Comparative Study of Liquid-Liquid Extraction and Solid-Phase Extraction Methods for the Separation of Sufentanil from Plasma before Gas Chromatographic–Mass Spectrometric Analysis

Abstract

Sufentanil (SF) is a highly potent synthetic opioid (1) used extensively in anesthesia (2)(3). Most of the techniques proposed for SF analysis in plasma samples are based on the RIA method described by Michiels et al. (4). Some methods using gas chromatography–mass spectrometry (GC-MS) have been reported (5)(6)(7). Plasma concentrations of SF in the analgesic range are extremely low, and pharmacokinetic studies require the development of sensitive GC-MS assay methods. Reliable and reproducible isolation of SF from plasma is the most important and most critical step in pharmacokinetic analysis. Among different extraction methods currently used in pharmaceutics, the use of solid-phase extraction (SPE) has grown dramatically. However, according to the literature, liquid-liquid extraction (LLE) is the technique used most frequently for isolating morphinomimetic compounds (4)(5)(6)(7)(8), whereas only one method using SPE with RIA has been reported (9). We performed comparative studies on the isolation of SF and alfentanil (AF; used as an internal standard) from plasma using LLE and SPE methods, and extracts were assessed using GC-MS. The method was applied to drug monitoring in intensive care patients. SF citrate and AF hydrochloride were purchased from Janssen Pharmaceutica. Lyophilized plasma (Lyphochek®) was purchased from Bio-Rad Laboratories. Deionized water was prepared using a MilliQ® Water System (Millipore). Methanol (Uvasol® grade), dichloromethane (Uvasol grade), isoamyl alcohol (analytical grade), propan-2-ol (analytical grade), 13.2 mol/L ammonia, and sodium hydroxide (Normapur®) were purchased from Merck. n -Heptane (analytical grade), 18 mol/L sulfuric acid, and ammonium phosphate monobasic were purchased from Carlo Erba. Acetic acid and Sigmacote® were purchased from Sigma Aldrich. Oasis® MCX 60-mg SPE columns (Waters Corporation) were used, and the vacuum manifold for semiautomatic processing of the columns was purchased from Supelco. The Oasis MCX is a mixed-mode, …