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.     

Matrix solid phase dispersion-assisted BCR sequential extraction method for metal partitioning in surface estuarine sediments

The BCR (the Community Bureau of Reference) of the European Union sequential extraction scheme for metal partitioning in estuarine sediments has been accelerated by using a matrix solid phase dispersion (MSPD) approach. The MSPD assisted BCR procedure consists of passing the extractants proposed by conventional BCR protocol (0.11 M acetic acid, 0.1 M hydroxylammonium chloride and 8.8 M hydrogen peroxide plus 1 M ammonium acetate) through the dispersed sample packaged inside a disposable syringe. Different silica-, magnesium- and aluminium-based materials were tested as dispersing agents and sea sand was found to offer the best performances. Variables for assisting the three stages of the BCR protocol were optimized, and accurate results were obtained when assisting the first and the third stages (exchangeable and oxidizable fractions, respectively). However, lack of accuracy was observed when assisting the second step (reducible fraction) and this result agrees with most of the assisted BCR procedures for which extracting the reducible fraction is the most troublesome stage. The organic matter oxidation (third stage) was successfully assisted by passing hydrogen peroxide at 50 °C through the dispersed sample inside de syringe just before passing ammonium acetate. Therefore, the time-consuming and unsafe conventional organic matter oxidation processes, commonly performed even for microwave/ultrasounds assisted BCR procedures, are totally avoided. Inductively coupled plasma-mass spectrometry (ICP-MS) was used as a selective detector. The target elements were Cd, Co, Cr, Mn, Ni, Sr and Zn (first stage), Cd, Co and Ni (second stage), and Co, Cr, Mn, Ni, Sr and Zn (third stage). Repeatability of the method (n = 7) was good, and RSDs values of 9, 10, 10, 8, 8, 3 and 8% was obtained for Cd, Co, Cr, Mn, Ni, Sr and Zn, respectively (first stage); 10, 9 and 9% for Cd, Co and Ni, respectively (second stage); and 6, 2, 3, 4, 7 and 9% Co, Cr, Mn, Ni, Sr and Zn, respectively (third stage). The procedure was also validated by analysing two certified reference materials (CRM 601 and CRM 701). Good accuracy was obtained for the target elements extracted at the first stage: Cd (4.0 ± 0.1 and 7.3 ± 0.09 μg g⁻¹ in CRM 601 and CRM 701, respectively), Cr (0.36 ± 0.008 and 2.21 ± 0.08 μg g⁻¹ in CRM 601 and CRM 701, respectively), Ni (8.0 ± 0.3 and 15.4 ± 0.3 μg g⁻¹ in CRM 601 and CRM 701, respectively) and Zn (262 ± 3 and 203 ± 3 μg g⁻¹ in CRM 601 and CRM 701, respectively). Also, good accuracy was observed for elements extracted at the third step: Cd (1.8 ± 0.09 and 0.29 ± 0.03 μg g⁻¹ in CRM 601 and CRM 701, respectively), Cr (145 ± 4 μg g⁻¹ in CRM 701), Ni (8.2 ± 0.7 and 15.1 ± 0.5 μg g⁻¹ in CRM 601 and CRM 701, respectively) and Zn (45 ± 0.7 μg g⁻¹ in CRM 701).     

Arsenic fractionation in agricultural soil using an automated three-step sequential extraction method coupled to hydride generation-atomic fluorescence spectrometry

A fully automated modified three-step BCR flow-through sequential extraction method was developed for the fractionation of the arsenic (As) content from agricultural soil based on a multi-syringe flow injection analysis (MSFIA) system coupled to hydride generation-atomic fluorescence spectrometry (HG-AFS). Critical parameters that affect the performance of the automated system were optimized by exploiting a multivariate approach using a Doehlert design. The validation of the flow-based modified-BCR method was carried out by comparison with the conventional BCR method. Thus, the total As content was determined in the following three fractions: fraction 1 (F1), the acid-soluble or interchangeable fraction; fraction 2 (F2), the reducible fraction; and fraction 3 (F3), the oxidizable fraction. The limits of detection (LOD) were 4.0, 3.4, and 23.6 μg L⁻¹ for F1, F2, and F3, respectively. A wide working concentration range was obtained for the analysis of each fraction, i.e., 0.013–0.800, 0.011–0.900 and 0.079–1.400 mg L⁻¹ for F1, F2, and F3, respectively. The precision of the automated MSFIA–HG-AFS system, expressed as the relative standard deviation (RSD), was evaluated for a 200 μg L⁻¹ As standard solution, and RSD values between 5 and 8% were achieved for the three BCR fractions. The new modified three-step BCR flow-based sequential extraction method was satisfactorily applied for arsenic fractionation in real agricultural soil samples from an arsenic-contaminated mining zone to evaluate its extractability. The frequency of analysis of the proposed method was eight times higher than that of the conventional BCR method (6 vs 48 h), and the kinetics of lixiviation were established for each fraction.     

A microwave-assisted sequential extraction of water and dilute acid soluble arsenic species from marine plant and animal tissues

This paper describes the use of dilute nitric acid for the extraction and quantification of arsenic species. A number of extractants (e.g. water, 1.5 M orthophosphoric acid, methanol-water and dilute nitric acid) were tested for the extraction of arsenic from marine biological samples, such as plants that have proved difficult to quantitatively extract. Dilute 2% (v/v) nitric acid was found to give the highest recoveries of arsenic overall and was chosen for further optimisation. The optimal extraction conditions for arsenic were 2% (v/v) HNO₃, 6 min⁻¹, 90 °C. Arsenic species were found to be stable under the optimised conditions with the exception of the arsenoriboses which degraded to a product eluting at the same retention time as glycerol arsenoribose. Good agreement was found between the 2% (v/v) HNO₃ extraction and the methanol-water extraction for the certified reference material DORM-2 (AB 17.1 and 16.2 μg g⁻¹, respectively, and TETRA 0.27 and 0.25 μg g⁻¹, respectively), which were in close agreement with the certified concentrations of AB 16.4 ± 1.1 μg g⁻¹ and TETRA 0.248 ± 0.054 μg g⁻¹.To preserve the integrity of arsenic species, a sequential extraction technique was developed where the previously methanol-water extracted pellet was further extracted with 2% (v/v) HNO₃ under the optimised conditions. Increases in arsenic recoveries between 13% and 36% were found and speciation of this faction revealed that only inorganic and simple methylated species were extracted.     

Measurement of methyl mercury (I) and mercury (II) in fish tissues and sediments by HPLC-ICPMS and HPLC-HGAAS

A procedure for the extraction and determination of methyl mercury and mercury (II) in fish muscle tissues and sediment samples is presented. The procedure involves extraction with 5% (v/v) 2-mercaptoethanol, separation and determination of mercury species by HPLC-ICPMS using a Perkin-Elmer 3 μm C8 (33 mm × 3 mm) column and a mobile phase 3 containing 0.5% (v/v) 2-mercaptoethanol and 5% (v/v) CH₃OH (pH 5.5) at a flow rate 1.5 ml min⁻¹ and a temperature of 25 °C. Calibration curves for methyl mercury (I) and mercury (II) standards were linear in the range of 0-100 μg l⁻¹ (r² = 0.9990 and r² = 0.9995 respectively). The lowest measurable mercury was 0.4 μg l⁻¹ which corresponds to 0.01 μg g⁻¹ in fish tissues and sediments. Methyl mercury concentrations measured in biological certified reference materials, NRCC DORM - 2 Dogfish muscle (4.4 ± 0.8 μg g⁻¹), NRCC Dolt - 3 Dogfish liver (1.55 ± 0.09 μg g⁻¹), NIST RM 50 Albacore Tuna (0.89 ± 0.08 μg g⁻¹) and IRMM IMEP-20 Tuna fish (3.6 ± 0.6 μg g⁻¹) were in agreement with the certified value (4.47 ± 0.32 μg g⁻¹, 1.59 ± 0.12 μg g⁻¹, 0.87 ± 0.03 μg g⁻¹, 4.24 ± 0.27 μg g⁻¹ respectively). For the sediment reference material ERM CC 580, a methyl mercury concentration of 0.070 ± 0.002 μg g⁻¹ was measured which corresponds to an extraction efficiency of 92 ± 3% of certified values (0.076 ± 0.04 μg g⁻¹) but within the range of published values (0.040-0.084 μg g⁻¹; mean ± s.d.: 0.073 ± 0.05 μg g⁻¹, n = 40) for this material. The extraction procedure for the fish tissues was also compared against an enzymatic extraction using Protease type XIV that has been previously published and similar results were obtained. The use of HPLC-HGAAS with a Phenomenox 5 μm Luna C18 (250 mm × 4.6 mm) column and a mobile phase containing 0.06 mol l⁻¹ ammonium acetate (Merck Pty Limited, Australia) in 5% (v/v) methanol and 0.1% (w/v) l-cysteine at 25 °C was evaluated as a complementary alternative to HPLC-ICPMS for the measurement of mercury species in fish tissues. The lowest measurable mercury concentration was 2 μg l⁻¹ and this corresponds to 0.1 μg g⁻¹ in fish tissues. Analysis of enzymatic extracts analysed by HPLC-HGAAS and HPLC-ICPMS gave equivalent results.     

Arsenic speciation in edible alga samples by microwave-assisted extraction and high performance liquid chromatography coupled to atomic fluorescence spectrometry

Twelve commercially available edible marine algae from France, Japan and Spain and the certified reference material (CRM) NIES No. 9 Sargassum fulvellum were analyzed for total arsenic and arsenic species. Total arsenic concentrations were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) after microwave digestion and ranged from 23 to 126 μg g⁻¹. Arsenic species in alga samples were extracted with deionized water by microwave-assisted extraction and showed extraction efficiencies from 49 to 98%, in terms of total arsenic. The presence of eleven arsenic species was studied by high performance liquid chromatography–ultraviolet photo-oxidation–hydride generation atomic–fluorescence spectrometry (HPLC–(UV)–HG–AFS) developed methods, using both anion and cation exchange chromatography. Glycerol and phosphate sugars were found in all alga samples analyzed, at concentrations between 0.11 and 22 μg g⁻¹, whereas sulfonate and sulfate sugars were only detected in three of them (0.6-7.2 μg g⁻¹). Regarding arsenic toxic species, low concentration levels of dimethylarsinic acid (DMA) (<0.9 μg g⁻¹) and generally high arsenate (As(V)) concentrations (up to 77 μg g⁻¹) were found in most of the algae studied. The results obtained are of interest to highlight the need to perform speciation analysis and to introduce appropriate legislation to limit toxic arsenic species content in these food products.     

Determination of chromium(VI) and lead in water samples by on-line sorption preconcentration coupled with flame atomic absorption spectrometry using a PCTFE-beads packed column

A new time-based flow injection on-line solid phase extraction method for chromium(VI) and lead determination using flame atomic absorption spectrometry was developed. The use of hydrophobic poly-chlorotrifluoroethylene (PCTFE)-beads as absorbent in on-line preconcentration system was evaluated. Effective formation of ammonium pyrrolidine dithiocarbamate complexes and subsequently retention in PCTFE packed column, was achieved in pH range 1.0-1.6 and 1.5-3.2 for Cr(VI) and Pb(II) ions, respectively. The sorbed analyte was efficiently eluted with isobutyl-methyl-ketone for on-line FAAS determination. The proposed packing material exhibited excellent chemical and mechanical resistance, fast kinetics for adsorption of Cr(VI) and Pb(II) permitting the use of high sample flow rates at least up to 15 mL min⁻¹ without loss of retention efficiency. For a preconcentration time of 90 s, the sample frequency was 30 h⁻¹, the enhancement factor was 94 and 220, the detection limit was 0.4 and 1.2 μg L⁻¹, while the precision (R.S.D.) was 1.8% (at 5 μg L⁻¹) and 2.1% (at 30 μg L⁻¹) for chromium(VI) and lead, respectively. The applicability and the accuracy of the developed method were estimated by the analysis spiked water samples and certified reference material NIST-CRM 1643d (Trace elements in water) and NIST-SRM 2109 (chromium(VI) speciation in water).     

Determination of potentially toxic heavy metals in traditionally used medicinal plants for HIV/AIDS opportunistic infections in Ngamiland District in Northern Botswana

The determination of four potentially toxic heavy metals, arsenic, chromium, lead and nickel in twelve plant species used for the treatment of perceived HIV and AIDS-associated opportunistic infections by traditional healers in Ngamiland District in Northern Botswana, a metal mining area, was carried out using atomic absorption spectrometry. The medicinal plants; Dichrostachys cinerea, Maerua angolensis, Mimusops zeyheri, Albizia anthelmintica, Plumbago zeylanica, Combretum imberbe, Indigofera flavicans, Clerodendrum ternatum, Solanum panduriforme, Capparis tomentosa, Terminalia sericea and Maytenus senegalensis contained heavy metals in varying quantities: arsenic 0.19–0.54 μg g⁻¹, chromium 0.15–1.27 μg g⁻¹, lead 0.12–0.23 μg g⁻¹ and nickel 0.09–0.21 μg g⁻¹ of dry weight. Chromium was found to be the most abundant followed by arsenic and lead. Nickel was undetectable in nine plant species. M. senegalensis contained the largest amounts of arsenic, chromium and lead. All metals determined were below the WHO permissive maximum levels. The possible maximum weekly intakes of the heavy metals following treatment regimes were insignificant compared to the provisional tolerable weekly intake levels recommended by WHO and the Joint FAO/WHO Expert Committee on Food Additives. This suggests that heavy metal exposure to patients originating from consumption of traditional medicinal plant preparations is within non health-compromising limits.     

On-line continuous flow ultrasonic extraction coupled with high performance liquid chromatographic separation for determination of the flavonoids from root of Scutellaria baicalensis Georgi

An on-line method, based on coupling dynamic ultrasonic extraction (DUE), continuously sampling the suspension of sample and solvent, high performance liquid chromatographic separation with diode array detection, has been developed for the determination of the flavonoids, including baicalin, baicalein and wogonin, from the root of Scutellaria baicalensis Georgi. Variables influencing the DUE were evaluated by orthogonal test. The extraction yields of baicalin, baicalein and wogonin in the roots of S. baicalensis Georgi obtained from five different cultivated areas are 73.8–131.5 μg mg⁻¹ (RSD ≤ 6.24%), 6.8–15.9 μg mg⁻¹ (RSD ≤ 5.36%) and 4.4–14.3 μg mg⁻¹ (RSD ≤ 5.30%), respectively. The limits of detection for baicalin, baicalein and wogonin are 0.30, 0.37 and 0.41 μg mL⁻¹, respectively. Linearity is from 0.55 to 109 μg mL⁻¹ for baicalin, from 0.51 to 105 μg mL⁻¹ for baicalein and from 0.53 to 102 μg mL⁻¹ for wogonin. Compared with off-line continuous flow-DUE, the proposed method would be more convenient for the determination of the analytes and the rapid optimization of the extraction process. The extraction yields of flavonoids obtained by the proposed method are comparable with those obtained by dynamic microwave assisted extraction, static ultrasonic extraction and reflux extraction. The result indicated that the proposed method is suitable to determine the active components in Chinese herbal medicine.     

A continuous approach for the determination of Cr(VI) in sediment and soil based on the coupling of microwave-assisted water extraction, preconcentration, derivatization and photometric detection

A dynamic system for the continuous leaching of Cr(VI) from sediment and soil based on both microwave assistance and iterative change of the flow direction of the extractant through the sample cell has been developed. The microwave-assisted extractor has been coupled to a photometric detector through a flow injection interface in order to develop a fully automated method. The Cr(VI) extracted was monitored after derivatization with 1,5-diphenylcarbazide. Two approaches are proposed which differ in the inclusion of a preconcentration minicolumn packed with a strong anion exchange resin. A 0.04 M ammonium buffer solution was used as extractant and 0.2 g of sample—river sediment spiked with 50 and 5 μg g⁻¹ for the method without preconcentration (method A) and with preconcentration (method B)—was subjected to 8-14 min of 300 W microwave-assisted extraction. The within-laboratory reproducibility and repeatability were 2.6 and 1.9 for method A, and 4.0 and 2.6 for method B. The proposed methods have been compared with the reference EPA method 3060/7196.     

Comparison of original and modified BCR sequential extraction procedures for the fractionation of copper, iron, lead, manganese and zinc in soils and sediments

This article describes a detailed comparison between the original BCR sequential extraction procedure, step 2 of which involves treatment with 0.1 mol l⁻¹ hydroxylammonium chloride at pH 2, and the revised BCR procedure (step 2: 0.5 mol l⁻¹ hydroxylammonium chloride at pH 1.5). An intermediate protocol was also evaluated in which 0.5 mol l⁻¹ hydroxylammonium chloride at pH 2 was used. The procedures were applied to five soil and sediment substrates: a sewage sludge-amended soil, two different industrially contaminated soils, a river sediment and an inter-tidal sediment. Extractable iron and manganese concentrations were measured to assess the effects of the procedural modifications on dissolution of the reducible matrix components. Trace elements copper, lead and zinc were also determined. Statistical analysis (two-tailed t-tests at 95% confidence interval) indicated that recovery of iron in step 2 was not markedly enhanced when the intermediate protocol was used. However, significantly greater amounts were isolated with the revised BCR scheme than with the original procedure. Copper behaved similarly to iron. Lead recoveries were increased by use of both modified protocols, with the greatest effect occurring for the revised BCR extraction. In contrast, manganese and zinc extraction did not vary markedly between procedures. The work indicates that the revised BCR sequential extraction provides better attack on the iron-based components of the reducible matrix for a wide range of soils and sediments.     

A new chelating resin containing azophenolcarboxylate functionality: synthesis, characterization and application to chromium speciation in wastewater

The synthesis of a new stable chelating resin from the polystyrene divinylbenzene copolymer is reported. The polystyrene is first functionalized with a phenolic group and then allowed to couple with diazotized anthranilic acid through the NN bond. The resulting polymer containing azophenolcarboxylate with an ONO chelating environment has been characterized by elemental analysis, hydrogen ion capacity, and water regain value. Its stability towards thermal and different chemical environments has been evaluated. The sorption capacity of the chelating resin for Cr(III) and Cr(VI) as a function of pH has been studied. The interesting point is that chromium(III) is selectively retained at ca. pH 5.0 and chromium(VI) at ca. pH 2.0. When packed in a column, the new material is able to separate Cr(III) from Cr(VI). Five replicate determinations of 10 μg Cr(III) and 10 μg Cr(VI) present in 100 mL solution gave recoveries of 96.9 ± 2.9% (for Cr(III)) and 96.2 ± 2.1% (for Cr(VI)) at the 95% confidence level. Calibration graph was linear over the concentration range of 0-250 μg L⁻¹ of chromium species with correlation coefficient (R) of 0.99994. The detection limits based on 3σ criterion were determined to be 0.6 μg L⁻¹ for Cr(III) and 0.9 μg L⁻¹ for Cr(VI). The developed method was successfully used for the speciation of chromium in wastewater.     

Determination of trace impurities in chromium matrices after separation from Cr(III) using the oxalate form of anion exchanger

A method has been developed for the separation and determination of a set of 11 impurities from chromium matrices using oxalate form of Amberlite IRA 93. Due to slower kinetics of formation of the anionic complex, Cr(III) passed in the effluent while impurities forming strong complexes rapidly are retained on the exchanger. The adsorption of impurities of interest is found to be uniform in pH range 2-6. The adsorbed impurities are eluted with 2 mol l⁻¹ HNO₃ and determined by inductively coupled plasma-optical emission spectrometer (ICP-OES). The percentage recoveries of Al, Bi, Cd, Co, Cu, Fe, Mn, Ni, Pb, Ga and Zn are in the range 88-101% and separation of matrix is >99.9%. The method has been applied for the analysis of two samples namely CrCl₃·6H₂O and Cr. The R.S.D. of the method is 5-6% at >10 μg g⁻¹ level and ∼15% at <1 μg g⁻¹ level. The process blank values are in the range sub-μg g⁻¹ and detection limits are in ng g⁻¹ range.     

Sequential injection analysis for benzophenone-4 and phenylbenzimidazole sulphonic acid in sunscreen sprays by solid-phase extraction coupled with ultraviolet spectrometry

A sequential injection UV method was developed to determine benzophenone-4 (BZ4) and phenylbenzimidazole sulphonic acid (PBS) simultaneously, these being the most commonly used UV-filters in aqueous formulations used as sunscreen sprays. The selective elution of both was performed by on-line solid-phase extraction, by retention on a SAX microcolumn and separation by varying the pH of elution. The sensitivity obtained was 0.042±0.001 ml μg⁻¹ for PBS and 0.0159±0.0003 ml μg⁻¹ for BZ4. The limit of detection was 1.6 μg ml⁻¹ for PBS and 0.6 μg ml⁻¹ for BZ4. The R.S.D. of the results was 1-6% for PBS and 1-12% for BZ4. The method was validated using commercial sunscreen formulations with concentrations determined by a liquid chromatographic procedure. The two procedures gave comparable results. Automation of the method means the amount of reagents used and residues generated are decreased. The system allows the required analysis sequence to be programmed using suitable software.     

A modified sequential extraction method for arsenic fractionation in sediments

A modified sequential extraction method was developed to characterize arsenic (As) associated with different solid constituents in surficial deposits (sediments), which are unconsolidated glacial deposits overlying bedrock. Current sequential extraction methods produce a significant amount of unresolved As in the residual fraction, but our proposed scheme can fractionate >90% of the As present in sediments. Sediment samples containing different As concentrations (3–35 μg g⁻¹) were used to assess the developed method. The pooled amount of As recovered from all the fractions using the developed method was similar (83–122%) to the total As extracted by acid digestion. The concentrations of As in different fractions using the developed scheme were comparable (89–106%) to the As fractions obtained by other existing methods. The developed method was also evaluated for the sequential extraction of other metals such as copper (Cu), cobalt (Co), chromium (Cr) and strontium (Sr) in the sediment samples. The pooled concentrations of these four individual metals from all the fractions were similar (96–104%) to their total concentrations extracted by acid digestion. During method development, we used extractants that did not contain chloride to eliminate formation of polyatomic ions of argon chloride (⁴⁰Ar³⁵Cl) that interfered with ⁷⁵As when analyzed using inductively coupled plasma mass spectrometer (ICP-MS). The results suggest that the developed method can reliably be employed for complete As and other metals’ fractionation in sediments using ICP-MS.     

Determination of chromium, cadmium and lead in food-packaging materials by axial inductively coupled plasma time-of-flight mass spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS) with a time-of-flight (TOF) analyser was used for the determination of chromium, cadmium and lead in six food-packaging materials (paper and paper board). The samples (0.20-0.25 g) were digested in concentrated nitric acid in a high pressure microwave oven at 180 °C within 15 min. Two different plasma conditions were applied: cool plasma conditions (0.76 kW; 0.85, 0.89 and 15.5 l min⁻¹ nebuliser, auxiliary and plasma gas flow rate, respectively) for the determination of chromium and normal plasma conditions (1.21 kW; 0.66, 0.68 and 13.6 l min⁻¹ nebuliser, auxiliary and plasma gas flow rate, respectively) for the determination of cadmium and lead. External calibration was used in combination with rhodium (40 ng g⁻¹) as an internal standard. The detection limits (DL = 3S.D./sensitivity) under the conditions used corresponded to 0.01 ng g⁻¹ (), 0.06 ng g⁻¹ (), 0.07 ng g⁻¹ (), 0.03 ng g⁻¹ () and 0.02 ng g⁻¹ ( and ). The precision (R.S.D.) for six replicate determinations (10 s integration time) of 1 and 10 ng g⁻¹ of each analyte varied from 0.72% () to 4.43% (). The contents of chromium, cadmium and lead in the examined materials were evaluated using the signals of , and . They were in the range: 0.25-0.50 μg g⁻¹ for Cr, not detected (nd) to 0.12 μg g⁻¹ for Cd and 0.28-0.35 μg g⁻¹ for Pb in paper and 0.50-0.64 μg g⁻¹ for Cr, nd to 0.09 μg g⁻¹ for Cd and 0.67-0.99 μg g⁻¹ for Pb in paper board.     

Preconcentrative separation of chromium(VI) species from chromium(III) by coprecipitation of its ethyl xanthate complex onto naphthalene

A rapid, sensitive and selective method is described for the determination of chromium(VI) in presence of 100-fold amounts of chromium(III) by flame atomic absorption spectrometry (FAAS) in conjunction with coprecipitative preconcentration of its ethyl xanthate complex onto naphthalene. The solid mixture consisting of the chromium(VI) complex together with naphthalene is dissolved in 8.0 ml of dimethyl formamide (DMF) and chromium(VI) content was established by FAAS. Calibration graphs were rectilinear over the chromium(VI) concentration in the range 0-200 μg l⁻¹. Five replicate determinations of 20 μg of chromium(VI) present in 1.0 l of sample solution gave a relative standard deviation of 3.1%. The detection limit corresponding to three times the standard deviation of the blank was found to be 0.5 μg l⁻¹. The developed procedure has been successfully utilized for the estimation of chromium(VI), chromium(total) (after oxidation with bromate) and chromium(III) (by subtracting chromium(VI) content from chromium(total) value contents of several tannery industries.     

Concentration levels of total and methylmercury in mussel samples collected along the coasts of Sardinia Island (Italy)

This paper reports the assessment of the total mercury (T-Hg) and methylmercury (MeHg) contamination of mussel samples collected by two sampling campaigns from along the coastline of Sardinia (Italy). T-Hg has been determined by a direct mercury analyser (DMA) whereas MeHg has been determined by gas chromatography-mass spectrometry (GC-MS) after acid extraction, and employs a novel NaBPh₄ derivatization method. The evaluation of the quality of measurements was carried out by analysing candidate certified reference material (CRM) BCR 710, for MeHg and T-Hg, and CRM IAEA-350 for T-Hg. In the analysed samples, the T-Hg concentrations range from 35 to 115 μg kg⁻¹ and from 40 to 830 μg kg⁻¹, for the two sampling campaigns, respectively, whereas the MeHg concentrations range from l5 to 51 μg kg⁻¹ and from 17 to 116 μg kg⁻¹. Consequently, the MeHg/T-Hg ratios range from 0.33 to 0.91 and from 0.14 to 0.98, respectively. Despite the increasing trend of Hg concentration from the first to the second sampling campaign, the T-Hg concentration of all the samples was much below the 0.5 μg g⁻¹ WHO limit, and the MeHg values ranged between 2.2 and 17.2 μg kg⁻¹, not exceeding the 43.5 μg kg⁻¹ tolerable daily residue level calculated for Italy.     

A new and direct method for the trace element determination in cauliflower by differential pulse polarography

Using the DPP polarograms of wet digested cauliflower sample in acetate buffer at pH values of 2, 4 and 6, Fe, Zn, Mo, Se, Cr, Cd, Pb, Ti and Cu quantities were determined. The best separation and determination conditions for Zn, Se and Mo was pH 2; for Cr, Zn, Mo and As was pH 4; for Pb pH 6, for Ti, Cu and Fe was pH 6-7 EDTA, for Cd pH 2 EDTA and for lead pH 6, all in acetate buffer. The trace element ranges for cauliflowers from two different seasons were (first figure for winter, the second for summer) for Se 120-250 μg g⁻¹, Fe 70-85 μg g⁻¹, Cu 320-150 μg g⁻¹, Ti 90-120 μg g⁻¹, Cr 130-630 μg g⁻¹, Zn 90-550 μg g⁻¹, Mo 170-230 μg g⁻¹, Cd 20 μg g⁻¹ (in winter) and Pb 130-300 μg g⁻¹ in dry sample. Cd was under the detection limit in summer. The length of digestion time had no effect on the recovery of copper, iron, molybdenum and zinc between 15 and 3 h of digestion.     

Determination of the alkyl- and methoxy-phenolic content in wood extractives by micellar solid-phase microextraction and gas chromatography-mass spectrometry

This work combines the utilization of the micellar media during the extraction step and the focused microwave-assisted extraction followed by the solid-phase microextraction-gas chromatography/mass spectrometry (SPME-GC/MS) to determine the alkyl- and methoxy-phenolic content in wood extractives. The proposed environmental-friendly method is mainly characterized by short analysis times (5 min for the microwaves extraction step) and for avoiding the use of organic solvents. Different surfactants were tried for the extraction process: the cationic surfactant CTAB and the non-ionic surfactants Triton X-100 and POLE, with similar extraction efficiencies (85.5-99.7%). The overall method presents limits of detection in the ng g⁻¹ region for the alkylphenols (from 7 to 150 ng g⁻¹) and in the μg g⁻¹ region for the methoxyphenols (from 0.80 to 22.9 μg g⁻¹). The vanillin was the compound most abundant in the wood extractives studied, with concentrations up to 116.2 mg kg⁻¹.