The modifying effect of the mouthpiece used in breath alcohol analysis was examined in terms of alcohol concentration in, and temperature of, the sample delivered. With repetitive testing, the standard Disposable Products mouthpiece (generally used for evidential breath analyses in Australia) was examined. The measured BAC and temperature values for tests with and without a mouthpiece were significantly different. Using an Allplastics brand mouthpiece, the reduction in BAC and temperature were 0.0027 g/100mL and 1.8 degree celsius. Further testing using the Disposable Products mouthpiece pre-warmed and cooled, when compared to using a mouthpiece at 20 degrees celsius, did not significantly alter BAC, but increased and decreased the measured temperature. The temperature reduction using a Disposable Products mouthpiece and a human subject who provided breath samples in a standardised fashion, was 1.0 degree celsius. The conclusions are that the mouthpiece modifies the breath sample delivered, lowering both BAC and temperature. The variations in BAC and temperature do not correlate with the change in alcohol air/water partition ratio of 6.7 percent per degree. Therefore, the correction of BAC readings to a standardised temperature is not straightforward. (A)
Samenvatting