Researchers at the Indian Institute of Technology, Roorkee, have synthesised a new compound that can be used to develop sensors for detecting picric acid, which is a major component of explosives.
The new compound, called beta-dicyanovinyl substituted porphyrinogen, has been found to be capable of detecting picric acid at even as low a level as 1.12 parts per million. The colour of the substance changed from reddish-pink to purple according to the concentration of picric acid. The substance can be reused any number of times, according to Dr Muniappan Sankar, leader of the research team.
The same substance can also be used to detect cyanide and fluoride ions when they are hidden within a mixture of other anions by unique colour changes. The simultaneous and independent ‘naked-eye’ detection of picric acid, cyanide and fluoride ions is an added advantage of the new chemo sensor.
Like picric acid, cyanide and fluoride ions can also be detected at low concentrations – at the micromolar or ppm level. The minimum dose for fluoride is 13 micromolar and for cyanide 8.4 micromolar. Here also the detection is through a change in colour.
Though cyanides are highly toxic, they also find use in a range of industrial processes from electroplating, metallurgy and heap leaching of gold ore to steel manufacturing and as raw material for synthetic fibres, resins and herbicides. “Release of cyanide ions into the environment due to its increased usage in industrial applications raises the risk of accidental or intentional release as a toxic contaminant. Both biological and environmental aspects necessitate development of selective cyanide-receptors,” explained Dr Sankar.
Similarly, fluoride-containing compounds such as sodium fluoride or sodium monofluorophosphate are used in topical and systemic fluoride therapy for preventing tooth decay, besides various products associated with oral hygiene. But soluble fluoride salts, of which sodium fluoride is the most common, are toxic, and have resulted in both accidental and self-inflicted deaths from acute poisoning.
Dr Sankar conducted the study in collaboration with colleague, Mandeep K. Chahal. They have published a report of their work in the Royal Society of Chemistry’s journal Dalton Transactions.