高分辨连续光源原子吸收光谱法测定煤中硫

Determination of sulphur in coal by high resolution atomic absorption spectrometry with continuum light source

提出一种用HNO3、HClO4和HF消解样品、高分辨连续光源原子吸收光谱法测定硫在富燃空气-乙炔火焰中形成的CS双原子分子的吸收来测定煤中硫的新方法。实验用含硫标准溶液和煤的标准物质优化了仪器条件,并用不同混合酸对煤样的消解方法进行了比较。对可能存在的光谱和化学干扰、有机溶剂对硫的化合物CS吸收的影响进行了研究。结果表明:除了Fe 258.045 nm线与CS 258.056 nm线的波长差小于0.015 nm外,其他元素干扰线与CS线的波长差均大于0.015 nm,因此可以通过仪器的高分辨率使这些干扰线与CS线分开,克服干扰;Fe 258.045谱线虽然不能与CS 258.056 nm谱线完全分离,但是该谱线在富燃乙炔空气火焰中的吸收强度很弱,不能形成真正的干扰;Pb与溶液中的SO42-反应产生Pb-SO4沉淀降低了CS的吸收,可在溶液中加入乙酸铵溶液,使SO42-从PbSO4沉淀中释放出来而消除铅的干扰;HNO3、HClO4对CS的吸收影响不明显;在研究的甲醇、乙醇、乙酸、乙腈和丙酮5种有机溶剂中,只有乙醇对CS吸收有较显著的抑制作用,丙酮和乙腈能显著提高CS的吸收。对于CS 3条吸收线(257.594,258.056,257.961 nm),硫校准曲线的线性范围均为50～1 000 mg/L,检出限分别为34 mg/L,21 mg/L,12 mg/L。本方法用于煤标准物质和煤层样品中硫的测定,测定值与认定值相符,测定结果的相对标准偏差在0.053%～0.082%间(n=5)。

The sample was digested with HNO3,HClO4 and HF.A new method of determining sulphur in coal by high resolution atomic absorption spectrometry with continuum light source based on the measurement the absorption of CS diatomic molecule formed in fuel-rich air and ethyne flame was proposed.The instrumental conditions were optimized using sulphur-bearing standard solution and certified reference materials of coal.The digestion methods of coal sample with different acid mixtures were compared.The possible existing spectral and chemical interference and the influence of organic solvent on the absorption of CS were studied.The results showed that,except that the wavelength difference between Fe 258.045 nm and CS 258.056 nm was smaller than 0.015 nm,the wavelength differences between the interference lines of other elements and CS line were all larger than 0.015 nm.There for,these interference lines could be separated from CS line by the high resolution of instrument,overcoming the interference.Although Fe 258.045 nm line could not be totally separated from CS 258.056 nm,its absorption strength in fuel-rich air and ethyne flame was very low and had no true interference.The generated PbSO4 precipitates from Pb and SO42-in solution reduced the absorption of CS,so ammonium acetate was added into solution to release the SO42-from PbSO4 precipitates to eliminate the interference of lead.The effect of HNO3 and HClO4 on the absorption of CS was not obvious.In five organic solvents including methanol,ethanol,acetic acid,acetonitrile and acetone,only ethanol showed obvious inhibition on the absorption of CS,and acetone and acetonitrile could significantly enhance the absorption of CS.For three absorption lines of CS（9 257.594 nm,258.056 nm and 257.961 nm）,the linear ranges of calibration curves of sulphur were all 50-1 000 mg/L.The detection limits were 34 mg/L,21 mg/L and 12 mg/L,respectively.The proposed method was applied to the determination of sulphur in certified reference material of coal and coal seam sample.The found results were consistent with the certified values,and the relative standard deviation（RSD,n=5） of determination results were 0.053 %-0.082 %.