Correction of temperature-induced spectral variation by continuous piecewise direct standardization

In process analytical applications it is not always possible to keep the me asurement conditions constant. Ho However, fluctuations in esternal variabl es such as temperature can have a strong influence on measurement results. For example, nonlinear temperature effects on near-infrared (NIR) spectra m ay lead to a strongly biased prediction result from multivariate calibratio n models such as PLS. A new method, called Continuous Piecewise Direct Stan dardization (CPDS) has been developed for the correction of such external i nfluences. It represents a generalization of the discrete PDS calibration t ransfer method and is able to adjust for continuous nonlinear influences su ch as the temperature effects on spectra. It was applied to shortwave NIR s pectra of ethanol/water/2-propanol mixtures measured at different temperatu res in the range 30-70 degrees C. The method was able to remove, almost com pletely, the temperature effects on the spectra, and prediction of the mole fractions of the chemical components was close to the results obtained at constant temperature.