Problems of Forensic Sciences 2003 Vol. 54 (LIV) 113-136
MEASUREMENT UNCERTAINTY IN DETERMINATION OF BLOOD ALCOHOL CONCENTRATION
Dariusz ZUBA
Institute of Forensic Research, Cracow
Streszczenie
Factors affecting measurement uncertainty in two methods of determination of blood alcohol concentration for forensic purposes: gas chromatography with use of the headspace technique and the ADH enzymatic method (spectrophotometric method) were analysed in this paper. The heterogeneity of the analysed material contributes most to analytical error, comprising from about 45% to about 65% of the total measurement uncertainty, depending on the method. This observation is very important, because many of the methods of determination of precision do not take into consideration assessment of error linked to the heterogeneity of the material. The value of the measurement uncertainty was also determined on the basis of the error propagation law, amounting to 7.0% for the chromatographic method and 5.7% for the ADH enzymatic method. When we take into consideration that each positive result of alcohol concentration is calculated in the Institute of Forensic Research on the basis of two independent analyses by means of the GC method and two analyses by means of the ADH enzymatic method, the error of blood alcohol concentration determination amounts to 3.6%. These results were compared with the values of errors estimated on the basis of routine determination. The error amounted to 6.0% for the GC method and 3.4% for the ADH enzymatic method. The performed theoretical analysis and the experimental results indicate that an uncertainty of alcohol concentration determination equal to 0.05‰ for concentrations lower than 1.0‰ and equal to 5% for higher concentrations should be assumed. These assumptions enable us to take into account in the obtained results all of the errors that can occur during the carrying out of analyses.
Słowa kluczowe
Uncertainty; Error; Alcohol.