Andreas Prange

Analysis of diluted sea-water at the ng L−1 level using an ICP-MS with an octopole reaction cell

An ICP-MS with an octopole reaction/collision cell was used for the multi-element determination of trace elements in sea-water. The use of a reaction or collision gas, respectively, reduces serious spectral interferences from matrix elements such as ArCl+ or ArNa+. On introducing He or H2 to the cell, detection limits of 0.3 ng L−1 for U to 20 ng L−1 for Fe and As were determined in 10-fold diluted sea-water. The trace elements V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Cd, Pb and U were determined in diluted sea-water samples (certified reference material: NASS-5, SLEW-3) with a trueness of ±20% to the certified values. For most of the elements an accuracy of better than 19% was achieved with no sample pre-treatment other than simple dilution.

Chemical labels and natural element tags for the quantitative analysis of bio-molecules

Besides the qualitative analysis of a bio-molecule or even a whole proteome, their quantitative determination is also a topic of growing interest, since only the quantity of proteins or changes in their abundance really reflects the status and changes of a biological system. Various approaches have recently been suggested for the comparative investigation of different sample states resulting in different proteomes (comparative proteomics) on the basis of either relative or absolute protein quantification. These use molecule specific mass spectrometry and stable isotope labels with different chemical properties, which are covalently bound to, or incorporated in vivo into the various protein species within the sample entities compared. Various groups in the field of analytical atomic spectrochemistry have recently been developing new strategies and analytical tools for the complementary implementation of elemental mass spectrometry (e.g. inductively coupled plasma mass spectrometry (ICP-MS)), which is still generally known as only a “metal” detector, in new, “non-traditional” application areas targeting bio-molecular chemistry or even the fast growing field of proteomics related research, which is currently dominated by ESI or MALDI based MS techniques. At this time, three main strategies are emerging for the complementary application of ICP-MS to bio-molecule quantification in life-sciences orientated research. These include (i) the utilisation of natural (hetero) element tags (covalently bound elements e.g. sulfur and phosphorus), which are present in nearly all protein bio-molecules, (ii) the controlled labelling of bio-molecules such as proteins, peptides or antibodys with ICP-MS detectable elements using bi-functional chelating agents (by means of a chemical reaction, which forms a covalent bond between the chelating agent and a specific functional site of the bio-molecule) and (iii) the chemical labelling of bio-molecules with nano-particles which contain elements detectable by ICP-MS. The idea behind all three strategies is to make bio-molecules detectable by ICP-MS and thus benefit from its high sensitivity, linearity and matrix robustness. This would allow the qualitative detection and quantitative determination of nearly all bio-molecules provided the stoichiometry of either the natural tag or the chemical label is known. This article will give a critical review of the latest developments in the field of quantitative proteomics and will highlight key applications of ICP-MS as a complementary tool to ESI or MALDI MS techniques for selected proteomics or biochemistry related applications. Special emphasis is placed on the quantification of bio-molecules using elements that are covalently bound to proteins or peptides and which show wide distributions in these bio-molecules as tags.

Hyphenated Techniques for Elemental Speciation in Biological Systems

he recognition of the fact thatin environmental chemistry,occupational health, nutrition,and medicine the chemical, biologi-cal, and toxicological properties ofan element are critically dependenton the form in which the element oc-curs in the sample has spurred rapiddevelopment of an area of analyticalchemistry referred to as speciationanalysis.

Inductively Coupled Plasma–Mass Spectrometry (ICP-MS) for Quantitative Analysis in Environmental and Life Sciences: A Review of Challenges, Solutions, and Trends:

This focal point review provides an overview of recent developments and capabilities of inductively coupled plasma mass spectrometry (ICPMS) coupled with different separation techniques for applications in the fields of quantitative environmental and bio-analysis. Over the past years numerous technical improvements, which are highlighted in this review, have helped to promote the evolution of ICP-MS to one of the most versatile tools for elemental quantification. In particular, the benefits and possibilities of using state-of-the-art hyphenated ICP-MS approaches for quantitative analysis are demonstrated with a focus on environmental and bio-analytical applications.

Determination of organometallic species by gas chromatography inductively coupled plasma mass spectrometry

The development is described of a gas chromatography inductively coupled plasma mass spectrometry (GC–ICP-MS) coupling system for the determination of organometallic species of tin, mercury and lead. The compounds are separated by GC using a 30 m long capillary column. A heated transfer line, made from quartz, directs the capillary column to just in front of the argon plasma and serves as the sample introduction system. The ionized elements are simultaneously detected on-line by ICP–MS. The real-time transient signals of the different isotopes are recorded, and an integration system allows one to calculate the retention times and to quantify the species after calibration. With the help of standard solutions the instrumental limits of detection for GC–ICP-MS of various organometallic species such as methyl, butyl or phenyl compounds of tin, mercury and lead have been calculated. The detection limit for tin is about 50 fg, for lead about 100 fg and for mercury about 120 fg. The reproducibility of different runs is better than 5%. For the application of GC–ICP-MS to environmental samples a new method using sodium tetraethylborate for direct ethylation of the ionic organotin species in wet sediments was adopted for a simultaneously multi-element in-situ ethylation of the tin, lead and mercury species.

Determination of element species at trace levels using capillary electrophoresis-inductively coupled plasma sector field mass spectrometry

The development and analytical characterization of a coupled capillary electrophoresis-inductively coupled plasma sector field mass spectrometer (CE-ICP-SFMS) system for the simultaneous determination of different species of As, Sb, Se and Te at trace levels are described. The species are separated by CE using a 55 cm×75 µm id fused silica capillary column. A newly developed interface with a special, low dead volume spray chamber allows the optimization of the fluid mechanical properties, thus preventing a suction effect between the nebulizer and the CE capillary. The ICP-SFMS instrument runs in the low resolution mode and is equipped with a grounded platinum electrode at the ICP torch in order to achieve the highest possible sensitivity. The CE-ICP-SFMS system developed provides stable electrophoretic conditions and allows reproducible separations to be obtained with RSDs below 3% for the migration times and below 8% for the peak areas. Excellent peak shapes down to 4 s and short analysis times of a few minutes are other important features of this combined instrument. Detection limits in the low µg L –1 region for compounds and in the picogram to femtogram range for the isotopes are achieved from standard solutions.

Total reflection X-ray spectrometry: method and applications

Abstract Total reflection X-ray fluorescence, abbreviated as TXRF, is a relatively young method for the determination of trace elements. It is a special variant of energy dispersive X-ray fluorescence analysis. The detection power of the TXRF method is 2–3 orders of magnitude better than that of conventional XRF, and allows multielement determination down to the ultra trace concentration level. The possibility of internal standardization based on an inherent universal calibration curve, the simple sample preparation and the minute sample masses required also make TXRF useful for routine investigations. The TXRF method is described and its characteristic features are elucidated; several examples of applications to aqueous and solid samples from the environment are given, demonstrating the capability of TXRF.

Determination of phosphorus in phosphorylated deoxyribonucleotides using capillary electrophoresis and high performance liquid chromatography hyphenated to inductively coupled plasma mass spectrometry with an octopole reaction cell

The determination of phosphorus in a biologically relevant sample matrix such as DNA is described. The analytical methodology used is based on a robust on-line coupling of capillary electrophoresis (CE) or high performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometry, equipped with an octopole reaction system (ORS-ICP-MS). Polyatomic ions formed in the plasma and the interface region of the ICP-MS that interfere with the determination of P at mass 31 were minimised by the addition of helium to the collision cell. Instrumental detection limits of 125 ng L−1 for 31P, and in the range of 18 to 49 ng L−1 for the other trace elements, were achieved under the conditions described. In order to demonstrate the high separation and detection efficiency of the system, the method developed has been applied to the element specific detection of phosphorus in monophosphorylated deoxynucleotides and to enzymatically digested calf thymus DNA after CE and HPLC separation, respectively. Both hyphenated techniques provide baseline separation of the four deoxynucleotide monophosphates (dNMP), which are present in the DNA chain. With CE-ICP-MS, detection limits for phosphorus down to 53 µg L−1 (2′-deoxyguanosin-5′-monophosphate, dAMP) (corresponding to 0.6 pg P absolute) have been achieved. RSDs of the migration times were about 5%. Using HPLC-ICP-MS, detection limits down to 3 µg L−1 (2′-deoxythymidine-5′-monophosphate, dTMP) (corresponding to 0.03 ng P absolute) were obtained. The migration/elution order of the deoxynucleotides investigated was obtained by comparison with the migration/retention times of commercially available dNMPs. Furthermore it was checked if HPLC-ESI-MS can be operated under the same chromatographic conditions for the confirmation of the elution order and for the characterisation of unknown peaks. Finally, flow injection analysis (FIA) was used for the quantification of the phosphorus content in the dNMP samples. Using FIA, detection limits for phosphorus of 2.5 µg L−1 corresponding to 25 pg phosphorus absolute were achieved.

Distribution of dissolved molybdenum, uranium and vanadium in baltic sea waters

This study presents dissolved molybdenum, uranium and vanadium profiles from eight stations in the main Baltic subregions. The elements were analysed by a new analytical procedure based on total-reflection X-ray fluorescence (TXRF). Mo and U reveal a strong, positive correlation with salinity (with r = 0.95 and 0.93, respectively). The estimated end-member concentrations (for S = 35 × 10−3) are consistent with North Atlantic Ocean water values, indicating conservative mixing with Baltic river waters as the dominating process. In contrast, dissolved V shows relatively low levels, with mean surface and deep layer values of 2.7 and 1.7 nmol kg−1, respectively. Compared with recently investigated Atlantic Ocean waters (normalized to S = 35 × 10−3), Baltic waters are deplated in dissolved V by more than 60%. The removal is attributed to scavenging processes by terrigenous and/or biogenic material during the course of mixing. However, the data did not indicate that precipitation or other removal processes were significant in the anaerobic waters.

Analysis for metal complexes with metallothionein in rat liver by capillary zone electrophoresis using ICP double-focussing sector-field isotope dilution MS and electrospray MS detection

The complementarity of ICP sector-field double-focussing (SF-DF) MS and electrospray MS detection in capillary zone electrophoresis (CZE) was studied for the identification and determination of metal complexes with metallothionein (MT) induced in the liver of a rat exposed to intravenously administered Cd2+. The MT fraction investigated was isolated by size-exclusion chromatography, preconcentrated by lyophilization and desalted. CZE-ICP MS allowed the separation of four mixed-metal complexes with one or more MT isoforms. Isotope dilution analysis was developed for the accurate quantification of the MT content in each of the species and the determination of the stoichiometry of the metal complex. A multi-isotope spike (33S,106Cd, 65Cu, 70Zn) was supplied on-line in the makup flow (6 l min−1) of a self-aspirating total consumption micronebulizer that served as the interface. The characterization of the MT fraction was completed by electrospray MS, allowing the determination of the molecular masses of the complexes formed and the identification of the ligands as MT-1 and MT-2 isoforms.