In-tube liquid phase microextraction; a novel sample preparation technique

Clean–up and preconcentration of samples are spent more than 80% of analysis time and significant amount of the target analytes can be lost during these steps and lead to noticeable errors in the final result. So sample preparation is a critical part in most analytical procedures [1]. Application of microextraction methods in determination of analytes is more common [2, 3]. In this study, a new sample preparation technique named in-tube liquid phase microextraction (IT-LPME) has been reported. In this method an injection port of high performance liquid chromatography (HPLC) and a stainless steel tube (like a loop of injection port of HPLC; volume about 20 µL) are used. When the injection port is in the load state, sodium hydroxide solution (0.2 M) is passed through the stainless steel tube. Then 1 mL of an organic solvent (e.g. n-hexane) containing ionisable compounds (previously extracted from 10 mL acidic aqueous sample) is passed through the tube. In this step, a thin layer of aqueous solution of sodium hydroxide is remained (adsorbed) onto the inner wall (inner surface) of stainless steel tube. So the ionisable compounds are back-extracted into the aqueous layer. The injection port is changed to the inject state and the extracted compounds enter into the HPLC column by mobile phase for further separation and determination.The performance of IT-LPME is illustrated by the extraction of some anti-inflammatory drugs (naproxen, diclofenac, and ibuprofen) in water as model compounds. Some important parameters such as the material, length, internal diameter and volume of the tube, concentration and volume of sodium hydroxide solution, type and volume of organic solvent, etc. were investigated. Under the optimum extraction conditions the enrichment factors were 57, 168, and 200 for naproxen, diclofenac, and ibuprofen, respectively. The linear ranges of the calibration curves were 1-500 µg L-1 for naproxen and diclofenac, and 20-10000 µg L-1 for ibuprofen. The detection limits were 0.3, 0.2, and 5 µg L-1 for naproxen, diclofenac, and ibuprofen, respectively. The overall extraction time was about 5 minutes. This technique is simple, fast, low cost, having high enrichment factors, and needs low sample volume. Also it is available to all laboratories even with low facilities.