Determination of remifentanil in human plasma by liquid chromatography-tandem mass spectrometry utilizing micro extraction in packed syringe (MEPS) as sample preparation.

Remifentanil is a synthetic short-acting opioid with a short half-life that is being used during anaesthesia of small children. In this work an LC-MS/MS method for remifentanil quantification in 20 μL volume of human plasma was developed and validated in connection with a clinical study on neonatal children. Sample preparation was performed with micro extraction in packed syringe (MEPS), which is a miniaturization of solid phase extraction. For this method a mixed phase sorbent M1 (C8, cation exchange), and a protocol for basic compound extraction was followed. Remifentanil-(13)C(6) was used as internal standard. For chromatographic separation, a C18 analytical column with gradient elution was used with mobile phase consisting of aqueous 0.1% formic acid and methanol. The total analysis time was 5.0 min and the measuring range was between 0.05 and 50 ng/mL. Precision and accuracy were with acceptance criteria of ±15%. Plasma samples were stable for 5 weeks at -20°C and for 4h at room temperature while 50% was lost after 24h. This method was successfully applied for remifentanil determination in clinical samples and results agreed with a reference method. With this method using MEPS, a low limit of quantification and much reduced sample volume was obtained as compared with previous methods.