SOFT 2004 Meeting Abstracts - Society of Forensic Toxicologists

P16
OPTIMIZING AN AUTOMATED SOLID-PHASE EXTRACTION PROCEDURE FOR
POSTMORTEM TISSUE SAMPLES
T. Stimpf1*, Department of Forensic Medicine, Medical University of Vienna, Sensengasse 2, A-1090
Vienna, Austria
Quality assurance regulations in forensic laboratories, efforts to reduce systematic errors, costs, time spent per case as
well as efforts to improve technician-safety all lead to the consideration ofautomated procedures for sample extraction.
In contrast to liquid-liquid extraction, solid-phase extraction (SPE) can be more easily automated by incorporating
robotics improving the sample quality in respect to the analyte yield and increasing consistency and laboratory
productivity .
Today, automated SPE procedures are widely used for the extraction of body fluids such as urine, serum, plasma and
whole blood. In postmortem forensic toxicology, however, these specimens are not always available and, with regard to
the investigation of the cause of death, human tissue samples - especially brain - can be highly important.
Drummer and Gerostamoulos pointed out that"... there is little evidence that extraction efficiencies ofdrugs from solid
tissues are likely to be much worse than with fluid specimens ifsuitable precautions are taken. These include a suitably
fluid homogenate prepared from the solid tissue with sufficient water or buffer" [I].
In an automated SPE procedure published by our working group, a crude extract from postmortem tissue samples could
be achieved, avoiding protein precipitation and the resulting loss ofanalytes by adsorption or occlusion.
In respect to the problem that tissue homogenates often do not easily pass through tightly-packed cartridges, it could be
shown that - after homogenization and dilution with large volumes of buffer solution - the resulting colloidal solution
could be directly applied to the polymeric sorbent [2].
For routine solid-phase extraction of tissue samples, several adaptations of the automated system ASPECTMXL,
operated under 735-sampler software V 5.1 for Win NT 4.0 (Gilson Inc., Middleton, WI, USA), were necessary.
• A large volume ofsample had to be applied in order to dilute the sample and dissolve protein bonds.
• The upper frit ofthe extraction cartridge had to be removed to minimize the risk ofclogging.
• A 5mL stainless steel sample loop for HPLC (Supeico, Bellefonte, PA, USA) was installed on the ASPEC
XL to avoid adsorption of analytes to synthetic plastic materials (transfer tubing).
• Special cleaning routines with 2N NaOH and 2N RN0 3 were used to remove any precipitated proteins. from
the system.
• The sample was applied very slowly to make use of "micellar chromatography", thus avoiding the adsorption
ofmacromolecular interferences with larger than pore-sized diameters to the polymeric sorbent.
• A pressure sensor was installed to compensate for inconsistent flow rates during loading, washing and
eluting.
When postmortem samples of tissue have to be extracted by automated SPE, monitoring of the overall system pressure
is essential. Pressure control allows for high-pressure release if clogging of the cartridge occurs, avoiding
contamination of the working area with the infectious sample; the aborted sample is then replaced to the sample tube.
1. O.H. Drummer, J. Gerostamoulos, Postmortem drug analysis: analytical and toxicological aspects. Therap.
Drug Monit. 24 (2002) 199-209.
2. T. Stimpfl, J. Jurenitsch, W. Vycudilik, General unknown screening in postmortem tissue and blood samples:
a semi-automatic solid-phase extraction using polystyrene resins followed by liquid-liquid extraction. J.
Anal. Toxieo!. 25 (2001) 125-129.
Keywords: automation, solid-phase extraction (SPE), tissue samples
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