A direct enzyme-linked immunosorbent assay for the detection of the short-chain sulfophenylcarboxylic acids (SPCs), the main metabolites of the linear alkylbenzenesulfonates, is reported. Six SPCs (2C3, 2C4, 3C4, 2C5, 3C5, 3C6), differing in the length of the alkyl chain (between C3 and C6) and in the position of the phenylsulfonic group versus the carboxylic group, have been synthesized. Antibodies have been raised against a mixture of the corresponding horseshoe crab hemocyanin conjugates prepared by coupling the carboxylic acid to the lysine amino acid residues. The immunoassay As115/3C4−HRP achieves an IC50 value of 23 nM (6.67 μg L-1) and a detection limit of 0.85 nM (0.24 μg L-1), using as standard analyte an equimolar mixture of the six SPCs. The immunoassay has found to work better in media with low or moderate ionic strength (4−30 mS cm-1). The decrease in the detectability produced by the potential formation of SPC salts with divalent cations such as Ca2+ can be prevented by lowering the pH of the assay medium below the pKa value of the SPC carboxylic group and using a buffer chelating with properties such as citrate buffer. The assay can be considered specific for short-chain SPCs since congeners with longer alkyl chains and other pollutants containing sulfonic groups in their structure do not interfere significantly in the assay. Preliminary experiments addressed to evaluate the potential application of this assay to environmental water samples demonstrate the usefulness of the assay.
报道了一种直接酶联免疫吸附测定法,用于检测短链
硫磺苯
羧酸(
SPCs),即线性烷基
苯磺酸的主要代谢产物。合成了六种
SPCs(2C3、2C4、3C4、2C5、3C5、3C6),它们在烷基链的长度(在C3到C6之间)和
苯磺酸根与
羧酸根的相对位置上有所不同。针对将
羧酸与赖
氨酸
氨基酸残基偶联所制备的相应马蹄蟹血蓝蛋白结合物的混合物,产生了
抗体。免疫测定法As115/3C4−HRP的IC50值为23 nM(6.67 μg L-1),检测限为0.85 nM(0.24 μg L-1),标准分析物为六种
SPCs的等摩尔混合物。研究发现,该免疫测定法在低或中等离子强度(4−30 mS cm-1)的介质中效果更佳。通过将测定介质的pH调至低于
SPC
羧酸根的pKa值,并使用具有螯合特性的缓冲液(如
柠檬酸盐缓冲液),可以防止与二价阳离子(如Ca2+)形成
SPC盐所导致的可检测性下降。该测定法可以认为是特异性针对短链
SPCs,因为烷基链较长的同类物质及其结构中含有
磺酸根的其他污染物在检测中不会显著干扰。初步实验评估了该测定法在环境
水样中潜在应用的有效性,展示了该测定法的实用性。