| A liquid chromatography with tandem mass spectrometry（LC-MS/MS）method was developed and validated to simultaneously determine metalaxyl-M and azoxystrobin in soil,potato,and potato foliage samples.The method was applied on the residual analysis of metalaxyl-M and azoxystrobin（suspension emulsion,39%）in soil,potato,and potato foliage samples after sprayed.Field trials were conducted in Guizhou and Hunan province at 2017,and in Heilongjiang,Anhui,Tianjin,Neimenggu,Henan,Shandong,Guangxi,Qinghai,Gansu and Shanxi province at2018.The residual analysis and risk assessment results could provide data for the safe application of metalaxyl-M and azoxystrobin in potato.The two target compounds were extracted from soil,potato,and potato foliage samples with acetonitrile,then purified by octadecyl silane and finally detected by LC-MS/MS.The method showed great linearity（determination coefficients≥0.9926）for metalaxyl（the residue definition of metalaxyl-M,0.0025–0.5μg/m L）and azoxystrobin（0.005-1μg/m L）.The limits of detection and quantification for metalaxyl were 1.92×10-14g and 0.005 mg/kg,azoxystrobin were 3.06×10-14g and0.01 mg/kg.The average recoveries in soil,potato,and potato foliage were83.07-92.87%for metalaxyl-M and 82.71-98.53%for azoxystrobin.The intra-day relative standard deviations（RSDs,n=5）were 0.30-7.82%for metalaxyl and0.30-8.96%for azoxystrobin.The inter-day RSDs（n=15）were all less than 8%.The results showed that the method was satisfied with the Chinese Pesticide Residues Test Standards（NY/T 778-2018）.In 2017,the pesticides were sprayed on potato at the recommended dosage（117g a.i./ha）and 1.5 times the recommended dosage（175.5 g a.i./ha）3-4 times with an interval of 7 days,the samples were randomly collected in each treated plot at 5,7 and 10 days after the last application.The terminal residual concentrations of metalaxyl-M and azoxystrobin in potato were<0.005–0.012 mg/kg and<0.010–0.021 mg/kg,respectively.In 2018,the pesticides were sprayed on potato at the recommended dosage（117 g a.i./ha）3 times with an interval of 7 days,the samples were randomly collected in each treated plot at 7 and 10 days after the last application.The terminal residual concentrations of metalaxyl and azoxystrobin in potato were<0.005–0.006mg/kg and<0.010–0.021 mg/kg,respectively.According to the terminal residue data,the dietary risk assessment of metalaxyl and azoxystrobin on potatoes was conducted,metalaxyl and azoxystrobin did not present health concerns to the population because the risk quotients were far below 100%,the risk to humans was acceptable. |
