1 Introduction
Forensic laboratories require both sensitive and rapid analytical methods for the determination of various substances in a variety of biological specimens. Undoubtedly, sample pre-treatment is the bottleneck in forensic analysis, the major reason being the diversity of the biological samples [1]. Other difficulties arise both from the instability of various substances in postmortem samples, as well as from postmortem changes that alter the nature of the sample matrix and complicate isolation, clean-up, and detection even more. The postmortem processes and the way they influence the concentration of opiates in the various compartments of the body have been extensively studied and discussed [2, 3]. Heroin undergoes rapid bioconversion after death. 6-Monoacetylmorphine (6-MAM) is deacetylated to morphine (MOR) [4], morphine glucuronides are de-conjugated to MOR [5], and MOR itself presents a significant loss in postmortem samples [6, 7]. Solid-phase extraction has become very popular in the pre-treatment of forensic samples despite the fact that it requires relatively large volumes of solvents. Disposable pipette extraction (DPX) is a new approach in sample pre-treatment, which has proved to be valuable in the analysis of drugs of abuse [8, 9] in common biological matrices, such as urine and blood. DPX requires low-cost equipment and consumables. It uses smaller volumes of solvents and therefore produces less waste. Moreover, it is efficient with smaller sample volumes. In contrast to solid-phase extraction columns, DPX uses loosely packed sorbent and therefore does not require vacuum for elution. The sample is aspirated into the tip, where it is actively mixed with the sorbent to form a suspension. Furthermore, it minimizes the necessary conditioning steps and therefore speeds up the procedure of sample pre-treatment. Moreover, DPX extraction can be easily automated.

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