本文建立了普通去离子水提取-双指示剂-酸碱滴定法测定土壤中HCO3-含量的方法.以不同性质的浸提用水配制HCO3-溶液,甲基红-溴甲酚绿混合指示剂指示终点,计算盐酸标准溶液滴定HCO3-的终点误差,结果表明,终点误差分别在0.1%~1.3%和-0.047%~-0.148%之间.对甲基红与溴甲酚绿混合指示剂的配比和用量进行了优化.在优化条件下,土壤中HCO3-添加回收率在98.7%~104.1%之间,日内、日间相对标准偏差低于10.1%,有证标准物质测定值的误差在-7.0%~8.3%,说明本方法具有很好的准确度和精密度.本研究解决了现行标准中土壤浸提用水需要煮沸除CO2,滴定终点难以确定的问题,具有简便、快速且准确的优点,适用于大批量土壤样品HCO3-的同时分析.
A method was developed for the determination of bicarbonate content in soil by ordinary deionized water extraction-bis-indicator-acid-base titration.The HCO3 solution was prepared in extracted water with different properties,and the end point was indicated by the mixed methyl red-bromocresol green indicator.The titration errors of the standard solution of hydrochloric acid for the titration of HCO3 were calculated,and the results showed that the titration errors ranged from 0.1% to 1.3% and-0.047% to-0.148%,respectively.The ratio and dosage of the mixed indicator of methyl red and bromocresol green were optimized.Under the optimized conditions,the recovery of HCO3- in soil was between 98.7% and 104.1%,and the relative standard deviation was less than 10.1%in intra-day and inter-day analyses.The relative errors of the determination value of the certified reference materials was between -7.0% and 8.3%,indicating good accuracy and precision of this method.This study solved the problem in the current standard that the water used for soil extraction needs to be boiled to remove CO2 and the titration endpoint is difficult to be determined.This method is simple,fast,and accurate,and suitable for the batch analysis of a large number of soil samples for HCO3-.