Elemental Speciation

Determination of phosphorylation sites in proteins and peptides

It has now been recognised that reversible phosphorylation of proteins at serine, threonine, and tyrosine residues is probably the most important regulatory mechanism in gene expression and protein synthesis. This cell signalling controlled by protein phosphorylation regulates many cellular functions at receptors, ion channels, transcription factors, kinases and contractile proteins. This demonstrates the need to understand reversible phosphorylation qualitatively (i.e., the site where the modification is taking place) and quantitatively (to what degree the site is modified).

The use of LC-SF-ICPMS is to be developed to establish methods for phosphorus selective detection. Phosphorylated peptides will be distinguished from unphosphorylated peptides using the element selective detection of LC-SF-ICPMS, and the molecular mass and sequence of the peptide then determined in a separate LC-MS and MS/MS experiment. This approach has the potential for detection of sub-stoichiometric occupation of phosphorylation sites as well as for a higher degree of automation than current methods. It may also be necessary to investigate the coupling of capillary electrophoresis with SF-ICPMS for use in peptide separations.

Download a poster presentation on this topic

Determination of Actinides in the Environment

The application of inductively coupled plasma mass spectrometry (ICP-MS) for the determination of the concentration and isotopic composition of the actinide elements, has a considerable speed advantage over more traditional methods such as alpha-spectrometry. Physical separation of the elements is not required, and the use of a pre-concentration step combined with ICP-MS results in much lower detection limits, typically femtogram or sub-femtogram. A number of element-specific chelating resins are available which are particularly suited to pre-concentration. One example is that of Tru-Spec resin, (Eichrom Industries Inc., Darien, IL) which has been used recently with good results1,2 with its application to Pneumatic Nebulisation-ICP-MS.

Download a poster presentation on this topic

Isotope Dilution for Speciation Studies

Multicollector ICP-Ms in clean-room facilityIsotope dilution mass spectrometry (ID-MS) comprises the modification of the sample natural isotopic composition by the addition of an isotopically enriched spike material. Species specific ID-MS requires that isotopically enriched analogues of the target analyte are synthesised, for this work 199Hg enriched CH3Hg+ has been prepared by direct methylation with methylcobalamin as the methyl group donor. The estimation of the uncertainty associated with an analytical measurement is increasingly being recognised as an essential part of the measurement process, allowing improved intercomparison of analytical results. ID-MS is regarded as a definitive analytical technique as the accuracy and precision obtainable are unsurpassed by alternative analytical methods and allows the estimation of a measurement uncertainty which is directly related to S.I. units and therefore meets the highest metrological standards. This project utilises liquid chromatography coupled with ICP-MS for species-specific ID-MS.

Download a poster presentation on this topic

Drug Screening for sulfur and other heteroatoms

Sulfur specific chromatogram obtained by SF-ICP-MS for a 100 mL injection of a 5.2 mg·g-1 solution of cimetidine (batch 92/085) (a) X1 scale; (b) X10 scale expansionWithin the pharmaceutical industry, the detection and identification of impurities/metabolites structurally related to the drug substance are of utmost importance. Conventional methods of analysis to detect, track, quantify and/or identify drug substance/or related impurities use molecular mass spectrometry via atmospheric pressure ionisation (API-MS) 1,2 or in the case of drug metabolism and pharmacokinetics use radiolabelling 3,4,5. A significant number of drug substances contain heteroatoms so an element selective detector such as ICP-MS is ideally suited.

Neither inductively coupled plasma-mass spectrometry nor electrospray alone will be adequate for the identification of unknown elemental species at trace levels 6. These two types of ion source can be readily combined to provide both selective elemental analysis and molecular identification7.

Download a poster presentation on this topic

Publications

Cartwright, A. J., Jones, P., Wolff, J. C. and Evans, E. H. (2005). Derivatisation of carboxylic acid groups in pharmaceuticals for enhanced detection using liquid chromatography with electrospray ionisation tandem mass spectrometry. Rapid Communications in Mass Spectrometry 19, 1058-1062.

Cartwright, A. J., Jones, P., Wolff, J. C. and Evans, E. H. (2005). Detection of phosphorus tagged carboxylic acids using HPLC-SF- ICP-MS. Journal of Analytical Atomic Spectrometry 20, 75-80.

Clough, R., Belt, S.T., Evans, E.H., Fairman, B. and Catterick, T. (2005). Uncertainty Contributions to Single and Double Isotope Dilution Mass Spectrometry with HPLC-CV-MC-ICP-MS for the Determination of Methylmercury in fish Tissue. Journal of Analytical Atomic Spectrometry
20, 1095.

Clough, R., Belt, S.T., Evans, E.H., Fairman, B. and Catterick, T. (2003). Investigation of Equilibration and Uncertainty Contributions for the Determination of Inorganic Mercury and Methylmercury by Isotope Dilution ICP-MS. Analytica Chimica Acta 500, 155.

Clough, R., Belt, S.T., Evans, E.H., Fairman, B. and Catterick, T. (2003). Isotope Dilution ICP-MS for Speciation Studies. Applied Spectroscopy Reviews 38, 101.

Evans, E.H., Wolff, J.C. and Eckers, C. (2001).  Sulfur-specific detection of impurities in cimetidine drug substance using liquid chromatography coupled to high resolution inductively coupled plasma mass spectrometry and electrospray mass spectrometry. Analytical Chemistry 73, 4722-4728.

Truscott, J.B. , Jones, P., Fairman, B.E. and Evans, E.H. (2001). Determination of actinides in environmental and biological samples using high-performance chelation ion chromatography coupled to sector-field inductively coupled plasma mass spectrometry . Journal of Chromatography A, 928, 91-98.

Truscott, J, B., Jones, P., Fairman, B.E. and Evans, E.H. (2001), Determination of actinide elements at femtogram per gram levels in environmental samples by on-line solid phase extraction and sector-field-inductively coupled plasma-mass spectrometry. Analytica Chimica Acta 433, 245-253.

Contact

Dr Hywel Evans