“…Among the standard techniques used for concentration and cleanup when dealing with biological samples are solvent extraction and adsorption onto columns of the nonpolar adsorbent Amberlite XAD-2. Both of these techniques have been used to prepare blood plasma samples for gas or liquid chromatographic determination of methaqualone (MTQ), a sedative, hypnotic drug (1)(2)(3)(4)(5)(6)(7)(8). An alternative to using adsorbent columns "off-stream" is the "on-stream" incorporation of them into the flow scheme of a liquid chromatograph as a "precolumn" in advance of the anaytical column.…”