Matching absorbance method

S. D. Gedney and A. Taflove, Perfectly matched absorbing boundary conditions, in Computational Electrodynamics The Finite-Difference Time Domain Method, Taflove and S. Hagness, Eds., Artech House, Boston (2000), 285-348. 

Organic and inorganic molecular species (except homonuclear molecules) absorb in the IR region. IR spectroscopy has the potential to determine the identity of an unusually large number of substances. Moreover, the uniqueness of a MIR spectrum confers a degree of specificity which is matched or exceeded by relatively few other analytical methods. This specificity has found particular applications for the development of quantitative IR absorption methods. However, these differ from quantitative UV/Vis techniques in their greater spectral complexity, narrower absorption bands, and the technical limitations of IR instruments. Quantitative determinations obtained from IR spectra are usually inferior in quality and robustness to those obtained with UV/Vis and NIR spectroscopy. In addition, univariate or linear cali-... 

Use of an integrated system incorporating CCC separation, PDA detector, and LC-MS proved to be a valuable tool in the rapid identification of known compounds from microbial extracts.6 This collection of analytical data has enabled us to make exploratory use of advanced data analysis methods to enhance the identification process. For example, from the UV absorbance maxima and molecular weight for the active compound(s) present in a fraction, a list of potential structural matches from a natural products database (e.g., Berdy Bioactive Natural Products Database, Dictionary of Natural Products by Chapman and Hall, etc.) can be generated. Subsequently, the identity of metabolite(s) was ascertained by acquiring a proton nuclear magnetic resonance ( H-NMR) spectrum. 

Exact matrix matching is not always feasible for example, the precise matrix composition may be unknown for various reasons. In such a case the standard additions method may be employed. The sample is spiked with at least two additions of known amounts of determinant in such a way that the matrix is not significantly altered, and the absorbance of spiked and unspiked samples is measured compared to that of aqueous standards, as shown in Figure 1. By extrapolation back to the negative extension of the concentration axis, the unknown concentration may be calculated. 

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