Infrared calibration curve

To use KBr discs for quantitative measurements it is best to employ an internal standard procedure in which a substance possessing a prominent isolated infrared absorption band is mixed with the potassium bromide. The substance most commonly used is potassium thiocyanate, KSCN, which is intimately mixed and ground to give a uniform concentration, usually 0.1-0.2 per cent, in the potassium bromide. A KBr/KSCN disc will give a characteristic absorption band at 2125 cm 1. Before quantitative measurements can be carried out it is necessary to prepare a calibration curve from a series of standards made using different amounts of the pure organic compound with the KBr/KSCN. A practical application of this is given in Section 19.9. 

It should be noted that the weighed amount of KBr/KSCN is constant and that although the problem of non-quantitative transfer of powder from the ball-mill grinder still exists it affects both the carrier and the organic compound equally. When the infrared spectra for the six discs have been obtained the calibration curve is prepared by plotting the ratio of the intensity of the selected... 

One cm3 of the reactant/product/catalyst mixture was sampled periodically during the reaction for the transmission infrared analysis (Nicolet Magna 550 Series II infrared spectrometer with a MCT detector). The concentrations of reactants and products were obtained by multiplying integrated absorbance of each species by its molar extinction coefficient. The molar extinction coefficient was determined from the slope of a calibration curve, a plot of the peak area versus the number of moles of the reagent in the IR cell. The reaction on each catalyst was repeated and the relative error for the carbamate yield measured by IR is within 5%. 

Near-infrared spectroscopy is quickly becoming a preferred technique for the quantitative identification of an active component within a formulated tablet. In addition, the same spectroscopic measurement can be used to determine water content since the combination band of water displays a fairly large absorption band in the near-IR. In one such study [41] the concentration of ceftazidime pentahydrate and water content in physical mixtures has been determined. Due to the ease of sample preparation, near-IR spectra were collected on 20 samples, and subsequent calibration curves were constructed for active ingredient and water content. An interesting aspect of this study was the determination that the calibration samples must be representative of the production process. When calibration curves were constructed from laboratory samples only, significant prediction errors were noted. When, however, calibration curves were constructed from laboratory and production samples, realistic prediction values were determined ( 5%). 

Polymer Structure. The reaction studied here is summarized in Equation 21. As shown in the experimental section, it is possible to prepare these polymers at various degrees of substitution. As the degree of substitution increases, the ratios of the infrared C=0/0H absorption peaks and the phenyl/aliphatic C-H absorption peaks increase in a linear manner (Table I). (It would be possible to determine the degree of substitution from such calibrated curves.) At the same time, the intensity of the OH band in the NMR spectra diminishes while a strong set of peaks due to the phenyl group forms. Elemental nitrogen analysis values for the modified polymers agree closely with the calculated values. In addition, the infrared spectra show the necessary carbamate N-H bands. These factors enable us to have confidence that the polymer structure is as shown in Equation 21. 

The use of a continuous GPC viscosity detector in conjunction with a DRI detector permits the quantitative determination of absolute molecular weight distribution in polymers. Furthermore, from this combination one can obtain Mark-Houwink parameters and the bulk intrinsic viscosity of a given polymer with a GPC calibration curve based only on polystyrene standards. Coupling these two detectors with ultraviolet and infrared detectors then will permit the concurrent determination of polymer composition as a function of molecular weight and... 

Differential thermal analysis was performed with the DuPont 900 differential thermal analyzer the heating rate was usually 10°C. per minute. To determine heats of reaction, the calorimeter attachment to the Du Pont instrument was employed. Planimeter determinations of peak areas were converted to heat values by using standard calibration curves. For the infrared spectra either a Beckman IR5A instrument or a Perkin Elmer 521 spectrophotometer with a Barnes Engineering temperature-controlled chamber, maintained dry, was used. Specimens for infrared were examined, respectively, as Nujol mulls on a NaCl prism or as finely divided powders, sandwiched between two AgCl plates. For x-ray diffraction studies, the acid-soap samples were enclosed in a fine capillary. Exposures were 1.5 hours in standard Norelco equipment with Cu Ko radiation. For powder patterns the specimen-to-film distance was 57.3 mm. and, for long-spacing determinations, 156 mm. 

The classical approach to the analysis of mixtures by use of infrared spectroscopy consists in identifying specific, strong bands that belong to a suspected component, obtain a pure spectrum of the suspected component, and then remove those in the spectrum of the mixture that are due to the identified compound. The process is repeated for the remaining bands in the mixture spectra. Once the component spectra are known for a mixture, a series of calibration curves is produced. These curves relate concentration to absorbance, using Beer s law. The concentration of the components of the mixture are then obtained by interpolation. The advantage of Fourier-transform, infrared spectroscopy is that components of a mixture may be... 

Analysis of oligomers for phenolic hydroxyl end groups was conducted by quantitative infrared spectroscopy. Hydroxyl absorbance at 3580 cm-1 was measured for a number of synthetic mixtures of bisphenol-A and bisphenol-A homopolycarbonate. A calibration curve for hydroxyl absorbance vs. weight percent hydroxyl end groups was constructed. Hydroxyl content of bisphenol-A oligomers was calculated from the calibration data. 

Air drawn through a vacuum pump into the gas cuvette of a nondispersive infrared spectrophotometer IR absorption by CO is measured using two parallel IR beams through sample and reference cell and a selective detector, detector signal amplified concentration of analyte determined from a calibration curve prepared from standard calibration gases (ASTM Method D 3162-91, 1993). 

Figure 34 Calibration curve for infrared band area versus hydrogen concentration.17...

In the spectroscopic method, the grafting percentages were evaluated with the aid of a calibration curve. The calibration was obtained by plotting the grafting percentages calculated on the basis of the percent in weight of polyacrylonitrile over that of bamboo versus the band intensity ratio between the nitrile absorption of polyacrylonitrile and the hydroxyl absorption of bamboo. For each calibration point, a certain given amount of polyacrylonitrile and bamboo were used and the KBr pellets were prepared quantitatively for infrared measurements. The infrared spectra were recorded on a Perkin-Elmer 580 infrared spectrophotometer in absorbance mode. Similar procedures were carried out to obtain the calibration curve for holocellulose-polyacryloni-trile copolymers. 

Experimental work has shown that the analysis of quartz in respirable dust by Infrared spectroscopy using a Multiple Internal Reflectance Accessory is a viable technique that is sensitive, accurate and simple to perform. Linearity of a calibration curve from 0 to 200 micrograms has been demonstrated. A detection limit of approximately ten micrograms of quartz was obtained. An accuracy of + 35% at a 95% confidence level was demonstrated by data obtained from participation in the NIOSH PAT Program. 

Near infrared (NIR) spectroscopy relies on the delivery of electromagnetic energy in the NIR band and then analyzing the transmittance or reflectance of this energy. The chemical specificity of the individual solvents can be determined, and by building calibration curves, the level of the solvent in the dryer mass can also be determined. 

The Beer-Lambert rules derived above (equation 7.3) apply equally to absorption of infrared radiation by molecules. Moreover, infrared absorption spectra possess an advantage over the more common ultraviolet absorption in the greater number of bands present. It is often possible to select an absorption band for each component of a mixture such that little or no interference occurs between them. For these reasons, infrared spectroscopy is often used quantitatively in the analytical laboratory to determine drug concentrations in solution. A calibration curve for the assay may be obtained (and Beer s law confirmed) by converting the printed spectrum... 

Figure 1. HPLC calibration curve for D, infrared detector.

Different characterization techniques were performed to establish the qualities of the block polymers containing e caprolactone. They included calibrated infrared (IR) determination of CL content, in-house gel permeation chromatography (GPC), GPC with univeral calibration curve, GPC equipped with low angle laser light scattering (LALLS/GFC), and Rheovlbron measurement of the transition temperatures. 

The temperature of solid specimens in the plasma was determined by means of an infrared radiation thermometer (Infrascope Model 3-1C00, Huggins Laboratories Inc., Sunnyvale, Calif.) attached to a chart recorder. This device employs a lead sulfide detector and suitable filters to permit remote measurement of 1.2 to 2.5/x radiation emitted by the specimen. Line filters and electrostatic shielding were employed to minimize interaction of the radiofrequency field with the infrared thermometer. To compensate for variations in emissivity and inhomogeneity in the optical field, empirical calibration curves were constructed based on measurements of new and partially oxidized graphite pellets in a con-... 

Biphenyl Fraction. The low molecular weight compounds, soluble in isooctane and hot methanol, were primarily biphenyl and o-, m-, and p-terphenyl. These products were identified by gas-liquid chromatography using a silicone gum rubber column (Figure 4) and a Carbowax 20M column with appropriate standards. The components were trapped and analyzed by infrared and NMR spectroscopy for confirmation. Biphenyl was present in sufficient quantity to be readily detected in the initial infrared spectrum and was isolated by sublimation. Quantitative data, obtained using the silicone column with appropriate calibration curves are presented in Table III. With the possible exception of biphenyl, the yields are very low considering the overall conversion noted. The o-, m-, and p-terphenyl ratio (1/0.4/1) indicates a preference for the para position beyond that expected for random attack. 

The ultimate development in the field of sample preparation is to eliminate it completely, that is, to make a chemical measurement directly without any sample pretreatment. This has been achieved with the application of chemometric near-infrared methods to direct analysis of pharmaceutical tablets and other pharmaceutical solids (74-77). Chemometrics is the use of mathematical and statistical correlation techniques to process instrumental data. Using these techniques, relatively raw analytical data can be converted to specific quantitative information. These methods have been most often used to treat near-infrared (NIR) data, but they can be applied to any instrumental measurement. Multiple linear regression or principal-component analysis is applied to direct absorbance spectra or to the mathematical derivatives of the spectra to define a calibration curve. These methods are considered secondary methods and must be calibrated using data from a primary method such as HPLC, and the calibration material must be manufactured using an equivalent process to the subject test material. However, once the calibration is done, it does not need to be repeated before each analysis. 

Qualitative evaluation of the Raman spectrograms proceeds in the same way as was shown for infrared spectroscopy. On the other hand, quantitative evaluation in Raman spectroscopy is executed by using calibration curves or tables that are usually supplied with a given spectrometer in the form of software for the evaluating computer. 

Consult your instructor on the proper operation of your instrument. Handle the infrared cell carefully, avoiding contact with water and the fingers. Fill the cell with pure m-xylene and obtain a spectrum on this from 2 to 15 p,m, being sure to record the last peak just before 15 pm (692 cm" )- Each time you run a sample, be sure to check 0% T by placing a card in the sample beam and adjust the pen to 0% T. Empty the cell, rinse and fill with p-xylene, and run a spectrum on this. Repeat for o-xylene. Run spectra on each of the standard mixtures. From the spectra of the pure substances, choose a peak of each isomer to measure. Using the baseline method (see Figure 16.11), measure PqIP for the peak for each compound. Prepare a calibration curve of the ratio of og PJP) J og PolP ri,o and of log(Po/P)para/ log(Po/E)ortho versus concentration for the meta and para isomers, respectively. See Chapter 20 and your CD for spreadsheet preparation using an internal standard. 

Fourier transform infrared spectroscopy was also used to determine the chain end functionality. To determine the hydroxyl functionality, neopentyl alcohol was used to construct a calibration curve. The dissociated 0-H stretching vibration appears at 3643 cm as shown in Figure 5. The calibration curve for the methoxycarbonyl end group was obtained with the MHMDPO model compound, which showed Ae C=0 stretching vibration at the same wavenumber, 1720 cm". The results are summarized in Table I. 

The infrared spectra give the ratio between ionized and nonionized carbocylic groups versus the TEA/OLA ratio. Figure 6, using a calibration curve from the sodium octanoate/octanoic acid system (15) to transfer IR intensities to concentrations. These bands were but little influenced by the addition of glycerol. Figure 7. 

Ideally, the intensity (/o) of infrared radiation incident upon a sample cell is reduced (to f) by the absorption of the samples. Actually, some of the incident energy is scattered by the sample and this scattered energy makes the Beer-Lambert law inaccurate, especially at high values of absorbance [4]. The baseline method for quantitative analysis is an empirical method used to establish a calibration curve of log (/q//) versus concentration. Infrared absorption bands may overlap neighboring bands or may appear on a sloping background, so transmittance is measured in practice as shown in Figure 8.13. The absorbance. A, is determined from measurements of / and 7o, then a calibration curve of absorbance versus concentration is plotted. 

High-molecular-weight aliphatic amines are used extensively in many industries. The total primary- and secondary-amine content of aliphatic amines can be determined easily and rapidly by functional-group analysis in the near infrared [9], using chloroform solvent and 5-cm fused-silica cells. Primary amines have characteristic absorption maxima at 2.02 /um and 1.55 m, whereas secondary amines absorb only at 1.55 fim. Quantitation is achieved by the calibration-curve method using a series of standard solutions of primary and of secondary amines. Most other methods for the determination of total primary, secondary, or tertiary amine in a mixture are lengthy or inaccurate, or are unsuitable for small samples. 

By using Eq. (9) as a calibration curve Fritzsche was able to determine the G-C content of deuterated DNA films by measuring the infrared spectra in the region 1400 to 1600 cm On the average, he found the difference between the g-c values determined by conventional methods and those calculated from the infrared absorption by Eq. (9) not to exceed the limits of 2 mole % G-C. 

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