在0.4 mol·L-1氢氧化钾溶液中甲醛与间苯三酚反应生成一种不稳定的橙色化合物,其吸收峰位于474 nm波长处.以此反应为基础提出了微量甲醛的分光光度测定方法,并采用流动注射技术,对显色反应的过程进行了严格控制并及时地测定所生成的不稳定橙色化合物的吸光度.甲醛质量浓度在10 mg·L-1以内与吸光度呈线性关系,在采样频率为每小时35个样品的条件下,所得检出限为0.023 mg·L-1.在7 mg·L-1浓度水平条件下连续测定11次,测得相对标准偏差为0.29%,试样中微量甲醛先从磷酸溶液中用蒸汽蒸馏法分离并吸收于氢氧化钾溶液中.

In an alkaline solution of 0.4 mol·L-1 KOH,formaldehyde was reacted with phloroglucinol to form an unstable orange colored product with absorption maxima at 474 nm.The above mentioned reaction was used in the rapid determination of micro-amounts of formaldehyde in foodstuffs and by the use of flow-injection technique,the course of the color reaction was controlled strictly and the absorbance of the colored product was measured timely.Linear relationship between the absorbance and concentration of formaldehyde was kept within 10 mg·L-1.At the sampling frequency of 35 sample per hour,the detection limit was found to be 0.023 mg·L-1.Precision of the method was tested at the concentration level of 7 mg·L-1 for 11 determinations,value of RSD obtained was 0.29%.Formaldehyde in the foodstuff sample was separated by steam distillation from a H3PO4 solution and the distillate was absorbed in dil.KOH solution.