Near-infrared spectroscopic determination of antioxidants and organic acids in rubbers assisted by a new multivariate calibration method based on direct orthogonalization

A newly introduced multivariate calibration method combining direct orthogonalization and classical least-squares is optimized and applied to the determination of the content of antioxidants and organic acids in rubber by near-infrared spectroscopy. A large calibration set was built for rubbers having varying values of the target parameters, which were previously determined by reference techniques. The results obtained for a validation set were compared with those rendered by partial least-squares, including several spectral pretreatment procedures.