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Speciation Analysis

Working Group 3.22

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The working group "Speciation Analysis" is responsible for the traceable quantification of elemental species with the focus on applications in clinical chemistry.

For the assessment of the biological, chemical and toxicological influences of elements in nature, it is indispensible to know – in addition to the total content of the elements, which is mostly regulated by legislation – also the contents of the compounds (species) in which the elements occur. As these element species have completely different properties, the relevance of a specific element fraction in a sample can be reliably assessed only in connection with a species-analytical characterisation.


Different compounds of a metal may show

  • a different solubility and, thus, a different mobility: e.g. As2S3 0.0005 g/L versus Na2HAsO4 610 g/L
  • a different toxicity: e.g. Hg2Cl2 LD50 210 mg/kg, MeHgCl LD50 29.9 mg/kg
  • a different bioavailability

This means that – depending on the compound – the same total quantity of an element can have quite different effects. This is, for example, illustrated by the following copper compounds:

Copper in different compounds with different toxicity: copper sulfate as fungicides in viniculture, copper gluconate as dietary supplement and ceruloplasmin as copper storage protein

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Research/Development

As far as possible, we use isotope dilution analysis mass spectrometry (IDMS) for the quantitative determination of the elemental species. Thereby, two different approaches can be distinguished: Species-specific IDMS and post-column IDMS. In the case of species-specific IDMS, spike and analyte have the same chemical and structural composition – only the isotope signature is different. Therefore, it is the ideal internal standard, which behaves identically to the analyte during sample preparation and detection and allows a traceable quantification.

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Clinical Chemistry

Illustration of traceability from blood sampling via reference materials to SI

Different national and international directives require measurement results of clinical parameters to be traceable to higher-order reference materials and reference methods. These directives are, among others, the EU Directive on in vitro diagnostic medical devices (98/79/EC) and the "German Medical Association Directive on Quality Assurance of Quantitative Laboratory Tests for Medical Purposes" (RiLiBÄK). For many clinical analytes, in particular for proteins, reference methods or matrix-matched reference materials are, however, lacking. We consider the improvement of this situation and the development of measurement procedures which yield results that are traceable to the SI as one of the focal points of our work.

Our objective is to develop reference methods for important markers in clinical diagnosis which provide results traceable to the SI and, thus, comparable and reliable. A distinction can be made between:

Traceable quantification of small moleculesTraceable quantification of small molecules

In addition to proteins, cells and ribonucleic acids, also small molecules such as creatine, uric acid and the like play an important role in clinical diagnosis. In some cases in which it is difficult to determine the complete proteins, a detour via their smaller units such as peptides and amino acids is often made. An example is the determination of selenomethionine to estimate the selenium status of a patient instead of selenium proteins.

In addition to proteins, cells and ribonucleic acids, also small molecules such as creatine, uric acid and the like play an important role in clinical diagnosis. In some cases in which it is difficult to determine the complete proteins, a detour via their smaller units such as peptides and amino acids is often made. An example is the determination of selenomethionine to estimate the selenium status of a patient instead of selenium proteins.
Selenium is an essential element whose physiological range is, however, very narrow. In the case of a daily dose of < 30 µg for an adult, deficiency symptoms may occur, whereas a daily dose of > 700 µg will probably cause symptoms of poisoning. Selenium is a part of important proteins such as glutathione peroxidase which is involved in the defense against oxidative stress. It has also been found that the simultaneous administration of selenium during chemotherapy reduces side-effects. The prevention of poisoning requires an exact determination of the selenium content in the blood. Selenomethionine is a frequently used marker, although it is not a component of the selenoproteins themselves which contain selenocysteine instead. In a free state, selenocystein is very instable, which renders a reliable quantification difficult. Within the scope of the iMERA plus project T2.J10 TRACEBIOACVTIVITY, a method for the traceable quantification of selenomethionine in serum has been developed using 76Se-marked selenomethionine and isotope dilution analysis.

Traceable quantification of metalloproteinsTraceable quantification of metalloproteins

Haemoglobin (http://www.rcsb.org/pdb/)

With approx. 30 % of the total proteome, metalloproteins represent an important group of potential biomarkers for diseases. Examples of this are haemoglobin and transferrin as markers for anemia and inflammatory diseases, superoxide dismutase, which protects the cells against oxidative stress, and ceruloplasmin, the copper storage protein which is a marker for Wilson's or Menke's disease. For many proteins, however, reference measurement procedures are available so far. This means that each measurement kit of the different manufacturers has reference areas of its own; comparability of the results is, therefore, in many cases problematic.

We mainly use species-specific isotope dilution analysis for the quantitative determination of metalloproteins. For this purpose, the protein which contains the functional metal in an isotopically enriched form – the so-called “spike” – is added to the sample at the beginning of the sample preparation. In the ideal case, the spike and the investigated protein will behave identically during sample preparation, separation and detection, so that possible losses or conversions will have no effect on the result.

 

Superoxide dismutase: exchange of copper and zinc with natural isotopic composition with copper and zinc enriched in one isotope.

Within the scope of the EMRP project "Opens external link in new windowMetrology for Metalloproteins - HLT05", species-specific spikes and measurement procedures for the determination of haemoglobin, transferrin, superoxide dismutase, ceruloplasmin and selenoprotein P as well as glutathione peroxidase have been developed in cooperation with partner organisations from all over Europe.

The results were applied within the EMPIR project Opens external link in new windowReMiND - 15HLT02 to the investigation of the role of these metalloproteins in the development of Alzheimer's disease.

Currently, potential reference measurement procedures for cardiac troponin are developed within the EMPIR project Opens external link in new windowCardioMet - 18HLT10.

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