ISOPROPANOL INTERFERENCE WITH BREATH ALCOHOL ANALYSIS - A CASE-REPORT

The presence of interfering substances, particularly acetone, has hist orically been a concern in the forensic measurement of ethanol in huma n breath. Although modern infrared instruments employ methods for dist inguishing between ethanol and acetone, false-positive interferant res ults can arise from instrumental or procedural problems. The case desc ribed gives the analytical results of an individual arrested for drivi ng while intoxicated and subsequently providing breath samples in two different BAC Verifier Datamaster infrared breath alcohol instruments. The instruments recorded ethanol results ranging from 0.09 to 0. 17 g /210 L with corresponding interferant results of 0.02 to 0.06 g/210 L over approximately three hours. Breath and venous blood specimens coll ected later were analyzed by gas chromatography and revealed in the bl ood: isopropanol 0.023 g/100 mL, acetone 0.057 g/100 mL and ethanol 0. 076g/100 mL. Qualitative analysis of the breath sample by GCMS also sh owed the presence of all three compounds. This individual had apparent ly consumed both ethanol and isopropanol with acetone resulting from t he metabolism of isopropanol. An important observation is that the bre ath test instruments detected the interfering substances on each breat h sample and yet they did not show tendencies to report false interfer ences when compared with statewide interferant data.