Increase Font Size Decrease Font Size

MESL Facilities

Contents

Overview

The Marine Environmental Studies Laboratory (MESL) in Monaco has expertise in the fields of marine analytical chemistry and pollution monitoring. In support of related activities, MESL maintains a suite of 11 laboratories equipped for the analysis of a wide range of potential pollutants. The facilities are used for the production of reference materials, technique development, routine analysis of samples from regional contaminant surveys and for research, especially relating to biogeochemical cycling of mercury and climate change studies based on interpreting carbon-13:carbon-12 isotope ratios in biomarkers. Finally, the laboratory facilities are also used to host regional training courses in the analysis of marine pollutants.

Figure 1 Trainees in the laboratory at MESL learning to techniques for the analysis of metals in the marine environment.

Inorganic Laboratories - Analysis of Metals and Organometallic Species

Sample Preparation

MESL is equipped with 5 laboratories for inorganic analyses. Separate laboratories are used for sample preparation and instrumental analysis. Sample preparation areas include a clean laboratory with laminar flow hoods.

Figure 2 A laminar flow hood provides a clean, dust-free environment for processing samples. It is especially important for analysing metals in sea water, given their very low concentrations.

Sample preparation relies firstly on dissolution of the material, generally sediment or biota. 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. The typical requirement for sediment digestions is 5 mL nitric acid + 2 mL hydrofluoric acid, followed by 0.8 g boric acid post-digestion. Alternatively, biota is digested with just 5 mL nitric acid. The microwave digestion system is a closed technique, which decreases the likelihood of sample contamination. High internal pressure and temperature speeds sample digestion, with most samples processed in minutes instead of hours or days. The system is equipped with 12 high-pressure Teflon vessels, allowing batch digestions of 8-9 samples plus the requisite quality control samples.

Figure 3 The inorganic laboratory is equipped with a CEM MARSX microwave digestion system for efficient sample dissolution.

Atomic Absorption Spectrophotometry (AAS)

A variety of state-of-the-art instrumentation is employed for measuring inorganic constituents. Considering firstly atomic absorption spectrophotometry (AAS), this technique is widely used for the determination of metals. The sensitivity varies with the element considered 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.

The AAS facility at 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 F-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.

Figure 4 MESL has two atomic absorption spectrophotometers for measuring trace metals.

MESL has a graphite furnace-AAS (GF-AAS) that gives much better sensitivity than F-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)

A Finnigan Element 1 double-focusing magnetic sector ICP-MS is 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. The method is rapid (~5 minutes per sample) and extremely sensitive. 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 technique is multi-element, with a wide range of metals can be determined simultaneously. ICP-MS can also be used to measure long-lived radionuclides such as uranium and plutonium. It is noteworthy that ICP-MS is an isotopic technique rather than an elemental one. This means not only that individual isotopes can be determined, but also that ICP-MS can be used in conjunction with isotope dilution analysis for optimal precision and accuracy. ID-ICP-MS is generally considered to be a definitive analytical technique.

Figure 5 A Finnigan Element 1 ICP-MS used for the sensitive and rapid analyses of several metals simultaneously.

The figure below illustrates the detection and high-resolution capabilities of the Element-1 ICP-MS. The top illustration shows the detection of uranium in regular tap water. At less than 1 mg L-1 total uranium, isotope ratios can be determined even for 234U, which is <50 pg L-1 in this example. The lower illustration shows the separation of a common spectral interference in ICP-MS: 56Fe (peak on left) with the polyatomic 40Ar16O (peak on right). In medium resolution mode, the analyte is easily resolved from its interference.

Figure 6 ICP-MS can be used to measure isotopes, exemplified by uranium here, and the high resolution that can be achieved separates some metal peaks from potential interferences.

Mercury and Methylmercury Analyses

The analytical techniques for mercury, being a volatile metal, differ somewhat from those for other metals. As noted for the AAS facilities, mercury can be determined by cold vapour AAS. Detection by atomic fluorescence is generally more sensitive than atomic absorption.

The mercury laboratory at MESL includes an AMA-254 for the direct analysis of mercury in solids, without the need for time-consuming sample dissolution. A small aliquot (<100 mg) is accurately weighed and placed directly into a metal boat. The sample is heated and the gaseous mercury is evolved, which then accumulates in the instrument on a gold foil. Once this pre-concentration stage is completed, the gold foil is heated and the gaseous mercury is flushed into an atomic fluorescence detector. The fully automated procedure is rapid, sensitive, precise and accurate.

Figure 7 AMA-254 for the direct analysis of mercury in solids.

Methylmercury has received much attention because it is more toxic to organism that inorganic mercury. Speciation analysis of mercury allows the simultaneous determination of inorganic and organometallic (methylmercury) forms. The method employs acid leaching, extraction into CH2Cl2, back-extraction into water, aqueous-phase ethylation, and collection on a Tenax column. The tenax trapped are heated and the gaseous species are separated by gas chromatography prior to detection by atomic fluorescence spectrometry (AFS).

Figure 8 Methylmercury is volatilised from solution and pre-concentrated onto tenax traps.

Figure 9 The tenax traps are heated and the volatile mercury compounds are analysed by GC-atomic fluorescence spectrometry (GC-AFS).

Organotin Compounds

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, concentrated by evaporation and analysed using a gas chromatograph equipped with a flame photometric detector (GC-FPD). This requires a 610 nm filter for the detector and a hydrogen-rich flame. For more details, see the methodology described elsewhere.

Organic Laboratories - Analysis of Petroleum and Chlorinated Hydrocarbons

Several organic contaminants in marine samples are analysed at MESL. The list comprises:

  1. Petroleum hydrocarbons
    • total petroleum hydrocarbons (TPH) by UV fluorescence
    • individual aliphatic hydrocarbons
    • individual polycyclic aromatic hydrocarbons (PAHs)
  2. Chlorinated pesticides
    • DDT and its breakdown products of DDE and DDD
    • hexachlorocyclohexanes (HCHs), including lindane
    • chlordanes,
    • endosulfan
  3. Other chlorinated contaminants, such as polycyclic biphenyls (PCBs)

Sample Preparation

Following freeze-drying, samples are sieved through vibrating stainless steel sieves with mesh size of 250 µm. Sieved sediments are homogenised prior to extraction. A series of internal standards comprising PCB 29, PCB 198, e-HCH and a-endosulfan D4 are added to the sediments for quantifying the overall recovery of the organochlorine fractions. Samples are then Soxhlet extracted for 8 h with a 250 mL mixture of hexane/methylene chloride (1:1, v/v). Alternatively, extraction can be carried out using a microwave extraction system. In either case, the extract is concentrated by evaporating off the solvent under a gentle flow of nitrogen.

Figure 10 Soxhlet extraction, whereby organic compounds are extracted from the solid sample matrix by refluxing with a mixture of hexane and methylene chloride.

Gas Chromatography

The sample extracts are determined by gas chromatography. MESL is equipped with several instruments.

Figure 11 View of the GC laboratory in MESL, showing various instruments and the red fume-extraction systems.

The gas chromatographs (GC) are set up for particular analyses, optimised with respect to the column used and the detector type. The various detectors include:

Figure 12 Injecting a concentrated extract into a GC-ECD for the determination of chlorinated hydrocarbons.

Gas Chromatography - Mass Spectrometry (GC-MS)

A mass spectrometer as detector for a gas chromatograph produces a powerful analytical tool with multiple applications. The instrument can be used for the analysis of complex mixtures of compounds with similar properties, notably PAHs. Also, the GC-MS enables compound verification / validation of measurements made by other GC procedures.

Figure 13 A conventional gas chromatograph - mass spectrometer (GC-MS).

MESL also has access to Gas Chromatography-Combustion-Isotope Ratio Mass Spectrometry (GC-C-IRMS). This instrument is used to measure the δ 13C in individual organic components. Potential applications include:

Figure 14 Gas chromatograph with a combustion - isotope ratio mass spectrometer (GC-C-IRMS) used for the determination of 13C:12C ratios in biomarkers.

Production of Reference Materials

Reference materials (RMs) are vital for laboratories to maintain their own Analytical Quality Control procedures. They are also useful for training programmes, intercomparison studies, together with method development and validation. MESL is one of the few producers worldwide of marine RMs.

Figure 15 MESL has produced >20 RMs in the past 30 years. A range of environmental matrices (sediment & biota) has been characterised with respect to various organic and metallic pollutants.

There are several steps involved in the production of reference materials. It is important that the material is of a uniform size and consistency. Accordingly, the material is freeze dried, ground and sieved. Following homogenisation, the material is bottled for distribution once the homogeneity has been tested and found acceptable.

Figure 16 A grinder is used to produce a fine powder.

Figure 17 The sample is mixed in a stainless steel homogeniser for two weeks prior to bottling.