气相分子吸收光谱法测定海水中的氨氮

采用气相分子吸收光谱法测定海水中的氨氮,并对相关影响因素进行探讨。结果证实,近海岸海水和河口水样品加酸固定后需调节pH值至中性;无须滤膜抽滤,可直接上机检测;所用溴酸盐混合储备液和40%氢氧化钠溶液在25℃保存不宜超过2周,超过25℃应现用现配;采集好的水样不宜长时间保存,应立即测定。方法在ρ(氨氮)为0.01~0.40 mg/L和0.10~2.00 mg/L范围内均具有良好的线性,r值均0.999;方法检出限为0.003 mg/L;实际样品和标准样品的RSD为1.0%~1.6%;加标回收率为94.0%~110%。与次溴酸盐氧化法相比,二者氨氮的测定结果无显著性差异,气相分子吸收光谱法测定氨氮的范围更宽,高浓度的氨氮样品可直接检测,减少稀释带来的误差。

Determination of Ammonia Nitrogen in Seawater by Gas Phase Molecular Absorption Spectrometry

The gas-phase molecular absorption spectrometry method was employed to determine the content of ammonia nitrogen in seawater, and relating factors that might influence the results were discussed.The results showed that when seawater samples from the coast and water samples from the river mouth were adjusted with acid to a neutral pH, there was no need for membrane filtration before direct analysis by the instrument.The storage of the mixed solution of bromate and the solution containing 40%of sodium hy-droxide should be no longer than two weeks and the storage temperature should be no higher than 25 ℃, otherwise the solutions should be remade fresh.The collected water samples should not be stored for a long period and they should be analyzed promptly af-ter collection.Using the gas-phase molecular absorption spectrometry method, good linear relationships were obtained for ammonia nitrogen in the mass concentration ranges of 0.01~0.40 mg/L and 0.10~2.00 mg/L, respectively, and the coefficient values r were both greater than 0.999.The method detection limit was 0.003 mg/L.RSDs of the actual samples and standards were in the range of 1.0%~1.6%, and the recovery rates were in the range of 94.0%~110%.Compared with the hypobromous acid oxida-tion method, there was no significant difference in the measurement results for ammonia nitrogen.Because of the large dynamic range for the detection of ammonia nitrogen, the gas-phase molecular absorption spectrometry method could be used for samples with high concentrations, which could reduce errors caused by dilution.