ICP-MS

One of the most powerful and sensitive testing techniques, inductively couple plasma–mass spectrometry (ICP-MS) has found application in fields as varied as water testing, food safety, and petroleum analysis.”

This month, Spectroscopy's Wavelength Tech Forum looks at the use of ICP-MS for elemental speciation (ES). Joining us for this discussion are Shona McSheehy, Thermo Fisher Scientific, and Dr. Laszlo Ernyei, Senior Chemist/Spectroscopist, SPEX CertiPrep.

One important area of development in ICP-MS is elemental speciation, with important applications in fields such as agriculture, biology, medicine, the environment, and geology. What are some of the most important advances that are coming out of this research?

McSheehy: The applications of elemental speciation now cover such a wide range of markets and research disciplines that it’s hard to keep up with the developments and progress in this field. Over the last few years, we’ve seen elemental speciation grow significantly in the medical and life science disciplines with ICP-MS sitting alongside ES-MS (and other similar techniques that generate molecular information about species) with the sum of information from the two techniques giving a more comprehensive answer about what is present in samples.

The significance of metals and the role they play in cell biology is being investigated by a number of groups that have found that traditional proteomic approaches just can’t find or characterize where and which metal is present in any given proteome and that ICP-MS has the potential to give them those answers. A paper last year in Nature reported just how diverse the range of metals incorporated into a microorganism can be and also demonstrated organism-specific assimilation, paving the way for more exciting discoveries about metals and their place in the proteome. The recently established Metallomics conference (which will be held in Muenster in June of this year) and the RSC Metallomics journal reflect the growth and anticipated impact this field will have in cell biology.

Applying elemental speciation in pharmaceutical and clinical disciplines is also on the rise. Many pharmaceuticals contain elemental species as the active ingredient and characterizing the mechanisms of these medicines is necessary to understand how and where they work and how to employ them in an efficient manner.

More of a result than an advance is the implementation of toxic species limitations in recent and upcoming legislation. All the initial hard work in the speciation field led to the understanding of where and just how much of some of the most toxic species exist in our environment (and food sources). This has driven legislation to include these elemental species in directives so that their presence in our environment can be controlled. Paradoxically, this will further drive the growth of speciation as we now strive to meet these demands and monitor our environment more extensively.

Ernyei: More and more studies from biologists are revealing the toxicological aspects of specific speciated ions to humans and the environment.

These studies have led to a demand for a new field of measurement in atomic spectroscopy, where not only the elemental composition but the chemical bonds can be investigated, thereby improving both separation techniques and characterization methods.

What barriers remain to further development in the area of elemental speciation analysis?

McSheehy: The main challenges in speciation analysis over the last few years still remain. Firstly, it’s necessary to handle samples in a controlled manner so that the species we are measuring are the same species that were present originally in the sample. Processing samples to render them “analyzable” invariably removes the species from the original matrix and throws them into a media that can promote chemical and thermal instability. Transformation or degradation of the original species is commonplace and more techniques that either avoid or measure the changes need to be developed. Secondly, as the number and diversity of species and sample type increases, the number of analytical standards and reference materials also needs to increase. Certified reference materials (CRMs) exist for some of the matrices and applications that have been more extensively investigated by elemental analysis (organotins in environmental samples, for example), but species-specific CRMs in the clinical and food safety disciplines are still lacking.

Ernyei: Speciation analysis opened up a new field of measurement in atomic spectroscopy, which will require new certified reference standards for LC-ICP-MS analysis. However, availability of these standards is limited. Also, keeping the targeted analyte in its original form during sample preparation is a significant challenge.

What are the next frontiers in this area, e.g., in terms of fields of application or refinements of what the technology (interpretation and application of findings/results) can tell us?

McSheehy: Hardware developments have helped analysts tackle the need for determining lower levels of species in lower sample masses than ever before. Chromatography that allows the processing of higher sample volumes (e.g., large volume injection in GC, on-line concentration in LC), sample introduction systems that work at a nanoliter/minute rather than milliliter/minute scale, and developments in ICP-MS that can significantly increase sensitivity, all offer potential for improvement in speciation applications.

Metal tagging and isotopically enriched species (that double as tracers and quantification standards) have proved their worth in many speciation studies. Use of tracers in metallomics and pharmaceutical research would prove useful in determining processes through which metals are incorporated and how the metals are regulated and transported through cells. However, with a lack of standards available, it is in the hands of the researchers to team up with chemists and/or biologists who can synthesize the necessary species from isotopically enriched elemental solutions. Metal tagging approaches open the ICP-MS door to essentially any species that will accept a tag. A quantitative tagging reaction holds the promise of quantifying proteins with ICP-MS at levels significantly lower to those measurable with ES-MS. Implementation and validation of these approaches is underway but is yet to be adopted on a wider scale by the classic proteomic community.

In cell biology or life science research, a parallel detection system of ICP-MS and ES-MS generates huge volumes of data. In organic MS, libraries are well on the way to assisting analysts in their data evaluation and streamlining a multidimensional library that could search both ICP-MS and ES-MS traces would alleviate what is currently a relatively intimidating data evaluation process.

Speciation analysis opened up a new field of measurement in atomic spectroscopy, which will require new certified reference standards for LC-ICP-MS analysis. However, availability of these standards is limited. Also keeping the targeted analyte in its original form during sample preparation is a significant challenge.

Ernyei: In recent years the hyphenated techniques have developed the required interfaces. The separation of the species is slow compared to the atomic spectrometric measurements; a big development has to come soon.

At this time the separation requires a very long time (several minutes) compared to the ICP-MS measurement (several milliseconds). When we can reduce the separation time significantly, then the cost of analysis will be reduced. Then it will be more cost effective to analyze a greater number of samples from varying matrices.