Ion pair solvent bar microextraction prior to UV-Vis spectrophotometry for determination of paraquat

A group of quaternary ammonium compounds, also known as quats, have been used as herbicides and anticholinergic drugs [۱]. Among quats, paraquat (PQ) is a very quick acting herbicide for broadleaf weed control in fields[۲]. Because the use of PQ results in pollution of surface and river water, it is essential to develop a rapid and accurate method for determining these compounds in environmental samples [۳]. Due to the permanent ionic character of quats, these herbicides are highly hydrophilic. Ion pair extraction is a suitable method for the partitioning of ionic and hydrophilic species with the help of counter ions of opposite charge in SBME systems [۴]. The ion pairing agent can be added to the donor solution before the extraction process or be dissolved in the membrane organic phase to form a neutral ion pair complex [۵]. From this perspective, surfactants can be used as effective ion pairing reagents to achieve this purpose. In this work, for the first time, a new analytical method based on ion pair solvent bar microextraction (IP-SBME) was introduced. In this two phase process, an anionic surfactant (SDS) was added initially into the donor solution to form a hydrophobic ion pair with the cationic analyte. Thereupon, the ion pair formed was enriched into organic solvent immobilized in the pores and lumen of the HF (toluene) and finally back washed with methanol. At optimum conditions, value of variables were set as pH ۶, concentration of SDS ۴ mM, stirring rate of ۴۰۰ rpm, time of extraction ۱۵ min, without addition of salt. Under the optimized extraction conditions, the method showed a good linear dynamic range (۱–۲۰۰۰ ugL-۱) with a lower limit of detection (۰.۳ ugL-۱) and excellent preconcentration factor (PF =۳۵۵.۳۴). Finally, the proposed method was successfully applied for the determination of PQ in soil samples.