沼液中乙酸含量比色测定法研究

Determination of acetic acid in the biogas slurry by a colorimetric method

为了建立一种能用于沼液中乙酸含量灵敏准确分析的常规检测方法,通过对沼液沉淀、脱色及过滤处理获得无色透明待测液,再利用乙酸与FeCl_3反应形成乙酸铁红色化合物的特性,研究了沼液中乙酸含量比色分析的可行性及准确度。结果表明:沼液预处理时,沉淀剂吸附乙酸导致待测液中乙酸测值偏低,在沉淀剂用量固定时其负偏差为一常数,可用该常数对乙酸测定结果进行校正;将脱色时间控制在10 min以内时,加入活性炭脱色剂对乙酸测定结果无影响;沼液预处理获得的含乙酸待测液与100.0 g·L^(-1)FeCl_3显色剂反应得到乙酸铁化合物,其在550 nm处的吸光值在显色后3.0～6.0 h内基本不变,其相对偏差为±5%;在沼液预处理待测液中,用乙酸铁比色法测定乙酸时的平均回收率为97.52%(RSD为1.44%,n=5)。该研究表明,乙酸铁比色法简单、灵敏且准确度高,适用于沼液中乙酸含量的常规测定。

The study was conducted to develop a sensitive and accurate method for determination of acetic acid in the biogas slurry.The colorless transparent liquid by sedimentation,decoloring and filtering operations on biogas slurry was prepared.On the basis of spectrometry feature of the red reaction product of acetic acid with FeCl3 solution,we studied the feasibility and accuracy of the colorimetry method for the determination of acetic acid in the biogas slurry.The results showed that the precipitation treatment could lead to a deviation value of acetic acid concentration,since precipitant could adsorb acetic acid.The minus deviation remained unchanging when the dosage of precipitant was constant,which could be used to adjust the measurement of acetic acid concentration.The activated carbon had no impact on the measurement of acetic acid concentration if the time of adsorption was controlled within 10 min.When reacted with 100.0 g·L-1 FeCl3,the absorbance of reaction product acetic iron compound at 550 nm was basically unchanged within 3.0~6.0 h,the relative deviation was±5%;After pretreatment of biogas slurry,the average recovery ratio in treatment fluids was 97.52%(RSD was 1.44%,n=5).This method was sensitive and accurate,which could be used as a conventional method of determining acetic acid in the biogas slurry.