Ultra-High-Speed Analysis of Melamine in Powdered Milk Using LDTD-MS/MS

Introduction

The deliberate contamination of powdered milk and pet food with melamine has become a serious social issue. If melamine is contained in food at high concentrations together with cyanuric acid, which is produced in the manufacturing process of melamine, contamination can lead to kidney stones and even kidney failure. In many cases, melamine is added for producing adulterated products, and when added, is done so at very high concentrations. In order to stop these sorts of adulterated products at the border, high-speed screening analysis that can be performed together with easy sample preparation is required. A widely reported analysis technique for melamine in powdered milk involves using LCMS and GCMS after performing pretreatment to remove impurities. This article describes an ultra-high-speed analysis of melamine in powdered milk without column separation by using a laser diode thermal desorption (LDTD) ion source together with the LCMS-8060. An ion source for ultra-high-speed screening analysis developed by Phytronix Technologies Inc. (https://phytronix.com/) in Canada was employed as the LDTD ion source. Mass spectrometry can be completed within a few seconds by sample vaporization using laser irradiation and subsequent APCI ionization. By applying samples to 96-well plates, up to 10 plates can undergo consecutive analysis. When using the LDTD ion source together with a Shimadzu LCMS-8060, each instrument can be utilized as necessary, such as for direct analysis using LDTD or for LC/MS analysis with column separation, simply by loading a method file with no need to disconnect the LDTD ion source from the LCMS-8060. This allows for MRM optimization of the compound for analysis on the LCMS-8060 and then ultra- high-speed analysis with LDTD using the determined MRM transitions. Conversely, polyspecimen analysis screening using ultra-high-speed analysis with LDTD can be performed first, and then using the results, LC/MS analysis can be performed with respect to a particular sample. In this way the combination of the LDTD ion source and LCMS-8060 can be used to switch between two completely different analysis methods according to the purpose of analysis. n this research, we connected an LDTD ion source, performed MRM optimization of melamine using DUIS (dual ion sources of ESI and APCI), and then used the obtained MRM transitions in ultra-high-speed analysis by LDTD-MS. In performing ultra-high-speed analysis by LDTD- MS, we used a mass spectrometry system comprising an LDTD ion source and the LCMS-8060 and used samples prepared by adding melamine to powdered milk and collecting the melamine using liquid-liquid extraction. The following introduces an example of analyzing melamine in powdered milk by switching between the two analysis systems of LCMS and LDTD-MS.

December 4, 2017 GMT