RESUMO
Blood is the primary material for quantitative toxicological analysis and interpretation of the results. However, in some cases like hit-and-run, it may be collected after a long time since the incident, resulting in the complete elimination or a significant decrease in the concentrations of potentially present drugs. If the suspect was injured and bloodstains were revealed, they can become the best or sometimes, the only material to be used to prove driving under the influence of drugs. In this context, the aim of this work was to develop a simple procedure that would allow for the estimation of drug concentrations in forensic bloodstains of unknown volume. In this work endogenous amino acids: valine and leucine were used to determine the unknown volume of blood from which the stain was formed. In order to isolate the analytes from bloodstains on different surfaces (plastic and cotton) the elution mixture consisted of an acetonitrile: water (60:40) and sodium chloride (0.9%) was used. The developed protocol was tested on 32 authentic forensic samples (mostly cases of people driving under the influence of amphetamine). The results of bloodstains analyses were compared with the results of whole blood analyses. The accuracy was in the range from -87.7 to +471.0%. However, for most of the cases, more accurate results were obtained. The differences between amphetamine values estimated from bloodstains and determined from whole blood were analysed using the Bland-Altman difference plots that revealed significant agreement. The variables concentrations estimated from bloodstains and concentrations calculated from whole blood were found to be strongly correlated. The Pearson correlation coefficients were: for plastic r(29) = 0.85 and for cotton r(25) = 0.91. This is the first work in which quantitative analyses of drugs in bloodstains have been attempted. A special protocol was developed for this purpose. The conducted research indicates that estimation of the concentration of drugs in bloodstains from the blood of an unknown volume is possible. The developed protocol has been extensively tested on authentic forensic samples and the obtained results were successfully compared with drug concentrations determined in whole blood. Nevertheless, the proposed method of estimating drug concentrations in bloodstains is characterized by many disadvantages, and the determined values should be treated with great caution, at best as estimates.
