Quantitation IR spectrometry

Molecular Weight Data. Molecular weight data for the total asphaltene and for asphaltene subfractions determined by vapor-pressure osmometry (VPO), low resolution MS, and quantitative IR spectrometry... 

Despite these enormous experimental difficulties, Berson and Pedersen accomplished the task, using trans-cyclopropane-l,2-d2. The synthesis was carried out as described in Section II. The analysis of cis-trans isomer ratios was effected by quantitative IR spectrometry, and the rotations were measured on the pure liquid cyclopropane in a specially designed cell. 

To test the proposed dissociation mechanism with (9-BBN)2, a detailed study is conducted using quantitative IR spectrometry [3]. (9-BBN)2 exhibits a very strong IR absorption at 1,570 cm" due to B-H bridges [4]. This method is convenient and more reliable and thus has an advantage over tedious GLC analyses. 

The hydroboration kinetics are studied by addition of alkenes to the solution of (9-BBN)j in the solvent maintained at 25 °C. The reaction mixtures are pumped through a sodium chloride IR cell. The rates of the disappearance of B-H bridges of (9-BBN)j at 1,570 cm are monitored by quantitative IR spectrometry. The absorbance is recorded on chart paper. 

The kinetic data obtained by quantitative IR spectrometry also reveal that for more reactive alkenes (cyclopentene, 2-methyl-1-pentene, 1-hexene, and 3,3-dimethyl-1-butene), the rate-determining step is the dissociation of the dimer, thereby showing first-order kinetics (Eq. 4.1). For the less reactive alkenes such as cyclohexene, the reaction of monomer also becomes the rate-determining step, and thus exhibits three-halves-order kinetics (Eq. 4.2 Table 4.6) [3], first order in cyclohexene, and half order in (9-BBN)j. For certain alkenes such as 2-methyl-2-butene and cis-3-hexene, neither of these two steps are a decisive ratedetermining step. Therefore, the reaction exhibits intermediate kinetic behavior between that of first-order and three-halves-order kinetics. 

The hydroboration of alkynes with (9-BBN)2 exhibits kinetics similar to those for the hydroboration of alkenes. The kinetics are studied (1) by pumping the reaction mixture through a sodium chloride IR cell and monitoring the disappearance of B-H bridges of (9-BBN)2 at 1,570 cm" by quantitative IR spectrometry [Ij and (2) by quenching the aliquots of the reaction mixture periodically with excess methanol and analyzing by GLC for residual alkyne. For the more... 

Molecular spectroscopic techniques have been widely used in pharmaceutical analysis for both qualitative (identification of chemical species) and quantitative purposes (determination of concentration of species in pharmaceutical preparations). In many cases, they constitute effective alternatives to chromatographic techniques as they provide results of comparable quality in a more simple and expeditious manner. The differential sensitivity and selectivity of spectroscopic techniques have so far dictated their specihc uses. While UV-vis spectroscopy has typically been used for quantitative analysis by virtue of its high sensitivity, infrared (IR) spectrometry has been employed mainly for the identihcation of chemical compounds on account of its high selectivity. The development and consolidation of spectroscopic techniques have been strongly influenced by additional factors such as the ease of sample preparation and the reproducibility of measurements, which have often dictated their use in quality control analyses of both raw materials and finished products. 

The problems and procedures for selecting variables for regression analysis can be illustrated by considering the use of near-IR spectrometry for quantitative analysis. Despite its widespread use in manufacturing and process industries, the underlying theory regarding specific spectral transitions... 

Table 16-1 gives the rough limits of each of the three regions. Measurements in the near-lR region are often made with photometers and spectrophotometers similar in design and components to the instruments described in earlier chapters for ultraviolet-visible spectrometry. The most important applications of this spectral region have been to the quantitative analvsis of industrial and agricultural materials and for process control. Applications of near-IR spectrometry are discussed in Section 17D. 

Modern IR spectrometry is a versatile tool that is applied to the qualitative and quantitative determination of molecular speries of all types. In this chapter we first focus on the. uses of mid-IR absorption and reflection spectrometry for structural investigations of molecular compounds, particularly organic compounds and species of interest in biochemistry. We then examine in less detail several of the other cqtplications of IR spectroscopy. 

Beer s Law shows mathematically, based on observed experimental facts, that there is a linear relationship between A and the concentration of an absorbing species if the path length and the wavelength of incident radiation are kept constant. This is an extremely important relationship in analytical spectroscopy. It forms the basis for the quantitative measurement of the concentration of an analyte in samples by quantitative measurement of the amount of absorbed radiation. The quantitative measurement of radiation intensity is called spectrometry. Beer s Law is used in all quantitative absorption spectrometry—IR absorption spectrometry, AAS, UV/VIS absorption spectrometry, and so on. 

Photopolymerization processes used to be difficult to measure quantitatively by conventional techniques such as dilatometry, UV spectrometry, IR spectrometry and gravimetry. Using a special TA apparatus one can determine the fractional conversion according to the measurement of the polymerization heat. The advantages of measuring the photochemical reaction heat are as follows (1) photopolymerization analysis can be carried out on the system with the photosensitive resin produced from multi-component compounds (2) film-shaped samples can be measured using a high-sensitivity apparatus and (3) kinetic analysis of the polymerization heat can be performed directly. 

L. Allen, Quantitative Determination of Carisoprodol, Phenacetin, and Caffeine in Tablets by Near-IR Spectrometry and Their Identification by TLC,... 

To reduce the complexity of using P-Tref to obtain calibration curves. Pigeon and Rudin [33] proposed an alternative technique using A-Tref and a dual IR spectrometry detector. The dual IR system proposed allowed them to measure both concentration and branching frequency as a function of elution temperature. The cahbration curve obtained by on-line dual IR spectrometry in A-Tref is identical to the one from P-Tref (Fig. 17). This eliminates the need to perform P-Tref on every sample and provides a fuUy quantitative Tref analysis. 

There are several disadvantages to quantitative analysis by IR spectrometry. Among these are the frequent nonadherence to Beer s law and the complexity of spectra. 

In contrast to mid-IR spectrometry, the most important uses of NIR radiation are for the routine quantitative determination of species, such as water, proteins, low-molecular-weight hydrocarbons, and fats, in products of the agricultural, food, petroleum, and chemical industries. Both diffuse-reflection and transmission measurements are used, although diffuse reflectance is by far the more widely used. 

Allen, L., Quantitative determination of carisoprodol, phenacetin, and caffeine in tablets by near-IR spectrometry and their identification by TLC. J. Pharm. ScL, 63 912-916 (1974). 

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