title: Screening for Adulterants in Liquid Milk Using a Portable Raman Miniature Spectrometer with Immersion Probe.
abstract: A portable Raman system with an immersion fiber optic probe was assessed for point-of-collection screening for the presence of adulterants in liquid milk. N-rich adulterants and sucrose were measured in this proof-of-concept demonstration. Reproducibility, limit of detection range and other figures of merit such as specificity, sensitivity, ratio of predicted to standard deviation, standard error of prediction and root mean squared error for cross validation were determined from partial least squares (PLS) and partial least squares with discriminant analysis (PLS-DA) calibrations of milk mixtures containing 50-1000 ppm (parts per million) of melamine, ammonium sulphate, Dicyandiamide, urea and sucrose. The spectra were recorded by immersing the fiber optic probe directly in the milk solutions. Despite the high scattering background which was easily and reliably estimated and subtracted, the reproducibility for four N-rich compounds averaged to 11% residual standard deviation (RSD) and to 5% RSD for sucrose. PLS calibration models predicted the concentrations of separate validation sets with standard errors of prediction of between 44 and 76 ppm for the four N-rich compounds and 0.17% for sucrose. The sensitivity and specificity of the PLS-DA calibration were 92% and 89%, respectively. The study shows promise for use of portable mini Raman systems for routine rapid point-of-collection screening of liquid milk for the presence of adulterants, without the need for sample preparation or addition of chemicals.
authors.affiliation: 1 School of Chemical Sciences, The University of Auckland, New Zealand.|2 MacDiarmid Institute for Advanced Materials and Nanotechnology, New Zealand.|3 The Photon Factory, The University of Auckland, New Zealand.|4 The Dodd Walls Centre for Photonic and Quantum Technologies, New Zealand.
authors.forename: Michél K
authors.initials: MK
authors.lastname: Nieuwoudt
authors.affiliation: 5 Fonterra Research & Development Centre, New Zealand.
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Holroyd
authors.affiliation: 4 The Dodd Walls Centre for Photonic and Quantum Technologies, New Zealand.|6 Department of Physics, The University of Auckland, New Zealand.
authors.forename: Cushla M
authors.initials: CM
authors.lastname: McGoverin
authors.affiliation: 1 School of Chemical Sciences, The University of Auckland, New Zealand.|2 MacDiarmid Institute for Advanced Materials and Nanotechnology, New Zealand.|3 The Photon Factory, The University of Auckland, New Zealand.|4 The Dodd Walls Centre for Photonic and Quantum Technologies, New Zealand.|6 Department of Physics, The University of Auckland, New Zealand.
authors.forename: M Cather
authors.initials: MC
authors.lastname: Simpson
authors.affiliation: 1 School of Chemical Sciences, The University of Auckland, New Zealand.|2 MacDiarmid Institute for Advanced Materials and Nanotechnology, New Zealand.
authors.forename: David E
authors.initials: DE
authors.lastname: Williams
mesh_terms: D000645:Ammonium Sulfate / Q000032:analysis; D000818:Animals; D005506:Food Contamination / Q000032:analysis*; D006146:Guanidines / Q000032:analysis; D057230:Limit of Detection; D008892:Milk / Q000737:chemistry*; D015203:Reproducibility of Results; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013395:Sucrose / Q000032:analysis; D014227:Triazines / Q000032:analysis; D014508:Urea / Q000032:analysis
chemical_list: D006146:Guanidines; D014227:Triazines; D013395:Sucrose; D014508:Urea; C004711:dicyandiamido; C011907:melamine; D000645:Ammonium Sulfate
keywords: Raman spectroscopy; milk adulteration; point-of-collection; portable raman; raman immersion probe