First use of handheld Raman spectroscopic devices and on-board chemometric analysis for the detection of milk powder adulteration

Abstract

Two handheld Raman spectroscopic devices in combination with chemometrics were explored as rapid, non-targeted screening tools for the detection of milk powder (MP) adulteration using melamine as an example contaminant. The first device (device 1) employs a unique laser setup and data processing software that decreases the spectral interference from background fluorescence which could allow for improved detection capabilities. The second instrument (device 2) is the first of its kind to combine advanced chemometric data processing directly on-board the portable device which could allow for more rapid analysis of complex samples through “pass/fail” results. In this work, the performance of these two devices were evaluated and compared to each other and to that of a benchtop Raman spectrometer for the detection of melamine-spiked MP samples. The portable devices had similar levels of performance as the benchtop Raman spectrometer in terms of sensitivity and specificity for classifying test samples as genuine MP or MP-melamine blends. High specificity (100%) for melamine adulterated MPs at concentrations ≥1.0% (w/w) for dry-blends and ≥0.30% for wet-blends in the validation set was found for the non-targeted, soft independent modeling of class analogy (SIMCA) model developed for portable device 2. A similar level of specificity was observed when the non-targeted model was tested using a blind set of test samples and on-board chemometrics. Additionally, SIMCA models for devices 1 and 2 correctly classified genuine MPs with 97 and 100% correct classifications, respectively. Device 1 had comparatively lower specificity for MP blends. These results indicate that the developed screening methods using the handheld Raman devices are potentially well-suited for rapid, routine field analysis of MP samples for detection of economically motivated adulteration.