0.6 Forensics  (Page 3/5)

The amount of alcohol in a breath analyzer sample is therefore proportional to the amount of potassium dichromate that is used up and also therefore to the loss of yellow color.

The Blood Alcohol Concentration (BAC) may then be calculated from the equation

BAC = 0.8 A/WR

Where W is a body weight of the individual being tested, A is the amount of alcohol in the body (in mL) and R is a “Widmark R Factor”, approximately 0.68 for men and 0.55 for women. In most states, a BAC of 0.1 percent is sufficient to be convicted for driving under the influence of alcohol; in some states the threshold BAC is even lower.

Part 4: Blood Stain Analysis Using Chemiluminescence

Investigators often find bloodstains during their examination of a crime scene. They also find stains that could be similar substance, something other then blood, such as red paint. How would you test a stain to see if it is blood? Human blood contains a pigment called hemoglobin, which is used to transport oxygen through our body. This pigment is used by number of tests to identify the presence of blood. One most common test used by investigators that reveals the presence of blood is the Luminol Test. In this test the bloodstain can be made to glow with a blue light due to chemoluminescent reaction of the luminol reagent with the iron (Fe) in the hemoglobin. Chemoluminescence is the reversed case of photoreaction: by a chemical reaction, an excited particle is formed, which looses its energy by producing a light quantum of light. The most important characteristic is that the light is emitted in cold. In other words, chemoluminescence happens when a molecule capable of fluorescing is raised to an excited level during a chemical reaction. Upon its return to the ground state, energy in the form of light is emitted. Luminol is one of the most outstanding molecules that emit appreciable amounts of light.

Part 5: Spot Tests and Analysis of a Dollar Bill

The urban legend that 3 out of 4 dollar bills, which usually have a life span of 9 years, are contaminated with trace amounts of cocaine is not only true but they could also be silent carriers of diseases such as Hepatitis C too (Note: SARS and AIDS cannot be spread by contaminated bank notes). The contamination arises from a dollar bill being used to snort cocaine or handled by a cocaine user, since cocaine is excreted in skin oils and the contamination is then spread in bank sorting machines. Interestingly, Australia introduced plastic currency in 1988 to prevent the ability of the crystalline structure of illicit drugs to gain a ‘foothold’ on paper money, to make it harder for counterfeiters to reproduce and to last four times longer. They now print polymeric notes for many countries including: Israel, Malaysia, Mexico and Romania.

Investigators often use Chemical Spot Tests (CST) as simple chemical reagents to test unknown suspect powders by observing a quick colour change that will confirm or deny the presence of a drug or a class of drugs. A caveat needs to be sounded here, since multiple compounds of the same class of drugs may give the same colour change, e.g benadryl with active ingredient, diphenhydramine, a first generation anti-histamine drug and since it has sedative properties is also used in sleep aids such as Tylenol PM where it is combined with acetaminophen (paracetamol). Consequently, this is by no means conclusive evidence for that, you would need to use more expensive, sophisticated instrumentation: such as gas chromatograph – mass spectrometer (GC-MS), Fourier transform – infrared (FT-IR) and UV- visible techniques but is obviously easier to do these simple, screening tests in the field.