Materials are making inroads into mass spectrometry, and an example is the use of advanced materials for enhanced ionization by transformation of a less-ionizable molecule to an easily ionizable one. Here we show the use of Pt nanoparticle-decorated nanotubes as highly active catalysts for the reduction of 2,4,6-trinitrotoluene to 2,4,6-triaminotoluene and subsequent easy detection of the product by in situ ambient ionization mass spectrometry. © 2017 American Chemical Society.

Pradeep Thalappil

Department Of Chemistry

Depanjan Sarkar

ionization

Mass spectrometry

Nanotubes

Yarn

2 ,4 ,6-TRIAMINOTOLUENE

2 ,4 ,6-TRINITROTOLUENE

Active catalyst

Advanced materials

AMBIENT IONIZATIONS

IONIZABLE MOLECULES

PT NANOPARTICLES

SPRAY IONIZATION

Nanocatalysts

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Analytical Chemistry

A new kind of ambient ionization method named superhydrophobic preconcentration paper spray ionization mass spectrometry (SHPPSI MS) is introduced, where superhydrophobicity and paper spray mass spectrometry (PS MS) are coupled. The SHPPSI MS requires only microliter amounts of analyte solutions, allows easy sampling procedure, and provides high sensitivity for a diverse array of analytes. It can be used to detect food adulteration at extremely low concentrations. The experimental methodology involves modifying one of the surfaces of a triangularly cut filter paper to make it acquire low surface energy by drop casting a green and ecofriendly superhydrophobic coating material over it followed by drying. A micrometer scale defect was made at close proximity to one of the tips of the paper using a pin. Preconcentration of the sample was accomplished by allowing a 10 μL droplet of an aqueous solution of the analyte to stand at the defect followed by drying naturally. The dried paper was used as the substrate for paper spray mass spectrometry by eluting the analyte with a suitable solvent. This novel technique was used to detect melamine in adulterated milk, whose detection at the ppt level in milk normally needs sophisticated instruments, a larger amount of sample, and a complex sampling procedure, including further purification and separation. The SHPPSI MS detects melamine directly from milk at the sub-ppb level by simply putting a microdroplet of adulterated milk at the substrate and eluting the sample with methanol. This paper-based technique can be a promising tool for direct sensing of analytes such as drugs in body fluids, pesticides in water and soil, etc. © 2019 American Chemical Society.

Sub-Parts-per-Trillion Level Detection of Analytes by Superhydrophobic Preconcentration Paper Spray Ionization Mass Spectrometry (SHPPSI MS)

The performance of semiconductor devices can be fine-tuned through chemical transformation of their nanostructured components. Such transformations are often carried out in controlled conditions. Herein, the use of electrospray deposition of metal ions from solutions in air is reported, to bring about chemical transformations across mm2-sized areas of nanostructures. This is illustrated with monolayer assemblies of ultrathin tellurium nanowires (NWs). The process does not require any reducing agent and can transform the NWs chemically, in the solid state itself, under ambient conditions. By using suitable masks, the beam of ions can be patterned to localize such transformations with nanometer precision to obtain aligned multiphasic NWs, containing atomically precise phase boundaries. By controlling the time of exposure of the spray, the scope of the process is further expanded to produce tellurium-metal telluride core–shell NWs. The method described here represents a crucial step for ambient processing of nanostructured components, useful for applications such as semiconductor device fabrication. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Particle and Particle Systems Characterization

Atomically Precise Transformations and Millimeter-Scale Patterning of Nanoscale Assemblies by Ambient Electrospray Deposition

Areca nut (seed of Areca catechu) is consumed by people from different parts of Asia, including India. The four major alkaloids present in areca nut are arecoline, arecaidine, guvacoline and guvacine. Upon cutting, the nut reveals two kinds of regions; white and brown. In our present study, we have monitored the formation of these two regions within the nut during maturation, using the non-invasive techniques of magnetic resonance imaging (MRI) and volume localized magnetic resonance spectroscopy (MRS). Electrospray ionization mass spectrometry (ESI MS) and desorption electrospray ionization mass spectrometry (DESI MS) imaging have been used to study the associated change in the alkaloid contents of these two regions during the growth of the nut. Our study reveals that white and brown regions start forming within the nut when the liquid within starts solidifying. At the final stage of maturity, arecoline, arecaidine and guvacoline get segregated in the brown region whereas guvacine gets to the white region of the nut. The transport of molecules with maturity and corresponding pattern formation are expected to be associated with a multitude of physiochemical changes. © 2016 Elsevier Ltd. All rights reserved.

Phytochemistry

Developmental patterning and segregation of alkaloids in areca nut (seed of Areca catechu) revealed by magnetic resonance and mass spectrometry imaging

Ionization of molecular species from one-dimensional (1D) tellurium nanowires (Te NWs) has been achieved at 1 V. Molecules with a range of chemical functional groups gave quality mass spectra with high signal/noise ratios and no fragment ions. Experiments suggest the possibility of emission of microdroplets of solution due to the intense fields at the ends or interfaces of nanostructures. It appears that electrolytic conduction of the solution wetting of the nanostructures and not the electronic conduction of the nanostructures themselves is involved in the ionization event. Anisotropy was seen when two-dimensionally aligned Te NWs were used for ionization. The orientation effect of aligned Te NWs on molecular ion intensity is demonstrated for many analytes including organic molecules and amino acids with experiments done using a silicon substrate having aligned Te NWs. These measurements suggest the possibility of creating a MS source that extends the applicability of mass spectrometry. Analysis of a variety of analytes, including amino acids, pesticides, and drugs, in pure form and in complex mixtures, is reported. These experiments suggest that 1D nanostructures in general could be excellent ionization sources. © 2015 American Chemical Society.

Fulltext

Anisotropic Molecular Ionization at 1 V from Tellurium Nanowires (Te NWs)

We report in-situ production and detection of intermediates at graphenic surfaces, especially during alcohol oxidation. Alcohol oxidation to acid occurs on graphene oxide-coated paper surface, driven by an electrical potential, in a paper spray mass spectrometry experiment. As paper spray ionization is a fast process and the time scale matches with the reaction time scale, we were able to detect the intermediate, acetal. This is the first observation of acetal formed in surface oxidation. The process is not limited to alcohols and the reaction has been extended to aldehydes, amines, phosphenes, sugars, etc.; where reaction products were detected instantaneously. By combining surface reactions with ambient ionization and mass spectrometry, we show that new insights into chemical reactions become feasible. We suggest that several other chemical transformations may be studied this way. This work opens up a new pathway for different industrially and energetically important reactions using different metal catalysts and modified substrate. [Figure not available: see fulltext.] © 2013 American Society for Mass Spectrometry.

Journal of the American Society for Mass Spectrometry

Studying reaction intermediates formed at graphenic surfaces

Ambient ionization is achieved by spraying from a carbon nanotube (CNT)-impregnated paper surface under the influence of small voltages (≥3 V). Organic molecules give simple high-quality mass spectra without fragmentation in the positive or negative ion modes. Conventional field ionization is ruled out, and it appears that field emission of microdroplets occurs. Microscopic examination of the CNT paper confirms that the nanoscale features at the paper surface are responsible for the high electric fields. Raman spectra imply substantial current flows in the nanotubes. The performance of this analytical method was demonstrated for a range of volatile and nonvolatile compounds and a variety of matrices. Low voltage: A carbon-nanotube-impregnated paper can be used to generate ions from organic molecules at potentials as low as 3 V. Common pesticides from the surface of an orange, ingredients of tablets, and a variety of analytes, such as amino acids, were characterized by this method. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Journal	Data powered by TypesetAnalytical Chemistry
Publisher	Data powered by TypesetAmerican Chemical Society
ISSN	00032700
Open Access	No