STANDARDIZATION OF FIBEROPTIC PROBES FOR NEAR-INFRARED MULTIVARIATE CALIBRATIONS

The standardization of Fourier transform near-infrared (FT-NIR) spectr ometers equipped with fiber-optic probes was investigated. FT-NIR spec tra of caustic brines for an industrial process were measured on two d ifferent instruments. Calibration transfer across the instruments and probes was studied by employing calibration models built on one instru ment to predict properties from spectra measured on the other. The tra nsfer was examined by using spectra without and with preprocessing. Th e preprocessing methods included a Savitzky-Golay (SG) derivative poly nomial filter, a procedure based on a finite impulse response (FIR) fi lter, and a combination of bath. In addition to being a preprocessing technique, the FIR filter is also a standardization method that transf orms the instrument response function of one instrument to match that of another. The transformation is performed over a moving processing w indow without the use of transfer standards. In this study, applicatio n of the FIR filter to first-derivative spectra provided the best mult ivariate calibration models and led to the successful transfer of cali bration across different probes and spectrometers.