Here's a rather lengthy cut & paste explaination;
"Luminol"
5-amino-2,3-dihydro-1,4-phthalazine-dione, or luminol has become a commonly used, and functional compound. Luminol is a relatively simple chemical containing only carbon, nitrogen, oxygen and hydrogen. It was discovered in the late nineteenth century and later improved upon. Luminol is used often in biochemistry and serves many purposes from Halloween fun to crime scene blood detection.
Luminol, (C8H7N3O2) has quite a few other names; these include: 5-amino-2,3-dihydro-1,4-phthalazine-dione, o-aminophthalyl hydrazide, 3-aminophthathic hydrazide, and o-aminophthaloyl hydrazide1. Its molecular weight is 177.16, and has a melting point of 319ºC-320ºC. Its solubility is less than 0.1grams per 100 milliliters at 19ºC, and looks like a yellow grainy substance. If reacted the luminol emits a green-blue light with varying intensity.
Luminol is a chemiluminescent compound, which means that a release of light is a result of a chemical reaction2. Fireflies are nature’s chemiluminescent creatures, they create a similar reaction to produce their own light source,(which can be seen at night in more rural areas.) This light is energy being released.
When luminol is placed in a basic solution such as perborate, permanganate, hyperchlorite, iodine, or hydrogen peroxide, and a catalyst such as iron, manganese, copper, nickel, or cobalt, the luminol is oxidized2. (A catalyst is the most important ingredient to the reaction, because the stronger the catalyst, the longer and brighter the light will glow.) Most metals aid in the reaction, but there are a few that actually repress the response2. Hydrogen peroxide works best as the base, it “burns” the luminol. Cobalt has proven to be the best metal catalyst2. The luminol creates light via oxidation, because the two nitrogen atoms are easily replaced by two oxygen atoms. As this reaction occurs, nitrogen gas is discharged, leaving the luminol in an excited state, with additional energy which is then released as light3. Amino acids, tegatose, fructose, glycerols, thiols, and serum albumin can also react with luminol to produce an intense light. No excitation source is needed to produce a glow, but a photomultiplier tube may be used to measure and detect the amounts of light2.
In 1895, two scientists named Wiedemann and Schmid, dissolved cathode-ray irriaded alkali halides such as NaCl, NaBr, KCl, and KBr, in water. They noticed a very weak bluish light. They also detected light production when irriaded calcium carbonate was “attacked” by aqueous hydrochloracetic acid, or phosphoric acid4.
Later in 1928, a chemist by the name of Albrecht discovered a specific chemical, that when placed in an aqueous alkaline solution emitted a blue-green light with a fair amount of intensity. Along with the light, virtually no heat was produced. This solution contained hydrogen peroxide along with a catalyst. The catalyst was an alkaline medium with a pH between ten and eleven. This specific chemical was to later on be called luminol5.
Albrecht also determined the maximum intensity of light in this new chemical to be 424nm; he also concluded that fresh luminol was very unstable in its light yield, and the light yield itself came from the dissolved oxygen, and favored a trace metal. These discoveries led to a compound that created a useful cold light source at relative ease5.
Halloween has always been a night of excitement for children, a night when they can pretend to be anything, and a night full of sugar. Many children carry green glow-sticks on Halloween to illuminate themselves for safety purposes. These light-sticks contain dilute H2O2 in a phthalic ester solvent in a capsule. This is the surrounded by a phenyl oxalate ester and 9,10-bis(phenylethynl) anthracene. When snapped, these two chemicals combine to produce luminol. The glow-sticks are green, because of other chemicals. At other events (such as fairs) multi-colored necklaces and bracelets are seen, and use this same type of compound to create their glow6.
Often, luminol is used in biology and biochemistry for a multitude of testing. Chromatography, (which is a method for sorting chemical substances) immunoassay, (measures minute concentrations of biological matter in blood) DNA probes, and DNA fingerprinting, all use luminol as a testing reagent, and it is used as a substrate in western blot detection7.
The most important and well-known use of luminol is in the field of forensic science. In 1937, a German forensic scientist, discovered the use of luminol in blood detection8. Blood, which is slightly alkaline, contains cells, water, enzymes, proteins, and hemoglobin9. Hemoglobin (which contains iron) carries oxygen to parts of the body. This hemoglobin reacts with the luminol as the catalyst10. Luminol can detect very small amounts of blood many years old.
Once an area is suspected to have blood (even if the area has been cleaned) luminol can be applied. The lights are turned out, and after a brief few seconds (approximately five seconds,) a glow may appear. Just because an area glows, does not necessarily mean blood is the culprit. Bleach, dyes, and other organic material can react with the luminol. For the most part, luminol is a very useful tool in murder and rape investigations9. Luminol has helped put many murderers and rapist in prison, when evidence seemed to be hidden.
Just because it can trace minuscule amounts of blood at an efficient manner, does not mean that it does not have any drawbacks in crime scene investigation. Because it can detect other chemicals and compounds, further testing is almost always required to determine if the reactant is blood. If so, then the process begins to establish the type of blood, and if it is the victim’s blood. If luminol is used, it can break down and cause a loss to several genetic markers used in genetic testing as well as destroy other important properties of the blood. While it can detect even small amounts of blood, the disadvantage is often that the small amount identified is diluted further by the luminol solution. For these reasons, luminol is encouraged to be used as a last resort in crime scenes to protect what little physical evidence there already is9.
The chemiluminescent properties of luminol are remarkable in the fact that instead of heat, reactions involving luminol produce a cool light that has become a useful tool for both the scientific community and average individuals. It has aided research in blood. Luminol has helped to make the world a safer place by aiding the forensic community in its investigations. It has helped to further genetic testing via DNA probes, and medical testing, and has created an relatively safe natural light that can be seen anywhere on Halloween night.