提出了气相分子吸收光谱法测定环境空气和废气中氨含量的方法。采集环境空气样品时,使用25 mL吸收管,加入25 mL 0.01 mol·L^-1硫酸溶液作为吸收液,以流量1.5 L·min^-1采样0.5~1.0 h;采集废气样品时,使用50 mL吸收管,加入50 mL 0.01 mol·L^-1硫酸溶液作为吸收液,以流量0.5 L·min^-1采样0.5 h。设置气相分子吸收光谱仪检测波长为214.7 nm(氘灯光源)或213.9 nm(锌空心阴极灯光源),加热温度为80~90 ℃。通过干扰试验,证实了Mn²⁺、苯胺、抗坏血酸、Mn⁷⁺、ClO^-会对氨的测定产生干扰,可通过氧化法、还原法、蒸馏法、稀释法对上述干扰物质进行消除。以质量浓度不大于14.0 mg·L^-1的氨标准溶液系列作为绘制校准曲线的母液。结果表明,氨校准曲线线性范围在4.00 mg·L^-1以内,方法检出限为0.008 mg·m^-3(环境空气)和0.03 mg·m^-3(废气)。对实际环境空气和废气样品分别进行3个浓度水平的加标回收试验,回收率为97.9%~106%,氨测定值的相对标准偏差(n=6)不大于2.5%,并通过配对样本F检验法确定该方法与现行有效的纳氏试剂分光光度法无显著性差异。

A method for the determination of ammonia in ambient air and exhaust gas by gas phase molecular absorption spectrometry was proposed. When collecting ambient air sample, 25 mL of 0.01 mol·L^-1 sulfuric acid solution as absorption solution was added into 25 mL-absorption tube, and then sampling was conducted for 0.5-1.0 h at flow rate of 1.5 L·min^-1. When collecting exhaust gas sample, 50 mL of 0.01 mol·L^-1 sulfuric acid solution as absorption solution was added into 50 mL-absorption tube, and then sampling was conducted for 0.5 h at flow rate of 0.5 L·min^-1. The detection wavelength of gas phase molecular absorption spectrometer was set as 214.7 nm (deuterium light source) or 213.9 nm (zinc hollow cathode light source), and the heating temperature was set in the range of 80-90 ℃. It was confirmed that Mn²⁺, aniline, ascorbic acid, Mn⁷⁺ and ClO^- would interfere on the determination of ammonia through interference test, and the interference substances above could be eliminated by oxidation, reduction, distillation and dilution methods. The series of ammonia standard solution with mass concentration no more than 14.0 mg·L^-1 was used as the mother liquor to draw the calibration curve. It was shown that the linear range of the ammonia calibration curve was within 4.00 mg·L^-1, with detection limits of 0.008 mg·m^-3 (ambient air) and 0.03 mg·m^-3 (exhaust gas). Test for recovery was made on the actual samples of ambient air and exhaust gas at 3 concentration levels by standard addition method, respectively, and the recoveries were in the range of 97.9%-106%, with RSDs (n=6) of the ammonia determined values less than 2.5%. Meanwhile, there was no significant difference between this method and the current effective Nessler's reagent spectrophotometry by F-test using paired samples.