Reflections and Recommendations on the Accuracy of ABTS Colorimetric Methods in Environmental Analysis

Colorimetric methods using 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) as a chromogenic reagent are widely used for oxidant detection in water samples. However, the coexisting natural organic matter, especially those having phenolic hydroxyl groups, can consume the formed ABTS·+ radical, leading to a reduced measured concentration using the ABTS method. Using phenols as model substances, the rate constants between ABTS·+ and deprotonated phenols could reach as high as 107∼109 M–1 s–1, approximately 4–6 orders of magnitude higher than those with protonated phenols. These reaction rates could decrease with an increase in ABTS concentration. Lowering the chromogenic pH and increasing the initial ABTS concentration can reduce the consumption of ABTS·+ by matrix components, but does not fully eliminate the reductive interference caused by para- or ortho-phenolic hydroxyl groups. Similar measurement deviations of the ABTS method were also observed during the analysis of real water samples. Relatively, utilizing 3,3′,5,5′-tetramethylbenzidine as the chromogenic reagent, the TMB method exhibits stronger anti-interference performance toward matrix components in both synthetic solutions and natural waters, making it suitable for the quantitative analysis of multiple oxidants. This work investigates the deviation characteristics of the ABTS method and provides several suggestions for the accurate and sensitive determination of oxidants in complex aqueous environments.