Salting out improves solid-phase extraction recoveries on Abselut-Tox (TM) 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 sub-
stances 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 interfer-
ences, particularly matrix components.
Recently, Abselut-Tox columns were introduced by Varian
Sample Preparation Products (Harbor City, CA) as a new ma-
terial for screening purposes by SPE. In fact, the first three let-
ters in the name stand for acidic/basic screen. The material is
a styrene-divinylbenzene copolymer (SDVB)with optimal par-
ticle and pore sizes to allow high and reproducible flow rates.
Among the claimed advantages are no channeling, no pH in-
stability, 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 hy-
drophobic 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 de-
veloping a suitable SPE methodology that provides adequate re-
coveries 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 Ab-
selut-Tox columns should not be confused with Abselut-Nexus
columns; the latter provide a more complicated interaction mechanism. When selecting our test drugs, we focused partic-
ularly on strongly acidic substances and/or polar substances be-
cause these are known to be problematic in both SPE and in
liquid-liquid extractions.