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WIREs Forensic Sci

Alcohol, its analysis in blood and breath for forensic purposes, impairment effects, and acute toxicity

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Abstract Alcohol (ethanol) is man's favorite recreational drug and the psychoactive substance most often encountered in forensic toxicology casework; impaired driving cases, sexual assaults, and drug intoxication deaths. Because of the legal consequences of a person's blood– or breath–alcohol concentration (BAC or BrAC), the analytical methods used must be accurate, precise, and fit for purpose. The gold standard method for determination of ethanol in blood and other biological specimens is gas–liquid chromatography with flame ionization detector, although some laboratories also use a mass spectrometric detector. Also widely used for legal purposes are breath–alcohol analyzers; at the roadside as screening tests and also as evidence for prosecution of traffic offenders. Evidential instruments determine ethanol in exhaled breath by infrared spectrometry at wavelengths of 3.4 and/or 9.5 μm or by electrochemical oxidation with a fuel‐cell detector. The impairment of body functions after drinking alcohol depend on the amount consumed (the dose), the speed of drinking and the BAC reaching the brain. After drinking 1–2 units of alcohol (~16 g ethanol) people become more talkative and feel less inhibited (BAC <50 mg%). Cognitive and psychomotor functions are impaired as BAC reaches 80 mg% and at 150 mg% the signs and symptoms of alcohol intoxication are much more obvious including slurred speech, lack of coordination, confusion, and combativeness. On reaching BACs of 300–400 mg% most people are incapacitated and/or unconscious with slow and shallow breathing and at risk of death from paralysis of respiratory centers in the brain stem. This article is categorized under: Toxicology > Alcohol Toxicology > Analytical Toxicology Toxicology > Drug‐Impaired Driving
Schematic diagram illustrating the analysis of volatile substances by gas–liquid chromatography (GLC). After dilution of the blood specimen (1 + 10) with n‐propanol as internal standard, the sample is allowed to equilibrate at 50 or 60°C before a sample of the vapor phase is removed and injected into the GLC instrument
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Scatter plot showing the high correlation between results of testing apprehended drivers with an evidential infrared breath analyzer (Intoxilyzer 5000) and the corresponding concentrations of ethanol determined in venous blood
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Continuous increase in breath‐alcohol concentration during a prolonged exhalation into a quantitative infrared breath analyzer (the Evidenzer) approved for use by police in Sweden and some other countries
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Typical infrared absorption spectrum of ethanol in the vapor phase showing the C–H bond stretching frequency at 3.4 μm and the C–O stretching frequency at 9.5 μm
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Scatter plot of blood‐ and breath‐alcohol concentrations from roadside tests of drivers apprehended by the police in Finland. Note that many different instruments were used for breath‐alcohol testing and results were not corrected for metabolism of ethanol between time of the roadside test and blood sample for forensic analysis
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Time–response curve illustrating electrochemical oxidation of ethanol in breath using a handheld analyzer widely used to screen driver sobriety at the roadside. The insert graph shows response of the same instrument to increasing concentrations of ethanol in the breath sample
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Examples of chromatographic traces obtained after headspace analysis of a mixture of volatile substances. The two GLC columns are denoted Rtx®‐BAC 1 plus and Rtx®‐BAC 2 plus and retention times are different for the seven volatile substances in the sample
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