Alcohol analysis and Forensic issues
Ethyl alcohol (Ethanol ) is the commonly used oldest drug consumed by a human for many years. Ethanol is a volatile liquid soluble in water and has a characteristic taste. Alcohols are a group of organic chemicals and have a hydroxyl group attached to the hydrocarbon chain of the molecule.
Alcohol is known to be a central nervous system depressant (CNS) and is correlated to the amount of alcohol present in the blood. The most common unit of blood alcohol concentration (BAC in %) can be expressed in grams of ethanol per 100 ml of blood. A person who is said to be legally intoxicated in most of the states in the United States is at a BAC of 0.08 %.
The blood alcohol concentration in a person depends on body weight, the number of beverages consumed, ethanol concentration, speed, and pattern of drinking. BAC also depends upon absorption, distribution, metabolism, and excretion (ADME) of ethanol, adiposity, and total body water content of the person.
The volume of the distribution of ethanol expressed by Widmark using a formula
where A is the volume of ethanol consumed, W is the body weight, R the distribution ratio, C is the blood ethanol concentration and 0.8 is the specific gravity of ethanol. The peak blood alcohol concentration varies and ranges between 15 minute-2 hours.
Alcohol present in the body is eliminated by liver metabolism through oxidation and the remaining alcohol is removed through breath, sweat, feces, and urine. The enzymes present in the liver (cytochrome P450) catalyze the conversion of ethanol to acetaldehyde. The acetaldehyde is then converted into acetic acid via acetaldehyde dehydrogenase.
Forensic and Clinical issues
Diving under the influence of alcohol is the most encountered forensic issue in most of the accidents and death cases. Driving is a divided attention task and it requires the coordination of hand, eye, muscles, and cognitive function. Alcohol causes slowness in reaction time, difficulty in information processing, and impaired driving. Accidents and crash risks are very high when blood alcohol concentration is greater than 0.04g/dl.
Field sobriety tests usually include walk and turn, one-leg stand, and horizontal gaze nystagmus. Horizontal gaze nystagmus is more reliable in predicting the concentration of alcohol in the blood other than walk and turn and one-leg stands the test. The horizontal gaze nystagmus test is the involuntary jerking of an eye while moving to the side. When the BAC level is 0.10 %, jerking of the eye begins even before the eyeball reaches 45 degrees. The field sobriety test is useful only if the BAC concentration is 0.08g/dl or above.
Plasma contains more water than blood and more alcohol per milliliter. Alcohol present in plasma or serum can be converted into BAC and can be done by dividing it by 1.18.
BAC can be measured using enzymatic and chromatographic methods. The enzymatic method depends upon the oxidation of alcohol to the aldehyde by the reduction of cofactor NAD+ to NADH. The chromatographic method is a popular method of forensic blood alcohol concentration. The technique is semi-automatable, highly reproducible, highly specific, and has the greatest amount of flexibility in analyzing the volatile compounds. Direct injection of biological samples can cause contamination and decreased performance. An aliquot of a blood sample containing a preservative and an anticoagulant is removed in duplicates and mixed with 2 mL of NaCl solution that contains 1.0 g/L of 1-propanol as the internal standard. The preservative is sodium fluoride which prevents the formation or contamination of bacteria in blood samples. Potassium oxalate is an anticoagulant that ensures blood remains homogenous without separating red cells and serum.
Breath alcohol instruments are very significant in identifying BAC directly. Breath collection is a non-invasive field test procedure. The procedure required only minimal operator training and also inexpensive laboratory equipment. One of the best known hand-held devices is fuel cell-based technology. In this technology, ethanol is converted into acetaldehyde and produces free electrons with the electric current generated is proportional to alcohol in the blood.
In 1938, there was another commercially available forensic breath analyzing instrument called Drunk-o-meter. In this instrument the person blew a balloon and air in the balloon was released into a chemical solution namely potassium permanganate. If the air contains alcohol the color of potassium permanganate changes color. Drunk-o-meter was replaced by Breathalyzer which is a portable instrument. The instrument uses a colorimetric technique that utilizes the oxidation of ethanol in potassium dichromate solution.
Urine can be used as a specimen for forensic analysis. The limitations of a urine sample for analysis is the collection and interpretation. Analysis and collection of samples increase the chances for contamination, adulteration substitution, or dilution. Interpretation of the urine analysis result is also a limitation.
Drugs including alcohol can be found in the saliva. Extreme care should be taken while examining alcohol content in saliva because contamination can also occur due to drugs present in the oral fluid. Mouth alcohol is dissipated generally by absorption and exhalation in 15 minutes and for alcohol breath test 15-20 minutes observation and waiting period are essential for a salivary alcohol test.