Emedinews:Insights on Medicolegal Issues:Failure to detect poison in chemical analysis by forensic lab

In some cases no trace of poison is found on analysis although from other circumstances it is quite certain that poison was the cause of illness or death. The possible explanations of a negative finding are:

• The poison may have been eliminated due to vomiting, stomach wash or diarrhea
• The whole of the poison may have disappeared from the lungs by evaporation or oxidation
• The poison after absorption may have been detoxified, conjugated and eliminated from the system
• Some drugs are rapidly metabolized, making extraction difficult.
• Some biological toxins and venoms, which are protein in nature cannot be separated from body tissues.
• Some organic poisons especially alkaloids may, by oxidation during life, or due to faulty preservation, or a long interval of time, or from decomposition of the body, deteriorate and cannot be detected.
• If the poison act slowly and death is delayed following production of irreversible organic changes, the poison may be completely metabolized and excreted.
• Many drugs may be present in very small amounts and these may require considerable amount of viscera for their identification.
• When the wrong or insufficient material has been sent for analysis.