Ion-pair vortex assisted liquid-liquid microextraction with back extraction coupled with high performance liquid chromatography-UV for the determination of metformin in plasma

• Ion-pair VALLME-BE is a suitable technique for the extraction of charged polar compounds.
• DEHPA was used as ion-pair reagent in the microextraction of metformin.
• Separation of metformin is for the first time performed using C1 column.
• The proposed method offer clear advantages over previously reported methods.

A new sample preparation method, ion-pair vortex assisted liquid-liquid microextraction (VALLME-BE), for the determination of a highly polar anti-diabetic drug (metformin) in plasma sample was developed. The VALLME-BE was performed by diluting the plasma in borate buffer and extracted to 150 µL 1-octanol containing 0.2 M di-(2-ethylhexyl)phosphoric acid as intermediate phase. The drug was next back-extracted into 20 µL of 0.075 M HCl solution. The effects of pH, ion-pair concentration, type of organic solvent, volume of extraction phases, ionic strength, vortexing and centrifugation times on the extraction efficiency were investigated. The optimum conditions were at pH 9.3, 60 s vortexing and 2 min centrifugation. The microextract, contained metformin and buformin (internal standard), was directly injected into a HPLC unit using C1 column (250 mm×4.6 mm×10 µm) and detected at 235 nm. The method was validated and calibration curve was linear with r2>0.99 over the range of 20–2000 µg L−1. The limits of detection and quantitation were 1.4 and 4.1 µg L−1, respectively. The accuracy was within 94.8–108% of the nominal concentration. The relative standard deviation for inter- and intra-day precision was less than 10.8%. The method was conveniently applied for the determination of metformin in plasma samples.

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