Evaluation of some Isolation Methods for Organomercury Determination in Soil and Fish Samples by Capillary Gas Chromatography—Atomic Fluorescence Spectrometry

Abstract

Three extraction methods, acidic KBr/CuSO₄ isolation-methylene chloride extraction. acidic KBr/CuSo₄ isolation-methylene chloride extraction with an alkaline digestion pretreatment, and an extration method at a milder condition with citrate buffer and dithizone in chloroform, were studied for methylmercury and ethylmercury determination in soils, sediments and fish samples by the recently developed capillary gas chromatography—atomic fluorescence spectrometry system (GC-AFS). The acidic KBr/CuSO₄-methylene chloride extraction and the acidic KBr/CuSO₄-methylene chloride extraction with an alkaline digestion pretreatment were shown to be the effective methods for soils/sediments and fish samples analysis, respectively. The presence of ethylmercury species in soils of the Florida Everglades, observed with the acidic KBr/CuSO₄ isolation and methylene chloride extraction procedure, was further confirmed with the dithizone complexation/extraction procedure. The GC-AFS analytical method offers high senstivity and selectivity for the determination of organomercury halides. The GC column maintenance, a critical step for organomercury halides analysis using GC, is also discussed.     

Single and Sequential Extraction in Sediments and Soils

Abstract

The determination of extractable trace metal contents in soils and sediments is currently performed in many laboratories to assess the bioavailable metal fraction (and related potential phyto-toxic effects) and the importance and possibility of mobilization of trace metals from polluted soil, sludge and sediment upon landfill application. Single and sequential extraction schemes are used for the assessment of the different “forms” of trace metals (e.g. “mobile/bioavailable”, “carbonate-bound” etc.). The lack of uniformity in the different extraction procedures used throughout the world does not allow the results to be compared or the procedures to be validated which has led to many criticisms in the past few years. Moreover, the lack of suitable reference materials for this type of operationally defined determinations did not enable the quality of the measurements to be controlled. Owing to the need for establishing common schemes for single and sequential extractions as well as for the improvement of the quality of extractable trace metal determinations in soil and sediments, the Community Bureau of Reference (BCR) has organised a project which results along with the state of the art of extractable trace metal determinations, use and applicability of extraction schemes and analytical limitations were decided to be thoroughly discussed in a workshop. This paper presents its main conclusions.     

Chemical Speciation and Fractionation in Soil and Sediment Heavy Metal Analysis: A Review

Abstract

Today it is generally recognized that the particular behaviour of trace metals in the environment is determined by their specific physicochemical forms rather than by their total concentration. Several chemical speciation and fractionation methods for heavy metal analysis in soils and sediments have been and are still being developed and applied. They primarily are intended to understand the particular environmental behaviour of metals, present in a variety of forms and in a variety of matrices.

Analytical developments, modifications of existing methods, and recent new approaches are reviewed and discussed. Techniques used include chemical extractions, ion-exchange/gel chromatography, filtration, centrifugation and sieving, selective solvent extraction.

Moreover, the application of these various techniques in different research fields over the last years is explored. The value and the limitations of speciation and fractionation techniques applied in specific experimental work is outlined. It is discussed to what extent these methods have, up to now, filled in the expectations or have been satisfactory in particular applications.     

Trace Metal Speciation and Research in Marine Geochemistry

Abstract

In order to precise the origin and behaviour of trace metals associated with coastal marine sediments, marine geochemists frequently utilize various methods of sequential extraction. The main objective is to test the potential mobility / stability of particulate metals in the natural environments. Several examples are presented in the article, namely: i/ Exchangeable Pb from podzolic soils of the drainage basin of a lagoon which sediments and phreatic waters are for a large part inherited from the surrounding soils; ii/ Evolution of particulate metals in an estuary; iii/ Mobility of metals at the sea bottom interface; iv/ Role of amorphous components of estuarine sediments and suspended matter; v/ Effects of dredging activities on solubility of metals in an estuary; vi/ Behaviour of heavy metals in lagoons.

Main results obtained from the extraction procedures are described, as well as particular difficulties encountered when applying some classical methods.     

A Comparison of Methods for the Determination of Available Trace Metals in Sea Water

Abstract

Two methods for the determination of available trace metals CCd, Pb, and Cu) in sea water are compared. One method employs anodic stripping voltammetry at controlled pH (8.1, 5.3, and 2); the other method involves sample pretreatment with Chelex-100 resin before ASV analysis. Differences in the results are discussed in terms of the definition of available metal and differences in the analytical methods.     

Two decades of chemical imaging of solutes in sediments and soils – a review

The increasing appreciation of the small-scale (sub-mm) heterogeneity of biogeochemical processes in sediments, wetlands and soils has led to the development of several methods for high-resolution two-dimensional imaging of solute distribution in porewaters. Over the past decades, localised sampling of solutes (diffusive equilibration in thin films, diffusive gradients in thin films) followed by planar luminescent sensors (planar optodes) have been used as analytical tools for studies on solute distribution and dynamics. These approaches have provided new conceptual and quantitative understanding of biogeochemical processes regulating the distribution of key elements and solutes including O₂, CO₂, pH, redox conditions as well as nutrient and contaminant ion species in structurally complex soils and sediments. Recently these methods have been applied in parallel or integrated as so-called sandwich sensors for multianalyte measurements. Here we review the capabilities and limitations of the chemical imaging methods that are currently at hand, using a number of case studies, and provide an outlook on potential future developments for two-dimensional solute imaging in soils and sediments.     

Speciation of Heavy Metals in Soils and Sediments. An Account of the Improvement and Harmonization of Extraction Techniques Undertaken Under the Auspices of the BCR of the Commission of the European Communities

Abstract

An account is presented of a series of investigations and collaborative studies, initiated by BCR, on current methods of metal speciation by extraction of soils and sediments with chemical reagents. It was established by extensive consultation with European experts that the diverse procedures used could be harmonized into agreed methods. These methods, including both single extractant and sequential extraction procedures were subjected to collaborative, interlaboratory trials and the results, presented briefly here, showed that it was both possible and desirable that reference soils and sediments, characterised by certified values for extractable contents, be prepared. As a consequence of these studies two soils have been prepared and will shortly be the subject of interlaboratory analysis with a view to certification of their EDTA and acetic acid extractable contents of some heavy metals. Following this workshop a feasibility study of the agreed sequential extraction procedure will, it is believed, shortly lead to certification of sediments for contents extractable by a defined sequential extraction procedure.     

Trace Element Speciation in Soils and Sediments Using Sequential Chemical Extraction Methods

Abstract

Several commonly used sequential chemical extraction procedures of heavy metals in soils and sediments are compared, and their advantages and disadvantages are discussed focusing on selected case studies. In particular, problems caused by handling of anoxic samples, and of specific phases (e.g. organic fractions and sulfides) are addressed.

Eventually, recommendations for the improvement of extraction selectivity as well as the reduction of readsorption effects are given.     

An Assessment of Dust Analyses: With Particular Reference to Lead and Certain Other Metals

Abstract

The last few years have shown an increase in the number of publications describing studies on dust as indicators of environmental pollution, especially by trace metals. The techniques of sampling and analysis used in these studies are reviewed, with particular attention to inconsistencies and differences which make data incomparable. The need for work on the development of standard methods is demonstrated. Only by the application of good quality control, reference materials and reliable techniques will an unsatisfactory situation be improved.     

The Stability of Precipitation Samples under Field Conditions

Abstract

Eight wet-only samplers. placed in one location were used to sample precipitation. Subsamples were taken from the sample bottles directly after the precipitation event and at regular intervals up to a period of 2100 hours and analysed, while the samples stayed in the samplers under field conditions.

Outliers were deleted by means of conventional statistical techniques. The resulting data base was tested by means of the F-test for consistency and for changes in the chemical composition of precipitation samples directly after sampling or after an extended stay under field conditions. Eighty-one percent of the samples showed consistent results and no clear indication of chemical changes was found.

Regression analysis indicated that the uncertainties for samples analysed after 1 week are less than 5% generally for the bulk elements and less than 14% for the trace elements. After a period of 400 hours the uncertainties for the buld elements increase to a level of 5–10% and 5–30% for the trace elements.

Contamination, as a result of handling the samples to obtain subsamples, seems the main cause for the increase of the concentrations which was observed.

Contamination during sample pretreatment and analysis in the laboratory is probably of minor importance.     

Recent Developments in Automated Determinations of Trace Level Concentrations of Elements and On‐Line Fractionation Schemes Exploting the Micro‐Sequential Injection—Lab‐On‐Valve Approach

Abstract

The determination of trace level concentrations of elements, such as metal species, in complex matrices by atomic absorption or emission spectrometric methods often requires appropriate pretreatments comprising separation of the analyte from interfering constituents and analyte preconcentration. In this context sequential injection (SI) and lab‐on‐valve (LOV) schemes have proven themselves as superb vehicles to act as front‐end microanalytical methodologies, particularly when employing solid‐phase extraction (SPE) procedures. In this communication, selected SPE‐procedures in the bead‐renewable fashion are presented as based on the exploitation of micro‐sequential injection (µSI‐LOV) using hydrophobic as well as hydrophilic bead materials. The examples given comprise the presentation of a universal approach for SPE‐assays, front‐end speciation of Cr(III) and Cr(VI) in a fully automated and enclosed setup, and the combination of SPE with fractionation schemes of environmentally interesting solid samples (such as soils or sediments) in order to conduct ecotoxicological studies.     

Determination of Airborne Nicotine by Automatic Two-Stage Thermal Desorption Gas Chromatography

Abstract

An automated two-stage thermal desorption technique has been developed for the determination of airborne nicotine. Pumped samples are collected on adsorbent tubes and analysed by capillary gas chromatography using flame ionisation detection. The preconcentration effect of the adsorbent compared to solvent trapping or solvent desorption methods permits shorter sampling times and precludes the need for a selective detector.

By use of a basic program all exposure volumes and component details are entered into a method run table and after analysis exposure levels are automatically calculated and printed in report form by the data handling system. Consequently a large throughput samples may be analysed automatically and efficiently with minimal analyst involvement or sample preparation.

The technique described was originally developed to sample airborne nicotine in workplace environments where tobacco is processed. Comparison between this technique and the standard NIOSH method for airborne nicotine is discussed.     

Solid-phase microextraction in bioanalysis: New devices and directions

The primary objective of this review is to discuss recent technological developments in the field of solid-phase microextraction that have enhanced the utility of this sample preparation technique in the field of bioanalysis. These developments include introduction of various new biocompatible coating phases suitable for bioanalysis, such as commercial prototype in vivo SPME devices, as well as the development of sampling interfaces that extend the use of this methodology to small animals such as mice. These new devices permit application of in vivo SPME to a variety of analyses, including pharmacokinetics, bioaccumulation and metabolomics studies, with good temporal and spatial resolution. New calibration approaches have also been introduced to facilitate in vivo studies and provide fast and quantitative results without the need to achieve equilibrium. In combination with the drastic improvement in the analytical sensitivity of modern liquid chromatography–tandem mass spectrometry instrumentation, full potential of in vivo SPME as a sample preparation tool in life sciences can finally be explored. From the instrumentation perspective, SPME was successfully automated in 96-well format for the first time. This opens up new opportunities for high-throughput applications (>1000 samples/day) such as for the determination of unbound and total drug concentrations in complex matrices such as whole blood with no need for sample pretreatment, studies of distribution of drugs in various compartments and/or determination of plasma protein binding and other ligand–receptor binding studies, and this review will summarize the progress in this research area to date.     

Quantitative Analysis of Persistent Organochlorines in Samples From Polar Regions a Challenge For The Analytical Chemist

Abstract

The study of the transport and fate of persistent polychlorinated compounds to remote areas such as polar regions requires analytical methods which are capable to detect fg to pg amounts in the main transport medium, the atmosphere, as well as their accumulation in the very short food chain. A list of requirements are given which have to be fulfilled for the detection of such compounds with sufficient reliability. Furthermore, problems observed during sample clean-up, separation and quantification of such low levels are discussed using practical examples, and proposals are made how to avoid them.     

Development and validation of a new direct sampling method for coarse mono- and mixed waste fractions bound in bales

Sampling of coarse waste materials is considered to be a particularly challenging task and is at the same time the most crucial step in the overall data acquisition process. Despite this fact, research work on new sampling methods or new scientific approaches to sampling has been rather limited over the last decades. This paper focuses on a completely new sampling procedure for coarse two-dimensional materials similar to municipal solid waste or packaging plastics. The developed method is especially suitable for materials with particle sizes >100 mm and is based on the ‘press-and-drill method’ introduced by researchers from Fachhochschule Nordhausen. The basic idea is to sample the material in its compressed form (e.g. as bales) with a drilling tool in order to gain increments. The study presented in this paper shows the results of two extensive test series applying this new sampling technique to a middle-calorific fraction produced from packaging material (mainly plastics, textiles and paper). In parallel, the state-of-the-art approach was also applied on the same materials to gain valuable reference data. Results from both approaches are used for the extensive validation of the new sampling method. The verification of accuracy was realised by doping the material with defined pieces of foil containing molybdenum sulphide (MoS₂) which acted as a tracer in the bale. The results obtained by the new direct bale sampling showed not only good accordance with the actual tracer content in each bale but also with results derived from the state-of-the-art approach. In this study, homogeneously distributed parameters (e.g. loss of ignition) were included just as inhomogeneously distributed elements (i.e. Cu). It is shown that sufficient representativeness for coarse materials (d₉₅ > 300 mm) is obtained despite relatively small sample amounts and without previous comminution of the material.     

Calibration of a Multipoint Sampling System Connected with a Photoacoustic Detector

Abstract

Photoacoustic detection of gases in the air phase in combination with a multipoint sampling device transfers about 100 mL of air from each sample location to the next one, causing a considerable disturbance when small systems are sampled. In reactive systems, such as trace gas exchange in soil samples, a correction is required to determine the kinetic behavior of the systems. But this kinetic behavior is required in turn to calculate the correction in a repeated sampling sequence. A model was developed for reaction kinetics (zero-order or first-order) within closed systems and the sample transfer between these systems by a CBISS MK2 multipoint sampling system, connected with a Brüel & Kjær photoacoustic detector. By regression, the reaction kinetics is determined, and by simulation of the system in the absence of sample transfer, corrected data are generated. Comparison of experimental and modeled data revealed that part of the sample is transferred directly two systems further. In addition, a slight memory effect of the detector was revealed. These effects were accounted for in the model. If the correction is not made, biased results are obtained for the reaction kinetics.     

Adoption of Common Schemes for Single and Sequential Extractions of Trace Metal in Soils and Sediments

Abstract

The various methods for determining the mode of occurrence of trace metals in sediments and soils have a long history which dates back to the determinations of the availability of metals for plant nutrition performed earlier. Various methods have been developed in the 70′s and 80′s dealing with both single and sequential extraction schemes. Although some schemes received wide acceptance, none of them developed into a commonly accepted procedure. As a result, the information obtained was site-specific and the interpretation of the results scientist-specific. The workshop on single and sequential extraction in sediments and soils held at Sitges     

Study of Analytical Methods for Iron Determination in Complex Organic Liquids by Atomic Absorption Spectrometry

Abstract

In the determination of iron in complex organic liquids by atomic absorption spectrometry (A. A. S.), methods of sample preparation, such as dilution with an organic solvent and sample pretreatment to destroy organic material, are investigated. Moreover, methods of analysis using calibration curve and standard additions are presented. The possible cause of error associated with iron determination in organic samples by flame (F-A. A. S.) and graphite furnace (GF-A. A. S.) atomic absorption spectrometry are discussed.

From all of these studies, the use of graphite furnace atomic absorption spectrometry after sample dilution with methyl isobutyl ketone, and the use of the method of standard additions are advised for iron determination.     

Comparison of action of mixed permanent chemical modifiers for cadmium and lead determination in sediments and soils by slurry sampling graphite furnace atomic absorption spectrometry

Slurry sampling atomic absorption spectrometry with electrothermal atomization was used to the determination of cadmium (Cd) and lead (Pb) in soils and sediments using permanent modifiers. Comparison of action of mixed permanent modifiers niobium (Nb)/iridium (Ir) and tungsten (W)/iridium (Ir) were studied in detail. The effect of amount of Ir, W and Nb on analytical signals of Cd and Pb was examined. The optimal amounts of modifiers for Cd and Pb determination were stated. Niobium carbide formation on graphite surface was studied for different pyrolysis temperatures. Finally for Cd determination in sediments and soils 200 μg of Nb mixed with 5 μg of Ir was used as permanent modifiers and 15 μg of Nb mixed with 200 μg of Ir for Pb determination. Suspensions were prepared in 5% HNO₃. The analytical procedure was optimized carefully basing on data from pyrolysis and atomization curves studies. Ammonium dihydrogen phosphate was used additionally as matrix modifier during Cd determination in samples in order to prevent interferences coming from matrix components. The analysis of CRMs confirmed the reliability of the proposed approach. The precision and accuracy of Cd and Pb determination by the described method for soils and sediments were acceptable.     

The analytical and economic importance of correctness in sampling

Sampling is part of quality evaluation as well as of the analysis. Probabilistic and non-probabilistic sampling methods are discussed, with examples of the severe financial consequences of incorrect sampling procedures. Only probabilistic methods (cross-stream and splitting) can be correct but their correctness depends on sample increment delimitation, increment extraction and integrity of increments and final sample. Recommendations are given for designing sampling procedures and designing sampling equipment. Common sources of error are described. The need for analytical specialists to be responsible for both sampling and sample processing is emphasized.