Developing a standardized procedure for SPE-enzyme-linked immunosorbent assay to provide high-quality quantification...

The trade-off between quality and difficulty is a challenge when quantifying ambient antibiotics at trace levels. Compared with the precise yet complicate methods such as mass spectrometry (MS) techniques, the enzyme-linked immunosorbent assay (ELISA) offer a simple alternative. While some studies applied it on quantifying environmental pollutants, diverse optimization procedures were employed and matrix effects were not well-addressed. Here, the quantification capability of solid-phase extraction (SPE) coupled with ELISA on ambient antibiotics was evaluated using a newly developed standardized procedure. SPE-ELISA first underwent more rigorous optimization using an overall performance index and three-dimensional recovery response surface. A series of quantitative indicators including precision (relative standard deviation reached 0.3 %), sensitivity (a minimal of 3.8 ng/L variation can be distinguished), limit of detection (0.3 µg/L without pretreatment), and recoveries (> 90 %) of SPE-ELISA were achieved and the corresponding conditions were revealed. To eliminate matrix effects, the standard addition method was adopted. This approach, coupled with the linearization of the nonlinear calibration curve, yielded highly accurate (errors of 9 % and 5.2 %) and reliable (standard deviation of 0.49 and 0.61) results on measuring simulated surface and wastewaters with 5 ng/L and 10 ng/L sulfamethoxazole, which were highly comparable to those of MS methods (P > 0.05). Overall, with more rigorous optimization and matrix effect eliminated, the standardized procedure in this study enabled SPE-ELISA to achieve high-quality quantification results. Considering the high throughputs, simple procedure, and low installation costs of SPE-ELISA, it could be a promising alternative for quantifying ambient antibiotics.