Multiplex Isotope Dimethyl Labeling Coupled With LC-MS For Quantitative Analysis Of Sulfonamides

Sulfonamides?SAs?are one of the most widely used antibiotics in livestock for their broad activity spectrum.Most of the SAs are excreted unchanged through feces and urine.Due to the lack of proper treatment or even directly using as manure in farm,considerable amount of SAs were released into environmental body.However,the residues of SAs in environment could induce some negative side effects,such as proliferation of antibiotic resistance bacteria and causing allergenic responses to animals.Therefore,it is critical to monitor their concentrations in the environment to protect the non-target living organisms from taking in these contaminants.Liquid chromatography-mass spectrometry?LC-MS?is one of most common quantitative methods to detect SAs.SAs containing same reactive amino functional group could be labeled by dimethyl labeling which is used to overcome matrix effect in detection of SAs by LC-MS.Multiplex dimethyl labeling was further developed to achieve a mass shift of 28,30,32,34or 36 Da by different isotope reagents.Five samples could be labeled in parallel with different isotope regents,respectively,and 4 real samples were quantified in a single LC-MS analysis.A multiplex solid phase isotope dimethyl labeling method was developed for the quantitative analysis of the trace level SAs in water.Furthermore,this method was applied in the analysis of ice samples in Daliao river estuary and 9 SAs were detected with the concentration from 185ng/L to 402 ng/L.As the pretreatment is essential in the analysis of complex samples,a new magnetic carbon nano material?Tol-MCNT?was prepared for magnetic solid phase extraction?MSPE?.Magnetic Fe₃O₄ particles were deposited onto the amino terminated carbon nanotubes?MWCNT-NH₂?through hydrothermal process,and further modified by using two different isocyanates as modifiers via the nucleophilic addition reaction.The resultant p-methyl-benzyl-MCNT?Tol-MCNT?with better adsorption performance was selected as adsorbent for MSPE,which could extract SAs from various milk samples with a enrichment factor of about 30.By combining the MSPE with LC–high resolution MS?MS?,a new method was developed and applied in the analysis of milk samplesfrom three brands.Four SAs were found with the concentration from unquantifiable to 72?ng/L,which were all well below the maximum residue limits according to the regulations of China and EU.A method for simultaneous determination of SAs in complex manure samples was developed based on MSPE,solid phase quadruplex isotope dimethylationand LC-MS.MSPE was used to enrich the SAs and reduce matrixes.Isotope dimethyl labeling could overcome the matrix effect,while the quadruplex labeling enabled analysis of 3 real samples in one LC-MS run,which could greatly improve the analytical throughput.This method showed good linearity?R²>0.99?and accuracy?intra-day accuracy and inter-day accuracy were 91.5%-104.3%and91.9%-108.4%,respectively?and sensitivity?LOD and LOQ were in the range of 0.05-0.5?g/kg and 0.2-1?g/kg,respectively?.With this method,manure samples were analyzed.From the results,7 SAs were found in the manures at the concentration in the range of ND-433.7?g/kg.These results indicated that the manures from farms was one of the main sources of environmental SAs..