Simultaneous determination of phosphorus. arsenic and germanium and the separation of silicon and arsenic by solvent extraction

A simple, rapid, accurate and reliable method for the simultaneous determination of phosphorus, arsenic and germanium as their heteropoly blue complexes is reported. The method involves selective extraction of phosphomolybdic acid at pH 1.0-0.8, and selective extraction of germanomolybdic acid by isooctyl alcohol at pH 0.4, followed by back-extraction of the germanomolybdic acid with water, and reduction of arsenomolybdic acid in the remaining aqueous phase. A rapid and reliable method is also reported for the simultaneous determination of arsenic and silicon by selective extraction of silicomolybdic acid with isooctyl alcohol at pH < 0.4 and the back-extraction of the silicomolybdic acid with water; arsenic is determined in the remaining aqueous phase. The procedure can be applied to the simultaneous determination of phosphorus, arsenic and silicon.     

Indirect polarographic determination of arsenic

A method for determination of arsenic(V) in the range between 1 x 10(-7) and 1.2 x 10(-6)M has been developed. These levels are reached by means of the multiplication factor yielded by use of 12-molybdoarsenic acid and the great sensitivity of polarographic determination of the Mo(VI) in the heteropoly acid. The procedure has been successfully applied to determination of arsenic in copper alloys, after selective extraction of phosphorus.     

Simultaneous determination of antimony,arsenic and copper by neutron activation analysis

A rapid procedure has been developed for the mutual separation of antimony and arsenic using tribenzylamine as the extracting agent. The extraction behaviours of Sb(III), Sb(V), As(III), As(V) and Au(III) have been studied as a function of the acidity of the aqueous phase. Various factors which affect the extraction of these complexes have been studied and optimized. The procedure was then applied to lead base alloy for the simultaneous determination of antimony, arsenic and copper. Chemical recoveries were quantitative and only about one hour is required for the chemical processing of duplicate samples.     

Comparison of arsenic acid with phosphoric acid in the interaction with a water molecule and an alkali/alkaline-earth metal cation

Recently, Wolfe-Simon has discovered a bacterium which is able to survive using arsenic(V) rather than phosphorus(V) in its DNA. Thus it is important to investigate some important structural and chemical similarities and dissimilarities between phosphate and arsenate. We compared the monohydrated structures and the alkali/alkaline-earth metal (Na(+), K(+), Mg(2+) and Ca(2+)) complexes of the arsenic acid/anions with those of the phosphoric acid/anions [i.e., H(m)PO(4)(-(3-m)) vs H(m)AsO(4)(-(3-m)) (m = 1-3)]. We carried out geometry optimization along with harmonic frequency calculations using ab initio calculations. Despite the increased van der Waals radius of As, the hydrated structures of both P and As systems show very close similarity (within 0.25 ? in the P/As···O(water) distance and within a few kJ/mol in binding energy) because of the increased induction energies by more polar arsenic acid/anons and slightly increased dispersion energy by a larger size of the As atom. In the metal complexes, the arsenic acid has a slightly larger binding distance (by 0.07-1.0 ?) and weaker binding energy because the As(V) ion has a slightly larger radius than the P(V) ion, and the electrostatic interaction is the dominating feature in these systems.     

Determination of arsenic in wheat flour by electrothermal atomic absorption spectrometry using a continuous precipitation-dissolution flow system

A precise, accurate automatic preconcentration method for the determination of total arsenic at the ng g(-1) level in wheat flour is proposed. The sensitivity of the method can be increased by a factor of 20 by precipitating As(V) from 10 ml of digested sample using a weakly acid silver solution. The Ag(3)AsO(4) precipitate is dissolved with 0.5 ml of 6 M ammonia and the resulting solution is collected in an autosampler cup of the ETAAS instrument. The limit of detection achieved in the determination of total arsenic using Pd(NO(3))(2) as modifier is 0.3 ng ml(-1). The proposed method avoids spectral interferences from cations as they do not precipitate with silver cation; anions, which are coprecipitated with silver, are tolerated at concentrations up to about 10 000 times that of As(V). The need to determine As at very low levels in wheat samples, where chloride and phosphate can occur at concentrations 50 000 and 300 000 times higher, respectively, that of arsenic, requires additional steps to suppress the interference of both anions.     

Determination of Dialkyltin Compounds in Poly(Vinyl Chloride) by High-Performance Liquid Chromatography

A high-performance liquid chromatography (HPLC) method has been developed for the analysis of dialkyltin compounds in polyvinyl chloride (PVC) materials. The PVC sample was first dissolved in tetrahydrofuran. Concentrated hydrochloric acid was then added to convert the dissolved dialkyltin stabilizers into the chloride forms, followed by extraction with hexane. The extracted dialkyltin chlorides were preconcentrated and were finally separated by HPLC. Separation was performed using a C₁₈ column and an eluent of aqueous methanol containing 8-hydroxyquinoline (oxine) as the completing agent. Photometric detection of the dialkyltin-oxine complexes was carried out at 380 mm. Under optimum experimental conditions, the detection limits for dimethyltin, dibutyltin and dioctyltin are 1.7 ng, 2.1 ng and 2.9 ng (all as tin), respectively. Residual dialkyltin stabilizers in several commercially available PVC products were successfully analyzed via this method.     

Selective determination of arsenic(III) and arsenic(V) with ammonium pyrrolidinedithiocarbamate, sodium diethyldithiocarbamate and dithizone by means of flameless atomic-absorption spectrophotometry with a carbon-tube atomizer

The extraction behaviour of arsenic(III) and arsenic(V) with ammonium pyrrolidinedithiocarbamate, sodium diethyldithiocarbamate and dithizone in organic solvents has been investigated by means of nameless atomic-absorption spectrophotometry with a carbon-tube atomizer. The selective extraction of arsenic(III) and differential determination of arsenic(III) and arsenic(V) have been developed. With ammonium pyrrolidinedithiocarbamate and methyl isobutyl ketone or nitrobenzene, when the aqueous phase/solvent volume ratio is 5 and the injection volume in the carbon tube is 20 μl, the sensitivities for 1% absorption are 0.4 and 0.5 part per milliard of arsenic, respectively. The relative standard deviations are ca. 3%. Interference by many metal ions can be prevented by masking with EDTA. The proposed methods are applied satisfactorily for determination of As(III) and As(V) in various types of water.     

Substoichiometric speciation for inorganic arsenic and methylated arsenic and its application to samples of marine organisms

A substoichiometric isotope-dilution method is described for the determination of monomethylarsonate, MeAs(V), and dimethylarsinate, Me₂As(V). After the separation of MeAs(V) and Me₂As(V) by extraction as their iodides into benzene, these methylated arsenic species are complexed with a substoichiometric amount of diethyldithiocarbamate in benzene, and the uncomplexed methylarsenic species are removed. The relative standard deviations for the substoichiometric extraction of MeAs(V) and Me₂As(V) are 0.55% and 1.1%, respectively. This substoichiometric speciation of methylated arsenic together with an earlier substoichiometric method for speciation of inorganic arsenic species was applied to the speciation of arsenic in an acid-digested solution of a macro-algae sample. It was demonstrated that almost all the arsenic in this solution was Me₂As(V) even after the digestion with nitric acid.     

Some new algorithms applicable to potentiometric titration in acid-base systems

The paper describes some regression equations adaptable for determination of parameters such as concentrations, equilibrium constants and hydrogen-ion activity coefficients in systems comprising hydrolysable salts of type MeB(u) and monoprotic and polyprotic acids or their salts. These equations are based on the charge and mass balances. Two unconventional types of regression equations are applied: (i) Padé functions W = G(1)(h)/G(2)(h) relating the sum (W) of V(0) ml of titrand and V ml of titrant, W = V(0) + V, to polynomial functions G(1)(h) and G(2)(h) of the hydrogen-ion activity, h, and (ii) functions of the type 1/W = phi(h), based on the Simms titration constants involved. The latter functions are notable for determination of acids and/or their salts in mixtures. The regression equations are developed for systems at constant ionic strength. The parameters of the system can be calculated by means of the computer program MINUITS. Other possibilities of the method, e.g., application to mixed complexes and extraction systems, are also presented.     

Selective substoichiometry for inorganic arsenic(V) by ion-pair extraction with pyrogallol/tetraphenyl-arsnium chloride and its application in the analysis of seaweed

Arsenic(V) is substioichiometrically extracted from 0.4–3 M sulfuric acid solutions into 1,2-dichloroethane with 1.0 × 10^?5 M teraphenylarsnium chloride in the presence of 2.0 × 10^?1 M pyrogallol. Reproducibility of the substoichiometric extractions with a constant amount of tetraphenylarsonium chloride is high (0.5% RSD). This substiochiometric extraction is very selective for arsenic(V) from arsenic(III), monomethylarsonic acid, and dimethylarsinic acid. The extraction combined with the isotope dilution principle was applied to the determination of arsenic(V) in an acid-digestd solution of a seaweed sample (Laminaria religiosa Miyabe) and to the determination of total arsenic in this sample.     

Photometric determination of trace uranium(VI), phosphorus(V), arsenic(V), and vanadium(V) in saturated aqueous solutions of poorly soluble compounds

A procedure for extraction-photometric determination of uranium(VI) was developed and procedures for the determination of phosphorus(V), arsenic(V), and vanadium(V) were modernized. The solubility of some poorly soluble uranium compounds in aqueous solutions was determined. Deceased.     

Capillary electrophoresis of inorganic anions

This review deals with the separation mechanisms applied to the separation of inorganic anions by capillary electrophoresis (CE) techniques. It covers various CE techniques that are suitable for the separation and/or determination of inorganic anions in various matrices, including capillary zone electrophoresis, micellar electrokinetic chromatography, electrochromatography and capillary isotachophoresis. Detection and sample preparation techniques used in CE separations are also reviewed. An extensive part of this review deals with applications of CE techniques in various fields (environmental, food and plant materials, biological and biomedical, technical materials and industrial processes). Attention is paid to speciations of anions of arsenic, selenium, chromium, phosphorus, sulfur and halogen elements by CE.     

Liquid extraction of molybdophosphoric and molybdoarsenic acids: application to the determination of phosphorus in the presence of arsenic

The radioisotopes phohphorus-32 and arsenic-74 have been used to study the extraction of molybdophosphoric and molybdoarsenic acids from aqueous solution with various organic solvents. A method is described for the gravivmetric determination of phosphorus in the presence of arsenic which makes use of solvent extraction with n-butyl acetate. The results obtained for the determination of phosphorus in various types of iron and steel are described.     

CZE for the speciation of arsenic in aqueous soil extracts

We developed two separation methods using CZE with UV detection for the determination of the most common inorganic and methylated arsenic species and some phenylarsenic compounds. Based on the separation method for anions using hydrodynamic sample injection the detection limits were 0.52, 0.25, 0.27, 0.12, 0.37, 0.6, 0.6, 1.2 and 1.0 mg As/L for phenylarsine oxide (PAO), p-aminophenylarsonic acid (p-APAA), o-aminophenylarsonic (o-APAA), phenylarsonic acid (PAA), 4-hydroxy-3-nitrobenzenearsonic acid (roxarsone), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenite or arsenious acid (As(III)) and arsenate (As(V)), respectively. These detection limits were improved by large-volume sample stacking with polarity switching to 32, 28, 14, 42, 22, 27, 26 and 27 microg As/L for p-APAA, o-APAA, PAA, roxarsone, MMA, DMA, As(III) and As(V), respectively. We have applied both methods to the analysis of the arsenic species distribution in aqueous soil extracts. The identification of the arsenic species was validated by means of both standard addition and comparison with standard UV spectra. The comparison of the arsenic species concentrations in the extracts determined by CZE with the total arsenic concentrations measured by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) indicated that CZE is suited for the speciation of arsenic in environmental samples with a high arsenic content. The extraction yield of phenylarsenic compounds from soil was derived from the arsenic concentrations of the aqueous soil extracts and the total arsenic content of the soil determined by ICP-AES after microwave digestion. We found that 6-32% of the total amount of arsenic in the soil was extractable by a one-step extraction with water in dependence on the type of arsenic species.     

Luminol Chemiluminescence with Heteropoly Acids and its Application to the Determination of Arsenate,Germanate, Phosphate and Silicate by Ion Chromatography

A flow-injection chemiluminescence (CL) method has been proposed for sensitive determination of arsenate, germanate, phosphate and silicate, after separation by ion chromatography (IC). The post-column detection system involved formation of heteropoly acid in a H₂SO₄ medium before the CL reaction with luminol in an NaOH medium. For separation, heteropoly acid formation and the CL detection reaction, pH requirements were not compatible. When present as a heteropoly acid complex with molybdenum(VI), ger- manium(IV) and silicon(IV) caused CL emission from oxidation of luminol, and such a CL oxidation of luminol was observed analogously for arsenic(V) and phosphorus(V) but with the addition of metavanadate ion to the acid solution of molybdate. Good sensitivity for the three analytes arsenic(V), ger- manium(IV) and phosphorus(V) could be given by a single set of reagent conditions, chosen carefully. Another set was suitable for determining phosphorus(V) and silicon(IV). The minimum detectable concentrations of arsenic(V), germanium(IV), phosphorus(V) and silicon(IV) were 10, 50, 1 and 10 μg l⁻¹, respectively. Linear calibrations for arsenic(V), germanium(IV), phosphorus(V) and silicon(IV) were established over the respective concentration ranges of 10–1000, 50–25000, 1–1000 and 50–1 μg l⁻¹. The proposed IC–CL method was successfully applied to analyses of a seaweed reference material, rice wine and water samples.     

Arsenic speciation in natural water samples by coprecipitation-hydride generation atomic absorption spectrometry combination

A speciation procedure for As(III) and As(V) ions in environmental samples has been presented. As(V) was quantitatively recovered on aluminum hydroxide precipitate. After oxidation of As(III) by using dilute KMnO₄, the developed coprecipitation was applied to determination of total arsenic. Arsenic(III) was calculated as the difference between the total arsenic content and As(V) content. The determination of arsenic levels was performed by hydride generation atomic absorption spectrometry (HG-AAS). The analytical conditions for the quantitative recoveries of As(V) including pH, amount of aluminum as carrier element and sample volume, etc. on the presented coprecipitation system were investigated. The effects of some alkaline, earth alkaline, metal ions and also some anions were also examined. Preconcentration factor was calculated as 25. The detection limits (LOD) based on three times sigma of the blank (N: 21) for As(V) was 0.012 μg L⁻¹. The satisfactory results for the analysis of arsenic in NIST SRM 2711 Montana soil and LGC 6010 Hard drinking water certified reference materials for the validation of the method was obtained. The presented procedure was successfully applied to real samples including natural waters for arsenic speciation.     

Emulsion membrane extraction of Am(III) and Am(IV) in systems with tertiary and secondary amines

The stability of emulsions, containing tri-n-octylamine and di-n-octylamine salts in the organic phase and nitric acid in the aqueous phase has been studied. Optimal conditions for the extraction of Am(III) and Am(IV) phosphorus tungstate complexes with such emulsions have been determined. Emulsion membrane extraction is shown to be more effective for this purpose than conventional liquid extraction.     

Single-halide anions in phosphorus(V) halide complexes: a raman investigation

Phosphorus(V) chloride and bromide complexes containing single-halide anions are surveyed in terms of characteristic phosphonium ion Raman shift patterns. Methods of preparation of Phase III phosphorus pentachloride are reviewed and some modes of formation proposed. The nature of the phosphonium cation-single-halide anion interaction is discussed on the basis of observed Raman shifts. With trihalide anions, similar shifts are observed but are strongly dependent on anion symmetry.     

Photometric Determination of Trace Arsenic in Aqueous Media

A new procedure has been proposed for the photometric determination of arsenic as its compounds with tetrazolium salts. The choice of 5(1,3-benzadioxole-5-yl)-2-(4-iodophenyl)-3-phenyl-2H-tetrazolium chloride as a reagent for arsenic has been substantiated. The developed scenario of sample preparation involves the gas extraction of arsenic as arsine from the reaction mixture and its absorption isolation from the gas phase into a reagent solution in a 10 : 3 : 12 water–butanol-1–dimethyl sulfoxide mixture. The procedure provides the determination of from 1 to 120 g/L arsenic.     

A chemical amplification method for the sequential estimation of phosphorus, arsenic and silicon at ng/ml levels by d.c. polarography

A method is described for the sequential determination of phosphorus, arsenic and silicon at ng/ml levels by d.c. polarography. These elements are converted into their heteropolymolybdates and separated by selective solvent extraction. Determination of the molybdenum in the extract gives an enhancement factor of 12 for determination of the hetero-atom. A further enhancement by a factor of 40 is achieved by determining the molybdenum by catalytic polarography in nitrate medium. Charging-current compensation is employed to improve precision and the detection limit. The detection limits for phosphorus, arsenic and silicon are 0.5, 4.7 and 3.1 mu/gl., respectively and the relative standard deviation is 2-2.5%.