Comparison of new solid-phase extraction methods for chromatographic identification of drugs in clinical toxicological analysis.

OBJECTIVES: Newly presented solid-phase extraction methods (Solid Phase Disc Extraction, SPEC-Plus, Multi-Modal, and Solid Phase Micro Extraction, SPME have been checked with respect to their applicability to clinical toxicological analysis. In comparison with conventional liquid/liquid-extraction and a common mixed-phase column technology, their use in general screening and selective extraction methodology is discussed. DESIGN AND METHODS: Recovery studies were performed with urine-based samples including model substances, as well as drugs and metabolites from native urine samples. Chromatographic performance of the resulting extracts is presented in some examples.
RESULTS: Liquid/liquid extraction, common mixed-phase column technique and the new SPEC-Plus, Multi-Modal disc extraction method gave the best recoveries with respect to broad-spectrum general screening. The purity of the concentrates was somewhat different, however. Solid-phase C18 and Solid-Phase Micro Extraction methodologies are better suited for selective drug extraction. In SPEC Disc or SPME extraction, the use of solvents is greatly reduced or omitted. Recovery of some volatile substances is enhanced. SPEC discs can be inserted directly into TLC chromatographic plates, SPME fibers into GC injection ports.
CONCLUSIONS: The new solid-phase extraction technologies offer advantages in different respects: The mixed-phase disc extraction SPEC 1 Plus AR/MP3 Multi-Modal delivers promising results with respect to broad-spectrum general screening. Solvent consumption is low, throughput times are short, the extracts are clean, and recovery rates are good, comparable, or even higher than with common mixed-phase column techniques. The new SPME extraction method shows benefits in dedicated, selective extraction procedures (e.g., analysis of volatile substances such as amphetamines). Sampling is solvent-free, the handling is easy, and the yields of extraction are good, but only for selected substances. Broad-spectrum general screening still remains problematic with this technique. Further examinations have to be carried out including a larger number of drugs of toxicological relevance. Headspace sampling by SPME offers a good alternative to conventional mechanized sampling in the analysis of volatile substances in biological samples, omitting the need for expensive instrumentation.