Warner C R, Daniels D H, Fitzgerald M C, Joe F L, Diachenko G W
Division of Food Chemistry and Technology, Food and Drug Administration, Washington, DC 20204.
Food Addit Contam. 1990 Sep-Oct;7(5):575-81. doi: 10.1080/02652039009373922.
The reaction of sulphite with formaldehyde to form hydroxymethylsulphonate (HMS), which is very stable under the controlled conditions of this assay, was used as the first step in an analytical procedure to determine foodborne sulphite. The effect of mobile-phase pH on the stability of HMS during high-performance liquid chromatography was studied. It was found that on-column HMS dissociation to formaldehyde and bisulphite increased with the pH of the mobile phase; therefore the relatively low pH 4.7, at which the dissociation of HMS was approximately 2%, was selected for the analysis. In addition, the release of sulphite from its reversibly bound forms in wine and other foods was examined as a function of the pH of the extraction medium by following the appearance of HMS formed from the reaction of the freed sulphite with formaldehyde. The rate of dissociation of the reversibly bound sulphite was relatively slow at pH 3 but very rapid at pH 7. This difference in kinetics was exploited to develop a procedure to determine free and reversibly bound sulphite in food. The method was challenged by post-reagent spiking studies, i.e. adding the sulphite spike after the food has been blended with the sulphite-protective formaldehyde solution but before proceeding with the remainder of the assay. An average recovery of 100% with a standard deviation of 5.2% (n = 45) was realized at levels of 5, 10 and 20 ppm by weight as sulphur dioxide. Recovery of the sulphite added as the bisulphite addition product of acetaldehyde, a model compound for reversibly bound sulphite, was 95%.
亚硫酸盐与甲醛反应生成羟甲基磺酸盐（HMS），在本分析方法的控制条件下，该物质非常稳定，此反应被用作测定食品中亚硫酸盐的分析程序的第一步。研究了流动相pH值对高效液相色谱分析过程中HMS稳定性的影响。结果发现，随着流动相pH值的升高，柱上HMS分解为甲醛和亚硫酸氢盐的程度增加；因此，选择相对较低的pH 4.7用于分析，此时HMS的分解率约为2%。此外，通过跟踪游离亚硫酸盐与甲醛反应生成的HMS的出现情况，研究了葡萄酒和其他食品中可逆结合形式的亚硫酸盐在不同pH值提取介质中的释放情况。可逆结合的亚硫酸盐在pH 3时分解速率相对较慢，但在pH 7时非常快。利用这种动力学差异开发了一种测定食品中游离和可逆结合亚硫酸盐的方法。该方法通过试剂加标后研究进行验证，即在食品与亚硫酸盐保护剂甲醛溶液混合后、但在进行其余分析步骤之前加入亚硫酸盐加标物。以二氧化硫计，在5、10和20 ppm重量水平下，平均回收率为100%，标准偏差为5.2%（n = 45）。作为可逆结合亚硫酸盐的模型化合物，乙醛亚硫酸氢盐加合物形式添加的亚硫酸盐回收率为95%。
