Objective Comparison of two methods for determining ammonium ion content in ambient air PM2.5.Methods 1/4 of the quartz filter membrane used to collect ambient air particles PM2.5 was cut into pieces,and ultrasound extracted by ultra-pure water,then centrifuged and filtered,and last the content of ammonium ion in PM2.5 was respectively determined by flow injection method and ion chromatography.Result The fitting curve of NH4+measured by ion chromatography in the range of 0.5～10.0 mg/L is y=0.0710+0.2214x-0.0058x2,r=0.9997.The detection limit of NH4+in PM2.5 is calculated to be 0.017 μg/m3,with a quantification limit of 0.068 μg/m3,the recovery rate is between 91.0%～96.6%,and the RSD is 0.05%～0.08%(n=6).The linear relationship of ammonium ion concentration measured by flow injection analysis in the range of 0.02～1.00 mg/L is good,with y=22.576x+0.1333,r=0.9999.The detection limit is 0.003 μg/m3,and the quantification limit is 0.012 μg/m3 with the recovery rate of 105%～114%and the RSD between 0.54%～2.06%(n=6).Using the two methods to measure 16 filter membrane samples,there was no statistically significant difference in the measurement results(t=1.080,P>0.05).Conclusion Both of the two methods have a good linear relationship,with good precision and accuracy.Compared with ion chromatography,flow injection analysis has the advantages of lower detection limit and shorter detection time.
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