Electrochemical measurement of breath-alcohol concentration: precision and accuracy in relation to blood levels.

This paper deals with the precision and accuracy of an electroanalytical device (Alcolmeter AE-D1) used for the determination of alcohol in human breath. Experiments were made under in vitro conditions with air-ethanol vapour mixtures and in vivo with human volunteers after they consumed alcohol. The standard deviation (SD) of single determinations of ethanol in breath or standard vapour increased with increase in the concentration in the samples. At a mean concentration of about 50 mg/dl blood ethanol equivalent, the SD in vitro was 1.5 mg/dl and in vivo 1.6 mg/dl. The blood and breath concentration-time profiles were well-matched after ethanol intake of 0.54, 0.72 and 0.90 g/kg body wt. The regression equation relating breath instrument reading (y) with blood alcohol (x) was y = -0.20 + 0.93x. The y intercept was not significantly different from zero and the correlation coefficient was 0.98. The breath alcohol determinations were, however, more variable at higher levels of blood-ethanol and the results were therefore evaluated with log transformations. The regression equation now became y = 0.91x with 95% confidence limits of y = 0.72x and y = 1.16x. For unbiased estimates of blood-ethanol concentration the instrument should be calibrated with a blood/breath ethanol ratio of 2,300:1.