angle between the sample normal and the spectrometer axis. 

Peak-area or peak-height ratios are calculated for the analyte and IS and plotted against the ratios of known concentration of the analyte and IS. 

A quantitative procedure should be validated for selectivity, calibration model, stability, accuracy (bias, precision), linearity, and limit of quantification (LOQ). Additional 

Kochanowski. The Determination of A9-Tetrahydrocannabinol (9THC) and 11-nor-9-Carboxy-A9-Tetrahydrocannabinol (THCCOOH) in Blood and Urine Using Gas Chromatography Negative Ion Chemical Ionisation Mass Spectrometry (GC-MS-NCI), Chemical Analysis (Warsaw), 51, 2006. 

Marquet. Progress of Liquid Chromatography-Mass Spectrometry in Clinical and Forensic Toxicology, Therapeutic Drug Monitoring, 24, no. 2, (2002). 

Moffat, M. D. Osselton, and B. Widdop, (eds.) Clarke s Analysis of Drugs and Poisons, 3rd ed. London Pharmaceutical Press, 2004. 

Mirceski, S. Komorsky-Lovric, M. Lovric, Square-Wave Voltammetry doi 10.1007/978-3-540-73740-7, Springer 2008 

Compound Limit of detection/M The linear range/M Reference  

For the analysis of surface-active, electroactive organic compounds, the adsorptive stripping SWV was used. The method was applied to numerous analytes. Several of them are listed in Table 3.2. Some examples of metal complexes which were used for the quantitative analysis of metal ions by adsorptive 

The determination of the nitrogen content in different cereal grains represents a nice example 66,67). The flour of the grain was mixed with 10% of lithium fluoride. The relative integrals Fn and Ff obtained are now plotted against the nitrogen content CN determined by classical analytical techniques (Fig. 11). The bent slope of the curve can be easily explained even with a crude picture. The integral F is proportional to the intensity of the photoelectron beam /  

This intensity now depends on two factors the concentration CN of the nitrogen in the compound and the attenuation S by inelastic scattering  

In first approximation S should decrease with increasing nitrogen concentration  

The polymer systems are often complex. For example, crystalline and amorphous regions coexist in semi-crystalline polymers. Any physical or chemical treatment of a polymer will induce structural changes, the knowledge of which is essential for a better 

I is the intensity of radiation after passage through the sample, c is concentration of the component (g/1), d is the thickness of the sample cell in centimetre 

A calibration curve is prepared, using absorbance versus concentration plot, so that the concentration of the unknown component can be determined. But quantitative analysis for a complex system like vulcanised rubber or a blend of two or three components, is not possible. The use of computers with the FTIR spectrometer, increases the rapid scanning capability, data processing for analysis of chemical or physical structural changes in polymers as a function of time over the entire mid-IR frequency. 

Quantitative analysis of such complex systems by data processing of digitised spectra has been recently developed by Koenig and co-workers [30]. Koenig has developed several methods for quantitative analyses  

The UV microscope may also be used as a microphotometer in which the transmittance from selected areas of the image is measured directly. The light 

The image analysis of UV photomicrographs is carried out by means of a microdensitometer using an X-Y scanning stage or a TV camera. However, the absorbance value obtained may be influenced by the methods of film development or by unevenness of illumination. It is difficult to eliminate the latter completely from the optical system of a UV microscope. 

Computed values of mean absorbance and accumulated area of measurement. 

Another basic program for the Zeiss UMSP 80 is LAMBDA-SCAN, which is useful for spectral analysis. The light intensities at fixed wavelength intervals are measured automatically and printed out as a spectrum. The bandwidth can be precisely set to within 1 nm and the spectra corrected for the influence of ambient light. 

The Leitz UVM microscope photometer system comes also with the PLUG computer program for single value measurements, and the SPECTRA program for spectral measurements. However, the latest Leitz MPV 3 system is not designed for UV light and its use as a UV microscope photometer requires special accessories. 

There is an inherent instability in the ion trap detedor that makes indusion of an internal standard mandatory for reliable quantitation. In this way, prior to estimating 

To obtain structural information of an analyte and to be able to identify components in unknown samples, qualitative methods are required. 

The simplest qualitative analysis involves a comparison of the retention times between a chromatographic peak containing an unknown compound and peaks obtained for reference samples using more than one stationary phase. 

Often there is a need for structural identification of unknowns without available reference compounds and the identification can be done in connection with the chromatographic separation. One approach is to run measurements directly on-line using HPLC as the separation technique with UV-detection and monitoring at several wavelengths, but this is often not enough for safety identification. The last 15 years have seen a rapid development of combined liquid chromatography-mass spectrometry instrumentation, and this technique is the most valuable tool in qualitative analysis today (se below). In the absence of a reference compound some unknown substances e.g., isomers of the desired compound may require NMR for their definitive identification. 

In quantitive analysis the goal is to determine the exact amount of analyte molecules in a sample. Most often two different analytes of equal concentration give different detector responses in chromatography, therefore the detector responses must be measured for known concentrations of each analyte. A standard curve is a graph showing the detector response as a function of the analyte concentration in the sample. For quantification analysis, three 

The external standard calibration method is a simple but less precise method and should only be used when the sample preparation is simple and small or no instrumental variations are observed. The method is not suitable for use with complicated matrices but is often used in pharmaceutical product analysis characterized by simple matrices and easy sample preparation. To construct a standard curve, standard solutions containing known concentrations of the analyte must be prepared and a fixed volume injected into the column. The resulting areas or heights of the peaks in the chromatogram are measured and plotted versus the amount injected. Unknown samples are then prepared, injected and analyzed in exactly the same manner, and their concentrations are determined from the calibration plot. The term external standard calibration implies that the standards are analyzed in chromatographic runs that are separate from those of the unknown sample. 

The methods of quantitation and the criteria for precise and accurate determination for LC are similar to those used in GC, though there are a number of important differences. External standard calibration—i.e. where the detector response to a solution of known concentration is measured and then a calibration curve is constructed—is the recommended method for quantitation in LC. It is imperative that the linearity of detector response is confirmed over the concentration range of interest with standards prepared in a matrix similar to the sample. Table 6.2 details detector characteristics. The increased precision obtained compared to GC is attributable to the 

The internal standardisation technique actually increases the analytical error due to the measurement of two peak areas and should be reserved for samples undergoing pretreatment of pre- or post-column derivatisation to account for variable sample recovery or conversion. Quantitative analysis when applied to gradient elution systems affords reduced accuracy and precision due to the practical disadvantages of constancy of flow, reproducibility of gradient formation and solvent mixing-demixing. 

Assuming constant instrumental conditions, the intensity of an ion current is a measure of the quantity of a sample. To determine the absolute amount of a sample, the intensities of an ion signal from a sample and a standard must be compared. This may be achieved as follows  

The primary result of IR transmission spectroscopy is the transmittance of the cell plus sample, (It)/(Io). 

The absorbance is calculated as -logio (It)/(Io) and is equated with E C1, the molar absorption coefficient (E ) multiplied by the concentration (C) multiplied by the pathlength (1) through the liquid. This is the Beer-Lambert law. 

The absorbance is a measure of energy lost from the radiation beam solely because of absorption by the sample. The experimental absorbance is a measure of the energy lost because of absorption by the sample, plus the energy lost because of reflection from the interfaces of the cell plus the energy lost because of unexplained baseline errors. The energy lost because of unexplained baseline errors may be positive or negative. 

Quantification requires knowledge of the beam path through the sample. Hence, the sample often needs to be modified to allow for a known geometry. Spectral subtraction, least square regression analysis, PLS and spectral deconvolution are some of the spectroscopic techniques widely used to quantify constituents in a multicomponent sample. For almost any type of spectroscopic analysis, this is usually the first step. It is especially important for polymers given the variations in spectra for the same polymer due to molecular weight, conformation, crystallinity, sample preparation, age and sampling method. 

Anyway, let us first take a look at each of the methods of quantitation in greater detail. 

The within-image quantitation is more correctly described as the signal contribution of a certain constituent to the overall signal. The relative signal contribution over the global image signal can be expressed by sq (%) defined as 

Absolute quantitative information is a concept linked to multiset image analysis and requires, as calibration methods do, the presence of a set of standard images with known composition and a set of unknown images, the concentration ofwhich wants to be predicted. 

Several aspects are worth to be commented on (a) the representativeness of the average concentration value used in the calibration/prediction step, (b) the configuration of the multiset used for quantitative information, and (c) the ability to do predictions at a global level and at a pixel level. 

The configuration of the multiset used for the analysis may also affect the quality of the final results. Two aspects should be taken into account the kind of information introduced in the multiset, that is, the composition of the calibration images used and the architecture of the multisets used for the calibration/validation steps. 

Due to the principle of the conservation of energy and momentum, a kinematic-factor K can be extracted, which is the ratio between the energy of the detected particle ( /) and the energy of the incident particle ( 0), namely 

There are two independent reactions, A B and 2B —C. The complete rate equation for each reaction is given. Two material balances are required that, in general, will have to be solved simultaneously. The required material balances are nothing more than design equations for an ideal FFR, written for two different species. We can choose the two species for which to write the design equations. 

For this problem, choosing A and R simplifies the mathematics a bit. As we shall see, this choice permits the two design equations to be solved sequentially, rather than simultaneously, and the design equation for A can be solved analytically. 

The result of solving the two material balances is values for the concentrations of A and B at the specified space time of 40 min. The concentration of C then can be calculated from stoichiometry. 

Rather than starting with the design equations, as developed in Chapter 3, we will begin this problem by writing material balances for A and B in a PFR, for a constant-density system. This approach provides a more fundamental, and perhaps safer, starting point. 

Area = cross-secti ial area of reactor (4 ) Length = dZ. 

An aim of many applications of PTR-MS is to determine the absolute concentration of one or more trace volatile organic compounds (VOCs) in air. PTR-MS is, in principle, capable of determining absolute compound concentrations without recourse to instrument calibration. However, as detailed below, there are various sources of uncertainty which can make such non-calibrated determinations relatively unreliable. Consequently, for many applications some form of instrument calibration is at least desirable, and perhaps essential. 

This chapter deals with issues encountered when using PTR-MS as a quantitative technique. It starts by showing how the concentration of a gas constituent can be calculated from a PTR-MS measurement without calibration, and then moves on to consider why calibration can be important. The most commonly used methods for trace gas calibration are then described. The chapter closes with a discussion of the accuracy, precision and limit of detection for PTR-MS measurements. 

The simplicity of PTR-MS is embodied in Equation 1.10, which we repeat below  

According to this equation, it is possible to determine the absolute concentration of compound M if the ratio t(MH + )/t(H30 + ) is measured and the reaction time t and the rate coefficient k are known. In Section 4.4, we will consider some of the limitations arising from the application of Equation 4.1. However, in this short section our aim is to demonstrate how the concentration of compound M can be calculated from the acquired PTR-MS measurements. 

Proton Transfer Reaction Mass Spectrometry Principles and Applications, First Edition. Andrew M. Ellis and Christopher A. Mayhew. 2014 Andrew M. Ellis and Christopher A. Mayhew. Published 2014 by John Wiley Sons, Ltd. 

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I This formula shows that if quantitative analysis in the infrared is to be possible, it is necessary to know the coefficients a( i ), therefore, either to have the pure substance, or to be able to obtain them from the literature... 

The aim of this work which enter in a research project on NDT, is to conceive a system of aid for interpretation and taking decisions, on imperfections in metallic fusion welds, we have studied and tested several segmentation techniques based on the two approaches ( contour and regions ). A quantitative analysis will be applied to extract some relatives geometricals parameters. To the sight of these characteristics, a first classification will be possible. 

A quantitative analysis to extract some relative geometrical parameters will be applied. To the sight of these characteristics, a first classification will be possible. We proceed as follow ... 

The external reflection of infrared radiation can be used to characterize the thickness and orientation of adsorbates on metal surfaces. Buontempo and Rice [153-155] have recently extended this technique to molecules at dielectric surfaces, including Langmuir monolayers at the air-water interface. Analysis of the dichroic ratio, the ratio of reflectivity parallel to the plane of incidence (p-polarization) to that perpendicular to it (.r-polarization) allows evaluation of the molecular orientation in terms of a tilt angle and rotation around the backbone [153]. An example of the p-polarized reflection spectrum for stearyl alcohol is shown in Fig. IV-13. Unfortunately, quantitative analysis of the experimental measurements of the antisymmetric CH2 stretch for heneicosanol [153,155] stearly alcohol [154] and tetracosanoic [156] monolayers is made difflcult by the scatter in the IR peak heights. 

Many additional refinements have been made, primarily to take into account more aspects of the microscopic solvent structure, within the framework of diffiision models of bimolecular chemical reactions that encompass also many-body and dynamic effects, such as, for example, treatments based on kinetic theory [35]. One should keep in mind, however, that in many cases die practical value of these advanced theoretical models for a quantitative analysis or prediction of reaction rate data in solution may be limited. 

Examples that use Raman spectroscopy in the quantitative analysis of materials are enonnous. Technology that takes Raman based techniques outside the basic research laboratory has made these spectroscopies also available to industry and engineering. It is not possible here to recite even a small portion of applications. Instead we simply sketch one specific example. 

Beeman J W and Haller E E 1994 Ga Ge photooonduotor arrays—design oonsiderations and quantitative analysis of prototype single pixels Infra. Rhys. Technology 25 827-36... 

This text covers quantitative analysis by electron energy-loss spectroscopy in the electron microscope along with instrumentation and applicable electron-scattering theory. 

The quantitative analysis of the scattering profile in the high q range can be made by using the approach of Debye et aJ as in equation (B 1.9.52). As we assume tiiat the correlation fiinction y(r) has a simple exponential fomi y(r) = exp(-r/a ), where is the correlation length), the scattered intensity can be expressed as... 

The simplest use of an NMR spectnim, as with many other branches of spectroscopy, is for quantitative analysis. Furthennore, in NMR all nuclei of a given type have the same transition probability, so that their resonances may be readily compared. The area underneath each isolated peak in an NMR spectnim is proportional to the number of nuclei giving rise to that peak alone. It may be measured to 1% accuracy by digital integration of the NMR spectnim, followed by comparison with the area of a peak from an added standard. 

The tliree-line spectrum with a 15.6 G hyperfine reflects the interaction of the TEMPO radical with tire nitrogen nucleus (/ = 1) the benzophenone triplet caimot be observed because of its short relaxation times. The spectrum shows strong net emission with weak E/A multiplet polarization. Quantitative analysis of the spectrum was shown to match a theoretical model which described the size of the polarizations and their dependence on diffrision. 

In this section, we apply the phase-change rule and the loop method to some representative photochemical systems. The discussion is illustiative, no comprehensive coverage is intended. It is hoped that the examples are sufficient to help others in applying the method to other systems. This section is divided into two parts in the first, loops are constructed and a qualitative discussion of the photochemical consequences is presented. In the second, the method is used for an in-depth, quantitative analysis of one system—photolysis of 1,4-cyclohexadiene. 

Silver nitrate is used extensively in qualitative and quantitative analysis. 

Kubinyi H 1995. The Quantitative Analysis of Structure-Activity Relationships. In Wolff M E (Editor) Burger s Medicinal Chemistry and Drug Discovery. 5th Edition, Volume 1. New York, John Wiley Sons, pp. 497-571. 

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