Automated Mixed Matrix Membrane Microextraction Prior to Liquid Chromatography for the Determination of Chlorophenoxy Acid Herbicides in Sewage Water Samples

Abstract

A new automated flow-through adsorption/desorption procedure using a multiwalled carbon nanotube immobilised mixed matrix membrane is described. The membrane consisted of 25% (w/w) multiwall carbon nanotube loading in a cellulose triacetate polymer matrix as support and was cast and embedded in a flow-through cell with a channel of an approximate length of 20 mm, a width of 2 mm, and a depth of 1.5 mm. The membrane immobilised with nanoparticles was activated using 1-octanol as a conditioning solvent. For the analyte adsorption process, 6 mL of the sample was passed through the cell at a flow rate of 0.2 mL min⁻¹. The entrapped target analytes were then desorbed dynamically with 60 µL of 2-propanal at a flow rate of 5 µL min⁻¹ prior to HPLC/UV analysis. The performance of the system was demonstrated for the determination of chlorinated phenoxyacetic acid herbicides in sewage water samples. Under the optimum conditions, the linearity of this method ranged from 50 to 1000 ng mL⁻¹, with a correlation coefficient (r) ≥ 0.993 and a detection limit varying from 15 to 20 ng mL⁻¹. Enrichment factors of up to 55 were achieved with relative recoveries of 95–99% and precision values of 6.1–7.5%.