气相转化-化学发光法测定土壤中的亚硝态氮

试验探究了将亚硝态氮(NO_2~-)还原转化为一氧化氮(NO)气体与化学发光法检测NO相结合的方法(气相转化-化学发光法,简称NC法)对土壤NO_2~-含量测定的适用性。在室温条件下,采用浓度为50%的冰醋酸提供酸性条件,以抗坏血酸为还原剂,将NO_2~-还原为NO气体,生成的NO被高纯氮气载入化学发光法氮氧化物分析仪的NO检测通道,实时记录NO信号值并积分信号峰面积,通过已知NO_2~-浓度系列的标准曲线,确定样品中的NO_2~-浓度。结果显示:NO信号值的峰面积与样品的NO_2~-浓度显著正相关(P0.01),线性检测范围为2~500μg·L~(-1)(以纯N计,下同),检出限为2μg·L~(-1),对土壤NO_2~-浓度的检出限为10μg·kg-1(以水土比为5∶1计),优于比色法的检出限15μg·kg-1;重复测定10次50μg·L~(-1)标准溶液的峰面积变异系数为1.2%,精度为1.2μg·L~(-1)(95%置信区间),对应的土壤NO_2~-浓度检测精度为6μg·kg-1,优于比色法的检测精度11μg·kg-1;检测已知浓度NO_2~-的回收率为90%~97%。与比色法相比,NC法测定酸性土壤NO_2~-浓度的准确度相当,精度更优,但该方法测定碱性土壤NO_2~-浓度的结果偏高,可能是碱性土壤中大量的Ca~(2+)、SO_4~(2-)和CO_3~(2-)对测定有干扰,而且NC法测定NO_2~-浓度的分析时间较比色法长,单个样品需8~15 min。

A gas phase conversion-chemiluminescence method for detecting nitrite concentrations in soils

A chemiluminescence method that detects nitric oxide(NO)combined with the conversion from nitrite to NO for measuring soil nitrite concentrations is reported. The applicability of the method is evaluated by comparing it with the colorimetry method. The chemilumi-nescence method involves a reaction system consisting of 50％glacial acetic acid and ascorbic acid in the purge vessel. At room tempera-ture, samples containing nitrite were injected into the purge vessel and nitrite was stoichiometrically reduced to NO by ascorbic acid under these acidic conditions. The produced NO was swept with pure nitrogen gas into the NO analyzer and the data was recorded while chemilu-minescence signals were generated. The concentration of nitrite in the samples was calculated by the curve between the peak areas of the NO signals and the corresponding standard nitrite concentrations. The results showed that peak areas of chemiluminescence signals were linearly positively correlated with the nitrite concentrations in the range of 2 to 500μg·L-1(P<0.01). The lowest detection limit of this method was 2 μg·L-1, equivalent to10μg·kg-1 in soil(water:soil=5:1), lower than that of the colorimetry method(15μg·kg-1). This method had a good precision of 1.2μg·L-1 within 95％confidence interval by repeating the measurements of standard nitrite concentration of 50μg·L-1 for ten times. The corresponding precision for soil nitrite concentration(6μg·kg-1)was also better than that of colorimetry(11μg·kg-1). The recovery rates were in the range of 90％～97％. Compared to the colorimetry, the chemiluminescence method had the same accuracy for detecting ni-trite concentrations in acid soils, but it overestimated the concentrations in alkaline soil because of the existence of Ca2+, SO2-4 , and CO2-3 in al-kaline soil. Moreover, the analysis times for each soil nitrite sample were approximately 8～15 min, which is time-consuming comparing to the colorimetry method.