title: Rapid, sensitive, and reproducible screening of liquid milk for adulterants using a portable Raman spectrometer and a simple, optimized sample well.
abstract: We have developed a powerful general spectroscopic method for rapidly screening liquid milk for adulterants by combining reflective focusing wells simply fabricated in aluminum with a small, portable Raman spectrometer with a focusing fiber optic probe. Hemispherical aluminum sample wells were specially designed to optimize internal reflection and sampling volume by matching the focal length of the mirror to the depth of focus of the laser probe. The technique was tested on milk adulterated with 4 different nitrogen-rich compounds (melamine, urea, dicyandiamide, and ammonium sulfate) and sucrose. No sample preparation of the milk was needed, and the total analysis time was 4min. Reliable sample presentation enabled average reproducibility of 8% residual standard deviation. The limit of detection interval measured from partial least squares calibrations ranged between 140 and 520mg/L for the 4 N-rich compounds and between 7,000 and 36,000mg/L (0.7-3.6%) for sucrose. The portability of the system and the reliability and reproducibility of this technique open opportunities for general, reagentless screening of milk for adulterants at the point of collection.
authors.affiliation: MacDiarmid Institute for Advanced Materials and Nanotechnology, PO Box 600, Wellington 6140, New Zealand; The Photon Factory, The University of Auckland, 23 Symonds St., Auckland 1142, New Zealand; School of Chemical Sciences, The University of Auckland, 23 Symonds St., Auckland 1142, New Zealand. Electronic address: m.nieuwoudt@auckland.ac.nz.
authors.forename: M K
authors.initials: MK
authors.lastname: Nieuwoudt
authors.affiliation: Fonterra Research and Development Centre, Private Bag 11029, Palmerston North, New Zealand.
authors.forename: S E
authors.initials: SE
authors.lastname: Holroyd
authors.affiliation: The Dodd-Walls Centre for Photonic and Quantum Technologies, PO Box 56, Dunedin 9016, New Zealand; Department of Physics, The University of Auckland, 23 Symonds St., Auckland 1142, New Zealand.
authors.forename: C M
authors.initials: CM
authors.lastname: McGoverin
authors.affiliation: MacDiarmid Institute for Advanced Materials and Nanotechnology, PO Box 600, Wellington 6140, New Zealand; The Photon Factory, The University of Auckland, 23 Symonds St., Auckland 1142, New Zealand; School of Chemical Sciences, The University of Auckland, 23 Symonds St., Auckland 1142, New Zealand; The Dodd-Walls Centre for Photonic and Quantum Technologies, PO Box 56, Dunedin 9016, New Zealand; Department of Physics, The University of Auckland, 23 Symonds St., Auckland 1142, New Zealand.
authors.forename: M C
authors.initials: MC
authors.lastname: Simpson
authors.affiliation: MacDiarmid Institute for Advanced Materials and Nanotechnology, PO Box 600, Wellington 6140, New Zealand; School of Chemical Sciences, The University of Auckland, 23 Symonds St., Auckland 1142, New Zealand.
authors.forename: D E
authors.initials: DE
authors.lastname: Williams
mesh_terms: D000818:Animals; D002138:Calibration; D005506:Food Contamination; D008892:Milk / Q000737:chemistry*; D017672:Nitrogen Compounds; D015203:Reproducibility of Results; D014227:Triazines
chemical_list: D017672:Nitrogen Compounds; D014227:Triazines
keywords: Raman; milk adulteration; portable Raman; sample wells