Explain why luminol is NOT considered to be 100% accurate all of the time. Use three examples to justify your response.

Luminol is a chemical that emit light with blue glow when mixed with appropriate oxidizing agent.

Luminol is used by forensic investigators to detect small quantities of blood at crime scenes, as it interacts with hemoglobin iron. Biologists use it to detect copper, iron, cyanides and specific proteins using western blotting in cellular assays.

why luminol is NOT considered to be 100% accurate all of the time. 

• Horseradish sauce catalyzes the oxidation of luminol through the enzyme horseradish peroxidase, emitting light at 428 nm (blue in the visible spectrum), which may result in a false positive.
• A variety of substances, such as copper or copper-containing chemical compounds ,and some bleaches, can also cause luminol chemiluminescence. As a result, if someone thoroughly cleans a crime scene with a bleach solution, residual cleaner creates the usual blue glow in the crime scene, which effectively camouflages organic evidence such as blood
• The existence of Luminol can prevent the performance of other tests on a piece of proof. It has however been shown that DNA can be successfully extracted from luminol reagent-treated samples.
• Excessive smoke in an enclosed space can cause positive effects with Luminol e.g. a car that someone always smokes in.

Example

in hair and blood analysis

It is important to differentiate between class evidence and individual evidence to recognize the weaknesses of forensic evidence. Substances such as blood and hair, which can be used to position a person in a general class but can not be used to classify an individual, are class proof. Blood typing, for example, can be used to decide if someone has blood from A, B, AB, or O, but can not point to an individual.

Spraying an area with a solution of luminol and hydrogen peroxide is a popular method to test for blood. The iron atoms within the hemoglobin molecules in red blood cells serve as a catalyst when blood is present, causing the luminol to emit an eerie blue glow. A perfect way to search for blood stains is to use this chemical reaction. However this reaction can also be catalyzed by other compounds. A variety of other chemicals may also create an eerie blue light, from bleach to horseradish, causing a forensic investigator to believe that blood is present when in fact, there is none.

in forensic chemistry

Chemistry plays an indispensable role in forensic science, which in our justice system is playing an increasingly vital role. Chemistry is used in any form of forensic evidence, from fingerprints to blood to DNA. But it is not possible to use forensic science alone to determine guilt. Above all, every justice system is a human enterprise, and humans are always going to be fallible.

Fingerprint and DNA analysis

To identify a person, individual evidence, such as fingerprints and DNA, may be used. Each molecule of DNA is a polymer that consists of millions of nucleotides known as repeating units. While 99.9 percent of the DNA of a person is similar to that of any other person, there are small differences in the composition and arrangement of the different nucleotides, making the DNA of each individual unique to them. DNA is sometimes used, however to remove a suspect rather than to validate one. Only a tiny fragment of DNA is sequenced when DNA experiments are performed on a sample, not the whole genome. It is often difficult to collect samples that are not tainted with the DNA of another person while obtaining DNA at a crime scene, rendering outcomes unreliable. DNA degrades over time. Often errors are made by the laboratory technicians who conduct the experiments. The final decision is open to interpretation as to whether a DNA profile matches that of a suspect.