Vibrational spectroscopy method validation

N. Broad, P. Graham, P. Hailey, et al., Guidelines for the development and validation of near-infrared spectroscopic methods in the pharmaceutical industry. In Handbook of Vibrational Spectroscopy, vol. 5, J.M. Chalmers and PR. Griffiths (eds), John Wiley Sons Ltd, Chichester, 3590-3610, 2002. 

A promising recent development in the study of nitrenium ions has been the introduction of time-resolved vibrational spectroscopy for their characterization. These methods are based on pulsed laser photolysis. However, they employ either time resolved IR (TRIR) or time-resolved resonance Raman (TRRR) spectroscopy as the mode of detection. While these detection techniques are inherently less sensitive than UV-vis absorption, they provide more detailed and readily interpretable spectral information. In fact, it is possible to directly calculate these spectra using relatively fast and inexpensive DFT and MP2 methods. Thus, spectra derived from experiment can be used to validate (or falsify) various computational treatments of nitrenium ion stmctures and reactivity. In contrast, UV-vis spectra do not lend themselves to detailed structural analysis and, moreover, calculating these spectra from first principles is still expensive and highly approximate. 

This book intends to supply the basic information necessary to apply the methods of vibrational spectroscopy, to design experimental procedures, to perform and evaluate experiments. It does not intend to provide a market survey of the instruments which are available at present, because such information would very soon be outdated. However, the general principles of the instruments and their accessories, which remain valid, are discussed. Details concerning sample preparation and the recording of the spectra, which is the subject of introductory courses, are assumed to be known. Special procedures which are described in monographs, such as Fourier transformation or chemometric methods, are also not exhaustively described. This book has been written for graduate students as well as for experienced scientists who intend to update their knowledge. 

Spectroscopic methods can provide fast, non-destructive analytical measurements that can replace conventional analytical methods in many cases. The non-destructive nature of optical measurements makes them very attractive for stability testing. In the future, spectroscopic methods will be increasingly used for pharmaceutical stability analysis. This chapter will focus on quantitative analysis of pharmaceutical products. The second section of the chapter will provide an overview of basic vibrational spectroscopy and modern spectroscopic technology. The third section of this chapter is an introduction to multivariate analysis (MVA) and chemometrics. MVA is essential for the quantitative analysis of NIR and in many cases Raman spectral data. Growth in MVA has been aided by the availability of high quality software and powerful personal computers. Section 11.4 is a review of the qualification of NIR and Raman spectrometers. The criteria for NIR and Raman equipment qualification are described in USP chapters <1119> and < 1120>. The relevant highlights of the new USP chapter on analytical instrument qualification <1058> are also covered. Section 11.5 is a discussion of method validation for quantitative analytical methods based on multivariate statistics. Based on the USP chapter for NIR <1119>, the discussion of method validation for chemometric-based methods is also appropriate for Raman spectroscopy. The criteria for these MVA-based methods are the same as traditional analytical methods accuracy, precision, linearity, specificity, and robustness however, the ways they are described and evaluated can be different. 

EIS and molecular simulations to smdy possible BSA adsorption on Zn-side electrode (including on bare surfaces and as electrodeposition progresses) Identify possibility of BSA adsorbing onto electrode and blocking sites of charge transfer Need to iteratively develop comprehensive models, including validation tests using vibrational spectroscopy and electrochemical methods... 

Protein-lipid interactions and particularly peptide-lipid interactions have been studied in supported bilayers by attenuated total reflection (ATR) FTIR spectroscopy. A slightly dated, but still valid comprehensive review on this method applied to supported bilayers has been published (20). Because IR light probes the vibrational properties of different classes of covalent bonds, this method is useful to examine lipids, peptides, and interactions between the two in the same sample. The most common parameter for assessing lipid structure and order is to study the stretching vibrations of the lipid acyl chains, for example as a function of peptide concentration or temperature. Such studies have lead to the conclusion that fusion peptides from viruses increase the lipid chain order of fluid phase bilayers and that... 

Tt is well-known that Werner determined the structure of a number of metal complexes by skillfully combining his famous coordination theory with chemical methods (30). Modern physico-chemical methods such as x-ray diffraction and infrared spectroscopy, used in the study of Werner complexes, have paralleled the development of these techniques. The results of these investigations have not only confirmed the validity of Werner s coordination theory but have also provided more detailed structural and bonding information. In early 1932, Damaschun (13) measured the Raman spectra of seven complex ions, such as [Cu(NH3)4]" and [Zn(CN)4j and these may be the first vibrational spectra ever obtained for Werner complexes. In these early days, vibrational spectra were mainly observed as Raman spectra because they were technically much easier to obtain than infrared spectra. In 1939, Wilson 35, 36) developed a new theory, the GF method," which enabled him to analyze the normal vibrations of complex molecules. This theoretical revolution, coupled with rapid developments of commercial infrared and Raman instruments after World War II, ushered in the most fruitful period in the history of vibrational studies of inorganic and coordination compounds. 

The uncertainties discussed in the preceding section prompted us to look for another "chemical method" to estimate the surface of supported ceria. As for alumina-supported oxides [12-16], the adsorption of CO2 has been considered, IR spectroscopy being prefered, with the aim of finding vibrations specific of CO2 interacting either with ceria or with alumina. This method has been applied although very recent results, mainly with alumina supported molybdenum questionned the validity of CO2 adsorption to measure the coverage of alumina... 

In the present project we have investigated whether surface enhanced resonance Raman spectroscopy (SERRS) could be used to study various types of DNA-chromophore interactions. In this technique, a silver colloid is added to the solution containing the molecule to be studied [34]. First, we had to test whether the complex, between dye and DNA, would remain unaltered upon adsorption to the silver colloid surface which is a necessary condition for a valid application of the method. A second system specific question concerns the useful information that can be extracted from frequency shifts and relative intensity alterations in the vibrational spectrum of the DNA-bound chromophore [35-37]. 

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