TMB-PA-DMA目视比色法测定水中余氯

Determination of residual chlorine in water by TMB-PA-DMA visual colorimetry

建立TMB(3,3',5,5'-四甲基联苯胺)–PA(磷酸)–DMA(N,N-二甲基乙酰胺)目视比色法现场测定水中余氯的方法。在国标法TMB目视比色法基础上,将TMB显色剂中盐酸浓度由0.10 mol/L提高至0.50 mol/L;加入DMA加速溶解TMB并防止TMB析出;加入PA消除铁的干扰并缓冲溶液的pH值。在0.50 mol/L盐酸溶液下,通过正交试验,确定TMB、PA、DMA最优组合:TMB为0.30 g/L,PA为1.00 mol/L,DMA为0.50%(体积分数)。结果表明:加入DMA后TMB溶解时间由约5 h缩短至30 s;加入PA消除铁干扰效果明显;水样无需事先用酸调节pH值,直接加入显色剂即可比色定量。用TMB–PA–DMA法测定水样中余氯,测定结果的相对标准偏差不大于3.7%(n=7)。分别用TMB–PA–DMA目视比色法和DPD分光法测定水样中余氯,二者的测定结果无显著差异。该方法简便高效,快速、准确,更适宜现场测定水中余氯。

A method of on-site determination of residual chlorine in water samples by TMB(3,3',5,5'-tetramethylbenzidine)–PA(phosphoric acid)–DMA(N,N-dimethylacetamide)visual colorimetry was established.Based on the national standard method of TMB visual colorimetry,the concentration of hydrochloric acid in TMB chromogenic agent was increased from 0.10 to 0.50 mol/L;adding DMA can accelerate the dissolution of TMB and prevent TMB precipitation;adding PA can eliminate interference of iron and buffer the pH value of solution.Under 0.50 mol/L hydrochloric acid,the optimal combination of TMB,PA,DMA was determined as followed:0.30 g/L TMB,1.00 mol/L PA,0.50%DMA.TMB was rapidly dissolved from 5 h to 30 s under DMA assisted solution;PA had obvious effect on eliminating iron interference;the water sample could be colorimetric and quantitative without adjusting pH value with acid in advance.TMB–PA–DMA visual colorimetry was used to determine residual chlorine in water samples,and the relative standard deviation was not more than 3.7%(n=7).There was no significant difference between TMB–PA–DMA visual colorimetry and DPD spectrophotometry for determination of residual chlorine in water samples.The method is simple,efficient,rapid and accurate,wich is more suitable for on-site determination of residual chlorine in water.