Abstract
Negligible depletion micro-extraction (nd-ME) plays an important role in measuring the freely dissolved concentration of pollutants but is suffered from a long equilibrium time. In this study, a novel method for in situ determination of freely dissolved methyl parathion (MP) by the electrochemical method was developed based on the nd-ME method. The parameters influencing the adsorption kinetic were investigated in the environmentally relevant ranges, including buffer concentration (5-200 mM), salinity (0-500 mM), and pH value (5.0-8.5). The equilibrium time can be achieved within 16 min between the freely dissolved MP and beta-cyclodextrin decorated reduced graphene oxide composites (β-CD/RGO). Under the equilibrium condition, the sorption coefficients (log KDOC) were 4.56 for Acros humic acid and 4.58 for Suwannee River humic acid, respectively, which were consistent with those by negligible depletion-solid phase microextraction (nd-SPME) with log KDOC = 4.23 for Acros humic acid and log KDOC = 4.27 for Suwannee River humic acid. The freely dissolved MP in water samples ranged from 3.96 to 4.44 µg L− 1, which were in agreement with those by nd-SPME (Cfree = 4.17–4.76 µg L− 1). According to the result, a novel method was developed in this study to estimate the freely dissolved concentration of pollutants using the electrochemical method.