Leaf Spray: Direct Chemical Analysis of Plant Material by Mass Spectrometry

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Eric Sorenson
Leaf Spray: Direct Chemical Analysis of Plant Material by Mass Spectrometry Jiangjiang Liu,† He Wang,† R. Graham Cooks,*,‡,§ and Zheng Ouyang*,†,§ †Weldon School of Biomedical Engineering, ‡Department of Chemistry, and §Center for Analytical Instrumentation Development, Purdue University, West Lafayette, Indiana 47907, United States Analytical Chemistry

ACS Publications
Published September 14, 2011
This research article written by the researchers Jiangjiang Liu, He Wang, R. Graham Cooks, and Zheng Ouyang at Purdue University demonstrated that Leaf Spray is a superior method of mass spectrometry for the determination of the chemical constituents of plant tissue. I became interested in this research article while I was working on my own laboratory research that seemed to parallel many of the same work the Purdue researchers were performing, but of course with a higher degree of expertise and technological advantage. I found myself researching the molecular and chemical components of Arabidopsis thaliana, the plant model organism, used extensively in plant genetic and metabolism studies. Specifically I was interested in the glucosinolate content in the plant. Glucosinolates are a group of plant thiogluciosides found in all members of the plant family Brassicaceae. This group of secondary metabolites is indicative of cellular differentiation and knowing their concentration within A. thaliana spatially and temporally would provide a wealth of information for how the plant controls and maintains cellular differentiation specifically in the unicellular trichome structures. I found my research to be quite demanding and frustrating through the means by which I was detecting glucosinolates. I was detecting the glucosinolates via indirect analysis by first homogenizing the plant tissue and diluting the components and then treating the samples to either strong base or enzyme and sequentially analyzing the left over metabolites. So I wasn’t actually detecting the glucosinolate compound for what it truly is, just a left over, a remnant of its presence. Furthermore I would not be able to distinguish the difference between glucosinolates, I would just see that glucosinolates are present not the actual identity of the glucosinolate. During this work I came into contact with a newly published article that was doing essentially the same work that I was, detecting glucosinolates in A. thaliana as well as other plants, and I was quite enthralled and became more interested in this article and the ins and outs of their experimental procedures. I was very interested by the fact that they were able to detect glucosinolates in vivo and directly in the plant tissue with no to very minimal sample preparation.

Leaf Spray is performed by taking a bit of plant tissue cut into a triangle, to generate the Taylor cone of emission of ions from the plant, and applying a high voltage to the posterior end and holding the sample up to the inlet of the mass spectrometer to generate a spectrum. The experimenters performed a number of different experiments showing the validity and prospect of Leaf Spray as a powerful means of chemical analysis. These experiments include; Solvent vs. no solvent, Spatial, choice of solvent, in vivo, developmental tissue, dehydrated plant tissue, and finally metabolic/temporal experiments.

The solvent vs. no solvent experiment showed that many plants, that have a high enough water content can produce a spectrum directly without the use of an added solvent. Some examples of these are grapefruit, tomato, cucumber, pepper, corn kernels and onions. Plants that could not generate a spectrum directly and required the use of a solvent, are spinach leaf, peanut seeds, and cranberry fruit. The experimenters wanted to know what effect did using solvent have on the plant and demonstrated this by taking a spectrum of green onion leaf with a dn without the use of methanol as a solvent. What was found was that the both...
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