1. Introduction

Introduction

Luminol reacts with haemoglobin in blood, as well as sodium hypochlorite (bleach), copper, and iron to produce a blue glow. The process is known as chemiluminescence. As luminol is sensitive, it is often used at crime scenes to detect blood. However, there are many factors that can affect the readings and give a false result. In this experiment, haemoglobin is substituted with iron (II) sulfate as iron (II) sulfate is easily accessible.  As some cleaning products might give false results, bleach, soap and detergent are used for the experiment. This may allow more accurate testing of haemoglobin in the future, which would help solve crimes.

Background Research
The test involves spraying suspected blood samples with a standard mixture of luminol dissolved in an alkaline, aqueous solution such as dilute hydrogen peroxide or sodium perborate (Quickenden & Creamer, 2001). The mixture then emits bright sparkles of blue light when it is sprayed on droplets of blood containing haemoglobin, which exerts a strong catalytic effect on the emission as it is well known that the luminol reaction produces significantly brighter chemiluminescence in the presence of a catalyst (Creamer, Quickenden, Apanah, Kerr & Robertson, 2003). Small traces of human blood as small as 1 ng can be detected by the pale blue chemiluminescence (Quickenden & Creamer, 2001). However, the mechanism behind this catalysis is not well understood. It is believed, on the whole, that the catalyst (usually in the form of a metal ion) forms some sort of intermediate complex or radical, which in turn leads to the excited state of luminol (Creamer, Quickenden, Apanah, Kerr & Robertson, 2003). Based on Cameron's (2012) experiment, the number of washes on the stained blood did not affect the strength of the reaction, but detergent does lessen the reaction strength. There have been interferences with the testing of haemoglobin. They generally produce a different spatial distribution of luminescence, as will the surface that is coated with interfering substances (Quickenden & Creamer, 2001). Based on a research done by Creamer et al. (2003) on things found in a modern home, turnips, parsnips, horseradishes, commercial bleach (NaClO), copper metal, some furniture polishes, some enamel paints and some interior fabric in motor vehicle produce a sufficiently intense chemiluminescence with luminol reaction to be easily mistaken as blood. Other known catalysts would include plant peroxides and iron or copper compounds (Quickenden & Creamer, 2001). However, things that could be mistaken for blood such as sauces, things similar in colour had no reaction although some research did show that some sauces do react with luminol (Cameron, 2012). Majority of these catalysts can be distinguished from human haemoglobin because they produce lower chemiluminescence intensities (Quickenden & Creamer, 2001).

Research Question
Does some types of cleaning products used to clean the area where blood was affect the brightness of the chemiluminescence of luminol or cause false results?

Hypothesis
Our hypothesis is that cleaning products, other than bleach, will not cause false results of luminol with iron (II) sulfate.

Independent variable(s)

• The cleaning product used [bleach (Chlorox), soap (Yuki), detergent (Ajax fabuloso)]

Dependent variable

• The brightness of the chemiluminescence of the material after being sprayed

Constants

• The volume of luminol used
• The concentration of the cleaning product used in the solution that the cloth is soaked in
• The concentration of luminol in the spray bottle