三酸分步消解-电感耦合等离子体质谱法测定土壤详查样品中23种金属元素

土壤详查样品具有数量大、基质复杂、有机质含量高的特点，传统上采用多种混合酸体系的消解方法，不仅会造成有机质消解不完全，消解后的溶液中常有黑色的碳质存在，而且样品消解后只用稀硝酸提取，一些难溶氧化物、硫酸盐、氟化物难以形成可溶性盐，致使提取不彻底，若用逆王水提取则易大量引入氯离子造成氯的多原子离子质谱干扰。本文针对上述问题，充分利用硝酸、氢氟酸、高氯酸的不同特性，采用电热板控温，三酸分步加入法消解土壤样品，对于消解后的样品，采用硝酸-盐酸（体积比20：1）作为提取剂，有效降低了氯的多原子离子质谱干扰且提取彻底。结果表明：本方法能够消解土壤中有机质和硅酸盐组分，具有试剂用量少、氯的质谱干扰小、操作流程简单、工作效率高等优点，方法检出限（3s）更低（0.0008~0.90mg/kg）。将该方法应用于暗棕壤、石灰岩土壤、黄棕壤国家标准物质中23种元素的测定，其测定结果明显优于传统的消解方法，相对标准偏差（RSD，n=6）为0.022%~5.83%，相对误差为-8.33%~9.17%，测定时与认定值相符。该方法具有较高的适用性和可靠性。

Determination of 23 Metal Elements in Detailed Soil Survey Samples by Inductively Coupled Plasma-Mass Spectrometry with Three Acid Stepwise Digestion

BACKGROUND: The soil detailed survey samples have the characteristics of large quantity, complex matrix, and high organic matter content. The traditional digestion method using a variety of mixed acid systems not only leads to incomplete digestion of organic matter, but also leaves black carbon in the solution after digestion. Because the sample is only extracted with dilute nitric acid, some insoluble oxides, sulfates, and fluorides are difficult to form soluble salts, resulting in incomplete extraction. If the reverse aqua regia is used during extraction, it is easy to introduce a large amount of chloride ions and cause the interference problem of chlorine multi-atomic ion mass spectrometry.
OBJECTIVES: In order to accurately determine 23 metal elements in soil. The analysis efficiency and quality can be improved by making full use of the different characteristics of nitric acid, hydrofluoric acid and perchloric acid in sample digestion.
METHODS: Soil samples were digested on electric heating plate, by stepwise addition of nitric acid, hydrofluoric acid and perchloric acid. For the digested samples, nitric acid-hydrochloric acid (20:1, V/V) mixed solution was used as the extractant, effectively reducing the interference of chlorine polyatomic ion mass spectrum and extracting elements thoroughly. Twenty-three metal elements in the soil were simultaneously determined by inductively coupled plasma-mass spectrometry (ICP-MS).
RESULTS: This method can effectively digest organic matter and silicate components in soil. It has the advantages of less reagent consumption,less mass spectrum interference of chlorine, simple operation process, high working efficiency, and lower detection limit (0.0008-0.90mg/kg, 3s). This method was applied to the national level standard substance such as dark brown soil, limestone soil, yellow brown soil samples for the determination of 23 elements, and the measurement result was superior to the traditional digestion method. The precision (RSD, n=6) was 0.022%-5.83% and relative error was -8.33% to 9.17%. The results are consistent with the certified values, indicating that the method is applicable and reliable.
CONCLUSIONS: The method for the simultaneous determination of 23 elements in soil samples by ICP-MS with three acid stepwise digestion has high applicability and reliability.