An evaluation of orthogonal signal correction applied to calibration transfer of near infrared spectra

Orthogonal signal correction (OSC) is a technique for pre-processing of, fo r example, NIR-spectra before they are subjected to a multivariate calibrat ion. With OSC the X-matrix is corrected by a subtraction of variation that is orthogonal to the calibration Y-matrix. This correction can then be appl ied to new spectra that are going to be used in predictions. The aim of thi s study is to investigate if the OSC transform makes the spectra less depen dent of instrument variation. This may result in easier calibration model t ransfer between different instruments without creating or re-analysing the whole calibration sample set. OSC was applied to MR-spectra that were used in a calibration for the water content in a pharmaceutical product. Partial Least Squares calibrations were then compared to other calibration models with uncorrected spectra, models with spectra subjected to multiplicative s ignal correction, and a number of other transfer methods. The performance o f OSC was on the same level as for piece-wise direct standardisation and sp ectral offset correction for each individual instrument and PLS-models with both instruments included. (C) 1998 Elsevier Science B.V. All rights reser ved.