Mercury speciation by coupling cold vapour atomic absorption spectrometry with flow injection on-line preconcentration and liquid chromatographic separation

A fully automated system for the direct determination of methylmercury (MeHg), ethylmercury (EtHg), phenylmercury (PhHg), and inorganic mercury (Hg(II)) at the ng/L level is described. It is based on solid phase extraction preconcentration incorporated in a flow injection (FI) system, high performance liquid chromatography (HPLC) separation, reduction combined with thermolysis and determination by cold vapour atomic absorption spectrometry (CVAAS). For preconcentration a microcolumn of bonded silica with octadecyl functional groups (C18 reversed phase material) was used as a sorbent for the mercury complexes formed on-line with ammonium pyrrolidine dithiocarbamate. Retained mercury species are eluted with a methanol-acetonitrile-water mixture and subjected to separation on an octadecylsilane (ODS) column before determination by CVAAS. The sensitivity of organo-mercury determination could be improved by using NaBH₄ as a reductant combined with a thermolysis step. In order to perform on-line measurements the preconcentration microcolumn was mounted in a pressure-tight casing. Limits of detection for MeHg, EtHg, PhHg and Hg(II) employing a sample volume of 58.5 mL were 9, 6, 10 and 5 ng/L, respectively. The relative standard deviation (RSD) calculated from 9 repeated measurements was found to be 3.6%, 5.5%, 10.4% and 7.6% for MeHg, EtHg, PhHg and Hg(II), respectively. Finally, the application of this method for speciation of mercury in fish and human urine is described.     

Conversion techniques in flow injection analysis: Determination of Sulphide by Precipitation with Cadmium Ions and Detection by Atomic Absorption Spectrometry

A flow-injection system is described for on-line conversion of a soluble species to an insoluble compound by means of a tag-material which subsequently can be determined. This approach is used for the determination of sulphide by flame atomic absorption spectrometry, cadmium(II) ions being used as the precipitating tag-reagent. Excess of cadmium(II) is collected on a chelating ion-exchanger and later eluted. The detection limit for sulphide was 10 μg l^?1 and the sampling rate was 100 h^?1. Typical relative standard deviation was 1.2%. Of the potential interferences tested, only phosphate had any effect.     

Extraction-spectrophotometric determination of sulphide and sulphite in waters based on formation of the bis(2,9-dimethyl-1,10-phenanthroline) copper(I) ion

A spectrophotometric method is described for the determination of sulphide or sulphite. The bis(2,9-dimethyl-1,10-phenanthroline)copper(II) ion is reduced at pH 10 by sulphide in the presence of formaldehyde and by sulphide and sulphite in its absence. The resulting copper(I) complex is extracted into chloroform and measured. With any convenient sample volume between 1 and 100 ml, the limits of detection are 0.1 mg for sulphide and 0.25 μg for sulphite. The method is unaffected by iron(II) and nitrite, in concentrations of 100 and 1000 mg l^-1, respectively.     

Spectrofluorimetric kinetic determination of selenium (IV) by flow injection analysis in cationic micellar medium

A sensitive catalytic kinetic spectrofluorimetric method for determining ng ml(-1) of selenium by flow injection analysis has been developed. The method, based on the catalytic effect of Se (IV) on the reduction of resorufin by sulphide, in the presence of cetylpyridinium chloride, is monitored spectrofluorimetrically (lambda(ex)=480 nm; lambda(em)=583 nm). The linearity range of the calibration graph is dependent on the concentration of sulphide. The variables affecting the rate of the reaction were investigated. The method is simple, rapid, precise, sensitive, and widely applicable. The limit of detection is 1 ng ml(-1) Se (IV), and the calibration range is 5-1000 ng ml(-1). Sampling rate is 60 samples h(-1), and the relative standard deviation of 12 determinations of 100 ng ml(-1) Se was 0.76%. The determination of Se (IV) in the presence of Se (VI) and total selenium is described. The method was applied to the determination of Se in selenium tablets, and several synthetic samples.     

Determination of mercury(II) ion by electrochemical cold vapor generation atomic absorption spectrometry.

A technique for determination of mercury is described; it is based on electrolytic reduction of Hg(II) ion on a graphite cathode, the trapping of mercury vapor and its volatilization into a quartz tube aligned in the optical path of an atomic absorption spectrometer. The electrochemical cell consisted of a graphite cathode and an anode operating with constant direct current for the production of mercury atoms. A pre-activated graphite rod was used as the cathode material. The optimum conditions for electrochemical generation of mercury cold vapor (the electrolysis time and current, the flow rate, the type of electrode and electrolyte) were investigated. The characteristic electrochemical data with chemical cold vapor using NaBH4-acid were compared. The presence of cadmium(II), arsenic(III), antimony(III), selenium(IV), bismuth(III), silver(I), lead(II), lithium(I), sodium(I) and potassium(I) showed interference effects which were eliminated by suitable separation techniques. The calibration curve is linear over the range of 5-90 ng ml(-1) mercury(II). The detection limit is 2 ng ml(-1) of Hg(II) and the RSD is 2.5% (n = 10) for 40 ng ml(-1). The accuracy and recovery of the method were investigated by analyzing spiked tap water and river water.     

A reverse-flow injection analysis method for the determination of dissolved oxygen in fresh and marine waters

A reverse flow injection method (rFIA) based on the Winkler titration chemistry, is reported for the determination of dissolved oxygen (DO) in natural waters. Manganese(II) sulfate is injected into a continuously flowing stream of sample and subsequently merges with a reagent stream of sodium hydroxide and sodium iodide. Manganese(II) hydroxide that is formed reacts with DO in the sample to form an oxidized manganese hydroxyoxide floc. Addition of 10% sulfuric acid dissolves this floc, and under acidic conditions, the triiodide ion formed is detected by photometry in a flow through cell at a wavelength of 440 nm. The method is rapid (48 measurements per h), repeatable (R.S.D. ca. 3%, n=3), and has a calculated detection limit of 0.25 mg l⁻¹ (P=0.001). No interference from nitrite or ferrous ions was observed at concentrations typically found in natural waters. The method has been successfully applied to on-line measurement of DO in sediment respiration reactors.     

Ion-selective chalcogenide electrodes for a number of cations

Ion-selective chalcogenide disc electrodes have been developed which are responsive to cations such as silver, lead, chromium(III), nickel, cobalt(II), cadmium, zinc, copper(II) and manganese(II) ions. Each was prepared by using the corresponding metal chalcogenide with silver sulphide. An electrode was assembled with both a compacted and a sintered disc. The sintered electrodes were more sensitive and stable than the compacted ones. Response to silver ion was 59.5 mV pAg , to lead, nickel, cadmium, zinc and copper(II) 29.5 mV pM and to chromium(III) 20 mV pM . Cobalt(II) and manganese(II) electrodes had a non-Nernstian response of 25 mV pM . Both selenides and tellurides can be used for potentiometric determination, but the manganese(II) electrode serves as an analytical tool only when the disc consists of manganese(II) telluride and silver sulphide.     

Atomic-absorption spectrophotometric determination of traces of manganese with thenoyltrifluoroacetone

An atomic-absorption spectrophotometric method for the determination of traces of manganese in solution with thenoyltrifluoroacetone (TTA) is described. Manganese(II) is extracted with 0.01M TTA in methyl isobutyl ketone (MIBK) at pH 9.5. The atomic-absorption of the organic phase at 279.5 nm is measured. Except for chromium, iron, hafnium, niobium, nickel, rhodium, tin, titanium and zirconium, microquantities of many other cations and anions do not interfere. Iron can be removed by MIBK extraction before the TTA extraction. The sensitivity of the method was 1.6 ng/ml for 1% absorption in aqueous solution. The method was successfully applied to the analysis of environmental waters. Manganese in the filtered fractions of water samples was reliably determined with relative standard deviations of 7% at the 5 mug/l. level and 1% at 50 mug/l.     

Mercury speciation and analysis in drinking water by stir bar sorptive extraction with in situ propyl derivatization and thermal desorption-gas chromatography-mass spectrometry

A method for mercury analysis and speciation in drinking water was developed, which involved stir bar sorptive extraction (SBSE) with in situ propyl derivatization and thermal desorption (TD)-GC-MS. Ten millilitre of tap water or bottled water was used. After a stir bar, pH adjustment agent and derivatization reagent were added, SBSE was performed. Then, the stir bar was subjected to TD-GC-MS. The detection limits were 0.01 ng mL(-1) (ethylmercury; EtHg), 0.02 ng mL(-1) (methylmercury; MeHg), and 0.2 ng mL(-1) (Hg(II) and diethylmercury (DiEtHg)). The method showed good linearity and correlation coefficients. The average recoveries of mercury species (n=5) in water samples spiked with 0.5, 2.0, and 6.0 ng mL(-1) mercury species were 93.1-131.1% (RSD<11.5%), 90.1-106.4% (RSD<7.8%), and 94.2-109.6% (RSD<8.8%), respectively. The method enables the precise determination of standards and can be applied to the determination of mercury species in water samples.     

A new chelating resin for preconcentration and determination of Mn(II), Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II) by flame atomic absorption spectrometry

A new polychelatogen, AXAD-16-1,2-diphenylethanolamine, was developed by chemically modifying Amberlite XAD-16 with 1,2-diphenylethanolamine to produce an effective metal-chelating functionality for the preconcentration of Mn(II), Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II) and their determination by flame atomic absorption spectrometry. Various physiochemical parameters that influence the quantitative preconcentration and recovery of metal were optimized by both static and dynamic techniques. The resin showed superior extraction efficiency with high-metal loading capacity values of 0.73, 0.80, 0.77, 0.87, 0.74, and 0.81 mmol/g for Mn(II), Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II), respectively. The system also showed rapid metal-ion extraction and stripping, with complete saturation in the sorbent phase within 15 min for all the metal ions. The optimum condition for effective metal-ion extraction was found to be a neutral pH, which is a great advantage in the preconcentration of trace metal ions from natural water samples without any chemical pretreatment of the sample. The resin also demonstrated exclusive ion selectivity toward targeted metal ions by showing greater resistivity to various complexing species and more common metal ions during analyte concentration, which ultimately led to high preconcentration factors of 700 for Cu(II); 600 for Mn(II), Ni(II), and Zn(II); and 500 for Cd(II) and Pb(II), arising from a larger sample breakthrough volume. The lower limits of metal-ion detection were 7 ng/mL for Mn(II) and Ni(II); 5 ng/mL for Cu(II), Zn(II), and Cd(II), and 10 ng/mL for Pb(II). The developed resin was successful in preconcentrating metal ions from synthetic and real water samples, multivitamin-multimineral tablets, and curry leaves (Murraya koenigii) with relative standard deviations of < or = 3.0% for all analytical measurements, which demonstrated its practical utility.     

Mercury speciation by coupling cold vapour atomic absorption spectrometry with flow injection on-line preconcentration and liquid chromatographic separation

A fully automated system for the direct determination of methylmercury (MeHg), ethylmercury (EtHg), phenylmercury (PhHg), and inorganic mercury (Hg(II)) at the ng/L level is described. It is based on solid phase extraction preconcentration incorporated in a flow injection (FI) system, high performance liquid chromatography (HPLC) separation, reduction combined with thermolysis and determination by cold vapour atomic absorption spectrometry (CVAAS). For preconcentration a microcolumn of bonded silica with octadecyl functional groups (C18 reversed phase material) was used as a sorbent for the mercury complexes formed on-line with ammonium pyrrolidine dithiocarbamate. Retained mercury species are eluted with a methanol-acetonitrile-water mixture and subjected to separation on an octadecylsilane (ODS) column before determination by CVAAS. The sensitivity of organo-mercury determination could be improved by using NaBH₄ as a reductant combined with a thermolysis step. In order to perform on-line measurements the preconcentration microcolumn was mounted in a pressure-tight casing. Limits of detection for MeHg, EtHg, PhHg and Hg(II) employing a sample volume of 58.5 mL were 9, 6, 10 and 5 ng/L, respectively. The relative standard deviation (RSD) calculated from 9 repeated measurements was found to be 3.6%, 5.5%, 10.4% and 7.6% for MeHg, EtHg, PhHg and Hg(II), respectively. Finally, the application of this method for speciation of mercury in fish and human urine is described. Received: 10 March 1997 / Revised: 29 January 1998 / Accepted: 5 February 1998     

Determination of trace amounts of sulphide in human red blood cells by high-performance liquid chromatography with fluorimetric detection after derivatization with p-phenylenediamine and iron(III).

A high-performance liquid chromatographic method based on pre-column fluorescence derivatization has been developed for the determination of trace amounts of sulphide. After the sulphide had been converted into a fluorescent derivative, thionine, by the reaction with p-phenylenediamine and Fe3+, it was separated on a reversed-phase column and detected fluorimetrically (excitation, 600 nm; emission, 623 nm). Sulphide ion can be determined in the range from 0.01 to 3.0 mumol dm-3 with a relative standard deviation (n = 5) of 2.54% at 0.02 mumol dm-3 and 1.74% at 1.0 mumol dm-3. The proposed method was applied to the determination of sulphide in human red blood cells from ten healthy subjects, by generating sulphide in a microdiffusion apparatus; the concentrations found ranged from 0.123 to 0.189 mumol dm-3.     

Spectrophotometric catalytic determination of ultra-trace amounts of selenium based on the reduction of resazurin by sulphide

A sensitive catalytic method for determining ng ml^? concentration of selenium is described. The method is based on the catalytic action of Se(IV) on the reduction of resazurin by sulphide, monitored spectrophotometrically at 605 nm. The linearity range of the calibration graph is dependent on the concentration of sulphide. The variables affecting the rate of the reaction were investigated and the optimum conditions were established. The method is simple, rapid, precise, sensitive and widely applicable. As low as 8.0 × 10^?4 μg ml^?1 of selenium can be determined. The relative standard deviation of seven determination of 10 ng Se was 0.7%. The determination of Se(IV) in the presence of Se(VI) and the determination of total selenium are also described.     

Adsorptive stripping voltammetric determination of copper(II) ion using phenyl pyridyl ketoneoxime (PPKO)

A sensitive and selective procedure is presented for the voltammetric determination of copper(II) ion. The procedure involves an adsorptive accumulation of Cu2+-PPKO on a hanging mercury drop electrode, followed by a stripping voltammetric measurement of reduction current of adsorbed complex at about -0.30 V (vs. SCE). The optimum conditions for the analysis of copper(II) ion include pH (5.8-7.0), 60 microgM PPKO and an accumulation potential of -0.5 V (vs. SCE). The peak current is proportional to the concentration of copper over the range 0.3-76 ng mL(-1) with a detection limit of 0.01ng mL(-1) with an accumulation time of 60 s. The speciation of different forms of complex between copper(II) ion and PPKO, using the Best (Martell program), followed pH measurement were examined. The method was applied to the determination of copper(II) ion content in real samples successfully.     

Determination of manganese with triethanolamine and o-tolidine by conventional and long-path photometry

A very sensitive method for the spectrophotometric determination of manganese is reported. To the sample is added triethanolamine (TEA) and sodium hydroxide to give a pH above 11; after atmospheric oxidation of manganese(II) to the green manganese(III)—TEA complex, sodium pyrophosphate is added and the solution is acidified. Manganese(III) thus forms a complex with pyrophosphate. Then o-tolidine is added and is oxidized in a 2e step to the intensely yellow quinonediimine, while manganese(III) is reduced to manganese(II). The absorbance is measured at 440 nm. The calibration curve is linear up to 1.6 μg Mn ml^-1 in the final solution; the limit of determination is 0.2 μg Mn ml^-1. For the 20-cm path cell, the respective data are 45 ng Mn ml^-1 and 2 ng Mn ml^-1. The only severe interferences are strong oxidants like dichromate or cerium(IV), which are readily reduced with sulfurous acid. Vanadium in amounts up to 2–3 times that of manganese can be dealt with by an appropriate blank solution; larger amounts of vanadium must be removed e.g. by a cupferron extraction.     

On the mechanism of electroreduction of sulphur-containing ligands induced by the electroreduction of transition metal cations

The large scale electrolysis of Zn(II), Cd(II), Hg(II), Cu(II), Ni(II), Co(II), Co(III), Fe(II), Mn(II), Cr(II), Cr(III), Bi(III), In(III) and Sb(III) at mercury electrodes in presence of mercaptoacetic acid, 3-mercaptopropionic acid, cysteine and thiourea was carried out and the products were investigated. In case of transition metal ions the catalytic reduction of organic compounds resulting in the formation of sulphide ions was found. There are two possible ways of the production of these ions: (i) consisting in the formation of a complex between transition metal ion and organic ligand which is subsequently, reduced, and (ii) direct electroreduction of organic compound on the electrode modifiied by the deposition of metal and metal sulphide. For both cases the mechanism of electroreduction was discussed.     

Separation of organotin compounds by ion-exchange chromatography and their determination by inverse voltammetry

An ion exchange procedure was developed for the enrichment, separation and quantification of butyltin and phenyltin species, which show very close half wave potentials by their voltammetric determination. As a case study the separation of dibutyltin (DBT) from triphenyltin (TPT) was investigated. Among different ion exchangers tested, the strong acid ion exchanger PUROLITE C100H, used for industrial purposes, was found to be the most suitable. By using a resin bed volume of 25 mL, a flow rate of the feed solution of 1 mL/min and 3 M HCl in methanol as eluent with a flow rate of 0.5 mL/min, a recovery rate of each species of about 80% could be achieved. The detection limit for the determination of DBT and TPT by anodic stripping voltammetry after their separation and enrichment by the above mentioned ion exchange procedure was found to be 0.4 ng/mL for DBT and 6 ng/mL for TPT in the feed solution, respectively. The applicability of the whole procedure was tested on a sediment candidate reference material of BCR (Bureau of Reference Community).     

A new chelating sorbent for metal ion extraction under high saline conditions

A new chelating polymeric sorbent was developed by functionalizing Amberlite XAD-16 with 1,3-dimethyl-3-aminopropan-1-ol via a simple condensation mechanism. The newly developed chelating matrix offered a high resin capacity and faster sorption kinetics for the metal ions such as Mn(II), Pb(II), Ni(II), Co(II), Cu(II), Cd(II) and Zn(II). Various physio-chemical parameters like pH-effect, kinetics, eluant volume and flow rate, sample breakthrough volume, matrix interference effect on the metal ion sorption have been studied. The optimum pH range for the sorption of the above mentioned metal ions were 6.0–7.5, 6.0–7.0, 8.0–8.5, 7.0–7.5, 6.5–7.5, 7.5–8.5 and 6.5–7.0, respectively. The resin capacities for Mn(II), Pb(II), Ni(II), Co(II), Cu(II), Cd(II) and Zn(II) were found to be 0.62, 0.23, 0.55, 0.27, 0.46, 0.21 and 0.25 mmol g⁻¹ of the resin, respectively. The lower limit of detection was 10 ng ml⁻¹ for Cd(II), 40 ng ml⁻¹ for Mn(II) and Zn(II), 32 ng ml⁻¹ for Ni(II), 25 ng ml⁻¹ for Cu(II) and Co(II) and 20 ng ml⁻¹ for Pb(II). A high preconcentration value of 300 in the case of Mn(II), Co(II), Ni(II), Cu(II),Cd(II) and a value of 500 and 250 for Pb(II) and Zn(II), respectively, were achieved. A recovery of >98% was obtained for all the metal ions with 4 M HCl as eluting agent except in the case of Cu(II) where in 6 M HCl was necessary. The chelating polymer showed low sorption behavior to alkali and alkaline earth metals and also to various inorganic anionic species present in saline matrix. The method was applied for metal ion determination from water samples like seawater, well water and tap water and also from green leafy vegetable, from certified multivitamin tablets and steel samples.     

Flow injection determination of iron by its catalytic effect on the oxidation of 3,3',5,5'-tetramethylbenzidine by hydrogen peroxide

A flow injection-photometric method has been developed for the determination of iron(II+III). The method is based on the catalytic effect of iron(III) on the hydrogen peroxide oxidation of 3,3',5,5'-tetramethylbenzidine to form a blue compound (lambda(max)=650 nm). In this catalyzed reaction, 1,10-phenanthroline acted as an effective activator. Iron(II) is also determined, being oxidized by hydrogen peroxide. Calibration graphs for iron(II) and iron(III) obtained under the optimized conditions were identical with each other and linear in the range 0.2-200 ng ml(-1) with a detection limit of 0.05 ng ml(-1) iron. The reproducibility was satisfactory with a relative S.D. of 1.0% for ten determinations of 5 ng ml(-1) iron(III). The proposed method was successfully applied to the determination of iron in river and lake water samples and can be determined free iron species.     

Bis(4-methylpiperidine-1-carbodithioato)-lead(II) and Bis(4-benzylpiperidine-1-carbodithioato)-lead(II) as Precursors for Lead Sulphide Nano Photocatalysts for the Degradation of Rhodamine B

Bis(4-methylpiperidine-1-carbodithioato)-lead(II) and bis(4-benzylpiperidine-1-carbodithioato)-lead(II) were prepared and their molecular structures elucidated using single crystal X-ray crystallography and spectroscopic techniques. The compounds were used as precursors for the preparation of lead sulphide nano photocatalysts for the degradation of rhodamine B. The single crystal structures of the lead(II) dithiocarbamate complexes show mononuclear lead(II) compounds in which each lead(II) ion coordinates two dithiocarbamato anions in a distorted tetrahedral geometry. The compounds were thermolyzed at 180 ℃ in hexadecylamine (HDA), octadecylamine (ODA), and trioctylphosphine oxide (TOPO) to prepare HDA, ODA, and TOPO capped lead sulphide (PbS) nanoparticles. Powder X-ray diffraction (pXRD) patterns of the lead sulphide nanoparticles were indexed to the rock cubic salt crystalline phase of lead sulphide. The lead sulphide nanoparticles were used as photocatalysts for the degradation of rhodamine B with ODA-PbS1 achieving photodegradation efficiency of 45.28% after 360 min. The photostability and reusability studies of the as-prepared PbS nanoparticles were studied in four consecutive cycles, showing that the percentage degradation efficiency decreased slightly by about 0.51–1.93%. The results show that the as-prepared PbS nanoparticles are relatively photostable with a slight loss of photodegradation activities as the reusability cycles progress.