碘褪色光度法间接测定空气中的甲醛含量

在硫酸介质中,痕量甲醛与过量重铬酸钾反应,剩余重铬酸钾在酸性条件下与碘化钾反应生成单质碘,利用I3-能产生紫外-可见吸收,在350nm处有最大吸收的原理,建立了碘褪色光度法间接测定微量甲醛含量的方法,并讨论了反应介质、试剂用量、加热时间、放置时间与温度的影响及共存离子的影响,确定了最佳反应条件。实验结果表明,体系溶液中甲醛质量浓度在0.225～1.575μg/mL范围内时符合朗伯-比耳定律,线性回归方程为A350=0.005+0.248ρ(μg/mL),相关系数r为0.999。该法适用于空气中的甲醛含量的测定,相对标准偏差RSD为1.28%～1.67%。

Determination of Formaldehyde in Air by Iodine Fading Spectrophotometry

A new spectrophotometric method for the determination of formaldehyde was proposed. It was based on the reaction of formaldehyde and excessive potassium bichromate in sulfuric acid medium. After the reaction,surplus potassium bichromate reacted with potassium iodide and iodine was formed. It had the maximum absorbance at 350nm. The optimum experimental conditions for the determination were studied. Beer＇s law was obeyed between the concentration of formaldehyde 0.225 to 1.575μg/mL and the decrease of the absorbance. The determined regressive equation was A350=0.005＋0.248ρ（μg/mL）,and the related coefficient r was 0.999. The method was applied to determine free formaldehyde in the air,and the RSD was between 1.28% and 1.67%.