Direct analysis of melamine in complex matrices using a handheld mass spectrometer

Abstract

A low temperature plasma ambient ionization source, coupled to a portable mass spectrometer (Mini 10.5), is used for the determination of melamine contamination in whole milk and related materials. Thermally assisted desorption and ionization of the analyte was achieved with the plasma probe. The small size, low power consumption and capability for direct sampling without pretreatment makes plasma ionization an appropriate ionization method for use with a handheld mass spectrometer. The standard discontinuous atmospheric pressure interface used to connect atmospheric pressure ion sources to mass spectrometers (Gao et al., Anal. Chem., 2008, 80, 4026-4032) was modified by using supplementary pumping to increase the ion transfer efficiency. Whole milk, fish, milk powder and other complex matrices spiked with melamine were placed on glass slides close to the vacuum inlet and analyzed without sample pretreatment. Quantitation in complex matrices was achieved using MS/MS of protonated melamine m/z 127 to yield the characteristic fragment ion of m/z 85. Analysis rates of two samples per minute, levels of melamine as low as 250 ng/mL in whole milk (below the regulatory level in the US of 1 ppm (1 microg/mL) or the European level of 2.5 ppm (microg/mL)), a linear dynamic range of 0.5-50 microg/mL and a relative standard deviation of ca. 7.6-16.2% were achieved. The importance of melamine to public health and the prior lack of a rapid, sensitive and yet highly specific field analysis method add to the relevance of this study.

Membrane Sampling with Microdialysis Coupled to HPLC/UV for On-line Simultaneous Determination of Melamine and Cyanuric Acid in Non-dairy Coffee Creamer

“…Several authors have proposed the direct analysis of MM in milk or pet food using various analytical methodologies. [15][16][17][18][19][20] The LOD for MM in the present study, after considering the 10-fold dilution of the samples, was rather low when compared with those from studies that did not involve prior sample preparation. Rambla-Alegre et al reported a direct injection method for the analysis of MM using HPLC-UV; they obtained an LOD (5 ppb) similar to ours.…”

“…Only a few methods have been proposed for the direct determination of MM in milk or pet foods. [15][16][17][18][19][20] Our proposed method described herein is a facile chromatographic method with membrane microdialysis sampling that allows the simultaneous quantification of MM and CA through direct analysis; it has the advantages that it is cheap and simple to operate and maintain. This developed on-line MD-HPLC system provides good linearity, precision, recovery, and sensitivity over the studied concentration ranges, making it a good choice for analyzing MM and its derivative, CA, in NCC.…”

“…[15][16][17][18][19][20] These methods include HPLC-UV, 15 Raman spectroscopy 16 direct-analysis-in-real-time mass spectrometry (DART-MS), 17 ultrasound-assisted extractive electrospray ionization mass spectroscopy (EESI-MS), 18 surface desorption atmospheric pressure chemical ionization mass spectrometry (DAPCI-MS), 19 and low-temperature plasma/tandem mass spectrometry (LTP-MS-MS). 20 Notably, most of the instruments used in these methodologies are very expensive; in addition, the limits of detection (LODs) of these methods are variable because of the intense noise caused by the matrix. Although Rambla-Alegre and coworkers used a widely available technique, HPLC with UV detection, to directly quantify MM in milk, the anionic surfactant sample dilution and anionic micellar chromatography techniques that they chose in that study would not allow us to extract and retain both MM and CA simultaneously.…”

Application of Tandem Mass Spectrometry for Analyzing Melamine

“…MEL can be desorbed/ionized upon N 2 laser irradiation by simply mixing the commonly adopted MALDI matrixes with melamine cyanurate in urine residue. The high-throughput MEL analysis method using low-temperature plasma (LTP) coupled with an ion trap mass spectrometer of bench top type or handheld mass spectrometer (Huang et al, 2010) have also been introduced recently. The mechanism involves thermally-assisted (from 20 o C to 170 o C) vaporization and plasma ionization of MEL.…”

Development of the Atmospheric Plasma Soft-Ablation Method (APSA) for Elemental Analysis of Materials on Heat-sensitive Substrates

“…A DBD jet operating at a low output power (<5 W) was first applied to desorption/ionization by Harper et al 7 Its suitability for the analysis of drugs, explosives, and food additives [8][9][10][11][12] was demonstrated, but its application to highly sensitive inorganic analysis using ICP-MS has not been studied.…”