Human breath simulator using controlled evaporator mixer to test the performance of a breath alcohol analyzer

We constructed a human-breath simulator using an injection-type controlled evaporator mixer (CEM) available for the performance test of a breath alcohol analyzer. The simulator was designed to spray an ethanol solution to a carrier gas through a CEM nozzle and to ensure complete evaporation using a heating device in the evaporator mixer. In terms of the ethanol mass concentrations of the test gas injected from the breath simulator, the measured values through the IR type breath analyzer and the calculated ones from the gas mixture equation were analyzed. As results of the analysis, a first-degree polynomial equation was derived to determine the correlation between the calculated and measured ethanol mass concentrations in the test gas. By the Bland-Altman plot of the measured ethanol mass concentrations and the calculated ones, it was found that the agreements between two values below 1000 μg l−1 were within the 95% limit of agreement, whereas the agreements between two values above 1000 μg l−1 were beyond the 95% limit of agreement. These results were considered to result from the deterioration of the measurement accuracy of the breath analyzer and errors in delivery of the true concentrations in the high ethanol mass concentrations above 1000 μg l−1.