Determination of Cr (Ⅵ) in Coal Ashby Microwave Alkaline Digestion and Inductively Coupled Plasma-Optical Emission Spectrometry
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摘要: 定量分析煤灰中Cr（Ⅵ）含量对于控制煤炭燃烧过程中产生的高毒性Cr（Ⅵ）的排放具有重要意义。现有的Cr（Ⅵ）定量分析方法主要是针对水、土壤、固体废弃物中的高浓度Cr（Ⅵ），前处理方法耗时长，检出限较高，不能有效测定煤灰中的低浓度Cr（Ⅵ）含量，因此有必要建立便捷、有效的煤灰中Cr（Ⅵ）高灵敏度检测方法。本文采用碱性提取剂，使用微波消解仪对煤灰进行前处理，对样品量、微波消解时间、微波消解温度等微波消解条件进行了优化，通过共沉淀法分离消解液中的Cr（Ⅲ）与Cr（Ⅵ），应用电感耦合等离子体发射光谱法测定Cr（Ⅵ）含量。结果表明，当样品量为0.2 g，微波消解温度为90℃，消解时间为60 min时能够保证煤灰中Cr（Ⅵ）的完全提取及准确测定。方法检出限为0.00033 μg/mL，测定下限为0.00134 μg/mL，实际样品的加标回收率平均值为87.2%。传统的二苯卡巴肼-紫外分光光度法的检出限为0.001 μg/mL。与传统方法相比，本方法检出限降低，提高了检测灵敏度。
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关键词:
- 煤灰 /
- 六价铬 /
- 微波碱消解 /
- 电感耦合等离子体发射光谱法
Abstract: Quantitative determination of Cr (Ⅵ) in coal ash is very important for controlling the emission of highly toxic Cr (Ⅵ) produced by coal combustion. Available quantification determination methods are mainly used for detecting high concentration Cr (Ⅵ) in water, soil and solid waste, which are not suitable for analyzing low concentration Cr (Ⅵ) in coal ash. The sample processing methods are time consuming and the detection limits are relatively high. Thus, it is necessary to develop a convenient, effective and highly sensitive determination method for Cr (Ⅵ) in coal ash. In this study, alkaline solvent and the microwave digestion system were used for pretreatment of coal ash. Through the experiments, the digestion conditions, which included sample amount, microwave digestion time, and microwave digestion temperature were optimized. The chemical co-precipitation method was used to separate Cr (Ⅲ) and Cr (Ⅵ) in the extracted solution. The concentration of Cr (Ⅵ) was determined by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). The results show that the optimum digestion condition is 0.2 g sample digested under 9℃ for 60 minutes. The determination limit is 0.00134 μg/mL (in Table 1), and the average matrix spike recovery of practical samples is 87.2% (in Table 2). The detection limit of this method is 0.00033 μg/mL (in Table 1), suggesting that the sensitivity of Cr (Ⅵ) was improved by 10 times than that of the traditional 1, 5-diphenylcarbohydrazide spectrophotometric method (0.001 μg/mL). -
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表 1 方法检出限和测定下限
Table 1. Detection limits and low determination limits of the method
分析项目 空白测定值 (μg/mL) 空白7次的测定值
(μg/mL)0.0014 0.0016 0.0017
0.0017 0.0016 0.0016
0.0017平均值 (μg/mL) 0.0016 标准偏差 (μg/mL) 0.000107 t值 3.143 检出限 (μg/mL) 0.00033 测定下限 (μg/mL) 0.00134 
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表 2 样品加标回收率测定结果
Table 2. Determination results of matrix spike recovery for practical samples
加标量
(μg)6次平行测定的
平均值 (μg)回收率
(%)RSD
(%)2 1.67 83.5 1.8 5 4.42 88.4 2.0 10 8.96 89.6 2.3
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