Study For Efficient Extraction And Accurate Detection Of Methenamine In Food

Methenamine is a kind of medicine, which is used for therapy of urinary tract infection and nephropathy. The mechanism of treatment is that formaldehyde has antibacterial activity, and the formaldehyde is derived from methenamine under acidic urine condition. Methenamine is commonly applied to control disease of livestock in farming practices. However, veterinary drug may be accumulated in edible animal tissues or sideline products when it is continuously used to the livestock. Moreover, the molecular formula of methenamine is C6H12N4, and its nitrogen content is 40%. As the high nitrogen content, it might be fraudulently added to protein-containing foods(such as dairy products) to increase the apparent protein content. Because formaldehyde that derived from methenamine has carcinogenicity, acute and chronic toxicity, methenamine may cause potential harm to public health. Therefore, it is necessary to develop a sensitive and effective method to analyze the methenamine in food products.This paper focused on determination of methenamine in food. There were several analytical methods were established for different matrices. Then, the principles of various methods were analyzed and discussed. The results were as follows:(1) A purification method combined cation exchange solid phase extraction(SPE) with stable isotope 13C15N-methenamine as an internal standard was established. Analytical equipments were gas chromatography triple-quadrupole mass spectrometry(GC-MS/MS) and liquid chromatography triple quadrupole mass spectrometry(LC-MS/MS). The methods were applied to determine the methenamine residues in dairy products, beancurd sticks and rice noodles, respectively. Limit of detection(LOD) was 2?g/kg in milk, 8?g/kg in milk powder and cheese, 0.6?g/kg in beancurd sticks and rice noodles. According to purification performance for the different types of SPE, the exchange adsorption mechanism for SPE to methenamine was discussed, and the mixed cation exchange SPE(Strata-X-C) was selected as the purification column. Then, the fragmentation patterns of methenamine were presumed in the mass spectrum.(2) A modified QuEChERS(quick, easy, cheap, effective, rugged, and safe) method was developed for the determination of methenamine in edible animal tissues and rice noodles by HPLC-MS/MS, and LOD was 1.5?g/kg in samples. Matrix effect were obvious in kidney and liver, they were 0.59 and 0.55, respectively. According to purification performance for the different sorbents and sulfates, the adsorption mechanisms for sulfates, octadecylsilane(C18) and primary secondary amine(PSA) to methenamine were discussed. Then, anhydrous sodium sulfate(Na2SO4) and PSA were selected to purify methenamine. Afterwards, the uncertainty of QuEChERS method was evaluated, and its mathematical model was established through analyzing the sources of uncertainty. The each uncertainty of the key factor was assessed, and the uncertainty report was listed.(3) The molecularly imprinted polymers(MIPs) of methenamine were synthesized by polymerization, and the synthesis mechanism was discussed. The morphology of MIPs and non-imprinted polymers(NIPs) was characterized. Then, the static and dynamic adsorption experiments were applied to indicate the adsorption capacity of MIPs and NIPs for methenamine. The Scatchard analysis was used to investigate the adsorption thermodynamics of polymers, and the fitting equation was listed. Acetonitrile was used as extractive solvent, 6mL of 5% aqueous ammonia – methanol was used as elution solvent. Then, the amount of MIPs was optimized as 50 mg. Afterwards, a MIP-SPE purification method was developed for determination of methenamine in eggs by HPLC-MS/MS, and LOD was 0.6?g/kg in samples. The results of recycling experiment indicated that the MIP-SPE was suit for reuse.(4) The interaction between methenamine and methacrylic acid(MAA) was demonstrated by molecular simulation software. The spatial structure of the complex was optimized, and the proportion between template and monomer was determined. The Fe3O4 magnetic particles were synthesized by co-precipitation, and they were modified with oleic acid. Then, the magnetic molecularly imprinted polymers(M-MIPs) of methenamine were synthesized. The functional group, morphology, crystal structure and magnetic properties for the materials were characterized. Static and dynamic adsorption experiments were applied to indicate the adsorption capacity of M-MIPs and M-NIPs for methenamine. Through analyzing the fitting equation, the adsorption thermodynamics of M-MIPs was consistent with the Langmuir model. Moreover, the adsorption kinetics of M-MIPs was consistent with the pseudo-second-order model. The selective adsorption of M-MIPs for methenamine was investigated. Acetonitrile was used as extractive solvent, 10 mL of 5% aqueous ammonia – methanol was used as elution solvent. Then, the amount of M-MIPs was optimized as 20 mg. Finally, a MISPE purification process was developed for the determination of methenamine in milk by GC-MS/MS, and LOD was 0.3?g/kg in samples.