Abstract:The rapid and accurate determination of ammonia nitrogen in sludge is of great significance for environmental assessment. Due to the shortcomings of cumbersome analysis steps, long processes, and toxic reagents in current ammonia nitrogen analysis methods, this article establishes a flow injection spectrophotometric method for determining ammonia nitrogen in sludge by optimizing extraction conditions and centrifugation methods. Under optimal conditions, 20 g of sludge sample was extracted using a 2.0 mol/L potassium chloride solution as the extraction solution. The solid-liquid ratio was 1:15, and the extraction was carried out by flipping and oscillating. The extraction solution was centrifuged at a speed of 4000 r/min for 15 minutes and then filtered under pressure using a 0.45 μm filter membrane. The content of ammonia nitrogen in the sludge was directly determined by subtracting the extraction agent blank using a fully automatic flow injection analyzer. The results showed that the mass concentration of ammonia nitrogen was linearly related to the corresponding peak area within the range of 0-10.00 mg·L-1, with a correlation coefficient of 0.9999. The detection limit of the method is 0.044 mg/kg, and the lower limit of determination is 0.176 mg/kg. Three different concentrations of actual samples were measured, and the relative standard deviation of the measurement results was 3.36% -7.17% (n=6). Two different sediment samples were spiked and recovered, with a recovery rate of 88.5%-108%. After actual sample analysis, this method was found to be consistent with the results of the national environmental protection standard HJ634-2012 potassium chloride extraction spectrophotometric method for the determination of ammonia nitrogen.