Elemental fractionation of Si, Al, Ti, Fe, Ca, Mn, P, and Ba in five marine sedimentary reference materials: results from sequential extractions

We report on the elemental results from sequential extractions of BCSS-1 (marine sediment), MESS-1 (estuarine sediment), MAG-1 (marine mud), SCo-1 (Cody shale), and NIST-1c (argillaceous limestone) to encourage future comparisons of sequential extraction results within the marine geochemical and paleoceanographic communities. We measured Si, Al, Ti, Fe, Mn, Ca, P, and Ba in sequential de-ionized water (loosely-bound), MgCl₂ (exchangeable), acetic acid (carbonate), hydroxylammonium hydrochloride (oxide), H₂O₂ (organic), Na₂CO₃ (opal), and residual (lithogenic) leaches. The protocol and selected elements were tailored to be most relevant to paleoceanographic geochemical studies instead of to environmental studies. Our results show that the sequential extraction procedure faithfully yields elemental distributions that are consistent with individual SRM lithologies. Our results also show that the procedure is typically reproducible within approximately 15%. However, in almost all cases, the procedure suffers from a systematic under-recovery of material when compared with the certified, bulk chemical analysis, and the under-recovery appears to be related to the lithology of the SRM. Similar under-recovery appears to be typical of sequential extraction procedures as reported by other previous studies. While this is problematic in assessing closure, it does not diminish the potential of inter-lab comparisons and first-order accuracy comparisons. We found that the elemental totals for the sequential extractions of MAG-1 compared best with the certified, bulk totals, and we recommend using this SRM to facilitate future accuracy assessments and inter-lab comparisons.     

On-line coupling of flow injection sequential extraction to hydride generation atomic fluorescence spectrometry for fractionation of arsenic in soils

A new flow injection on-line sequential extraction procedure coupled with hydride generation atomic fluorescence spectrometry (HG-AFS) was developed for rapid and automatic fractionation of arsenic in soils. The developed methodology involved a three-step sequential extraction procedure with deionized water, KOH solution, and HCl solution. 25 mg of the soil sample packed into a microcolumn (4 mm i.d. × 3 cm long) was dynamically extracted by continuously pumping each individual extractant through the column. The extracted arsenic solution was merged with 4% (m/v) K₂S₂O₈ solution for on-line oxidation of all arsenic species into As^V. The total extracted arsenic was on-line detected by HG-AFS, and quantitated using an on-line standard addition calibration strategy. The total time for the three-step sequential extraction and on-line detection lasted only 10 min. The developed methodology offers several advantages over conventional batch sequential extraction protocols, including minimization of readsorption/redistribution problem, improvement of accuracy, high speed, less amounts of sample/reagents required, less risk of contamination and analyte loss. The developed methodology was successfully applied to the fractionation of arsenic in certified soil reference materials.     

A Sequential Extraction Method Measures the Toxic Metal Content in Fly Ash from a Municipal Solid Waste Incinerator

The purpose of this research was to develop an optimized pretreatment procedure for toxic metals (Pb, Cd, Zn and Cu) content in fly ash from a municipal waste incinerator. In addition, modified sequential extraction procedures were used to characterize the chemical composition of the fly ash samples. The sequential extraction resolved the fly ash elements into the following chemical forms: soluble, exchangeable, carbonate, oxide, organic, and silicate compounds. Certified reference city waste incineration ash (BCR.176) was used as target ash samples. A H₂O₂+HNO₃+HF mixed acid digestion solution with a low temperature evaporation procedure was selected as optimal for the fly ash digestion. The digested solution was analyzed by inductively coupled plasma mass spectrometry (ICP‐MS), which effectively determined the concentrations of the toxic metal elements in BCR.176. Except for Cd, the recovery of Pb, Zn, and Cu under H₂O₂+HNO₃+HF digestion and their sequential extraction procedures were higher than 95%. The relative standard deviations (RSD) for recoveries of the four elements were within 10%. Furthermore, the sequential extraction procedure's results provided information on the potential mobility of the studied elements. Most of the Cd was bound to water‐soluble and carbonate material in the fly ash samples. Most of the Pb, Zn, and Cu was released to carbonates and bound to organic matter in the fly ash samples.     

Electrothermal atomic absorption spectrometric determination of vanadium in extracts of soil and sewage sludge certified reference materials after fractionation by means of the Communities Bureau of Reference modified sequential extraction procedure

A modified three-step sequential extraction procedure proposed by the Commission of European Communities Bureau of Reference (BCR) was applied to certified reference materials of three different soil groups (rendzina, luvisol, cambisol) and sewage sludge of different composition originating from a municipal water treatment plant in order to assess potential mobility and the distribution of vanadium in the resulting fractions. Analysis of the extracts was carried out by electrothermal atomic absorption spectrometry with Zeeman background correction using transversely heated graphite atomizers. Extracts showed significant matrix interferences which were overcome by the standard addition technique. The original soil and sludge certified reference materials (CRMs) and the extraction residue from the sequential extraction were decomposed by a mixture of HNO₃–HClO₄–HF in an open system. The content of V determined after decomposition of the samples was in very good agreement with the certified total values. The accuracy of the sequential extraction procedure was checked by comparing the sum of the vanadium contents in the three fractions and in the extraction residue with the certified total content of V. The amounts of vanadium leached were in good correlation with the certified total contents of V in the CRMs of soils and sewage sludge. In the soils examined, vanadium was present almost entirely in the mineral lattice, while in the sewage sludge samples 9–14% was found in the oxidizable and almost 25% in the reducible fractions. The recovery ranged from 93–106% and the precision (RSD) was below 10%.     

An improved sequential extraction method to determine element mobility in pyrite-bearing siliciclastic rocks

A sequential extraction method was developed for pyrite-bearing (FeS₂) siliciclastic rocks. The focus of this study was to enhance the procedure by an improved oxidation step to completely dissolve not only organic matter but also microcrystalline pyrite. In the first experiment, four oxidation procedures were compared for pure pyrite at extraction temperatures of 25°C and 85°C with hydrogen peroxide (H₂O₂) as the main oxidant. It was found that pyrite dissolution was most effective by using a mixture of H₂O₂, ammonium acetate (NH₄OAc) and nitric acid (HNO₃) at 25°C. This procedure dissolved >90% pyrite, and detected >75% using solute iron measurements. The difference between these two results was explained by reprecipitation of secondary iron minerals. The procedure worked best at 25°C, since solvent evaporation at 85°C amplified iron oversaturation and precipitation. For the pyrite-bearing siliciclastic rocks, two sequential extraction schemes were compared to optimise solid–solvent ratio, extraction step order and type of solvent. Eventually, the most effective step order identified for siliciclastic rocks containing pyrite and little organic matter was to first (1) remove the exchangeable fraction, followed by (2) dissolution with acid and afterwards (3) with a reducing agent. The (4) oxidation step was performed last.     

New data on the mobility of Pt emitted from catalytic converters

The mobility and speciation of Pt was investigated in dust deposited in highway tunnels and in gully sediments. For this, a sequential extraction technique was used in combination with a microwave digestion procedure, followed by detection of Pt with high resolution ICP-MS. A digestion procedure using HNO₃/HCl/H₂O₂ was developed and its efficiency tested for environmental materials. Total Pt contents ranged from approximately 100 to 300 g/kg. The high share of chemically mobile Pt in the tunnel dust (up to about 40%) indicates that Pt is predominantly emitted in a mobile form from the converter. The absence of a mobile fraction in the gully sediment is explained by the elution of Pt by run-off. Except for the mobile and easily mobilised fractions none of the other fractions of the sequential extraction contains Pt, neither in the dust samples nor in the gully sediment.     

Evaluation of a sequential extraction for the speciation of thorium in soils from Baotou area, Inner Mongolia

Sequential extraction procedures were widely applied for speciation of radioactive elements. In this study, the sequential extraction procedure developed by Martínez-Aguirre was employed for quantification of different chemical forms of thorium in the soil. The total amount of thorium in contaminated soil was much higher by four-fold than the local background value. The soil properties affect the amount of thorium and distribution of fractions in contaminated soil. Results showed that the proportion of thorium in soils from Baotou was found as the residual fraction (F5 + F6) > absorbed fraction (F3), coprecipitated fraction (F4) > carbonates fraction (F2) and exchangeable fraction (F1) that could be available to plants. The recovery, calculated by ratio of the sum of the six fractions to the pseudo-total content of thorium, was in the range from 96% to 110%. A comparison was carried out between the sequential extraction and the single extraction to evaluate the selectivity of the extractants. It was found that the amount of thorium of absorbed fraction (F3) was higher in the single extraction than that estimated in the sequential extraction, possibly duo to transform of the labile form. While for non-residual fraction analysis, the single extraction scheme was a desirable alternative to the sequential extraction procedure. According to correlativity analysis of various fractions, it might be predicted that how the non-residual fractions of thorium were directionally transformed into interrelated fractions under the changes of conditions.     

A sequential extraction procedure for an insight into selenium speciation in garlic

A sequential extraction procedure was developed for the fractionation of different classes of selenium species present in garlic. The consecutive steps included leaching with water, extraction of cell-wall bound species after lysis with a mixture of cellulase, chitinase and β-glucanase completed by a proteolytic attack, extraction with HCl to liberate the residual organic bound species and finally, extractions with sulfite solution and CS₂ to complete the mass balance by the recovery of Se⁰ and Se²⁻, respectively. Selenium speciation in the aqueous fractions was probed by anion-exchange and ion-pairing reversed-phase HPLC-ICP MS after purification by preparative size-exclusion LC. It was found to be strongly affected by the sample redox conditions. The peak identity was matched with a mixture of 9 compounds expected to be present in allium plants; electrospray QTOF MS turned out to be unsuccessful. Selenite, selenate and selenomethionine were the dominating species present.     

Determination of molybdenum in extracts of soil and sewage sludge CRMs after fractionation by means of BCR modified sequential extraction procedure

A modified three-step sequential extraction procedure proposed by the Commission of European Communities Bureau of Reference (BCR) was applied to certified reference materials of three different soil groups (rendzina, luvisol, and cambisol) and sewage sludge of different compositions originating from a municipal water treatment plant in order to assess potential mobility and the distribution of molybdenum in the resulting fractions. In the soils examined, molybdenum was present almost entirely in the mineral lattice, the content of molybdenum in the fractions of the studied reference materials of sludges was predominant in the fraction, represents Mo bound to organic matter and sulphide.The internal check of accuracy was performed on the results of the sequential extraction by comparing of the extractable amounts of molybdenum in the sequential procedure with the results of the pseudototal digestion of original samples. The recovery ranged from 96 to 101% and the precision (RSD) in the extracts was below 10%.     

Comparison of metal analysis in sediments using EDXRF and ICP-OES with the HCl and Tessie extraction methods

The work presents an investigation on metal availability in sediments during 13 months using the dispersive-energy X-ray fluorescence (EDXRF) and atomic emission spectrometry with induced argon plasma (ICP-OES) techniques and single extraction (0.1 mol l⁻¹ HCl) and Tessie’s sequential speciation methods. The EDXRF technique could yield essentially the same profile as ICP-OES for the seasonal variation of metals in sediments, but in a more practical way. The sequential extraction procedure (SEP) was more efficient in metal dissolution than single extraction. The Pb, Ni, Al, Cr, and Fe elements were less efficiently extracted with single extraction in relation to sequential extraction. For Co both methodologies were equivalent, but for Cu and Mn the extraction was higher with single extraction. Single extraction does not mobilize Pb, Ni, Al, Cr, and Fe adsorbed on oxides and bound to organic matter. However for Cu and Mn, not only extracted these metals from the four fractions, but it also dissolved part of the fifth fraction (residual). Principal Component Analysis discriminated seasonal variations in the content of several metals, mainly Fe, Co, Ni, and Zn. The mobility of metallic ions in the sediments is conditioned to the seasonal flow of organic and inorganic material coming from the river or by the erosion of adjacent soils.     

A comparative study of trace enrichment of chlorophenols in water by extraction with C6 and C8 alkanes and by C18 reversed-phase adsorption

The efficiency, reproducibility and sensitivity ofn-hexane and iso-octane extraction and of C₁₈ reversed-phase adsorption for accumulation of 4-chloro-, 2,4-dichloro-, 2,4,5- and 2,4,6-trichloro-, 2,3,4,6-tetrachloro- and pentachlorophenol from aqueous solutions were compared. In extraction procedures the acetyl and pentafluorobenzoyl derivatives of chlorophenols were extracted from water. In adsorption procedure chlorophenols adsorbed on a Sep-Pak C₁₈ cartridge were eluted with acetone and after that derivatized analogously.All three procedures were found to be applicable for an efficient trace enrichment of chlorophenols in water, the proper choice being dependent on the required sensitivity of the analysis. Lower detection limits of single compounds at 10 ng·1^–1 levels were achieved by adsorption procedure owing to the more uniform and for most chlorophenols higher adsorption than extraction recoveries as well as owing to the possibility of treating larger volumes of water samples. The extraction procedure could be successfully applied to the concentrations of chlorophenols in water 1g·1^–1.Owing to its higher efficiency and better sensitivity the C₁₈ reversed-phase adsorption procedure was chosen as the more suitable one for the determination of chlorophenol levels in surface, ground and drinking waters. The conversion of chlorophenols accumulated from a water sample parallel to both acetyl and pentafluorobenzoyl derivatives and the analysis of both types of derivatives on two basically different gas Chromatographic columns were recommended for a more reliable identification and quantitation of the compounds analyzed.     

A highly sensitive method for detection of bisphenol A in water samples based on functionalised Fe3O4@SiO2@nylon66

A simple and sensitive method was developed for preconcentration and determination of bisphenol A (BPA) in environmental samples by high performance liquid chromatography (HPLC). The hydrophilic silicon-dioxide- and nylon66-functionalised magnetic material (Fe₃O₄@SiO₂@nylon66) was used as a sorbent for magnetic solid-phase extraction (MSPE). With the anhydrous microemulsion reaction, the Fe₃O₄@SiO₂@nylon66 had shown great characteristics such as good magnetic responsivity, water dispersibility and stability. Based on the materials, various extraction parameters including pH, extraction time, elution time, the number of sorbents, sample volume and elution times were optimised. The whole extraction procedure could be accomplished within 20 min and the materials could be used more than 10 times after regeneration. Under the optimised conditions, different types of water samples (Tap water, river water, sea water and underground water) were successfully analysed to verify the applicability of the proposed method. The recoveries of different samples ranged from 88.54% to 104.46%. An enrichment factor of 250 was achieved with 0.05 μg/L detection limit. Thus, the developed MSPE is a potential technique that can be used for water samples preconcentration or combined with other analytical methods for determination of BPA.     

Estimation of ecotoxicological potential of contaminated sediments based on a sequential extraction procedure with supercritical CO2 and subcritical H2O solvents

Sediment samples were taken from the Tisza–Szamos area and Gödöll lake system. A new sequential extraction scheme in a supercritical extractor using supercritical CO₂, subcritical H₂O, and a subcritical mixture of 90% H₂O and 10% CO₂ as solvents was employed. This procedure provides relevant information about environmentally mobile heavy metal fractions (water-soluble, bicarbonate-forming) of sediments during a reasonably short time (5 h). The environmental mobility of Zn and Cd was found to be the highest among the sediments involved in these investigations. This mobility represents detectable ecotoxicity, which can be tested with the subcritical water extracts. Performance of pollen tube growth (PTG) test and the ecotoxicological stable isotope metabolic assay (ESIMA) was compared. Potential ecotoxicity of aqueous extracts was reliably detectable by PTG test during a relatively short time (1 day).     

A comparison of an optimised sequential extraction procedure and dilute acid leaching of elements in anoxic sediments, including the effects of oxidation on sediment metal partitioning

The effect of oxidation of anoxic sediment upon the extraction of 13 elements (Cd, Sn, Sb, Pb, Al, Cr, Mn, Fe, Co, Ni, Cu, Zn, As) using the optimised Community Bureau of Reference of the European Commission (BCR) sequential extraction procedure and a dilute acid partial extraction procedure (4 h, 1 mol L⁻¹ HCl) was investigated. Elements commonly associated with the sulfidic phase, Cd, Cu, Pb, Zn and Fe exhibited the most significant changes under the BCR sequential extraction procedure. Cd, Cu, Zn, and to a lesser extent Pb, were redistributed into the weak acid extractable fraction upon oxidation of the anoxic sediment and Fe was redistributed into the reducible fraction as expected, but an increase was also observed in the residual Fe. For the HCl partial extraction, sediments with moderate acid volatile sulfide (AVS) levels (1-100 μmol g⁻¹) showed no significant difference in element partitioning following oxidation, whilst sediments containing high AVS levels (>100 μmol g⁻¹) were significantly different with elevated concentrations of Cu and Sn noted in the partial extract following oxidation of the sediment. Comparison of the labile metals released using the BCR sequential extraction procedure (ΣSteps 1-3) to labile metals extracted using the dilute HCl partial extraction showed that no method was consistently more aggressive than the other, with the HCl partial extraction extracting more Sn and Sb from the anoxic sediment than the BCR procedure, whilst the BCR procedure extracted more Cr, Co, Cu and As than the HCl extraction.     

Selectivity assessment of an arsenic sequential extraction procedure for evaluating mobility in mine wastes

An optimized sequential extraction (SE) scheme for mine waste materials has been developed and tested for As partitioning over a range of pure As-bearing mineral phases, their model mixtures, and natural mine waste materials. This optimized SE procedure employs five extraction steps: (1) nitrogen-purged deionized water, 10 h; (2) 0.01 M NH₄H₂PO₄, 16 h; (3) 0.2 M NH₄-oxalate in the dark, pH3, 2 h; (4) 0.2 M NH₄-oxalate, pH3/80 °C, 4 h; (5) KClO₃/HCl/HNO₃ digestion. Selectivity and specificity tests on natural mine wastes and major pure As-bearing mineral phases showed that these As fractions appear to be primarily associated with: (1) readily soluble; (2) adsorbed; (3) amorphous and poorly-crystalline arsenates, oxides and hydroxosulfates of Fe; (4) well-crystalline arsenates, oxides, and hydroxosulfates of Fe; as well as (5) sulfides and arsenides. The specificity and selectivity of extractants, and the reproducibility of the optimized SE procedure were further verified by artificial model mineral mixtures and different natural mine waste materials. Partitioning data for extraction steps 3, 4, and 5 showed good agreement with those calculated in the model mineral mixtures (<15% difference), as well as that expected in different natural mine waste materials. The sum of the As recovered in the different extractant pools was not significantly different (89–112%) than the results for acid digestion. This suggests that the optimized SE scheme can reliably be employed for As partitioning in mine waste materials.     

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.     

Comparison of single and sequential extraction procedures for the study of rare earth elements remobilisation in different types of soils

With the continual increase in the utilisation of rare earth elements (REE) for industrial and agricultural purposes, research into the environmental and biogeochemical behaviour of REE had attracted much interest in recent times. This study principally describes the distribution of REE in four different types of soils like lateritic soil (S-1), in situ natural soil (S-2), soil contaminated by mining activity (S-3) and accidentally polluted soil (S-4) utilizing the optimised BCR sequential extraction procedure and partial extractions with various types of single extractants such as unbuffered salt solutions 0.1 M NaNO₃, 0.01 M CaCl₂, 1 M NH₄NO₃; complexing agents 0.005 M DTPA and 0.05 M EDTA; acid solutions 0.43 M CH₃COOH and 1 M HCl. Comparison of the sum of the four BCR fractions, which included an aqua regia attack on the residue, with the pseudo-total aqua regia digest values to assess the accuracy of the BCR partioning approach has been undertaken. Partial extraction results with several single extractants have also been reported for all the REE elements including yttrium which have been analysed by the optimised BCR procedure. Results obtained after 24 h extraction with each of the single extractant have also been discussed. The extraction with 1 M HCl during 24 h yielded similar quantities of REE as those released under the combined steps of 1, 2 and 3 of the BCR sequential extraction for all the four different type of soil samples indicating that this reagent can be used successfully to estimate the total extractable contents of REE in various types of soil samples.     

Oxidative extraction versus total decomposition of soil in the determination of thallium

An aqua regia extraction and a total decomposition of soil were compared in terms of thallium determination. A sequential extraction of soil, according to the BCR protocol, was also performed for additional information on thallium distribution in soil fractions. Certified reference material—soil GBW 07401 of Chinese origin, containing 1 ± 0.2 ppm of thallium was used in these experiments. Thallium was determined by flow injection-differential pulse-anodic stripping voltammetry (FI-DP-ASV). Only 35% of total thallium was extracted in the aqua regia extraction, while the total decomposition led to satisfactory recovery. The sequential extraction showed that only 5% of thallium in GBW 07401 is dissolvable in the four BCR procedure fractions, and that 95% of the element is entrapped in the residual parent matter. These results show that the aqua regia extraction does not ensure complete thallium extraction from soil. Surprisingly, the total decomposition is significantly less time consuming than the aqua regia extraction.     

Assessment of heavy metals leachability from metallo-organic sorbent-iron humate-with the aid of sequential extraction test

The sequential extraction test, known as a BCR procedure, was used to assess a leachability of heavy metals (Zn, Cd, Pb, Cu) from the metallo-organic sorbent—iron humate—loaded with these metals. The sequential test allowed to discriminate between various fractions of heavy metals, namely the acid-extractable fraction, the fraction bound to Fe oxides, and the fraction bound to organic matter. It was proven that the heavy metals are bound mainly to Fe oxides and organic matter, and thus they may be relatively hardly liberated into the environment. The BCR sequential extraction test exhibited a very good repeatability, when it was applied to the loaded sorbent—relative standard deviations were typically lower than 10%.     

Ultrasound-assisted sequential extraction method for the evaluation of mobility of toxic elements in contaminated soils

A method for the fast sequential extraction of toxic elements in contaminated soil samples using an ultrasonic water bath, followed by determination with inductively coupled plasma optical emission spectrometry (ICP-OES), was developed and compared with other methods introduced in the literature. The five-step sequential extraction (Tessier scheme) was shortened using ultrasound-assisted sequential extraction (UASE). The optimization of the five-step sequential extraction was based on the analysis of SRM 2710 using Tessiers’s method as a reference. Several extracting solutions with different sonication times and temperatures were tested in the optimization procedure. Concentrations of arsenic, cadmium, copper, lead, and zinc were determined in SRM 2710, SRM 2711, and contaminated soil samples with high accuracy and precision. The certified acid-leachable concentrations of the SRM 2710 were obtained for all elements investigated by using an optimized UASE method. Tessiers’s method yielded total element concentrations that were too high. The determination of zinc in SRM 2711 yielded concentrations that were too low, whereas arsenic determination yielded concentrations that were too high by the UASE method and analysis by ICP-OES. The analysis of the SRMs showed that the UASE method is highly comparable with the other methods used for such purposes. The major advantages of the UASE method are the high treatment rate (40 samples simultaneously with a sonication time of 54 min) and a low sample and reagent usage.