The Alchemist: Luminol

A Magic Solution

Thanks to shows like CSI, many people know what Luminol is and what it does. Luminol is used by investigators to detect blood stains, even those that have been cleaned up. The solution glows a light blue when the luminol comes into contact with a catalyst, such as blood. Luminol can not only detect blood, but it demonstrates the distribution of the blood, which can tell investigators a lot of information about a crime scene. Because of this, it becomes a valuable tool in investigators tool kits. Luminol is as the TV shows make it, however, there are some draw backs to this magic solution.

What it is

As mentioned before, most of us have seen luminol being used on popular CSI shows. It is one of the tools portrayed that actually lives up to the expectations of forensics laid out by Hollywood. Evidence technicians scour crime scenes in hopes of finding even the most minuscule evidence that will help break open the case. When you go somewhere or touch someone or something, there is usually transfer of material, however small. People believe that cleaning something until it’s no longer visible means that it’s entirely gone. However, this is not the case. Many times there will be some trace evidence left. So if someone cleans up blood, there will be some tiny particles left on the surface that will survive for many years. Luminol only requires a very small amount of catalyst to react so even the smallest amounts of blood can be detected. Investigators will spray an area with luminol and if there is blood present, the magical blue glow will appear. These traces will be photographed to record the pattern. It may reveal hand prints, foot prints, smears or prints from shoes. It may reveal a pattern that can tell investigators more about where the attack happened or what type of weapon was used. (Different weapons make different blood spatter patterns.)

However, there are some drawbacks to luminol. Luminol is only a presumptive test for blood due to the fact other chemicals can act as a catalyst for the reaction to bring about the blue glow. Substances that can give a false positive are chemicals in bleach, other metals such as copper, some paints and cleaners, as well as certain plant matter. Experienced technicians claim to be able to tell the difference between a false positive and a true positive. Because of the possibility of a false positive, additional presumptive tests are used. The luminol does not affect these other tests. However, the use of luminol can damage other evidence in the area, such as enzymes, and protein markers. The glow only lasts around thirty seconds. Unlike in many forensic shows, luminol is generally used as a last resort. It can very useful because it can reveal a blood spatter pattern that wasn’t visible to the naked eye. It can uncover the piece of evidence that breaks open the case.

How it Works

Luminol, chemically known as ,5-Amino-2,3-dihydro-1,4-phthalazinedione isn’t a liquid chemical. It’s actually an off white/yellow crystalline solid. It is usually dissolved in water to form a solution. In order to create the incredible potion used by crime scene investigators, it must first be mixed with other chemicals which allow the reaction to take place. One necessary component is a strong oxidizing agent such as hydrogen peroxide. Another necessary component is a basic (pH above 7) solution, which can be created by adding a substance with basic properties, such as sodium
hydroxide, NaOH. Bases are substances that can accept hydrogen ions. This is necessary because in a neutral solution, luminol has a positive and negative charge. In a basic solution, luminol forms an anion, which is a molecule that is negatively charged. So in this case, the OH^- essentially steals the hydrogens from the nitrogens, forcing the oxygens to rearrange their electrons in order to take on the negative charge. This is done for both nitrogens of the molecule, creating a dianion, a molecule with two negative charges.

This will allow the luminol to be oxidized by the oxidizing agent, in this case hydrogen peroxide. Oxidizing simply means combining with oxygen. The final piece of the puzzle is a catalyst. A catalyst is a substance that causes or accelerates a chemical reaction, but does not actually take part in the reaction. This is where iron in the hemoglobin in blood comes in. It acts as the catalyst in this situation, that is, it allows luminol to be oxidized by hydrogen peroxide. In the presence of iron hydrogen peroxide breaks down into oxygen and water.

Then the O2 oxidizes the luminol creating 3-aminophthalate. This reaction releases energy which is transferred to the electrons of the new molecule, promoting them to a higher energy level. As the electrons drop from a more unstable energy level to a more favorable one, the electrons release the excess energy as photon of energy, light, which is what causes the blue chemiluminescence.

Conclusion
Luminol is an incredible chemical that can be extremely useful in the field of forensics. It's glow can reveal cleaned up blood that isn't visible to the naked eye. The iron in blood acts as a catalyst for the reaction between luminol and hydrogen peroxide. This reaction releases energy, which is what causes the blue glow, revealing any blood splatter pattern. There are some drawbacks to luminol, it may give a false positive in some cases and it can damage other evidence in the area. Luminol used as much as portrayed on TV, it's usually a last resort in real life. But it can give investigators the piece of evidence they need to solve the case.