Near-Infrared Spectrum Qualification via Mahalanobis Distance Determination

The use of near-infrared reflectance analysis (NIRA) for the quantitation of components of complex mixtures is well established. The lack of qualitative feedback in this approach is a major drawback. In view of this, it is believed that qualitative evaluation of the sample spectrum is also necessary for routine application of the NIRA technique. A method for qualifying a spectrum for application of a quantitative equation is described. The method involves generation of a quantitative equation, followed by the development of a qualitative equation based on the Mahalanobis distance algorithm, which is used to determine if the spectrum is suitable for analysis. This approach is demonstrated for the determination of lincomycin in an agricultural premix. The determination of proper control limits on the Mahalanobis distance is discussed. The improvement in precision obtained with the use of spectral selection is reviewed.