| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 97825 | Forensic Science International | 2008 | 5 Pages |
On the basis of simultaneously sampled postmortem blood specimens from the left and right femoral veins the pre-analytical variation of methadone measurements was evaluated and compared to the analytical variation. The material consisted of a series of 27 duplicate samples from routine autopsy cases comprising mainly drug addicts. A chiral LC–MS/MS method was used for measurement of the R- and S-enantiomers of methadone and its main metabolite 2-ethyl-1,5-dimethyl-3,3-diphenylpyrrolinium (EDDP). The analytical CV% was determined to be in the range 3–4% for methadone enantiomers and 4–6% for EDDP enantiomers. The total measurement uncertainty (CVT) was estimated from the pre-analytical variation (CVPA), analytical variation proper (CVA), and variation related to calibration (traceability) (CVCal) according to the relationship CVT=CVPA2+CVA2+CVCal20.5. Uncertainty related to calibration concerned a component related to the purity of drug reference compound and a contribution from the production of calibrator solutions (CVCal < 1%). Pre-analytical sampling variation was estimated from the duplicate measurements of blood samples after subtraction of the analytical component. The pre-analytical variation amounted to a CV% of 19–21% for R- and S-methadone and 30–38% for R- and S-EDDP, i.e. considerably larger than the other components. Due to the squared addition principle, the resulting total uncertainty (CVT) became largely identical to the CVPA, i.e. 19–21% for R- and S-methadone and 31–38% for R- and S-EDDP enantiomers. Accordingly, CVT exceeded CVA by a factor 5 or more. Dominance of the pre-analytical component of variation may also be likely for other compounds measured in postmortem blood samples. Thus, the width of the 95%-uncertainty interval (±2 CVT) for a postmortem measurement is largely determined by the pre-analytical component of variation. This should be kept in mind when judging on the uncertainty of postmortem measurement results.
