Detecting Poisons Using Chromatography

Pesticides are one of the best methods used to protect the crops we grow to feed the burgeoning world population. In some parts of the world, pesticides are used more freely and with less regulation than they warrant – especially given their toxicity. Unfortunately, this means that pesticides are relatively freely available – and for some people they are the poison of choice.

A recent paper published in the Indian Journal of Applied Research – Detection of Pesticides in Viscera Samples by Thin Layer Chromatography – has looked at how chromatography, especially thin layer chromatography, could be used to analyse pesticide poisoning.

Death and pesticides

There are several different categories of pesticides used in Indian agriculture. The most common types are organophosphates, organochlorines and carbamates – with organophosphates the most widely used. They are used to control the pests that feed on plants – but, sadly they are also found in the post mortems of suicide and murder victims across India.

The paper reports how pesticides are used because of their ease of availability, fast actions and small lethal doses. Many pesticides have adverse effects on human physiology including:

• mutagenic effects – an agent that causes mutations in genetic material above the level normally expected,
• teratogenic effects – an agent that causes developmental problems in an embryo or foetus, and
• neuropathic effects – an agent that damages the nervous system.

When a death is linked to pesticide poisoning, either from suicide or foul play, the analysis of visceral samples such as the stomach, liver, kidney or spleen can give investigators an idea of the type and quantity of pesticide used. In the research paper, the team report on the extraction of pesticides from viscera samples, and their purification and identification by thin layer chromatography.

Not a case of TLC

The pesticides were extracted from the samples using steam distillation and solvent extraction. A range of different solvent systems were used to extract the pesticides from the samples including n-hexane, acetone, cyclohexane, chloroform and benzene. Over 70 samples were analysed by thin layer chromatography with over 40 testing positive for pesticide residues including organophosphorus, organochlorines and carbamate pesticides.

The researchers noted that some pesticides had very low R_f values – the ratio of the distance travelled by the solute when compared to the solvent used in the chromatography run – that necessitated different solvents. Sample preparation is key to obtaining good quality chromatograms – a topic discussed in the article, Issues with Sample Preparation. Although thin layer chromatography presents a simple and relatively cheap means of analysing viscera samples for pesticides, the authors note that for highly accurate and reliable analysis, gas chromatography should be the preferred option.