MESL Facilities Inorganic Laboratories
- Inorganic Laboratories - Analysis of Trace Elements and Organometallic Species
- Atomic Absorption Spectrophotometry (AAS)
- Inductively Coupled Plasma - Mass Spectrometry (ICP-MS)
- Mercury Analyzer
- Hyphenated techniques for speciation analysis: Gas Chromatography – Atomic Fluorescence Spectroscopy (GC-AFS)
- Hyphenated techniques for speciation analysis: Gas Chromatography - Flame Photometric Detector (GC-FPD)
Inorganic Laboratories - Analysis of Trace Elements and Organometallic Species
MESL is equipped with 5 laboratories for inorganic analysis. Separate laboratories are used for sample preparation and instrumental analysis. Sample preparation areas include a clean laboratory with laminar flow hoods. Class 100 clean–room installation allows the manipulation of environmental samples without the risk of their contamination.
Sample preparation is a key procedure in chemical analysis. A microwave digestion system (CEM MARSX) allows rapid and efficient sample dissolution using the same acids as in conventional hot plate methods, although usually with smaller volumes.
Atomic Absorption Spectrophotometry (AAS)
A variety of state-of-the-art instrumentation is employed for measuring trace elements. Atomic Absorption Spectrophotometry (AAS) is a widely used technique for the determination of metals. The sensitivity varies with each element and the type of AAS instrumentation. One limitation of the technique is that elements must be determined one at a time. However, an autosampler allows unattended and overnight analytical runs.
MESL has a Varian SpectrAA 220 Fast Sequential Flame-AAS, which is used for the analysis of minor constituents and certain trace constituents. Not only is Flame-AAS rapid and easy to use, it provides excellent precision for homogeneity studies. This instrumentation is also used for measuring total mercury by cold vapour-AAS (CV-AAS) and for performing hydride generation-AAS (HG-AAS) analyses. In CV-AAS and HG-AAS modes, the vapour cell replaces the burner head.
MESL has a graphite furnace-AAS (GF-AAS) that gives much better sensitivity than Flame-AAS procedures. The Varian SpectrAA Zeeman 220 is used for the analysis of trace and ultra-trace constituents. Zeeman background correction provides optimal separation from spectral interferences.
Inductively Coupled Plasma - Mass Spectrometry (ICP-MS)
Inductively Coupled Plasma Mass Spectrometry (ICP-MS) is the most powerful technique for the analysis and quantification of trace elements. ICP-MS allows multi-elemental simultaneous analysis across the periodic table covering mgL-1 to sub pgL-1 concentration ranges. One of the main features of mass spectrometry is that this technique offers the ability to determine both isotopic abundances and isotopic ratios with precision and accuracy regardless of sample type.
Isotope ratio measurements have been increasingly become popular, especially for investigating the fine isotopic variations existing in nature, for chronological dating of geological samples and subsequent determination of environmental contamination, for nuclear material accounting and pollution control, and for biological studies involving tracer experiments using stable isotopes or long lived radionuclides. Concentrations of major, minor, trace and ultra-trace elements can be determined on the basis of isotopic ratios.
ICP-MS can be used in conjunction with isotope dilution (ID) analysis for optimal precision and accuracy. ID-ICP-MS is generally considered to be a potentially primary method of measurement for trace elements.
The most severe limitation of ICP-MS is polyatomic interferences on the elemental signals, originating from argon and/or the sample matrix. The unequivocal separation of analyte ions from spectral interferences is a prerequisite of accurate and precise elemental and isotopic analysis. High mass resolution is the universal means for this separation and provides a way to identify and eliminate interferences. Elimination of interferences enables accurate and reliable quantitative multi-element analyses at trace levels, even without sample preparation.
In May 2009, MESL was equipped with a single collector high resolution ICP-MS Nu Instruments AttoM®. The Nu Instruments AttoM® provides ultimate performance in single collector high resolution ICP-MS. This instrument takes advantage of fully adjustable resolution and unique electrostatic scanning technology that provides fast scan speeds over large mass ranges. The possibilities of obtaining high precision isotope ratios on non-interfered or interfered isotopes, flexibility and accessibility make it an advanced research tool. This instrument will enable MESL to measure ultra-trace elements in marine samples and to perform isotopic analysis. Highly precise isotopic analysis will enable detection of extremely small natural isotopic variations. Precise measurements of isotope ratios will be applied to tracer experiments where sources of environmental contamination may be identified.
A Finnigan Element 1 double-focusing magnetic sector ICP-MS is also used for trace, ultra-trace, and isotopic analyses. This instrument has a high resolution mass spectrometer, thereby allowing complete separation of spectral interferences for unequivocal analyte measurement. Detection limits of sub pg L-1 are achievable for many elements, making the detection limit of the technique limited primarily by the cleanliness of the sample blank.
The analytical techniques for mercury, being a volatile metal, differ somewhat from those for other metals. The mercury laboratory at MESL includes an AMA-254 Mercury Analyser (Altec) for the direct analysis of total mercury in solids, without the need for time-consuming sample dissolution.
Hyphenated techniques for speciation analysis: Gas Chromatography – Atomic Fluorescence Spectroscopy (GC-AFS)
Speciation analysis of mercury allows the simultaneous determination of inorganic and organometallic (methylmercury) forms. Methylmercury has received much attention because it is more toxic to organisms than inorganic mercury. The method used at MESL employs acid leaching, extraction into organic solvent, back-extraction into water, aqueous-phase ethylation, and collection on a Tenax column. The Tenax column is then heated and the gaseous species are separated by Gas Chromatography prior to detection by Atomic Fluorescence Spectrometry (GC-AFS).
Hyphenated techniques for speciation analysis: Gas Chromatography - Flame Photometric Detector (GC-FPD)
Another series of organometallic analyses conducted at MESL is that of organotin compounds, notably tributyltin (TBT). Like methylmercury, the different species are volatilised by ethylation. The organotin species are extracted into hexane and analysed using a Gas Chromatograph equipped with a Flame Photometric Detector (610 nm cut-off filter and a hydrogen rich flame).References:
- Organotin speciation analyses in marine biota using sodium tetrethylborate ethylation and gas chromatography with flame photometric detection. Applied Organometallic Chemistry, 16:355-359. (2002).