Detection of hydrocarbons by Laser Assisted Paper Spray Ionization Mass Spectrometry (LAPSI MS)

Students of Indian Institute of Technology Madras, Pallab Basuri, Depanjan Sarkar won the award for research work of Detection of hydrocarbons by Laser Assisted Paper Spray Ionization Mass Spectrometry(LAPSI MS). They carried their project work under guidance of  Prof. Thalappil Pradeep.

We have introduced a new ambient ionization technique named ‘Laser Assisted Paper Spray Ionization Mass Spectrometry’ (LAPSI MS). In LAPSI MS, a 532 nm ≤10 mW pen torch laser pointer was shown to a triangular paper along with high voltage to enhance the paper spray ionization. The analyte solution was continuously pushed through a fused silica capillary, using a syringe pump, at a preferred infusion rate. LAPSI MS promises enhanced ionization with high signal intensity of polycyclic aromatic hydrocarbons (PAHs), which are normally not ionizable with other mass spectrometric techniques. LAPSI MS works both in positive and negative modes of ionization. A clear enhancement of signal intensity was visualized in the total ion chromatogram for an analyte in presence of the laser. 


We speculate that the mechanism of ionization is field assisted photoionization. The field-induced distortion of the potential well can be large in paper spray as the fibers constituting the paper are separated at tens of nanometers apart and consequently the analyte molecules are subjected to very large electric fields. LAPSI MS can be used for monitoring in situ photo-assisted reactions like, the decarboxylation of mercaptobenzoic acid in presence of gold and silver nanoparticles and dehydrogenation reaction of 2,3-dihydro-1Hisoindole, for example. As an application we have shown that the paraffin oil which is usually non ionizable by paper spray or by electrospray ionization can be efficiently detected using this technique. As a real life application, such impurities like mineral oils were detected in commercially available coconut oil.

Dr. Harsh Vardhan, Minister of Science and Technology, awarded the Gandhian Young Technological Innovation (GYTI) Appreciation to Pallab Basuri, Depanjan Sarkar, Indian Institute of Technology Madras at the GYTI 2018 Awards function held at Rashtrapati Bhawan on March 19, 2018.

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