Rapid spectrophotometric determination of permanganate index (CODMn) in water by 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS)

Abstract

In this study, a novel and rapid spectrophotometric method for accurately measuring permanganate index (COD_Mn) in water samples was developed using 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS) as an indicator. Under acidic conditions, ABTS is rapidly oxidized by residual potassium permanganate in the digest solution, forming a stable green ABTS^•+ radical within just 20 s. Subsequently, ABTS^•+ can be accurately quantified by visible spectrophotometry at a wavelength of 415 nm. In the range of 0 to 4.46 mg/L, the absorbance change of ABTS^•+ at 415 nm showed a strong linear relationship with the concentration of COD_Mn (R² = 0.999). The method has high sensitivity, with a low limit of detection for COD_Mn of 0.010 mg/L. It is worth noting that the ABTS method is resistant to chloride ion interference and demonstrates high accuracy when applied to real water samples, with recovery rates ranging from 98.59 % to 99.93 %. Compared to the national standard titration method and other previously reported spectrophotometric methods, the ABTS method is simpler and more environmentally friendly. In conclusion, the proposed ABTS spectrophotometric method represents a promising approach for the accurate and rapid determination of COD_Mn in water, providing a feasible alternative to traditional methods for COD_Mn determination.