Acid-induced homogenous liquid-phase microextraction: application of medium-chain carboxylic acid as extraction phase

In this research, a novel homogeneous liquid-phase microextraction method was successfully developed based on applying octanoic acid as low-density extraction solvent. The method was applied for extraction and determination of chlorophenols (CPs) as model compounds. Twelve milliliter of the sample solution was poured into a home-designed glass vial. Sixty microliter of octanoic acid was solved in water sample by adjusting pH and ionic strength. By rapid addition of 75 μL of concentrated HCl (6 M), a cloudy solution was obtained. Phase separation occurred at 5000 rpm for 5 min. After that, 20 μL of the collected phase (approximately 26 μL) was injected into the HPLC-UV instrument for analysis. The effect of some parameters such as the volume of concentrated HCl (phase separation reagent), ionic strength, extraction time, centrifugation time, and the volume of extracting phase on the extraction efficiency of the CPs were investigated and optimized. The preconcentration factors in a range of 159-218 were obtained under the optimal conditions. The linear range, detection limits (S/N = 3), and precision (n = 3) were 1- 200, 0.3-0.5 μg/L, and 4.6-5.1%, respectively. Tap water, seawater, and river water samples were successfully analyzed for the existence of CPs using the proposed method and satisfactory results were obtained.