碱熔-氟离子选择性电极法测定土壤氟含量

用碱熔法处理3个土壤样品,采取不同澄清时间的上清液及过滤后的沉淀物分析土壤氟含量。结果表明,上清液中氟含量测值随着澄清时间的延长而增加,24 h内增加迅速,而后增速趋缓,58 h后基本达到平衡。3个样品澄清平衡后的测值比澄清10 h的测值分别增加了39.4%、21.8%和27.8%。综合澄清平衡后的上清液及沉淀物得到的土壤氟含量测值比高温热水解法的测值仍然分别偏低0.48%、6.17%和11.88%,这是由于溶液中阳离子的存在使氟离子活度降低造成的。采用传统的碱熔法和高温热水解法分别研究了27个土壤样品的氟含量,碱熔法测值与高温热水解法测值相比普遍偏低,相对偏低在4.23%~34.82%之间,平均相对偏低19.12%。

DETERMINATION OF FLUORIDES IN SOILS BY THE ALKALINE MELING-FLUORIDE ION-SELECTIVE ELECTRODE METHOD

The alkaline melting method was used for the pretreatment of three soil samples. The fluoride contents of the supernatant at different times and those of the defecation scum after filtering were analyzed.The results indicated that the fluoride contents increased with defecation time.Rapid increase occurred in the first twenty-four hours,the fluoride contents almost reached equilibrium in the solution about fifty-eight hours later.The fluoride contents of three soil samples increased by 42.8%,21.8% and 27.8% over those with ten hours of defecation, respectively.As a result of the deduction of ionic activity of fluoride due to the existence of cations in the solution,the summations of the fluoride contents for the three samples both in the supernatant and defection scum were 0.48%,6.17% and 11.88% lower than those obtained by the pyrohydrolytic decomposition method,respectively.The fluoride contents of twenty-seven samples were measured by the traditional alkaline melting method and the pyrohydrolytic decomposition method,respectively.The measured values by the alkaline melting method were normally lower than those by the pyrohydrolytic decomposition method with a range of 4.23%~34.82%,averaging 19.12%.