If we modify the filter paper by coating it with carbon nanotubes, then the applied potential can be reduced to even 1 volt, says Pallab Basuri.

IIT Madras researchers have used a novel approach to analyse various saturated and unsaturated hydrocarbons directly from solutions. Using the novel technique, the researchers could detect paraffin oil in coconut oil. The extent of paraffin oil contamination in coconut oil bought from the local market was as high as 10%.

Using a novel approach, researchers at Indian Institute of Technology (IIT) Madras have for the first time been able to use mass spectrometry to analyse various saturated and unsaturated hydrocarbons directly from solutions. Ionizing the constituent molecules of a hydrocarbon sample for detection using mass spectrometry has not been easy till date as hydrocarbons do not tend to lose or gain electrons to form ions.

Using the novel technique — laser-assisted paper spray ionisation mass spectrometry — the research team led by Prof. T. Pradeep from the institute’s Department of Chemistry could detect various hydrocarbons, importantly, paraffin oil contamination in coconut oil samples. Though it is common knowledge that vegetable oils are adulterated, the extent of contamination with paraffin oil was as much as 10%. “It was shocking to see such high levels of mineral oil contamination in coconut oil meant for cooking,” says Prof. Pradeep. “We could detect down to 1% paraffin oil present in coconut oil.”

The results were published in the journal Analytical Chemistry.

Detecting ions using paper spray ionisation mass spectrometry is known already. In this method, a regular filter paper containing the sample is subjected to high electrical potential and the charged droplets and the ions derived from them are analysed using a mass spectrometry. But this method cannot be used for detecting hydrocarbons.

So the researchers turned to the humble laser pointer used commonly during presentations to turn the stubborn hydrocarbons to emit ions for the measurement. Tiny amounts of the sample to be analysed were added to the filter paper kept at about 10 mm from the mass spectrometer and subjected to an electrical potential of 1 kV. Ionization of hydrocarbon molecules began the moment the tip of the paper containing the sample was exposed to the laser.

The hydrocarbons molecules present in the sample get trapped between the cellulose fibres, which make the paper. “And when an electrical potential is applied, the molecules experience an intense electric field. This is because the molecules are trapped between the fibres which are about 10 microns apart,” says Prof. Pradeep.

“When 1 kV potential is applied, the electric field experienced by the molecule is comparable to the field experienced by electrons moving around the nucleus, but not sufficient enough for them to jump out. When we shine the laser, the small energy supplied is enough to cause ionisation,” explains Prof. Pradeep.

Different potentials had to be applied to cause different hydrocarbons to get ionised for the same laser. “If we modify the filter paper by coating it with carbon nanotubes, then the fibres will be in the nanometer range and the applied potential can be reduced to even 1 volt,” says Pallab Basuri from the Department of Chemistry, IIT Madras and first author of the paper. “This throws open new possibilities for detecting food adulteration, water quality and environmental contamination.” The detection limit of the analytes is in the range of nanogram quantities.

According to Basuri, the paper strips containing the samples can be shipped to the place of analysis from remote locations. By varying the composition of the paper and structure of the fibres, it might become possible to store the paper strip containing the sample for future analysis.

Published in The Hindu on April 28, 2018