Quantitative infrared spectroscopic analysis

Quantitative infrared spectroscopic analysis can be carried out on blood serum to determine the relative amounts of lipid that are present. Triglycerides, phospholipids and cholesteryl esters are the classes of lipid which occur in blood serum. These compounds occur naturally in concentrations which make infrared analysis attractive, and the necessary preliminary separation is simple. These classes of compounds can be characterised using infrared spectroscopy by their carbonyl bands. The peak maxima are as follows ... 

W. Kimmer, Quantitative Infrared Spectroscopic Analysis of Multicomponent Systems, Jena Rev, 50, 5, 166-170, 1960. 

Analysis for the purpose of accurately determining the quantity of a chemical species existing in a sample is called quantitative analysis. Quantitative infrared spectroscopic analysis mainly deals with the intensity of an infrared absorption band. In this chapter, basic aspects of quantitative spectroscopic infrared analysis for a target substance (the analyte) in solution samples are described. The subjects to be described include the characteristics of a Fourier transform infrared (FT-IR) spectrometer, the relation between percentage transmittance and absorbance, Lambert-Beer s law on the relationship between the intensity of an infrared band and the concentration of a sample, the use of a working curve in quantitative analysis, and the origins of deviations from Lambert-Beer s law. 

Quantitative infrared spectroscopic analysis is based on Beer s law that directly relates the concentration of an analyte (target of analysis) in a sample solution with the intensity (in absorbance) of an absorption band of the analyte [1], As Beer s law, which can be derived from Maxwell s equations, is physically established, a reliable model for quantitative analysis can be built on it. 

In addition to these problems in applying the single-band method to quantitative infrared spectroscopic analysis, the single-band method is not suitable for determining the molar ratios of two or more substances existing in a sample. The single-band method, which depends only on the selected key band, does not utilize all the other bands in the observed infrared spectrum. Thus, it is reasonable to seek an alternative method that makes the optimum use of an entire infrared absorption spectrum for quantitative analysis. 

Chemometrics [2-6], a suite of the multivariate data analyses techniques, has been developed to overcome the hmitations of the single-band method. These techniques utilize all the infrared absorption bands over a wide wavenumber region as multivariate data for quantitative analysis, and can handle multicomponent samples simultaneously. In other words, the methods of chemometrics in quantitative infrared spectroscopic analysis are mathematical procedures to apply the concept of Beer s law to various problems in order to extract from them as much usefiil information as possible. In this chapter, the term spectroscopic calibration or just calibration is used to represent such procedures. 

By expressing spectral information and component data as vectors, all the scalar parameters in Beer s law are now replaced by a matrix equation A = CK. This relation can accommodate any number of chemical components by altering the matrix size. The matrix formulation is thus the basis for quantitative infrared spectroscopic analysis. In practice, however, this equation does not hold strictly, because most of the observed data contain uncertain factors such as noise. To remove the uncertain factors from A, a matrix composed of the uncertain factors is introduced. This matrix, which is denoted by R, is called the residual matrix (or error matrix). Then, the equation is rewritten as... 

Imaging studies were done on copolymers prepared by the polymer modification route because of the availability of the precursor polymers of various molecular weights. The protected copolymers were compounded with triphenylsulfonium hexafluoroantimonate (13% w/w) in cyclohexanone. One micron thick films were spin coated on NaCl plates, baked at 140°C for 5 minutes to expel solvent and then subjected to infrared spectroscopic analysis before and after exposure. Exposure to 18 mJ/cm2 at 254 nm caused no change in the infrared spectrum. However, when the films were baked at 140°C for 120 sec. following exposure, deprotection was quantitative based on loss of the characteristic carbonate C = O absorption and... 

The various problems connected with the use of infrared spectroscopy in pesticide research have been reviewed by Frehse (1963). The paper dealt with qualitative and quantitative analysis, determinations of residues, and special problems such as methods of extraction, cells, solvents, and measuring attachments to be used. Frehse has given many references to the literature concerning the infrared spectroscopic analysis of various food crops for pesticides, e.g., aldrin, alodan, chlorbenside, DDT, dieldrin, endrin, ethion, lindane, malathion, tedion, endosulfan, biphenyl, captan, pentachloronitrobenzene, 2,4-DB, MCPB, and methylisothiocyanate. The infrared band(s) used for the determinations have also been given. 

An early compilation of established quantitative infrared polymer/additive methods was published [164] no update seems to be available. Various reviews on quantitative (surface) IR analysis have appeared [18,130,159,165,166,166a]. Several textbooks discuss basic considerations concerning quantitative analysis by vibrational spectroscopy [167-169]. Data processing techniques for quantitative analysis are covered by Koenig [170], in particular regarding theory and application of FTIR to the characterisation of polymers. Hummel [171] has also discussed quantitative IR spectroscopic analysis of additives. 

Perhaps the most revolutionary development has been the application of on-line mass spectroscopic detection for compositional analysis. Polymer composition can be inferred from column retention time or from viscometric and other indirect detection methods, but mass spectroscopy has reduced much of the ambiguity associated with that process. Quantitation of end groups and of co-polymer composition can now be accomplished directly through mass spectroscopy. Mass spectroscopy is particularly well suited as an on-line GPC technique, since common GPC solvents interfere with other on-line detectors, including UV-VIS absorbance, nuclear magnetic resonance and infrared spectroscopic detectors. By contrast, common GPC solvents are readily adaptable to mass spectroscopic interfaces. No detection technique offers a combination of universality of analyte detection, specificity of information, and ease of use comparable to that of mass spectroscopy. 

Two infrared absorption methods (i.e., FTIR) and a Raman spectroscopic method were used to quantify polymorphic clopidogrel bisulfate Form-I and Form-II [16,17]. In addition, qualitative analysis of these polymorphs was also conducted using FTIR [16], where each sample was scanned over in the spectral region of 450-4000 cm-1 at a resolution of 4 cm-1. The sampling procedure used KBr pellets, loaded to contain approximately 3% of analyte. It was found that absorption bands associated with C-Fl and C-O bonds were stronger for Form-II relative to Form-I, and that unique absorption bands for Form-I and Form-II were observed at 841 and 1029 cm-1, respectively. These absorption bands were reported to be useful in the quantitative or qualitative analysis of clopidogrel polymorphs. 

In contrast to the well-known difficulties of traditionally applied quantitative IR spectroscopy of mixtures in solid (powdered) samples, the near-infrared reflectance analysis (NIRA) technique [32] has gained importance over the last decade and can now be implemented on a variety of commercially available Instruments In a number of applications to Industrial, agricultural and pharmaceutical analyses. Both the NIRA instruments equipped with grating monochromators and those fitted with filter systems feature built—In microprocessors with software suited to the Intrinsic characteristics of this spectroscopic alternative. Filter Instruments generate raw optical data for only a few wave-... 

Abstract Spectroscopic methods such as NIR, Fourier transform infrared, and Raman are becoming increasing important in pharmaceutical research and manufacturing. This chapter reviews both quantitative and qualitative applications of spectroscopic analysis for pharmaceutical products. Several applications of these technologies to stability testing are discussed. 

Journal of Applied Polymer Science 62, No.ll, 12th Dec. 1996, p. 1903-11 SURFACE AND INTERFACIAL FOURIER TRANSFORM INFRARED SPECTROSCOPIC STUDIES OF LATEXES. XVI. QUANTITATIVE ANALYSIS OF SURFACTANT IN MULTILAYERED FILMS Niu B J Urban M W North Dakota State University... 

The improvement in computer technology associated with spectroscopy has led to the expansion of quantitative infrared spectroscopy. The application of statistical methods to the analysis of experimental data is known as chemometrics [5-9]. A detailed description of this subject is beyond the scope of this present text, although several multivariate data analytical methods which are used for the analysis of FTIR spectroscopic data will be outlined here, without detailing the mathematics associated with these methods. The most conunonly used analytical methods in infrared spectroscopy are classical least-squares (CLS), inverse least-squares (ILS), partial least-squares (PLS), and principal component regression (PCR). CLS (also known as K-matrix methods) and PLS (also known as P-matrix methods) are least-squares methods involving matrix operations. These methods can be limited when very complex mixtures are investigated and factor analysis methods, such as PLS and PCR, can be more useful. The factor analysis methods use functions to model the variance in a data set. 

A classic method is to digest the PHB-containing cell culture with sodium hypochlorite and measure the turbidity of the suspension produced by release of the polymer granules. Alternatively the polymer can be extracted into chloroform solution and its infrared absorbance at 1728 cm determined quantitatively. Another spectroscopic method involves hydrolysing and dehydrating the polymer to crotonic acid with concentrated sulphuric acid and assaying this by conventional quantitative UV analysis. ... 

With this rapid growth of near-infrared spectroscopic research in the health sciences, it is time for a text such as this. The authors have combined more than 35 years of industrial and university research experience in this volume. The pharmaceutical presentation is arranged in a logical progression theory, instrumentation, physical manipulation (blending, drying, and coating), analysis (both qualitative and quantitative), and finally, validation of the method. The varied mathematics used in NIR, called chemometrics, are only briefly mentioned. Detailed explanations and applications are covered in texts or chapters devoted to the subject [1-4]. 

Modern spectroscopy plays an important role in pharmaceutical analysis. Historically, spectroscopic techniques such as infrared (IR), nuclear magnetic resonance (NMR), and mass spectrometry (MS) were used primarily for characterization of drug substances and structure elucidation of synthetic impurities and degradation products. Because of the limitation in specificity (spectral and chemical interference) and sensitivity, spectroscopy alone has assumed a much less important role than chromatographic techniques in quantitative analytical applications. However, spectroscopy offers the significant advantages of simple sample preparation and expeditious operation. 

In order to perform qualitative and quantitative analysis of the column effluent, a detector is required. Since the column effluent is often very low mass (ng) and is moving at high velocity (50-100 cm/s for capillary columns), the detector must be highly sensitive and have a fast response time. In the development of GC, these requirements meant that detectors were custom-built they are not generally used in other analytical instruments, except for spectroscopic detectors such as mass and infrared spectrometry. The most common detectors are flame ionization, which is sensitive to carbon-containing compounds and thermal conductivity which is universal. Among spectroscopic detectors, mass spectrometry is by far the most common. 

An important tool for the fast characterization of intermediates and products in solution-phase synthesis are vibrational spectroscopic techniques such as Fourier transform infrared (FTIR) or Raman spectroscopy. These concepts have also been successfully applied to solid-phase organic chemistry. A single bead often suffices to acquire vibrational spectra that allow for qualitative and quantitative analysis of reaction products,3 reaction kinetics,4 or for decoding combinatorial libraries.5... 

---