Speciation of very low amounts of arsenic and antimony in waters using dispersive liquid–liquid microextraction and electrothermal atomic absorption spectrometry

A new procedure for the determination of inorganic arsenic (III,V) and antimony (III,V) in water samples by dispersive liquid–liquid micro extraction separation and electrothermal atomic absorption spectrometry (ETAAS) is presented. At pH 1, As(III) and Sb(III) are complexed with ammonium pyrrolidine dithiocarbamate and extracted into the fine droplets formed when mixing carbon tetrachloride (extraction solvent), methanol (disperser solvent) and the sample solution. After extraction, the phases are separated by centrifugation, and As(III) and Sb(III) are determined in the organic phase. As(V) and Sb(V) remain in the aqueous layer. Total inorganic As and Sb are determined after the reduction of the pentavalent forms with sodium thiosulphate. As(V) and Sb(V) are calculated by difference. The detection limits are 0.01 and 0.05 µg L^− 1 for As(III) and Sb(III), respectively, with an enrichment factor of 115. The relative standard deviation is in the 2.9–4.5% range. The procedure has been applied to the speciation of inorganic As and Sb in bottled, tap and sea water samples with satisfactory results.     

Differential determination of arsenic(III) and arsenic(V), and antimony(III) and antimony(V) by hydride generation-atomic absorption spectrophotometry,and its application to the determination of these species in sea water

A method is described for the differential determination of As(III) and As(V). and Sb(III) and Sb(V) by hydride generation-atomic absorption spectrophotometry with hydrogen-nitrogen flame using sodium borohydride solution as a reductant. For the determination of As(III) and Sb(III), most of the elements, other than Ag⁺, Cu²⁺, Sn²⁺, Se⁴⁺ and Te⁴⁺, do not interfere in an at least 30,000 fold excess with respect to As(III) or Sb(III). This method was applied to the determination of these species in sea water and it was found that a sample size of only 100 ml is enough to determine them with a precision of 1.5–2.5%. Analytical results for surface sea water of Hiroshima Bay were 0.72 μgl^?1, 0.27 μgl^?1 and 0.22 μgl^?1 for As(total), As(III) and Sb(total), respectively, but Sb(III) was not detected in the present sample. The effect of acidification on storage was also examined.     

Extractive spectrophotometric and fluorimetric determination of boron with 2,2,4-trimethyl-1,3-pentanediaol and carminic acid

Boric acid at μg/ml or ng/ml level can be extracted from 1-6M hydrochloric acid into 2,2,4-trimethyl-1,3-pentanediol solution in chloroform and thus separated from many ions which interfere in the usual spectrophotometric methods. The boron is determined directly in the organic phase without back-extraction into water, by adding a solution of carminic acid in a mixture of sulphuric and glacial acetic acids (1+2 v/v) and measuring the absorbance at 549 nm. The molar absorptivity is 2.58 × 10⁴ l.mole⁻¹.cm⁻¹ and Beer's law is valid for the 0.05–0.4 μg/ml boron range. In the fluorimetric method, 509 or 547 nm can be used as the excitation wavelength and 567 nm for emission measurement, giving a linear response in the 8–120 ng/ml boron range. Both methods have been applied to determination of boron in plants and natural waters with good precision and accuracy.     

Optimization of a single-drop microextraction method for multielemental determination by electrothermal vaporization inductively coupled plasma mass spectrometry following in situ vapor generation

A headspace single-drop microextraction (HS-SDME) method has been developed in combination with electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for the simultaneous determination of As, Sb, Bi, Pb, Sn and Hg in aqueous solutions. Vapor generation is carried out in a 40 mL volume closed-vial containing a solution with the target analytes in hydrochloric acid and potassium ferricyanide medium. Hydrides (As, Sb, Bi, Pb, Sn) and Hg vapor are trapped onto an aqueous single drop (3 µL volume) containing Pd(II), followed by the subsequent injection in the ETV. Experimental variables such as medium composition, sodium tetrahydroborate (III) volume and concentration, stirring rate, extraction time, sample volume, ascorbic acid concentration and palladium amount in the drop were fully optimized. The limits of detection (LOD) (3σ criterion) of the proposed method for As, Sb, Bi, Pb, Sn and Hg were 0.2, 0.04, 0.01, 0.07, 0.09 and 0.8 µg/L, respectively. Enrichment factors of 9, 85, 138, 130, 37 and 72 for As, Sb, Bi, Pb, Sn and Hg, respectively, were achieved in 210 s. The relative standard deviations (N = 5) ranged from 4 to 8%. The proposed HS-SDME-ETV-ICP-MS method has been applied for the determination of As, Sb, Bi, Pb, Sn and Hg in NWRI TM-28.3 certified reference material.     

Determination of fluoride in feed mixtures by capillary isotachophoresis

An isotachophoretic (ITP) method for the determination of fluoride in feed mixtures was developed. A sample of feed mixture, after extraction with 1 M HCl, was analysed using a ZKI 02 column-coupling isotachopherograph. Leading electrolytes for presentation and analytical capillaries consisted of 0.008 M HCl-0.022 M -aminocaproic acid (EACA)-0.001 M CaCl₂-0.05% hydroxypropylmethyl cellulose (HPMC) and 0.002 M HCl-0.005 M EACA-0.05% HPMC, respectively. The terminating electrolyte was 0.01 M tartaric acid. The fluoride released from samples by microdiffusion in 25% perchloric acid was determined using an Ionosep 900.1 single capillary isotachopherograph with 0.002 M HCl-0.005 M EACA-0.05% HPMC as the leading electrolyte and 0.002 M tartaric acid as the terminating electrolyte. The detection limit, depending on the sample treatment, was as low as 4 μg/g as fluoride. A comparison of the developed ITP method with ion- selective electrode method was carried out.     

Simultaneous determination of germanium,arsenic, tin and antimony by molecular emission cavity analysis after hydride generation and gas chromatographic separation

Arsenic (0.1–5 μg), antimony (1–40 μg), tin (0.5–10 μg) and germanium (0.2–10 μg) are determined simultaneously by reduction to their hydrides with sodium tetrahydroborate(III), followed by gas chromatographic separation on a column of 10% E-301 silicone gum rubber on Porapak Q, and measurement of the emissions at 490 nm in an oxygen/hydrogen flame within a cavity. Detection limits for 1-ml samples are 35 ng As, 400 ng Sb, 85 ng Sn and 100 ng Ge. A more sensitive determination of arsenic (0.05–3 μg) and antimony (0.1–5 μg) in binary mixtures is also described; the detection limits are 15 ng As and 40 ng Sb.     

Investigation of electrochemical hydride generation coupled to microwave plasma torch optical emission spectrometry for the determination of arsenic: analytical figures of merit,interference studies and applications to environmentally relevant samples

A continuous flow thin layer electrolysis cell with a Pt cathode in combination with a microwave plasma torch operated with Ar as working gas was used for the optical emission spectrometric determination of As with the hydride technique. Under the optimised conditions the limit of detection (3σ) in the case of the As(I) 228.81 nm emission line was 81 ng mL^?1. Especially the influence of the transition metals Cu(II), Fe(III) and Ni(II), of the hydride forming elements Sb(III), Se(IV) and Sn(II) and of Na on the determination of As was studied. Cu(II) was found to be the strongest interferent, as in the presence of 100 µg mL^?1 of Cu(II) the signal for 3 µg mL^?1 of As was reduced to 4% of the signal without interferent. Sn(II) and Sb(III) were found to yield an increase of the signal for As. L-cysteine and KI/ascorbic acid (1 : 1) at a concentration of 2% were found effective to reduce the interferences of Cu(II), Fe(III) and Ni(II). For a solution containing 3 µg mL^?1 of As and 100 µg mL^?1 of Ni(II) it was shown that in the presence of L-cysteine or KI/ascorbic acid the signal for As was 99% and 94% of the one without interferent, whereas it was only 43% without masking reagents. The procedure could be used for the determination of As in a digested coal fly ash standard reference material (NIST SRM 1633a®) with a certified value of 145 ± 15 µg g^?1 for As. A concentration of 131 ± 15 µg g^?1 was found. Additionally, As could be determined in two process water samples from a copper refinery. It was found that the amount of As determined with ECHG-MPT-OES agrees well with the values determined by FAAS and ICP-OES at the 0.02 and 1.6 g L^?1 level, respectively.     

Optimization of a flow injection system with amperometric detection for arsenic determination.

A selective and sensitive analytical procedure for rapid arsenic determination by gas-diffusion flow injection analysis with amperometric detection was developed. The method is based on the arsenite reduction by NaBH(4). Derived arsine diffuses through a PTF membrane into the acceptor flow stream and is amperometrically determined on a platinum working electrode. The limit of detection (3 sigma) at room temperature was 5 microg/dm(3) of As(III). The relative standard deviation for a 1 mg/dm(3) As(III) standard was 1.96% for six repetitive injections. Arsenic(V) was determined after its prereduction with potassium iodide. Arsenic determination was not interferred with by 1 mg/dm(3) Sb(III), 5 mg/dm(3) Sn(II), 10 mg/dm(3) Se(IV), 1 mg/dm(3) As(V), 1 mg/dm(3) hydrasine, 1 mg/dm(3) Fe(II) or 0.5 mg/dm(3) Fe(III) solution. The throughput of this method was 60 analyses per hour. This method was successfully applied to arsenic determination in some power plant waste water samples.     

Methyl isobutyl ketone extraction of iodide complexes from sulphuric acid-potassium iodide media and back-extraction into an aqueous phase

The methyl isobutyl ketone extraction of 15 elements (Cu, Ag, Zn, Cd, In, Tl, Ge, Sn, As, Sb, Bi, Se, Te, Mo and Pd) as iodide complexes from 0.1-5 M sulphuric acid/0.01-0.5M potassium iodide media has been studied. At the optimum potassium iodide concentrations, and a 1:2 v v ratio of organic to aqueous phase, Cu(II), Ag, Cd, In(III), Tl(III), Sb(III), Bi, Te(IV) and palladium(II) are completely extracted in a single step from 1-5M sulphuric acid. All these elements except palladium are also quantitatively extracted from 0.05-0.5M iodide/2M sulphuric acid. Zn, Sn(IV) and As(III) are completely extracted at high acid and iodide concentrations, and at the highest concentrations of acid and iodide investigated, Ge is partly extracted and Mo(VI) is slightly extracted. The extraction of Se(IV) is incomplete because of its reduction to the elemental state by iodide. The back-extraction of the elements has also been investigated and the forms in which they are extracted and potential analytical separations and interferences are discussed.     

Determination of total arsenic by batch hydride generation atomic absorption spectrometry in injectable drugs containing high levels of Sb(V) as N-methylglucamine antimonate

A procedure for the determination of arsenic by batch hydride generation atomic absorption spectrometry (HG AAS) in commercial samples of injectable drugs, containing high concentrations of Sb(V), is described. The procedure is based on the complexing effect for Sb of citric, oxalic and acetic acids as reaction media. Aqua regia was used for sample digestion prior to As determination by HG AAS. The following experimental conditions for the determination of total As, as As(V), were evaluated: the acid medium and its concentration, sodium tetrahydroborate concentration, purge time, and influence of the different oxidation states of As. The effect of the delay time after mixing of sample and acid solution was also studied. Optimized conditions were: 10% (m/v) citric acid, 1.5% (m/v) sodium tetrahydroborate solution and 30 s for purge time. A delay time of 1 h was required after the digested sample had been mixed with citric acid, before As determination could be carried out. No interference on As(III) and As(V) signals was observed in the presence of up to 1 mg Sb(V). The tolerance limits for Ni(II), Cu(II) and Pb(II) were 1 mg, 100 μg and 100 μg, respectively. Recovery tests for As(III) and As(V) resulted in values between 97 and 101%. Characteristic mass and detection limit (3σ), using the recommended conditions, were 0.52 and 0.8 ng, respectively, for total As.     

Monitoring the effluents of the trichloroacetic acid process by high-performance liquid chromatography

A simple and rapid high-performance liquid chromatographic method for the simultaneous determination of small amounts of nitric acid and trichloroacetic acid in process effluents was developed. Acidic components of the effluents were separated on a reversed-phase C₁₈ column using 0.15 M ammonium sulphate as mobile phase and determined quantitatively by UV absorption at 210 nm. The detection limits for nitric acid and trichloroacetic acid were 1.4 and 10 μg/l, respectively.     

Extraction chromatography with bis(2-ethylhexyl)phosphoric acid for separation of tin(IV)

Tin is extracted from 0.01M hydrochloric acid on a silica-gel column impregnated with bis(2-ethylhexyl)phosphoric acid, stripped with 5M hydrochloric acid, and then determined spectrophotometrically as its Pyrocatechol Violet complex at 555 nm. Tin has been separated from several multicomponent mixtures containing arsenic, antimony, bismuth, lead and copper, and determined in various alloys.     

A simple spectrophotometric procedure for the determination of antimony (III) and (V) in antileishmanial drugs

A spectrophotometric method for the selective determination of antimony (III) and (V) in antileishmanial drugs is described. The procedure is based on the reaction of Sb(III) with bromopyrogallol red (BPR) in neutral solution. As a consequence of the Sb-BPR complex formed, the absorbance of BPR, at 560 nm, decreases proportionally to the amount of Sb(III) in the analyte solution. The calculated apparent molar absorptivity and determination limits are 3.67 × 10⁴ L?·?cm^–1?·?mol^–1 and 1.65 × 10^–6 mol/L, respectively. Sb(V) is determined after reduction to Sb(III) by iodide. The Sb(V) content determined in ten samples of Glucantime varied from 75.40 ± 0.97 to 94.47 ± 1.0 mg/mL. Sb(III) was detected in all samples analyzed, and mean values ranged from 5.19 ± 0.16 to 10.52 ± 0.15 mg/mL. The method is suitable for the routine quality control of pharmaceutical formulations.     

Atomic fluorescence spectrometric determination of trace amounts of arsenic and antimony in drinking water by continuous hydride generation

A highly sensitive and simple method has been developed for the determination of As(III), total As, Sb(III) and total Sb in drinking water samples by continuous hydride generation and atomic fluorescence spectrometry (HGAFS). For As determination, water samples aspirated in a carrier of 2 mol l(-1) HCl were merged with a reducing NaBH(4) 3%(m/v) solution, with sample and NaBH(4) flow rates of 12.5 and 1.5 ml min(-1) respectively. The hydride generated in a 170 cm reaction coil was transported to the detector with an Ar flow of 400 ml min(-1), and a limit of detection between 5 and 20 ng l(-1) was obtained. For Sb determination, 2.5 mol l(-1) HCl and 2%(m/v) NaBH(4) were employed, with respective flow rates of 9.7 and 2 ml min(-1). The hydride generated in a 50 cm reaction coil was transported to the detector with an Ar flow rate of 300 ml min(-1), and a limit of detection between 6 and 14 ng l(-1) was obtained. Determination of the total concentration of these elements was obtained after a previous reduction with KI. Recovery studies of different added concentrations of these species in natural water samples were between 93 and 104% for As(III), 96-103% for As(V), 93-101% for Sb(III) and 90-119% for Sb(V).     

Determination of arsenic and antimony in electrolytic copper by anodic stripping voltammetry at a gold film electrode

A simple procedure is described for the determination of arsenic and antimony in electrolytic copper. The copper is digested with nitric acid and copper is separated from arsenic and antimony by passing an ammoniacal solution of the sample through a column of Chelex-100 resin. After digestion with sulphuric acid and reduction to arsenic(III) and antimony(III) with sodium sulphite in 7 M sulphuric acid at 80°C, both arsenic and antimony are deposited at-0.30V and their total is determined by anodic stripping; antimony is then selectively deposited at -0.05 V for anodic stripping. The lower limits of determination are 56 ng As and 28 ng Sb per gram of copper; relative standard deviations (n = 5) are in the ranges 6.1–15.0% for 5.5—0.5 ppm arsenic in copper and 4.1–6.8% for 2.6—0.6 ppm antimony.     

Determination of trimethylselenonium iodide, selenomethionine, selenious acid, and selenic acid using high-performance liquid chromatography with on-line detection by inductively coupled plasma mass spectrometry or flame atomic absorption spectrometry

An analytical method has been developed for the determination of selenious acid, selenic acid, trimethylselenonium ion, and selenomethionine. The four selenium compounds were separated by HPLC on a column (25 cm×4 mm I.D.) of the anion-exchanger ESA Anion III with a mobile phase (1.5 ml/min) of 0.0055 M ammonium citrate (pH 5.5). Detection was carried out using an on-line inductively coupled plasma mass spectrometer (ICP-MS) or a flame atomic absorption spectrometer (FAAS) as the selenium-specific detector. The chromatographic parameters and the chemical factors affecting the separation of the selenium species were optimized. The four selenium compounds could be separated within 8 minutes. The detection limits of the coupled HPLC–FAAS system were approximately 1 mg Se/l for each compound (100 μl injection), estimated as three times the base-line noise of the chromatograms. More powerful selenium detection was achieved with an ICP-MS. Selenium was measured at m/z 78. To increase the nebulization efficiency, the Meinhard concentric glass nebulizer was replaced by an ultrasonic nebulizer. The ICP-MS signal intensity was increased with the ultrasonic nebulization by a factor of 7 times for selenious acid and 24 to 31 times for trimethylselenonium ion, selenomethionine, and selenic acid compared to that with the Meinhard nebulization. The detection limits achieved by the HPLC–ICP-MS with the ultrasonic nebulization were 0.08 μg Se/l for trimethylselenonium ion, 0.34 μg Se/l for selenious acid, 0.18 μg Se/l for selenomethionine, and 0.07 μg Se/l for selenic acid, respectively.     

Extractive separation and spectrophotometric determination of tungsten as phosphotungsten blue

Phosphotungsten blue is produced by tin(II) reduction of tungstate solution complexed with phosphate at a w/w ratio of W/P = 5, in 4M hydrochloric acid medium, and extracted with isoamyl alcohol; thus tungsten is separated from Fe(III), Ni, Co, Cr(III), V(V), As(V), Sb(III), Bi, Si, U(VI), Ca and Cu(II). In presence of bismuth (0.5 mg/ml), 99.7% W is separated in a single extraction. After alkaline back-extraction, tungsten is determined spectrophotometrically as phosphotungsten blue; it is measured at 930 nm in aqueous solution or at 900-960 nm after isoamyl alcohol extraction, the Beer's law ranges being 0.08-0.6 and 0.16-0.72 mg/ml respectively. The methods are shown to give satisfactory results in the analysis of practical samples containing some milligrams of tungsten.     

Ion chromatography of nitrite at the ppb level with photometric measurement of iodine formed by post-column reaction of nitrite with iodide

The difficulty in ion-chromatographic determination of nitrite in aqueous solutions containing a high concentration of chloride arises mainly from incomplete resolution of the peaks for these anions on the separation column whose efficiency is not high. A photometric measurement of iodine formed by a reaction of nitrite with iodide has been found to make it possible to determine, chromatographically, trace amounts of nitrite without any interference from chloride; chloride does not oxidize iodide to produce iodine. The proposed method was based on the separation of nitrite from matrix anions on a silica-based anion-exchange column with a 1.5·10⁻³ M phthalate eluent (pH 5.0), followed by photometric measurement of the iodine (as triiodide) formed via a post-column reaction of the separated nitrite with iodide. The optimal conditions for the post-column reaction were established by varying the concentrations of iodide, copper(II) and nitric acid in a post-column-reaction solution and the length of a reaction tube. A calibration graph for nitrite, plotted as peak heights versus concentrations, was linear up to 1.50·10⁻⁵ M (690 ppb). The detection limit, defined at S/N=3, was 1.00·10⁻⁷ M (4.60 ppb) nitrite. The presence of chloride ions up to 0.01 M did not give any interference to the determination of nitrite. This method was successfully applied to the determination of nitrite in lake water, river water, sewage works water and snow samples without any pretreatment.     

Adsorptive stripping voltammetric determination of antimony

A new method is described for the determination of antimony based on the cathodic adsorptive stripping of Sb(III) complexed with 2′,3,4′,5,7-pentahydroxyflavone(morin) at a static mercury drop electrode (SMDE). The reduction current of the adsorbed antimony complex was measured by 1.5th-order derivative linear-sweep adsorption voltammetry. The peak potential is at −0.51 V (vs. SCE). The effects of various parameters on the response are discussed. The optimized analytical conditions were found to be: supporting electrolyte, chloroacetic acid (0.04 mol/l, pH 2.3); concentration of morin, 5×10⁻⁶ mol/l; accumulation potential, −0.25 V (vs. SCE); scan rate, 100 mV/s. The limit of detection and the linear range were 7×10⁻¹⁰ mol/l and 1.0×10⁻⁹3.0×10⁻⁷ mol/l Sb(III) for a 2-min accumulation time, respectively. This method has been applied to the determination of Sb(III) in steel and brass samples and satisfactory results were obtained. The adsorptive voltammetric characteristics and composition of the Sb(III)–morin complex were studied.     

Detection of traces of oxidized and reduced sulfur compounds in small samples by combination of different high-performance liquid chromatography methods

Depending on the sulfur species, picomoles of different inorganic sulfur compounds can be detected and separated by HPLC in one arrangement in a sample volume less than 50 μl. The combination of fluorescence labelling of reduced inorganic sulfur compounds such as sulfide (S²⁻), sulfite(SO₃²⁻ and thiosulfate (S₂O₃²⁻) with monobromobimane followed by an extraction of elemental sulfur (S°) by chloroform treatment enables the detection of all mentioned sulfur compounds as well as sulfate (remaining aqueous phase) in the same sample. While the derivatized sulfur compounds could be detected by their fluorescence emission at 480 nm, elemental sulfur is identified by its UV absorption at 263 nm. Sulfate in the remaining aqueous phase is detected by HPLC with indirect UV detection at 254 nm. Detection ranges for the different sulfur compounds examined are as follows: sulfide (5 μM to 1.5 mM), sulfite (5 μM to 1.0 mM), thiosulfate (1 μM to 1.5 mM), elemental sulfur (2 μM to 32 mM) and sulfate (5 μM to >1 mM).