Analysis Of Melamine In Food And Environmental Samples By Liquid Chromatography-mass Spectrometry

With the development of society, people pay more attention to pollution on food safety. After the case of"pet food in USA"and"Sanlu milk in china", The analytical technique of melamine and other toxic and harmful pollutants in environment field has become a hotspot of analytical chemistry research. Since low content of melamine in food and environment, complex matrix, and high sensitive, high selective is required, high performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS) are become important method for melamine analysis. But, the difficulty is the development of a fast and reliable pretreatment method to real sample.This paper described molecularly imprinted solid phase extraction for determination of melamine in milk samples and microwave-assisted extraction for determination of melamine in egg samples. In addition, the melamine content in environmental water samples and melamine bowl under microwave irradiation were investigated.This thesis includes the following five parts:1. This section firstly introduces the characteristics and source, the dangers, the cases and current detection methods for melamine. Secondly, description of the development and application of LC/MS for melamine analysis in environmental and food samples. Then, introduction of the molecularly imprinted solid phase extraction and microwave-assisted extraction. Finally, description of the purposes and contents for the thesis.2. A molecularly imprinted solid phase extraction (MISPE) coupled with high performance liquid chromatography/ion trap mass spectrometry was used to determine melamine in milk. Melamine was extracted in 1% trichloroacetic acid and acetonitrile (8/2,v/v), then supernatants were cleaned up using MISPE. The condition of molecularly imprinted solid phase extraction which influence on extraction efficiency and matrix-induced enhancement is investigated. It explores the LC separation method by C18 column without ion pairre agent in mobile phase. Melamine was detected by electrospray ionization in positive ion mode. Quantitation of positive samples was performed using the internal standard method. This MISPE procedure could eliminate matrix interference and had good recoveries.3. A systematic study of the microwave-assisted extraction coupled to high performance liquid chromatography/mass spectrometry for determination of melamine in egg samples has been described. The influence of extraction solvent, extraction temperature and microwave radiation time on the yield were studied. Comparing with conventional methods, the microwave extraction technique has advantage of short time, low solvent consumption, and high recovery. This pretreatment method could eliminate matrix interference and had good recoveries.4. A sensitive and accurate method for determination of melamine and cyromazine in environmental water samples by high performance liquid chromatography-ion trap mass spectrometry has been developed. The extraction results of melamine and cyromazine with four different kind of columns (PCX,HLB,C18/OH,C18) was investigated. The analytes in water samples were concentrated on PCX solid phase column, and chromatographic separated on a CN column with methanol-water (30:70,v/v)isocratic elution, followed by an electrospary positive ionization mass spectrometric quantitative detection by monitoring m/z127 for melamine and m/z167 for cyromazine. The proposed method was successfully applied to analysis of different environmental water samples. Experimental results showed that the existence of melamine in environmental water samples is ubiquitous.5. To study migration amount of melamine from melaminebowl to food simulants under microwave heating by HPLC. The effects of simulating solutions type, microwave heat power, microwave irradiation time on melamine migration amount were studied. The results show that when microwave irradiation for 5 min with medium-high heating power, and 4 % acetic acid were used as food simulants, the migration amount was over the maximam limited value issued by national standard. Moreover, more unknown compounds migrate from melamine tableware under acid condition when used microwave. The proposed reason relating to destroyed of bowl surface structure was verified by experiment.