Joseph A. Caruso, Professor, Department of Chemistry, University of Cincinnati
Professor Joseph Caruso of the University of Cincinnati recently spoke with us about metallomics methods and applications with ICP-MS.
What is the field of metallomics?
Caruso: Well, basically it follows some of these fields that you can see on slide 2 – genomics, proteomics, glycomics, metabolomics – all of these are widely researched fields. The area of metallomics, as an area itself, is to a lesser extent. To finish answering your question, I’ve got a couple of definitions here (see slide 3). These were just published last year, so the field is fairly new. Pure and Applied Chemistry is the journal of the International Union of Pure and Applied Chemistry, who sets these definitions for chemistry. Now these definitions are official. Metallomics being the study of metal and metalloid species in biological systems and their interactions and connections with metal ions, metal species with genes, proteins, metabolites — just the whole gamut.
In studying metallomics, does it differ from analyzing for metals?
Caruso: Yes, it does. When analyzing for metals it’s a relatively simple process, where we put the sample containing the metal in the solution. With metallomics, the sampling process and the presentation to the detector is much more complicated and we typically use a chromatography interface after the sample preparation. So you can see here (slide 4), that we can do some kind of chromatography coupled with elemental mass spectrometry, which is ICP-MS, and look for low levels of detection. The important words in this slide are screening and quantification. However, we need identifications because these samples are very complex and we do that by some type of molecular mass spectrometry (in this case, it happens to be electrospray).
Does it derive from any other studies?
Caruso: It is essentially derived from the total metal analysis to what we call speciation, where we not only look at the total metal but we want to look at its various forms. For example, arsenic comes in four common forms: inorganic and organic forms that make those up.
Why is chromatography necessary?
Caruso: Well with the elemental mass spectrometry, the plasma essentially destroys the whole sample and gives us an abundance of singly positive charged ions. So we really can’t get any information about the samples unless we have standards. Basically, we use chromatography with standards to analyze and ultimately identify the particular species. That, of course, is only as good as you have standards or can generate standards to do this.
What types of chromatographic techniques to you use?
Caruso: Liquid chromatography is very common and very often used in its various modes, which could be reversed phase, ion exchange, and others, depending upon the type of metal we want to analyze. Or anything that can be detected by ICP-MS, such as sulfur and phosphorus as some of the halogens.
This interview has been edited for length and clarity.