Simultaneous determination of arsenic, selenium and antimony species using HPLC/ICP-MS

A new method for the simultaneous separation and determination of four arsenic species [As(III), As(V), monomethylarsonic acid and dimethylarsinic acid], three selenium species [Se(IV), Se(VI) and selenomethionine] as well as Sb(III) and Sb(V) is presented. The speciation was achieved by on-line coupling of anion exchange high-performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometry (ICP-MS). Chromatographic parameters such as the composition and pH of the mobile phase were optimised. Limits of detection are below 4.5 μg L^–1 (as element) for Sb(III) and the selenium species and below 0.5 μg L^–1 for the other species. Precisions of retention times were better than 2% RSD and of peak areas better than 8% RSD for all the species investigated. Received: 13 January 1999 / Accepted: 4 March 1999     

Preservation procedures for arsenic speciation in a stream affected by acid mine drainage in southwestern Spain

A preservation study has been performed for arsenic speciation in surface freshwaters affected by acid mine drainage (AMD), a pollution source characterized by low pH and high metallic content. Two sample preservation procedures described in the literature were attempted using opaque glass containers and refrigeration: i) addition of 0.25 mol L⁻¹ EDTA to the samples, which maintained the stability of the arsenic species for 3 h; and ii) in situ sample clean-up with a cationic exchange resin, in order to reduce the metallic load, which resulted in a partial co-adsorption of arsenic onto Fe precipitates. A new proposed method was also tried: sample acidification with 6 mol L⁻¹ HCl followed by in situ clean-up with a cationic exchange resin, which allowed a longer preservation time of at least 48 h. The proposed method was successfully applied to water samples with high arsenic content, taken from the Aguas Agrias Stream (Odiel River Basin, SW Spain), which is severely affected by AMD that originates at the nearby polymetallic sulfide mine of Tharsis. The speciation results obtained by liquid chromatography–hydride generation–atomic fluorescence spectrometry (HPLC-HG-AFS) indicated that during the summer the main arsenic species was As(V) at the hundred μg L⁻¹ level, followed by DMA (dimethyl arsenic) and As(III) below the ten μg L⁻¹ level. In winter, As(V) and As(III) increased at least fivefold, whereas the DMA was not detected.     

Chromium determination in sea water by electrothermal atomic absorption spectrometry using Zeeman effect background correction and a multi-injection technique

Electrothermal atomic absorption spectrometry (ETAAS) applying a Zeeman effect background correction system (ZEBC) and a tranverse heated atomizer was used to directly determine chromium in sea water. Calcium chloride (at a concentration of 20 mg L^–1) was applied as chemical modifier with optimum charring and atomization temperatures of 1600°C and 2000°C, respectively. The detection limit was 0.2 μg L^–1, by injecting 20 μL aliquot of sea water sample. This detection limit could be reduced further to 0.05 μg L^–1, using multiple injections (injection of five 20 μL aliquot of sea water). The accuracy of the methods developed were confirmed by analyses of different certified reference materials. Finally, interferences from major and minor components of sea water are studied. Received: 20 February 1997 / Revised: 26 May 1997 / Accepted: 8 June 1997     

Spectrophotometric determination of total inorganic arsenic with hexamethylene ammonium-hexamethylenedithiocarbamate in nonionic triton X-100 micellar media

We have developed a cost-effective and sensitive spectrophotometric method for the determination of arsenic at trace level using a new reagent, hexamethylene ammonium-hexamethylenedithiocarbamate (HMA-HMDTC). Here we show that arsenic reacts with HMA-HMDTC in acidic conditions to yield the As(HMDTC)₃ complex. We studied the Beer’s law at 256 nm, which showed linearity over the concentration range 0.2–1.0 μg/mL of arsenic. We have shown that molar absorptivity, Sandell’s sensitivity and the detection limit of the method are 6.06 × 10⁴ L/mol cm, 0.0012 μg/cm² and 0.060 μg/mL, respectively. We have applied this new method to the determination of arsenic in drinking water.     

Determination of lead in wine by hydride generation atomic fluorescence spectrometry in the presence of hexacyanoferrate(III)

A rapid, accurate, and precise method is described for the determination of Pb in wine using continuous-flow hydride generation atomic fluorescence spectrometry (CF-HGAFS). Sample pretreatment consists of ten-fold dilution of wine followed by direct plumbane generation in the presence of 0.1 mol L⁻¹ HCl and 1% m/v K₃[Fe(CN)₆] with 1% m/v NaBH₄ as reducing agent. An aqueous standard calibration curve is recommended for Pb quantification in wine sample. The method provides a limit of detection and a limit of quantification of 0.3 μg L⁻¹ and 1 μg L⁻¹, respectively. The relative standard deviation varies between 2–6% (within-run) and 4–11% (between-run) at 3–30 μg L⁻¹ Pb levels in wine. Good agreement has been demonstrated between results obtained by CF-HGAFS and direct electrothermal atomic absorption spectrometry in analyses of red and white wines within the concentration range of 9.2–25.8 μg L⁻¹ Pb.     

Chromatographic determination of phenylarsenic compounds

Urinary arsenic speciation is considered to be an effective procedure to differentiate between toxic inorganic and less toxic organic arsenic exposure. The aim of the present work was to develop a new method for the simultaneous determination of the main arsenic species so far detected in urine: arsenite (As(III)), arsenate (As(V)), methylarsonic acid (MA), dimethylarsinic acid (DMA), and arsenobetaine (AsB). The method is based on anion exchange HPLC coupled on-line to an inductively coupled plasma mass spectrometer (ICP-MS) for element specific detection. Experimental parameters, such as column type and composition of the mobile phases were optimized in order to get best separation, little matrix interferences, lowest detection limits, and short total times of analyses. Best chromatographic conditions were obtained by using a Dionex AS14 anion exchange column and a gradient elution with tetramethylammonium hydroxide and ammonium carbonate as eluting compounds. The detection limits (3 σ) were found to be in the sub μg L^–1 range. The method was applied to analyze different urine samples from persons with and without consumption of seafood. To avoid significant matrix influences, samples (24 h urine) had to be diluted 1 : 5 with water and were filtered through a 0.45 μm filter prior to analyses. Special attention was focused on the validation of the method according to the regulations of the “Deutsche Forschungsgemeinschaft” (DFG) for the analyses of hazardous substances in biological materials. Received: 22 December 1997 / Revised: 18 February 1998 / Accepted: 22 February 1998     

Separation and preconcentration of Se(IV)/Se(VI) speciation on algae and determination by graphite furnace atomic absorption spectrometry in sediment and water

A novel method for the separation and preconcentration of Se(IV)/ Se(VI) with algae and determination by graphite furnace atomic absorption spectrometry (GFAAS) has been developed. The Se(VI) is extracted with algae from the solution containing Se(IV)/Se(VI) at pH 5.0, and the remaining Se(IV) is then preconcentrated pH 1.0. The detection limits (3σ, n = 11) of 0.16 μg L^–1 for Se(IV) and 0.14 μg L^–1 for Se(VI) are obtained using 40 mL of solution. At the 2.0 μg L^–1 level the relative standard deviation is 2.6% for Se(IV) and 2.3% for Se(VI). The method has been applied to the determination of Se(IV)/Se(VI) in sediment and water samples. Analytical recoveries of Se(IV) and Se(VI) added to samples are ?97 ± 5% and 102 ± 6% (95% confidence), respectively. Received: 10 February 1999 / Revised: 21 June 1999 / /Accepted: 22 June 1999     

Flow injection on-line sorption preconcentration of platinum in a knotted reactor coupled with electrothermal atomic absorption spectrometry

A flow injection on-line sorption preconcentration method for the electrothermal AAS determination of platinum has been developed. The pyrrolidine dithiocarbamate complexes of either Pt⁴⁺ or Pt²⁺, formed in 0.7 mol L^–1 HNO₃, are on-line adsorbed on the inner walls of a PTFE knotted reactor and subsequently eluted with methanol. An enhancement factor of 112 and a detection limit (3 σ) of 10 ng L^–1 along with a sampling frequency of 21 h^–1 are achieved with a 90 s preconcentration time at a sample flow rate of 8.8 mL min^–1. The relative standard deviation is 2.5% for 0.4 μg L^–1 Pt. The method has been applied to the determination of platinum in blood samples. Received: 6 October 1997 / Revised: 26 November 1997 / Accepted: 3 December 1997     

Methods for the separation and quantification of arsenic species in SRM 2669: arsenic species in frozen human urine

Two independent liquid chromatography inductively coupled plasma-mass spectrometry (LC/ICP-MS) methods for the separation of arsenic species in urine have been developed with quantification by standard additions. Seven arsenic species have been quantified in a new NIST frozen human urine Standard Reference Material (SRM) 2669 Arsenic Species in Frozen Human Urine, Levels 1 and 2. The species measured were: arsenite (As(III)), arsenate (As(V)), monomethylarsonate (MMA), dimethylarsinate (DMA), arsenobetaine (AB), arsenocholine (AC), and trimethylarsine oxide (TMAO). The purity of each arsenic standard used for quantification was measured as well as the arsenic species impurities determined in each standard. Analytical method limits of detection (L _D) for the various species in both methods ranged from 0.2 to 0.8 μg L⁻¹ as arsenic. The results demonstrate that LC/ICP-MS is a sensitive, reproducible, and accurate technique for the determination of low-level arsenic species in urine. Measurements of the arsenic species 3 years after initial production of the SRM demonstrate the stability of the arsenic species in the urine reference material.     

Chelating resin preconcentration and Hg(II) assisted elution followed by differential-pulse anodic stripping voltammetry for the determination of Cd, Cu, and Pb in seawater

A new and efficient Hg(II) back-elution method for the desorption of Cd, Cu, and Pb from Chelex-100 chelating resin was developed. A smaller eluent volume and shorter elution time can be achieved using an Hg(II) containing eluent rather than pure nitric acid. Owing to the remaining Hg(II) ion in the effluent, a mercury thin-film electrode is formed in-situ during the anodic stripping voltammetric determination without any further addition of Hg(II). The results indicate that all the analytes in seawater matrix can be completely adsorbed on Chelex-100 resin from the sample at pH 6.5, and subsequently eluted from the resin with an acid solution of 5 × 10^–4 mol/L Hg²⁺ + 1 mol/L HClO₄. The detection limits obtained from the differential-pulse anodic (μg L^–1 to ng L^–1) stripping voltammetry are at sub-ppb to ppt (μg L^–1 to ng L^–1) levels permitting to determine Cd, Cu and Pb traces in seawater. The analytical reliability was confirmed by the analysis of the certified reference material CASS-II (open ocean seawater). Received: 22 April 1997 / Revised: 5 August 1997 / Accepted: 7 August 1997     

Organic solvent-soluble membrane filters for the preconcentration and spectrophotometric determination of iron(II) traces in water with Ferrozine

An organic solvent-soluble membrane filter (MF) is proposed for the simple and rapid reconcentration with subsequent spectrophotometric determination of trace levels of iron (II) in water. Iron (II) is collected on a nitrocellulose membrane filter as ion associate of an anionic complex, which is formed by iron (II) and Ferrozine and a cation-surfactant. The ion-pair compound and the MF can be dissolved in small volumes of 2-ethoxyethanol and the absorbance of the resulting solution is measured at 560 nm against a reagent blank with molar absorptivity of 4.01 × 10⁴ L mol^–1 cm^–1. Beer’s law is obeyed over the concentration range 0–10 μg L^–1 of iron (II) in water and the detection limit is 0.03 μg L^–1 with a 50-fold enrichment factor. The proposed method can satisfactorily be applied to the determination of iron (II) in natural water and sea water. Received: 23 June 1998 / Revised: 21 July 1998 / Accepted: 25 August 1998     

Rapid and simple chromatographic separation of V(V) and V(IV) using KH-phthalate and their determination by flame atomic absorption spectrometry

A method was developed for the chromatographic separation of V(V) and V(IV) based on the different sorption forces of these vanadium species in C18 columns in presence of KH-phthalate. The vanadium species were detected with a flame atomic absorption spectrometer with acetylene/N₂O flame. The detection limits (3σ) of V(V) and V(IV) were 0.18 μg/mL and 0.15 μg/mL, respectively. The relative standard deviations (N = 5) are 4.2% and 3.4% for 20–20 μg/mL V(V) and V(IV), respectively. The sampling frequency is 75/h. Because of the special interaction occurring between phthalate and V(IV) on the C18 column and the acetylene/N₂O flame atomic absorption detection, practically no interferences can be detected even in large inorganic matrix. Received: 20 February 1997 / Revised: 2 June 1997 / Accepted: 7 June 1997     

Gaseous sample introduction for the determination of silicon by ICP-AES

The generation of volatile species of silicon as a means to introduce silicon into an inductively coupled plasma has been studied. It is based on the reaction between silicon and fluoride ions in sulfuric acid media and it was carried out using different flow injection mountings. The first mounting works with an injection of 100 μL concentrated sulfuric acid and 150 μL silicon standard solution in a continuous 0.05 mol L^–1 NaF solution flow. The method shows a linear response between the intensity of emission at 251.611 nm line and the silicon concentration from 0.1 to 200 μg mL^–1, with a reproducibility of 2% and a detection limit of 0.004 μg mL^–1. The second mounting produces the volatile species by the reaction between two opposed aerosol flows in a home-made nebulization chamber. This chamber has a Cross-Flow and a Meinhard nebulizer at either end. A linear response ranging from 0.1 to 1000 μg mL^–1 of silicon solution is obtained and the reproducibility rises to 8%.The detection limit reached is 0.02 μg mL^–1. The silicon content in real water samples was determined by applying both the above-mentioned methods and a third method for reference. Received: 6 November 1996 / Revised: 19 December 1996 / Accepted: 3 January 1997     

Anionic cartridge preconcentrators for inorganic arsenic, monomethylarsonate and dimethylarsinate determination by on-line HPLC-HG-AAS

 Preconcentration anionic cartridges in combination with hyphenated FI-HG-AAS and HPLC-HG-AAS have been evaluated for the preconcentration and quantification of total toxic arsenic and of inorganic arsenic, monomethylarsonate and dimethylarsinate species, respectively. Optimum retention and elution parameters of the species on the anionic cartridges are evaluated and the quality parameters of the analysis are reported. The detection limits for the arsenic species under study range from 0.1 μg L^-1 to 0.6 μg L^-1. The proposed method was successfully applied to the determination of arsenic species in spiked fresh water. Received: 2 April 1996/Revised: 22 July 1996/Accepted: 25 July 1996     

Determination of trace amounts of lead in mussels by flow-injection flame atomic-absorption spectrometry coupled with on-line minicolumn preconcentration

A minicolumn packed with poly(aminophosphonic acid) chelating resin incorporated in an on-line preconcentration system for flame atomic-absorption spectrometry was used to determine ultratrace amounts of lead in mussel samples at μg L^–1 level. The preconcentrated lead was eluted with hydrochloric acid and injected directly into the nebulizer for atomization in an air-acetylene flame for measurement. The performance characteristics of the determination of lead were: preconcentration factor 26.8 for 1 min preconcentration time, detection limit (3σ) in the sample digest was 0.25 μg g^–1 (dry weight) for a sample volume of 3.5 mL and 0.2 g sample (preconcentration time 1 min), precision (RSD) 2.3% for 25 μg L^–1 and 2.0% for 50 μg L^–1. The sampling frequency was 45 h^–1. The method was highly tolerant of interferences, and the results obtained for the determination of lead in a reference material testify to the applicability of the proposed procedure to the determination of lead at ultratrace level in biological materials such as mussel samples. Received: 1 November 2000 / Revised: 8 January 2001/ Accepted: 11 January 2001     

Flow injection analysis with in-line solid phase extraction for the spectrophotometric determination of sulfonated and unsulfonated Quinoline Yellow in Cologne

An integrated solid-phase spectrophotometry/ FIA  method is  proposed for the determination of the synthetic colorant matter Quinoline Yellow (QYWS) in the presence of its unsulfonated derivative QYSS. The procedure is based on the retention and preconcentration of the low level QYSS on a C-18 silica gel minicolumn, followed by sequential measurement of its absorbance at λ = 410 nm after its elution with methanol. The applicable concentration range, the detection limit and the relative standard deviation were the following: for QYWS, from 0.10 to 30.0 mg L^–1; 0.013 mg L^–1; and 0.6%; and for QYSS, between 10 and 1,000 μg L^–1; 2 μg L^–1; and 1.3%, respectively. The method was applied to the determination of small amounts of QYSS present in QYWS in Colognes. Percentages of recovery between 98% and 99% were obtained in all instances. The method was also satisfactorily applied to the determination of these compounds in samples of commercial Colognes comparing the results for QYWS with those offered by an HPLC reference method and also validating the results chemometrically. Received: 21 January 2000 / Revised: 17 March 2000 / Accepted: 22 March 2000     

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     

Polarographic determination of cyanide as nickelcyano complex in blood plasma after selective extraction in a methylene blue impregnated polyethylene column

A method for the determination of cyanide in blood plasma by differential pulse polarography (DPP) is described without a drastic acidification of the sample. Cyanide was determined as tetracyanonickelate(II)-anion complex after a microwave-acid assisted cleanup and a selective complex extraction in a polyethylene methylene blue (PE-MB) impregnated column. The cyano complex was eluted from the column with water/acetonitrile and determined by pulse-polarography at –380 mV (Ag/AgCl). The linear range of calibration was obtained from 1.2 to 9.6 μg of cyanide with r = 0.99 and RSD = 9% of 1.2 μg of cyanide. A detection limit of 40 μg L^–1 was calculated and the recoveries of cyanide from spiked samples were about 80%. This method was compared with the classical pyridine-pyrazolone method. Received: 3 September 1997 / Revised: 21 January 1998 / Accepted: 24 January 1998     

Flow injection spectrofluorimetric determination of iron(III) in water using salicylic acid

A simple and fast flow injection fluorescence quenching method for the determination of iron in water has been developed. Fluorimetric determination is based on the measurement of the quenching effect of iron on salicylic acid fluorescence. An emission peak of salicylic acid in aqueous solution occurs at 409 nm with excitation at 299 nm. The carrier solution used was 2 × 10⁻⁶ mol L⁻¹ salicylic acid in 0.1 mol L⁻¹ NH₄⁺/NH₃ buffer solution at pH 8.5. Linear calibration was obtained for 5–100 μg L⁻¹ iron(III) and the relative standard deviation was 1.25 % (n = 5) for a 20 μL injection volume iron(III). The limit of detection was 0.3 μg L⁻¹ and the sampling rate was 60 h⁻¹. The effect of interferences from various metals and anions commonly present in water was also studied. The method was successfully applied to the determination of low levels of iron in real samples (river, sea, and spring waters).     

Determination of EDTA in used fixing solutions by capillary electrophoresis

A capillary electrophoretic method for the determination of EDTA has been developed. EDTA was converted to Ni(II)-EDTA prior to separation, separated from Fe(III)-EDTA, thiosulphate, bromide and polythionates using a fused silica capillary (57 cm × 75 μm I.D.) filled with a borate buffer (50 mmol L^–1; pH 8.5; applied voltage, 30 kV) and detected at 214 nm. The separation time is about 6 min. The detection limit achieved is 2 × 10^–6 mol L^–1 for EDTA. This method was applied for the determination of free EDTA in used fixing solutions. Received: 27 February 1998 / Revised: 28 April 1998 / Accepted: 20 May 1998