Impact of Biological Matrix and Isolation Methods on Detectability and Interlaboratory Variations of TLC Rf-Values in Systematic Toxicological Analysis

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Abstract
The retention behavior of 8 basic and neutral drugs [amphetamine, caffeine, fluphenazine, imipramine, lignocaine, metrotrimeprazine, nitrazepam and nortriptyline], extracted from [human] plasma, blood and liver by 5 different methods (XAD-2, Extrelut, Elut-X, Elut-C18, chloroform) and developed in 3 chromatographic systems [MeOH, Me OH:BuOH:NaBr, CHCl3:MeOH (KOH)] was observed in parallel in 2 laboratories. The corrected Rf-values were compared with reference data from a data base with data for pure drugs. The biological matrix and/or the extraction severely lowered the precision and, to a lesser extent, the accuracy of the Rf-values as compared to pure drug data and to reference Rf-values. The intra- and interlaboratory variation was smallest in the MeOH system and largest in the CHCl3:MeOH (KOH) system. The observed irreproducibility is caused by the biological matrix (extraction has a large negative impact on the potentials of TLC in identification procedures). Precision and accuracy of extracted drugs were independent of the biological matrix and on the extraction method used.