Quantification of melamine in infant formula using a handheld Raman spectrometer – Performance boost with customized Arduino-controlled rotation setup

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This study investigated the performance of a handheld Raman spectrometer in quantifying melamine in infant formula. Furthermore, the spectrometer's standard stationary sample holder was compared to a custom-built sample rotation unit. The Raman spectra were divided into a calibration set, which was used to construct the partial least squares regression (PLS-R) models, and a test set, which served the purpose of evaluating the model performance with independent samples. It was found that it was possible to reduce the prediction error of melamine in infant formula by up to about 70% using the simple in-house constructed rotation setup. Compared to the rotation setup, even an increased number of point measurements using the spectrometer's standard sample holder was not able to compensate for the lack of representative sample presentation of the inhomogeneous solid mixture to the Raman spectrometer. Moreover, it was found that the custom-built rotation unit enabled faster sample measurements by an adaption of spectrometer parameters. At the same time, the prediction error of the test set samples was kept far lower than with the stationary setup.