On-bead Stable Isotopic Dimethyl Labeling Combined With LC-MS For The Quantification Of Sulphonamides

Sulfonamides（SAs）are widely used antibiotics in clinical and veterinary fields.Due to the excessive use of sulfonamides,a part of SAs enter into the environmental media,which increase the resistance of the patholoen bacterials and cause harm to the ecological environment.In order to monitor their concentration level,it is essential to establish an accurate and rapid method to quantitatively analyze the SA pollutants in complex environmental samples.Currently,the analytical technology of SAs and their metabolites in the complex environmental samples is mainly relied on high sensitivity analytical instruments.Liquid chromatography-mass spectrometry（LC-MS）is one of the most widely methods used in this area.In quantitative analysis by LC-MS,isotope internal standard method is most reliable.However,due to the commercial unavailability and high price,this method is not applicable when lots of targtets need to be quantified.In contrast,stable isotope labeling method can overcome this problem.In this dissertation,stable isotope-dimethyl labeling method was successfully introduced to the LC-MS quantification of SAs.Since the concentration of SAs in the environmental samples is usually at a trace level,so a magnetic solid phase extraction（MSPE）technique was incorporated to enrich these targets.Meanwhile,the dimethyl labeling of SAs was carried out on the beads after the capturing of SAs（on-beads labeling）.For the synthesis of magnetic nanomaterials,the conditions were systematical investigated and Fe₃O₄@SiO₂-C18 magnetic nanoparticles with uniform particle size and good distribution were obtained through a three-step approach including solvent thermal reduction reaction,silylation reaction and alkylation reaction.The synthsized magnetic nanoparticles have a good adsorption property for SAs.The adsorption properties of the three adsorbent materials were compared in the experiment.Finally,Fe-C MNPs was selected as the adsorbent for the MSPE process.Then the MSPE process and labeling conditions such as amount of labeling regents,pH,temperature and reaction time for dimethyl labeling method（both in-solution and on-bead）were carefully optimized.Compared with the conventional in-solution labeling,the on-bead labeling could greatly reduce the amount of the labeling reagent,improve the labeling efficiency,and save the reaction time.By integrating the optimized MSPE,dimethyl labeling and HPLC-HRMS,we established a new method for quantitative analysis of SAs.To verify the capability in analysis of trace SAs in complex samples,lake water（sampled from the campus lake）spiked with trace amount of SAs was chosen in the experiment.By analyzing the lake water sample which contained 12 SAs with different concentrations（from 0.01⁵ ppb）,satisfying results were observed,including good reproducibility（RSD<10%,n=3）,linearity（R2≥0.99）and good accuracy（0.82¹.07）over the tested concentration range.The recoveries of MSPE for these 12 SAs are about 85.1¹00.5%（note: recovery is not envolved in calculation of the concentration）,and the LODs are in the range of 0.01 to 0.2 ppb.These results confirm that this new method could be applied in the analysis of trace SAs in complex environmental samples.