Ultraviolet Spectral Features Affecting Computer-Aided Multiwavelength Quantitation of Multicomponent Mixtures Using Phenothiazines as Model

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Abstract
Modern quantitation of multicomponent mixtures with ultraviolet spectroscopy is tending towards application of computer-aided calculations where mathematical overdetermination has been favored for reducing random errors in such analysis. Application of this procedure has however been made difficult by the observation of anomalous results. Additional sources of error is reported in the present study. Error patterns were traced to features of the spectra of components of the standards rather than the spectra of the mixtures to be analyzed alone. Calculation efficiency correlated inversely with isoabsorptive points of the standard spectra in the calibration matrix. New computational indices, relative total absorptivity and relative total absorbance, (RTA), calculated by the integration of absorption spectra of the components was shown to be a measurement that could be employed to optimize limit of quantitation of components present at low levels. RTA could be optimized separately for each component and could be a useful tool in automatic weighting factor allocation in future multicomponent analysis routines. Mixtures of chlorpromazine (CPZ) and its sulfoxide (CPZSO) which is of medical, forensic and industrial interest has been chosen as a model in this study. The optimized wavelength range for analysis of CPZ-CPZSO was determined to be 270–360 nm.