“…Solid phase extraction (SPE) was carried out using Varian Bond Elute SAX cartridges (100 mg, 1 ml, Palo Alto, CA) connected to a Varian Vac Elut 20 manifold and a vacuum pump. Although we have essentially adopted the procedures of de Vriendt et al [6] for SPE and HPLC, we found that, in our hands, the recovery from this procedure was low and variable, so slight modifications were made in the composition and volume of the eluent used in removing GHB from the SPE column. Our final adopted procedure was as follows: the cartridge was first conditioned serially with 1 ml of methanol, 6 ml of 10% acetic acid, and 1 ml of water at an approximate flow rate of 1 ml/min.…”