WAVELENGTH CALIBRATION TRANSFER BETWEEN DIODE-ARRAY UV-VISIBLE SPECTROPHOTOMETERS

The need to obtain expeditious results in control analyses of complex mixtures has turned multivariate calibration procedures into major choices for routine analyses. The inherent complexity of the calibration process and the practical need for analyses to be carried out as near the manufacturing line as possible occasionally entail calibrating with a different instrument from that subsequently employed for the analytical measurements proper. This paper exposes the problems potentially arising in transferring calibrations between diode array UY-Vis spectrophotometers. Basically, such problems originate in wavelength differences between spectrophotometers, even if they meet the manufacturer's specifications and the pharmacopoeia recommendations. We developed a straightforward method for harmonizing instrumental responses on the basis of reference wavelengths corresponding to zero values in the first-derivative spectra for potassium dichromate and benzoic acid standards. The method was applied to the analysis of binary mixtures of theophylline and doxylamine by multiple linear and partial least-squares regression with the use of one spectrophotometer for calibration and four others for analyses.