In-situ concentration and determination of mercury by graphite furnace atomic absorption spectrometry with Pd-Rh as the chemical modifier

A method has been proposed for the determination of mercury by cold vapor generation graphite furnace atomic absorption spectrometry (CV-GFAAS) with Pd-Rh as coating and chemical modifier. The trapping efficiency for mercury with Pd-Rh was higher than with Pd alone. The characteristic mass of the method, which gives an integrated absorbance of 0.0044 s, was found to be 55 pg and the absolute detection limit (3 σ) of 37 pg was obtained with the proposed modifier. The method was successfully applied to the determination of mercury in standard reference water samples, wastewater samples and cosmetics with a recovery range of 95–104%. Received: 10 April 1998 / Revised: 20 August 1998 / Accepted: 23 September 1998     

Determination of mercury in biological tissues by graphite-furnace atomic absorption spectrometry with an in-situ concentration technique.

A method has been described for the determination of total mercury by graphite-furnace atomic absorption spectrometry (GFAAS) using an in-situ concentration technique with a Pd-Zr coating and a chemical modifier. The characteristic mass, which gives an integrated absorbance of 0.0044 s, was found to be 42 pg and an absolute detection limit (3sigma) of 33 pg was obtained with the proposed modifier. The total mercury values in standard reference materials, including Mussel (GBW08571), Bovine liver (GBW08306), Peach leaf (GBW08501) and Tea leaf (GBW080001), were determined using the proposed method, and the results were consistent with reference values. The method had been successfully applied to the determination of mercury in biological tissue samples with a recovery range of 94-105%.     

Flow-injection spectrofluorimetric determination of ethylenethiourea

A flow-injection configuration is proposed for the fluorimetric determination of ethylenethiourea. The procedure is based on the inhibitory effect of ethylenethiourea on the oxidation of thiamine to thiochrome by mercury(II). A linear calibration graph was obtained between 0.1 and 2.0 μg mL^–1, with a sampling rate of 40 samples per hour and a relative standard deviation of about 1.11%. The usefulness of the method was tested for the determination of ethylenethiourea residues in water, milk, potatoes, pear, grape and apple. Received: 26 January 1998 / Revised: 6 April 1998 / Accepted: 9 April 1998     

Flow-injection spectrofluorimetric determination of ethylenethiourea

A flow-injection configuration is proposed for the fluorimetric determination of ethylenethiourea. The procedure is based on the inhibitory effect of ethylenethiourea on the oxidation of thiamine to thiochrome by mercury(II). A linear calibration graph was obtained between 0.1 and 2.0 μg mL^–1, with a sampling rate of 40 samples per hour and a relative standard deviation of about 1.11%. The usefulness of the method was tested for the determination of ethylenethiourea residues in water, milk, potatoes, pear, grape and apple. Received: 26 January 1998 / Revised: 6 April 1998 / Accepted: 9 April 1998     

Microcolumn packed with YPA(4) chelating resin on-line separation/preconcentration combined with graphite furnace atomic absorption spectrometry using Pd as a permanent modifier for the determination of trace mercury in water samples

A new method using a microcolumn packed with YPA₄ chelating resin as solid-phase extractor has been developed for the separation and preconcentration of trace Hg prior to its measurement by GFAAS with Pd as a permanent modifier. Various parameters such as the amount of the modifier, pH, sample flow rate, the concentration and volume of eluent have been studied in order to find the best conditions for the determination of mercury. The detection limit of the method (3σ) for Hg based on an enrichment factor of 100 was 0.2 ng ml⁻¹. A characteristic mass of 114 pg was obtained for mercury using Pd as a permanent modifier. The relative standard deviation was 2.8% at the 10 ng ml⁻¹ level (n = 5). The method has been applied to the determination of trace mercury in environmental water samples and the recoveries for the spiked samples are in the range of 91-105%.     

Determination of antimony in wine by hydride generation graphite furnace atomic absorption spectrometry

 A method was developed for the determination of Sb in wine by electrothermal atomic absorption spectrometry, based on preconcentration by hydride generation with collection directly in the graphite furnace. Thiourea was added for prereduction of Sb(V) to Sb(III). The hydride was directly generated from diluted wine. Palladium was used as modifier in the collection step; the overall efficiency of the hydride/trapping system was found to be 67%. Sb was determined in several samples of red wine; the concentrations found were in the range 0.6 to 5.7 μg/L Sb. The detection limit of the method was 39 pg Sb, corresponding to 0.13 μg/L Sb in wine when 0.3 mL wine was analyzed. Received: 3 November 1995/Revised: 22 February 1996/Accepted: 24 February 1996     

Determination of antimony in wine by hydride generation graphite furnace atomic absorption spectrometry

 A method was developed for the determination of Sb in wine by electrothermal atomic absorption spectrometry, based on preconcentration by hydride generation with collection directly in the graphite furnace. Thiourea was added for prereduction of Sb(V) to Sb(III). The hydride was directly generated from diluted wine. Palladium was used as modifier in the collection step; the overall efficiency of the hydride/trapping system was found to be 67%. Sb was determined in several samples of red wine; the concentrations found were in the range 0.6 to 5.7 μg/L Sb. The detection limit of the method was 39 pg Sb, corresponding to 0.13 μg/L Sb in wine when 0.3 mL wine was analyzed. Received: 3 November 1995/Revised: 22 February 1996/Accepted: 24 February 1996     

Laser ablation-atomic fluorescence approach for the determination of mercury

A method for the determination of mercury in solid samples using laser ablation coupled with atomic fluorescence spectroscopy has been developed. An Nd-YAG laser was used for ablation and the vaporised and atomised material was rapidly led to an atomic fluorescence detector, where excitation and emission took place. The experimental approach was applied to the assessment of different procedures as sensitive as possible for implementing standard addition methods. Calibration curves were recorded using the prepared standards, which exhibited linear ranges between 0.5–100 μg/g, with excellent regression coefficients in all instances (0.9907). The precision, expressed as RSD %, was 3 and 4% for contents of 1 and 30 μg/g, respectively, in the same pellet; and 7 and 12% for the same contents and different type of pellets. The method has been applied to the determination of mercury in CRM of sewage sediment and a sludge sample with a known amount of mercury determined by an interlaboratory study. The results obtained show good agreement with those expected. Received: 21 December 1998 / Revised: 12 April 1999 / Accepted: 14 April 1999     

Fractionation of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and planar polychlorinated biphenyls by high performance liquid chromatography on a pyrenyl-silica column

Analytical procedures for the determination of polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated dibenzofurans (PCDF) and non-ortho polychlorinated biphenyls (PCB) require a fractionation step to separate PCDD/F from planar PCB and the bulk of PCB. An HPLC method which achieves the separation of the bulk of PCB (0–6 mL of hexane), mono-ortho PCB (6–8 mL of hexane), non-ortho PCB (8–15 mL of hexane) and PCDD/F (15–50 mL of toluene) on a PYE column (2-(1-pyrenyl) ethyldimethylsilylated silica gel) in a single step without the use of backflush as other authors proposed was developed. The method shows a good accuracy and precision and it is linear in the range studied, e.g from 5.8 to 2420 pg injected in HPLC for TCDD/F, from 28.8 to 12100 pg for PeCDD/F, HxCDD/F, HpCDD/F and from 57.6 to 24200 pg for OCDD/F. It has been successfully applied to the analysis of technical mixtures of PCB (Aroclors), a pine wood sample and several water samples of different origins. Received: 29 November 1998 / Revised: 25 February 1999 / Accepted: 3 March 1999     

Fractionation of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and planar polychlorinated biphenyls by high performance liquid chromatography on a pyrenyl-silica column

Analytical procedures for the determination of polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated dibenzofurans (PCDF) and non-ortho polychlorinated biphenyls (PCB) require a fractionation step to separate PCDD/F from planar PCB and the bulk of PCB. An HPLC method which achieves the separation of the bulk of PCB (0–6 mL of hexane), mono-ortho PCB (6–8 mL of hexane), non-ortho PCB (8–15 mL of hexane) and PCDD/F (15–50 mL of toluene) on a PYE column (2-(1-pyrenyl) ethyldimethylsilylated silica gel) in a single step without the use of backflush as other authors proposed was developed. The method shows a good accuracy and precision and it is linear in the range studied, e.g from 5.8 to 2420 pg injected in HPLC for TCDD/F, from 28.8 to 12100 pg for PeCDD/F, HxCDD/F, HpCDD/F and from 57.6 to 24200 pg for OCDD/F. It has been successfully applied to the analysis of technical mixtures of PCB (Aroclors), a pine wood sample and several water samples of different origins. Received: 29 November 1998 / Revised: 25 February 1999 / Accepted: 3 March 1999     

Elimination of sulfide interference by sodium hypochlorite solution in the cold vapor atomic absorption spectrometric determination of mercury using tin(II) reduction in alkaline medium

An addition of sodium hypochlorite solution effectively eliminated the interference by sulfide in the cold vapor atomic absorption spectrometric determination of mercury using tin(II) reduction in alkaline medium. Mercury ranging from 0.01 to 0.5 μg could be determined within ±10% error in 100 mL of sample solution containing 10 mg of sulfide by the addition of 1 mL of 10.4%(w/v) sodium hypochlorite solution. The proposed method is rapid (5 min per determination) and has good reproducibility (3.0%). Received: 20 May 1998 / Revised: 7 July 1998 / Accepted: 10 July 1998     

Determination of Cobalt with a Tungsten Tube Atomizer by Electrothermal Atomic Absorption Spectrometry and its use for the Analysis of Biological Materials

 The determination of cobalt by electrothermal atomic absorption spectrometry with a tungsten tube atomizer has been investigated. The absolute characteristic mass (the mass of element giving 0.0044 abs.) of cobalt by the atomizer was 5.8 pg and the detection limit was 0.65 ng/ml (3S/N). The interferences caused by large amounts of interferents like Al, Ca, Cu, Fe, K, Mg, Na, Pb and Zn were evaluated and most of these elements were found to interfere with the cobalt signal. Ammonium thiocyanate as a chemical modifier was found to be efficient to eliminate the severest interferences. The accuracies of the recommended method were found to be almost satisfactory for the determination of cobalt in biological materials, as shown by a comparison with the reported values of NIST materials at the 0.02–0.4 μg/g level. Received August 24, 1998. Revision February 9, 1999.     

Determination of total and methyl mercury in human permanent healthy teeth by electrothermal atomic absorption spectrometry after extraction in organic phase

A simple and sensitive method has been developed for determination of inorganic and methyl mercury in biological samples by ETAAS. For determination of methyl mercury; it was transferred to toluene phase by acid leaching extraction method. For total mercury after digestion of samples; it was extracted to toluene phase by means of the chelating agent diethyldithiocarbamate. Formation of complex between MeHg and diethyldithiocarbamate enhance the MeHg signal and increases the reproducibility. Furthermore, Pd-DDC was used as modifier for both mercury and methyl mercury determinations. The optimization performance was independently carried out by modifying the parameters such as temperature of mineralization, atomization and gas flow rate for methylmercury and inorganic mercury in ETAAS. The limits of detection were 0.15 and 0.12 μg g⁻¹ for methyl mercury and total mercury, respectively. The repeatability of the measurements of whole procedure were 15.8% for methyl mercury and 16.9% for total mercury determination. The accuracy of the method has been investigated by means of spiking different amounts of methylmercury and inorganic mercury to the samples. The recoveries were found within the range of 88-95% for methyl mercury and 85-92% for total mercury. For determination of total mercury, the method was validated by CVAAS. The obtained results by the present procedure were in good agreement with those of the CVAAS. The proposed method was applied for 30 human permanent healthy teeth (without filling) which significant positive correlations were found among number of amalgam filling and total mercury and MeHg.     

Sensitive reaction rate method for the determination of low levels of formaldehyde with photometric detection

A simple and rapid method is proposed for the determination of ultra trace amounts of formaldehyde. It is based on the catalytic effect of formaldehyde on the oxidation of Brilliant cresyl blue by bromate. The reaction is monitored photometrically by measuring the decrease in absorbance of the dye. Formaldehyde in the range of 0.005–2.300 μg/mL can be determined with a limit of detection of 0.003 μg/mL. The relative standard deviation for ten replicate measurements of 1.5 μg/mL formaldehyde is 0.1%. The method was used for the determination of formaldehyde in real samples with satisfactory results. Received: 26 May 1998 / Revised: 30 September 1998 / Accepted: 3 October 1998     

Determination of mercury in mineral coal using cold vapor generation directly from slurries,trapping in a graphite tube,and electrothermal atomization

A rugged and reliable method for the determination of mercury in coal without sample digestion, based on chemical vapor generation (cold vapor technique) from slurried coal samples has been developed. It involves collection of the mercury vapor in a graphite tube, treated with gold or rhodium as permanent modifier, and determination by electrothermal atomic absorption spectrometry. Mercury quantitatively leached out of the investigated coal reference materials into 1 mol l⁻¹ nitric acid within 48 h when the coal was ground to a particle size of ≤50 μm, except for one sample (BCR 180), which had to be ground to ≤30 μm, or a leaching time of 72 h had to be used. No detectable quantity of mercury was generated directly from the slurry particles, but it was not necessary to filter the solution. The greatest advantage of the method is that only a minimum of reagents and sample handling steps are required, a prerequisite for accurate results in routine analysis. The results were well within the 95% confidence level of the certificate or close to the information value of the reference materials investigated. The characteristic mass of 110 pg obtained with gold as the permanent modifier is close to values reported for direct analysis of solutions, showing close to 100% trapping efficiency for mercury. A limit of detection (LOD) of 90 pg absolute was obtained with this modifier, which corresponds to an LOD of 0.009 μg g⁻¹ Hg in coal. This is based on 1 ml of slurry containing 10 mg of coal, and is an order of magnitude lower than the lowest mercury content in the investigated reference materials.     

Separation of organic and inorganic arsenic species by HPLC-ICP-MS

The HPLC separation of eight anionic, cationic or neutral arsenic species (arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine, arsenocholine, trimethylarsine oxide and tetramethylarsonium ion) on a high-capacity, anion-exchange column (Ion Pac AS 7, Dionex) was studied. The separation was performed during one run with a nitric acid gradient ranging from pH 4–1.3. The influence of sodium dodecyl sulfate (SDS), sodium octyl sulfate (SOS) and 1,2-benzenedisulfonic acid (BDSA) as ion pairing eluent modifiers was investigated. In addition the effect of elevated temperatures (30 to 40 °C) was studied. The best results were obtained at room temperature of 20 °C with 0.05 mM benzenedisulfonic acid as the eluent modifier. The chromatograph was connected to an ICP-MS via a cross-flow nebulizer. Detection limits obtained with the optimized chromatographic separation were 0.16–0.60 μg As L^–1 for different species. The proposed speciation method was applied to the determination of arsenic species in the DORM-2 reference material (Dogfish Muscle) and in aqueous extracts of mushrooms collected on arsenic contaminated ground. Received: 3 August 1998 / Revised: 17 September 1998 / Accepted: 21 September 1998     

Determination of tin in marine sediment slurries by electrothermal atomic absorption spectrometry using palladium-magnesium nitrate as chemical modifier

 A method was optimized for the determination of tin in slurries of marine sediment samples using palladium-magnesium nitrate as chemical modifier and Triton X-100 (0.1%) surfactant as stabilizer. To obtain a complete pyrolysis of the slurry sample, two charring steps were used, the first at 480 °C and the second at 1300 °C. The precision and accuracy of the method were studied using the Reference Material PACS-1 (marine sediment) from National Research Council Canada. The detection limit (LOD) was 57.6 μg kg^-1. The method was applied to the determination of tin in marine sediment samples from the Galicia coast. Received: 16 February 1996/Revised: 26 March 1996/Accepted: 12 April 1996     

A new vapor generation system for mercury species based on the UV irradiation of mercaptoethanol used in the determination of total and methyl mercury in environmental and biological samples by atomic fluorescence spectrometry

A new vapor generation system for mercury (Hg) species based on the irradiation of mercaptoethanol (ME) with UV was developed to provide an effective sample introduction unit for atomic fluorescence spectrometry (AFS). Preliminary investigations of the mechanism of this novel vapor generation system were based on GC–MS and FT–IR studies. Under optimum conditions, the limits of determination for inorganic divalence mercury and methyl mercury were 60 and 50 pg mL⁻¹, respectively. Certified reference materials (BCR 463 tuna fish and BCR 580 estuarine sediment) were used to validate this new method, and the results agreed well with certified values. This new system provides an attractive alternative method of chemical vapor generation (CVG) of mercury species compared to other developed CVG systems (for example, the traditional KBH₄/NaOH–acid system). To our knowledge, this is the first systematic report on UV/ME-based Hg species vapor generation and the determination of total and methyl Hg in environmental and biological samples using UV/ME–AFS. Figure A new vapor generation system for mercury species using mercaptoethanol under UV irradiation was developed as an effective sample introduction unit for atomic fluorescence spectrometry     

On chromium direct ETAAS determination in serum and urine

A simple, accurate and reliable method for direct electrothermal atomic absorption spectrometric (ETAAS) determination of chromium in serum and urine samples without any preliminary sample pretreatment is described. Instrumental parameters are optimized in order to define: the most suitable atomizer, optimal temperature program and efficient modifier. An appropriate quantification method is proposed taking into account a matrix interference study. Pyrocoated graphite tubes and wall atomization, pretreatment temperature of 700 °C, atomization temperature of 2600 °C, hydrogen peroxide as modifier and standard addition calibration are recommended. The accuracy of the method proposed for Cr determination in serum and urine was confirmed by comparative analysis of parallel samples after wet or dry ashing as well as by the analysis of two certified reference materials: Serum, Clin Rep 1 and Lypochek Urine, level 1. The detection and determination limits achieved for both matrices are 0.08 μg/L and 0.15 μg/L respectively. The relative standard deviation varied between 15 and 18 % for the chromium content in the samples in the range 0.08–0.2 μg/L and between 4 and 7 % for the chromium content in the range 0.2–2.0 μg/L for both matrices.      

Direct determination of nickel in petroleum by solid sampling–graphite furnace atomic absorption spectrometry

A procedure for the direct GFAAS determination of Ni in petroleum samples using a solid sampling strategy is proposed. Palladium was used as conventional modifier. Central composite design multivariate optimization defined the optimum temperature program and the Pd mass, allowing calibration using aqueous analytical solution. The limit of detection (LOD) at the optimized conditions was 0.23 ng of Ni, for typical sample masses between of 0.10 and 0.60 mg. Linearity at least up to 11 ng of Ni and a characteristic mass of 45 pg were observed, defining a dynamic range between 0.52 and 110 μg g⁻¹. Typical coefficients of variation (n = 10) in the analysis of oil reference materials were 7%. Method validation was performed both by the analysis of oil certified reference materials and by comparison with an independent method (ASTM 5863-B). No statistically significant difference was observed between obtained and expected values. The total determination cycle lasted 5 min, equivalent to a sample throughput of 6 h⁻¹ for duplicate determinations.