Simultaneous Determination Of Multiple β-lactam Antibiotics In Water By LC-MS/MS

Antibiotics are irreplaceable on human health and animal husbandry.In recent years,with the improvement of people’s living quality and the development of animal husbandry,the demand for antibiotics gradually increased.The massive and continuous use of antibiotics can make them long-term residue in the environment.At present,the research on antibiotics in environmental water mainly focused on sulfonamides,quinolones,tetracycline and macrolide antibiotics.Due to the four-membered ring in the β-lactam antibiotics molecule,the stability of the β-lactams is weaker than that of other antibiotics,so the study of the residues of β-lactam antibiotics in the environmental water was insufficient.However,the effect of the residues of β-lactam antibiotics on human health and ecological safety can not be ignored.9 β-lactam antibiotics,amoxicillin,ampicillin,cefaclor,cephalexin,cefotaxime,cefazolin,ceftiofur,penicillin G,penicillin V,were chosen as the target compounds to study their instrument analysis method and pretreatment method in water.The conditions of the final optimized instrument were as follows: The LC-MS/MS equipped with electrospray ionization source(ESI)was operated on the multi reaction monitoring(MRM)mode to analyze the target antibiotics.0.1%(v:v)formic acid-1 g/L ammonium formate aqueous and acetonitrile were used as the inorganic(A)and the organic(B)mobile phases,respectively.The correlation coefficients(R2)of the standard curves were between 0.994-0.998.Solid sample extraction(SPE)was used as the sample pretreatment method.The pH of the sample,the type of eluent and the volume of the eluent were optimized.The optimized results were that the pH of the sample was 6,with 4 mL of 5% formic acid-methanol solution as the eluent.The recoveries of 9 target antibiotics were in the range of 61.4%-108.1% and the relative standard deviations(n = 3)were less than 8.3%.The detection limits were less than 1.5 ng/L.A total of 23 sampling sites were selected for the analysis of the target antibiotics in the main sewage outfall,estuary and reservoir around Dalian by means of the optimized instrumental analysis method and sample pretreatment method.The results showed that the target antibiotics were detected at 18 sampling sites with the detection concentration between 0.7ng/L and 2.8 μg/L,and the total concentration of antibiotics in each sampling points were between ND(Non detected)and 2.8 μg/L.9 target antibiotics were all detected,of which amoxicillin and penicillin G have the largest detection rate and detection concentration.The detection rates and of amoxicillin and penicillin were 34.8%.The total concentration of amoxicillin and penicillin were 6.4 μg/L and 7.1 μg/L,respectively.According to the data of sampling points,it was found that the reservoirs were less affected by β-lactam antibiotics.However,in the estuaries and outfalls,the contents of β-lactam antibiotics were relatively high,may be the main source of the β-lactam antibiotics were from the discharge of sewage and waste water and industrial wastewater.