Switchable polarity solvents for preconcentration and simultaneous determination of amino acids in human plasma samples

In this study, liquid phase microextraction based on the application of a switchable polarity solvent (LPME-SPS) is introduced for the preconcentration and determination of nineteen amino acids in biological samples. For this purpose, a switchable polarity solvent was prepared based on the application of 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU), methanol and carbon dioxide. After microextraction, phase separation was performed by the addition of sodium hydroxide, which leads to alteration of the ionisation state of the solvent. The structure of the solvent was identified using 1H NMR, 13C NMR and infrared spectroscopic analyses. Also, the physical properties of the switchable solvent, including miscibility and polarity were studied. The central composite design (CCD) of response surface methodology (RSM) was used to optimize the parameters affecting the extraction efficiency. Under optimal conditions, the calibration curves of nineteen amino acids prepared from the data of high performance liquid chromatography coupled to online fluorescence detection (HPLC-FLD), were in a concentration range of 0.5–300 μmol L−1, with correlation coefficients higher than 0.996. Limits of detection and quantification were in the ranges of 0.01–0.6 μmol L−1 and 0.3–2.2 μmol L−1, respectively. This procedure was efficiently used to determine target analytes in human plasma samples. Also, the relative recoveries ranged from 81.3 to 102.1%.