土壤中全硫测定——硫分析仪选择及方法优化

Determination of total sulfur in soil:selection of sulfur analyzer and method optimization

全硫含量是土壤调查项目中的必测项目。在燃烧法直接测定固体样品的硫分析仪中,高频红外碳硫仪检测限低,检测速度快,燃烧温度高,测定土壤标准物质的准确度高,是快速测定土壤中全硫的最佳仪器。应用高频红外碳硫仪测定样品过程中,坩埚空白、通氧流量、样品称样量、助熔剂添加量、定量方法等均会对测定结果准确度产生影响。通过对上述影响条件进行优化,研究确定了测定土壤中全硫含量的最佳条件:在严格控制坩埚空白的前提下,通氧流量设定为2~3 L/min,依次称取0.1 g样品(精度:0.0001 g)、0.5 g纯铁(精度:0.001 g)和1.0 g钨粒助熔剂(精度:0.001 g)混合后上机分析,对不同浓度样品进行分段校正。值得注意的是,本研究证实了利用化学物质标准品建立工作曲线的可行性,为后期仪器优化和改进提供了宝贵思路。国家土壤标准物质测定结果的相对标准偏差(RSD)小于2%(n=6),测定值与标准值相对误差(RE)的绝对值小于1%(n=6),方法检出限为4.50μg/g,说明方法的准确度和精密度高,适用于低含硫量土壤样品的批量检测。

Total sulfur content is a mandatory item in soil investigation projects.In the sulfur analyzer that directly determines solid samples using the combustion method,the high-frequency infrared carbon-sulfur analyzer has the advantages of low detection limit,fast detection speed,high combustion temperature,and high accuracy in determining soil standard substances,making it the best instrument for rapid determination of total sulfur in soil.In the process of sample determination using high-frequency infrared carbon-sulfur analyzer,the crucible blank,oxygen flow rate,sample weight,flux addition amount,and quantitative method would all affect the accuracy of the measurement results.By optimizing the above influencing conditions,the optimal conditions for analyzing the total sulfur content in soil were determined:in the case of strictly controlling the crucible blank,the oxygen blowing flow rate was set to 2-3 L/min,and 0.1 g of sample(accuracy:0.0001 g),0.5 g of pure iron(accuracy:0.001 g),and 1.0 g of tungsten particle flux(accuracy:0.001 g)were mixed and then analyzed on machine.Samples of different concentrations were calibrated in sections.It is worth noting that this study has confirmed the feasibility of establishing a working curve using chemical substance standards,providing valuable ideas for instrument optimization and improvement in the later stage.The relative standard deviations(RSDs)of the measured results of national soil standard substances were less than 2%(n=6),the absolute value of the relative errors(REs)between the measured values and the standard values were less than 1%(n=6),and the detection limit of the method was 4.50μμg/g,indicating that the method had high accuracy and precision,and was suitable for batch testing of soil samples with low sulfur concentrations.