Detection of Melamine in Milk Products by Surface Desorption Atmospheric Pressure Chemical Ionization Mass Spectrometry

Department of Applied Chemistry, East China Institute of Technology, Fuzhou, 344000 PR China.
Analytical Chemistry (Impact Factor: 5.64). 05/2009; 81(7):2426-36. DOI: 10.1021/ac900063u
Source: PubMed


Without any sample pretreatment, trace amounts of melamine in various milk products were rapidly detected noting the characteristic fragments (i.e., m/z 110, 85, and 60) in the MS/MS spectrum of protonated melamine molecules (m/z 127) recorded by using surface desorption atmospheric pressure chemical ionization mass spectrometry. Signal responses of the most abundant ionic fragment (m/z 85) of protonated melamine were well correlated with the amounts of melaime in milk products, showing a dynamic range about 5 orders of magnitude. The limit of detection (LOD) was found to be 3.4 x 10(-15) g/mm(2) (S/N = 3) for the detection of pure melamine deposited on the paper surface, which was much lower than that for detection of melamine in powdered milk (1.6 x 10(-11) g/mm(2), S/N = 3) or liquid milk (1.3 x 10(-12) g/mm(2), S/N = 3). The significant difference in LOD was ascribed to the relatively strong molecular interactions between melamine and the matrix such as proteins in the milk products. As demonstrated using desorption electrospray ionization (DESI) for melamine detection, weakening the molecular interaction between analytes and proteins is proposed as a general strategy to improve the sensitivity of ambient mass spectrometry for direct detection of analytes bound in protein matrixes. The relative standard deviation (RSD) and the recovery of this method were found to be 5.2 approximately 11.9% and 87 approximately 113%, respectively, for the detection of melamine in milk products. A single sample analysis was completed within a few seconds, providing a particularly convenient way to rapidly screen melamine presence in milk products.

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Available from: Bin Hu, Nov 11, 2014
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    • "Several analytical methods were developed to detect and quantify melamine and its analogs in food since its first detection in China (Liu, Todd, Zhang, Shi, & Liu, 2012). Mass spectrometry based methods, including DAPCI-MS (Yang et al., 2009), EESI-MS (Zhu, Gamez, Chen, Chingin, & Zenobi, 2009) and LC-MS/MS (Smoker & Krynitsky, 2008; Turnipseed, Casey, Nochetto, & Heller, 2008) have been used as confirmatory and/or screening for melamine, due to their high selectivity and low detection limits. However, the main limitations of mass spectrometry techniques rely on its high cost and complexity. "
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    • "However, ambient mass spectrometry is a rapidly growing field that provides fast and direct analysis of solid sample surfaces or liquid samples introduced on a suitable surface (Alberici et al. 2010; Weston 2010; Huang et al. 2010; Chen et al. 2010). For that, different ambient ionization MS methods, such as atmospheric pressure desorption/ionization on porous silicon (AP-DIOS) (Huikko et al. 2003), desorption electrospray ionization (DESI) (Takáts et al. 2004), direct analysis in real time (DART) (Cody et al. 2005), desorption atmospheric pressure chemical ionization (DAPCI) (Takáts et al. 2005), and desorption atmospheric pressure photoionization (DAPPI) (Haapala et al. 2007), have been successfully used in the direct analysis of compounds from various samples, such as body fluids (Cody et al. 2005; Chen et al. 2006), fruits, plant leaves (Luosujärvi et al. 2010), milk (Yang et al. 2009), banknotes (Cody et al. 2005), textiles (Cody et al. 2005; Chen et al. 2007), and pharmaceutical formulations (Ifa et al. 2009; Green et al. 2010), just to mention a few, without any sample pretreatment. The most used ambient MS technique is DESI that employs a pneumatically assisted charged spray to desorb and ionize the analytes (Takáts et al. 2004). "
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    • "c o m / l o c a t e / f o o d c h e m melamine is a potential adulterant because of its high nitrogen content (66% by mass). In fact, many different methods including LC–MS/MS, APCI-MS and ESI-MS have been developed for detection of melamine in milk products (Turnipseed, Casey, Nochetto, & Heller, 2008; Zhu, Gamez, Chen, Chingin, & Zenobi, 2009; Yang et al., 2009) in parallel with the principal analytical method proposed by the US Food and Drug Administration (FDA, Smoker & Krynitsky, 2008). However, the high cost instrumentation, staff training and infrastructure associated with MS techniques limit their widespread use. "
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    ABSTRACT: The Kjeldahl method and four classic spectrophotometric methods (Biuret, Lowry, Bradford and Markwell) were applied to evaluate the protein content of samples of UHT whole milk deliberately adulterated with melamine, ammonium sulphate or urea, which can be used to defraud milk protein and whey contents. Compared with the Kjeldahl method, the response of the spectrophotometric methods was unaffected by the addition of the nitrogen compounds to milk or whey. The methods of Bradford and Markwell were most robust and did not exhibit interference subject to composition. However, the simultaneous interpretation of results obtained using these methods with those obtained using the Kjeldahl method indicated the addition of nitrogen-rich compounds to milk and/or whey. Therefore, this work suggests a combination of results of Kjeldahl and spectrophotometric methods should be used to screen for milk adulteration by these compounds.
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