Development and applications of electromembrance extraction methods across hollow polymer inclusion membrance for analysis of drugs and herbicides

Abstract

Electromembrane extraction (EME) has become an effective method in the development of sample preparation technique. In this study, a novel microextraction method based on the EME and employed with hollow polymer inclusion membrane (HPIM) was developed in order to get better stability and reproducibility compared to the conventional EME. HPIM was prepared by dipping the glass capillary tubes into a solution of the desired proportions of cellulose triacetate (CTA), tris(2-ethylhexyl)phosphate (TEHP) and di-(2-ethylhexyl)phosphoric acid (D2EHPA) or Aliquat 336 in dichloromethane. Three basic drugs, namely amphethamine, methamphetamine and 3,4-methylenedioxy-N-methylamphethamine (MDMA) were selected as the target analytes to evaluate the extraction efficiency of the new approach. Parameters affecting the extraction efficiency, including the composition of HPIM, pH of sample, extraction voltage and extraction time were investigated in detail. Under the optimized conditions, enrichment factors in the range of 97-103 fold were obtained from 3 mL sample solution with a 10 min extraction time and an applied voltage of 300 V across the HPIM. A comparison was also made between the newly developed approach and the conventional EME as well as standard sample preparation methods (liquid-liquid extraction) used by the Toxicology Unit, Department of Chemistry, Malaysia. The applied voltage in EME is an important parameter for efficient extraction of the analyte, however, when dealing with extremely high voltage, instability occurs due to the formation of bubbles. This limitation has stimulated the development of the exhaustive simultaneous EME across HPIM with the aim of employing a bubbleless electrode for the determination of selected cationic and anionic pesticides present in the environmental water samples. Bubbleless electrode was prepared to solve the bubble formation problem during the extraction process. Cationic herbicides namely paraquat (PQ) and diquat (DQ) as well as anionic herbicides namely (4-chlorophenoxy)acetic acid (4-CPA) and 2-(2, 4-dichlorophenoxy)acetic acid (2,4-D) were selected as the model analytes to evaluate the extraction performance of this new approach. Under the optimized conditions, the enrichment factors in the range of 152–185-fold were obtained from 4 mL of river water sample with a 20 min extraction time and an applied voltage of 3000 V. The proposed method provided good linearity with the correlation coefficients ranging from 0.9982 to 0.9997 over a concentration range of 1–1000 ng/mL. The detection limits of the method for the herbicides were in the range of 0.3–0.4 ng/mL, with the relative standard deviations ranged between 4.8% and 8.5%. A comparison was also made between the newly developed method with that of conventional EME setup using normal electrode.