Comparative Study on the Methods of Sample Treatment in the IC-Determination of Fluorine and Chlorine in Coal

The adaptability of 2 methods (i.e., Ⅰ. combustion-hydrolysis method and Ⅱ. oxygen bomb method) for pretreatment of coal samples in IC-determination of fluorine and chlorine in coal was comparatively studied. CRM's of coal containing F^- and Cl^- were used in the testing. The CRM's were treated separately by the 2 methods, and the sample solutions were analyzed by the same procedure for their contents of F^- and Cl^-. It was shown by the experimental results, that ① the values of detection limit (3S/N) found by method Ⅱ (F^- 0.036 μg·g^-1, Cl^- 0.099 μg·g^-1) were lower than those found by method Ⅰ (F^- 0.072 μg·g^-1, Cl^- 0.198 μg·g^-1); ② analytical results of F^- and Cl^- obtained by both of the methods were found in consistency with the certified values of the CRM's, while the results of Cl^- were shown to be better in accuracy and precison, as the values of relative error between the results found and the certified values attained in the range within 1.0%; ③ results for F^- obtained by method Ⅱ were less accurate than those obtained by method Ⅰ, as in the former case, values of relative error were ranged from -6.5% to -4.0%, and in the letter case, values of relative error were ranged from 0.36% to 3.6%. Furthermore, the method Ⅱ was not suitable for treatment of coal samples with ash contents higher than 25%.