Laboratory evaluation of a new evidential breath-alcohol analyser designed for mobile testing--the Evidenzer

The Evidenzer is a new kind of forensic breath-alcohol analyser, designed for use both at a police station (stationary) and also in a police vehicle (mobile) at the roadside. In this paper we report the accuracy and precision of the Evidenzer, determined under controlled laboratory conditions. The results were compared with a well-established breath-alcohol instrument (Intoxilyzer 5000S) and also with the concentration of alcohol in venous blood. Twenty healthy volunteers (10 men and 10 women) consumed ethanol (0.4 g/kg) in 15 minutes starting two to three hours after their last meal. Venous blood and breath were obtained for determination of ethanol at 15-30 minute intervals for up to four hours post-dosing. There was a good overall agreement between the two breath-alcohol instruments and the mean bias was only 0.003 mg/L (95% limits of agreement of -0.016 to 0.023 mg/L). The standard deviation (SD) of measuring ethanol in breath was about the same for both instruments, being 0.006 mg/L, and this corresponds to a relative precision or coefficient of variation (CV) of 4.7%. When the Evidenzer was used to analyse ethanol vapour (0.50 mg/L) generated from a wet-bath simulator, i.e. in-vitro conditions, the coefficient of variation was 0.7% indicating high analytical precision. The concentration of ethanol in venous blood and breath were highly correlated (r = 0.95) although systematic differences existed depending on time after drinking when comparisons were made. Both breath-alcohol instruments gave results higher than venous blood alcohol in tests made at 15 minutes after the end of drinking whereas at all later times the venous blood-alcohol concentration was higher