Evaluation of breath alcohol instruments. I. In vitro experiments with alcolmeter pocket model.

An Alcolmeter Pocket Model breath alcohol device, on an electrochemical (fuel cell) oxidation principle for ethanol analysis, has been evaluated under in vitro conditions. The result of a test is displayed on an analogue meter within 20--30 seconds after sampling: replicate tests may be made within 3--5 minutes. The electrochemical detector used was found to respond to acetaldehyde, methanol, isopropanol and n-propanol vapours besides ethanol, but it was insensitive to acetone vapour. The Alcolmeter response with a 0--2.0 mg/ml scale was linearly related to ethanol vapour concentration up to 1.0 mg/ml blood alcohol equivalent concentration; above this level the response was curvilinear, the Alcolmeter reading being too low. The standard deviation of an ethanol vapour determination in vitro was +/-0.0175 mg/ml at a mean concentration of 0.902 mg/ml. The accuracy of the device expressed as percent recovery at 0.50, 1.0 and 1.4 mg/ml blood alcohol concentrations was 96.8%, 98.3% and 88.3%, respectively. When the Alcolmeter was was calibrated at 0.50 mg/ml and used occasionally each day over an 18-day period, the drop in initial calibration was 0.01 mg/ml per week.