Mean centering and computation of scalar net analyte signal in multivariate calibration

Lorber has identified the net analyte signal (NAS) vector as the part of th e gross signal which is orthogonal to the pure spectra of the interferents. For calculation of multivariate analytical figures of merit, such as sensi tivity and signal-to-noise ratio, the NAS vector must be converted into a s calar NAS. The traditional methods for calculating the scalar NAS amount to taking the Euclidean norm of the NAS vector. For mean-centered data, strai ghtforward implementation of this recipe leads to an artifact: one value fo r the scalar NAS corresponds to two values for analyte concentration, i.e., the conversion is not unique. This paper details the origin of the problem and proposes a simple solution. The improved calculation of scalar NAS is illustrated on the near-infrared prediction of weight per cent oxygen deliv ered by the oxygenate methyl tert-butyl ether in standard reference materia l gasoline ampoules. (C) 1998 John Wiley & Sons, Ltd.