Salting Out Improves Solid-Phase Extraction Recoveries on Abselut-Tox™ Columns for Broad Spectrum Drug Screening

Broad-spectrum drug screening is frequently applied in forensic and clinical toxicology, drugs and driving and doping, for example. It requires that all toxicologically relevant substances be isolated, detected, and identified, regardless their structure and/or polarity. This comprehensive screening is also known as Systematic Toxicological Analysis (STA). Solid-phase extraction (SPE) has become the technique of choice for sample work up and isolation in STA (1--4). The key issues in this step are to retain all relevant toxicants and at the same time to remove all non-relevant substances and interferences, particularly matrix components. Recently, Abselut-Tox columns were introduced by Varian Sample Preparation Products (Harbor City, CA) as a new material for screening purposes by SPE. In fact, the first three letters in the name stand for acidic/basic screen. The material is a styrene-divinylbenzene copolymer (SDVB) with optimal particle and pore sizes to allow high and reproducible flow rates. Among the claimed advantages are no channeling, no pH instability, no secondary interactions, excellent mass transfer, and high capacities. However, it should be noted that these columns exhibit a single retention mechanism, specifically relatively weak hydrophobic interactions between the SDVB skeleton and the drug of interest. Given the fact that toxicologically relevant substances may differ widely in character (acidic, neutral, basic, zwitterionic) and/or in polarity, this may cause difficulties in developing a suitable SPE methodology that provides adequate recoveries of all substances of interest and that allows satisfactory removal of matrix interferences at the same time. This paper describes our experiences with Abselut-Tox SPE columns for broad spectrum drug screening in plasma. The Abselut-Tox columns should not be confused with Abselut-Nexus columns; the latter provide a more complicated interaction