Dyes, analysis DRIFTS

Collection of multiple data sets for each time span, with frequent alternation of the polarization, is an essential feature of our protocol. This provides some protection against the effects of drifts in laser power, photomultiplier quantum yield, and absolute calibration of the TAC, photochemical decomposition of the dye, and any other long-term processes that may alter the measured fluorescence response curves. Separate analysis of each data set is necessary to provide an indication of the uncertainty in run-to-run reproducibility and to detect and delete the rare spurious data set. 

Ink analysis and related analyses of questioned documents have come to rely heavily on IR spectroscopy. As with paints, applications evolved from traditional IR through DRIFTS techniques and now employ principally MSR Inks are analyzed in situ or on sampling substrates such as KBr plates. like paints, inks produce IR spectra representative of mixtures unlike paints, inks rarely have a layered structure. Regardless, spectra of inks do contain information that is useful for classification. For example, a study of 108 inks demonstrated that distinctive absorption bands could be rationalized on the basis of ink composition and then employed to divide the test population into two groups. As shown in Figure 12.7, one group contained C—C stretching characteristic of an epoxy resin and features associated with triarylmethane dyes, as shown in... 

DRIFT spectroscopy of microscopic amounts of dye mixtures extracted from small textile samples has been reported raw and pretreated data matrices were interpreted with the use of chemomet-rics (PCA, SIMCA, FC) [145]. DRIFTS can readily detect 200 ng quantities of pure, standard dyes. Bridge et al. [42] have qualitatively characterised acid dyes (Cl Acid Red 17, Red 18, Red 44, Red 88, Blue 45 and Yellow 17) applied to wool and nylon. Near-infrared diffuse reflectance spectroscopy was evaluated for its ability to analyse solid antioxidant blends [146]. These opaque materials do not transmit near-IR light. This fast method effectively predicts weight percentage composition with a precision comparable to the currently accepted HPLC method of analysis, and can identify blend types and contaminated materials. 

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