It is time for a special issue dedicated to elemental speciation analysis

It is with great honour that we present you with a themed issue representing focal points of innovation in elemental speciation analysis. Five years have passed since the last special issue was devoted to the field, which was adopted as a topical research theme by atomic spectroscopy in the early days. In fact the definition of elemental speciation analysis is inherently linked to inorganic analysis defining molecules containing metal(oid)s or hetero-elements as chemical species of one or more elements. The concept of elemental speciation was perceived as a logical expansion of elemental analysis increasing the level of complexity by adding molecular information. Is this still true? Nowadays, the boundaries between elemental and molecular mass spectrometry are blurring. In fact it is possible to perform an essential elemental speciation analysis task by high resolution electrospray mass spectrometry. The accurate and selective measurement of isotopologues enables to extract elemental traces from LC-MS measurements. Whenever an elemental species is amenable to efficient electron ionization or electrospray ionization, the only advantage of inorganic mass spectrometry relies in the quantitative aspect of the analytical exercise. In fact, the potential of species unspecific quantification cannot be disregarded and there are many important applications. Success of accurate species quantification often relies on the availability of high quality species-specific standards. In many cases there is either a complete lack of standards or the standards are not certified for purity or even well characterised, severely compromising the accuracy of the speciation data. Species-unspecific quantification by inorganic analysis was introduced to overcome these severe limitations. However, it cannot be used as a stand-alone method for the characterization of reference materials since analyte losses or species transformation, potentially occurring during sample preparation or analysis cannot be accounted for.

Recently, the production of species-specific spikes for complex molecules such as proteins emerged, allowing the introduction of primary elemental speciation methods. In this innovative field, the trend is to combine biotechnological approaches such as recombinant protein production or in vivo synthesis of labelled amino acids, with elemental analysis. Hence it is not totally surprising that the metrology community is actively driving the field by developing certified reference materials based on elemental and molecular mass spectrometry. These activities producing protein standards will have a great impact in laboratory medicine, where currently the implementation of traceability of analysis is ongoing.

Another point of innovation in elemental speciation analysis (has always been and is still) is separation science. This is reflected in our special issue, e.g., by the focus on monolithic separations with great potential for intact protein analysis, and the introduction of turbulent chromatography in combination with elemental mass spectrometry. Moreover, the emerging interest in the field of nanotechnology and the complete lack of reliable analytical techniques in the field led to the rediscovery of field flow fractionation as a promising fractionation technique when combined with multiple detectors, including elemental detectors. Such an approach has increasingly been used in environmental analysis and has been more recently applied to nanotoxicology, drug delivery, metabolic and protein/nanoparticle interaction studies.

More than a decade ago in analogy to the modern system level “omics” approaches, the term metallomics was coined and many scientists saw a change in the face and scope of the field. As a consequence, biologically oriented method developments further on were not presented as elemental speciation approaches anymore, but were rather flagged as metallomics approaches. Evidently, the field of metallomics is embracing research beyond the pure analytical exercise focusing on the biological and biomedical role of metals, interrogating their interaction with other “omes”. However, compared to other “omics” disciplines, there is no mature technological platform offering comprehensive routine analysis of the metallome, hence the implementation of novel analytical strategies (with atomic spectroscopy as the core technology) continues to be a topical research theme.

This special issue comprises two critical reviews, a perspective, twelve original papers, a technical note and a short communication. Together, these highlight the complexity and role of speciation measurements in providing information relevant to health and environmental safety and compound-specific metabolism. The articles cover a range of elemental species of different types (e.g., inorganic Cr species, fine particulate carbon, As species, metalloproteins, aminoacids and peptides and metallodrugs) and samples of different complexity (e.g., tobacco products, fish oil, soils, human blood serum and cells). The issue includes recent work on the production of protein spikes (e.g., for selenoprotein P and haemoglobin) for accurate protein isotope dilution quantification via the elemental tag. It is clear that there is an increasing effort by the analytical community on the development and validation of reference methods that are invaluable to provide reference values to trials and proficiency testing schemes as well as to develop new “speciated” reference materials. It is hoped that this collection of excellent papers will help to broaden the horizons for future developments in this field. We would like to thank all the authors for their contributions and hope that you enjoy reading them.

Guest Editors,

Heidi Goenaga-Infante

Gunda Koellensperger

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