Rapid Determination of Mercury in Water by Stripping Voltammetry at a Gold-Modified Carbon Electrode

A procedure was developed for determining mercury in natural water by stripping voltammetry on a gold-modified carbon electrode. The concentration dependence of the anodic stripping current of mercury is linear in the range 0.02–5 g/L Hg(II). The interference of Fe(III), Cu(II), Cl^–, Br^–, I^–, and F^– ions with the determination of mercury was studied. Ozonation was used for rapid sample preparation. The detection limit for mercury was 0.02 g/L at an electrolysis time of 5 min.     

Fluorimetric determination of aluminium in water by sequential injection through column extraction

A fluorimetric procedure for the determination of aluminium with matrix removal in drinking water is proposed. The system is based both on the solid phase extraction of aluminium on a new chelating resin (XAD-4 modified by grafting salicylic acid) and the fluorimetric detection of a complex formed between 8-hydroxyquinoline-5-sulfonic acid (HQS) and Al(III), after elution of the resin by hydrochloric acid. The sorption and elution of aluminium were studied in both competitive and non-competitive conditions, varying pH, flow-rates, volume and concentration of reagents, as well as time contact. The optimised procedure allows determination of Al³⁺ at the sub-ppb level (LOD: 0.2 g L^–1 for 1 ml of sample) within a working range of 0.2–500 g L^–1. The analytical procedure was successfully employed for the determination of aluminium in drinking water during and after flocculation/coagulation treatment processes.     

Sensitive Method for Trace Determination of Mercury in Wines Using Electrothermal Atomic Absorption Spectrometry

An accurate, simple and precise method for total mercury determination in wines is described. Liquid/liquid extraction of inorganic and organic mercury species directly from untreated wine samples is recommended as a preconcentration procedure prior to determination by electrothermal atomic absorption spectrometry (ETAAS). Ammonium pyrrolidinedithiocarbamate was used as complexation agent. The optimal instrumental parameters for ETAAS measurement of mercury species extracted are proposed. The detection limit for total mercury determination is 0.2µgL^–1. The relative standard deviation is 15–22% for mercury in wine in the range of 0.2–5µgL^–1. The proposed procedure has been successfully applied to the determination of mercury in bottled wines in Bulgaria and Macedonia.     

Potentiometric determination of mercury(II) and thiourea in strong acid solution using an ion-selective electrode with AgI-based membrane hydrophobised by PTFE

Summary The potentiometric determination of mercury(II) and thiourea (TU) in strong acid solution (pH 0–1) by using an all-solid-state ion-selective electrode with (Ag₂S 25%, AgI 25% and PTFE 50% m/m)-membrane is described. The linear response, 43 mV(pHg)^–1 and 80 mV(pTU)^–1, has been obtained in the concentration range from 10^–2 to under 10^–5 mol/l. By direct potentiometry at pH 0 mercury(II) can be determined in the presence of up to 10^–3 mol/l of iron(III). The change in potential in the tested concentration range of thiourea indicates the formation of Ag(TU) _1.4 ⁺ at the exposed surface of the membrane. This stoichiometry is in good agreement with that calculated from the average Ag/TU ratio in the potentiometric titration. The investigated electrode can be used as a good sensor for mercury(II) and thiourea in strong acid media and a wide variety of practical analytical systems.     

Stripping voltammetric determination of trace amounts of mercury using a carbon paste electrode modified with 2-mercapto-4(3H)-quinazolinone

A carbon paste electrode modified with 2-mercapto-4(3H)-quinazolinone was used for the voltammetric determination of mercury(II). Mercury was preconcentrated onto the surface of the modified electrode only by the complexing effect of the modifier without application of potential (i.e. in open-circuit conditions). After exchange of the medium, the accumulated amount of mercury(II) was determined by differential pulse anodic stripping voltammetry. The response depended on the concentration of mercury in the bulk solution, preconcentration time, and other parameters. The detection limit was 0.1 g 1^–1 Hg(II) for a preconcentration time of 15 min. Preconcentration for suitable times yielded a linear calibration graph from 0.5 to 6000 g 1^–1 Hg(II). For multiple determinations (5 runs), the relative standard deviation was 5% for a concentration of 100 g 1^–1 Hg(II). The proposed procedure was used to determine trace mercury in plant and sewage sludge samples with good results.On leave from Hainan University, Hainan Peoples Republic of China     

Time-based on-line preconcentration cold vapour generation procedure for ultra-trace mercury determination with inductively coupled plasma atomic emission spectrometry

A time-based sequential dispensing on-line column preconcentration procedure for mercury determination at trace levels by cold vapour generation inductively coupled plasma atomic emission spectrometry (CV-ICP-AES), by means of a unified module of a preconcentration column and a gas–liquid separator (PCGLS) is described. The complex of mercury formed on-line with ammonium pyrrolidine dithiocarbamate (APDC) is retained on the surface of the hydrophobic poly(tetrafluoroethylene) (PTFE) turnings, which are packed into the lower compartment of the PCGLS. Subsequently, mercury vapour is generated directly on the PTFE turnings by reductant SnCl₂ and separated from the liquid mixture via the PCGLS by argon purge gas. The outlet of the PCGLS is connected directly to the torch adapter of the plasma without the normal spray chamber and nebulizer. With 60-s preconcentration time and 12.0 mL min^–1 sample flow rate, the sampling frequency is 30 h^–1. The calibration curve is linear over the concentration range 0.02–5.0 g L^–1, the detection limit (c_L) is 0.01 g L^–1 and the relative standard deviation (s_r) is 3.1% at the 1.0 g L^–1 level. The proposed method was evaluated by analysis of BCR CRM 278 (Mytilus Edulis) reference material and applied to the determination of total mercury in digested urine, blood and hair samples.     

Determination of Arsenic in Food Samples by Hydride Generation – Atomic Absorption Spectrometry

A method for the determination of trace amounts of arsenic in food samples using flow injection analysis and atomic absorption spectrometry with hydride generation (FI-HG AAS) was developed. The parameters of the flow injection system and the hydride generation were optimized with respect to reagent concentrations, atomization temperature, injection volume, reaction coil length and carrier flow rate. The limits of detection and quantification were 0.34µgL^–1 and 1.2µgL^–:1, respectively, and the analytical curve is linear up to 30.0µgL^–1 arsenic. The relative standard deviation for 12 replicates varies between 5% for 4.0µgL^–1 As and 1.8% for 30.0µgL^–1 As, with an injection frequency of up to 135h^–1. Interferences from Ni(II), Cu(II), Fe(III), Cr(III), Mo(II), Bi(III), Se(IV), Se(VI), Sb(III) and Sb(V) could be masked with a mixture of ascorbic acid-KI in a 5.0molL^–1 HCl solution. The accuracy of the proposed method was evaluated by using certified reference materials of biological samples, and the method was used to determine the content of arsenic in fish and coffee beans.     

Spectrophotometric and derivative spectrophotometric determination of nickel with hydroxynaphthol blue

The reaction of nickel(II) cation with hydroxynaphthol blue (HNB) in aqueous media at pH 5.2–6.0 results in a red complex that is stable for at least 2h. Beer's Law is obeyed up to 3.2 g/ml of nickel(II) with an apparent molar absorptivity of 1.38 × 10⁴l/mol/cm at 563 nm. This paper proposes procedures for nickel determination by ordinary and first-derivative spectrophotometry. The results demonstrate that the linear dynamic range is 0.08–3.20 g/ml with a limit of detection of 23 ng/ml for ordinary spectrophotometry, compared with 21–800 ng/ml and 6 ng/ml, respectively, for first-derivative spectrophotometry. Calcium(II), magnesium(II), barium(II), strontium(II), cadmium(II), lead(II), manganese(II), bismuth(III) and molybdenum(VI) ions do not interfere for at least 1001 mass ratios. The main interferents are cobalt(II), titanium(IV), aluminium(III), mercury(II) and copper(II). The interferences of titanium(IV), aluminium(III), zirconium(IV) and iron(III) can be masked by fluoride and mercury(II) and copper(II) with thiosulfate or thiourea. The derivative method is applied to nickel determination in standard brasses and the results demonstrate that there is no significant difference between the results and certified values at the 95% confidence level.     

Trace analysis of mercury by a radiochemical displacement method using cobalt(III) diethyldithiocarbamate

A radiochemical displacement method was utilized for the determination of traces of mercury in water taking advantage of its ability to displace cobalt from cobalt(III) diethyldithiocarbamate tagged with⁶⁰Co. The method is found to be applicable in the concentration range of 50–200 g/ml mercury. The interfernces from various cations like Fe(III), Co(II), Cu(II), Pb(II) and Ag(I) ions were studied.     

Nuclear magnetic resonance investigation of intramolecular scrambling processes in meso-(2,3-butylenediamine)tetraacetate. Diamagnetic complexes of transition metal ions

Summary The acetate scrambling processes (, conversion and N inversion) occurring in the complexes formed from meso-(2,3-butylenediamine)tetraacetic acid (BDTA) with zinc(II), cadmium(II), mercury(II), scandium(III), yttrium(III) and lanthanum(III) ions have been investigated by line shape analysis of their n.m.r. spectra. Between 308 and 373 K fast conversion between and isomers and slow nitrogen inversion occur except for mercury(II) and yttrium(III) in the latter case. H^* = 2.3±0.1 kJ mol^–1 and S^* = –6.9±0.2 mol^–1 J K^–1 for the mercury complex; H^* = 2.6 ±0.2 kJ mol^–1 and S^* = –5.5±0.5 mol^–1 JK^–1 for the yttrium complex. Exchange mechanisms proceeding through different reaction intermediates are discussed on the light of the results obtained in this work as well as previously on other polyaminepolycarboxylate complexes of the same ions.     

Differential Pulse Stripping Voltammetry of Mercury(II) Ions at a Cylindrical Carbon-Fiber Microelectrode in the Presence of Au(III) Ions

The determination of Hg(II) ions in aqueous solutions containing Au(III) ions was studied using differential pulse stripping voltammetry at a cylindrical carbon-fiber (d= 30 m) microelectrode fabricated from a pitch at 2800°C. At the [Au(III)]/[Hg(II)] ratio higher than 25, the anodic voltammogram of mercury accumulated in the potential range from 0.2 to –0.2 V for 40–200 s exhibited a current peak at 0.62–0.72 V. The peak height and area were directly proportional to the concentration of Hg(II) in the range (1–1000) × 10^–10M. The results of determining Hg(II) in waters of different origin are reported.     

Spectrophotometric determination of iron after separation of its 9,10-phenanthrenequinone monoximate on microcrystalline naphthalene

A sensitive and selective spectrophotometric method has been developed for the determination of iron as Fe(II) or Fe(III) using 9,10-phenanthrenequinone monoxime (PQM) as the complexing agent. Fe(II) and Fe(III) react with PQM to form coloured water insoluble complexes which can be adsorbed on microcrystalline naphthalene in the pH ranges 3.7–6.2 and 2.0–8.4, respectively. The solid mass consisting of the metal complex and naphthalene is dissolved in DMF and the metal determined spectrophotometrically by measuring the absorbances Fe(II) at 745 nm and Fe(III) at 425 nm. Beer's law is obeyed over the concentration range 0.5–20.0 g of iron(II) and 20–170.0 g of Fe(III) in 10 ml of DMF solution. The molar absorptivities are 1.333 × 10⁴ 1 · mole^–1 · cm^–1 for Fe(II) and 2.428 × 10³1· mole^–1 · cm^–1 for Fe(III). The precision of determination is better than 1%. The interference of various ions has been studied and the method has been employed for the determination of iron in various standard reference alloys, bears, wines, ferrous gluconate, human hair and environmental samples.     

Speciation analysis of mercury in water samples by cold vapor atomic absorption spectrometry after preconcentration with dithizone immobilized on microcrystalline naphthalene

Trace amounts of inorganic mercury (Hg²⁺) and methylmercury cations (MeHg²⁺) were adsorbed quantitatively from acidic aqueous solution onto a column packed with immobilized dithizone on microcrystalline naphthalene. The trapped mercury was eluted with 10 ml of 7 mol L^–1 hydrochloric acid solution. The Hg²⁺ was then directly reduced with tin (II) chloride, and volatilized mercury was determined by cold vapor atomic absorption spectrometry (CVAAS). Total mercury (Hgt) was determined after decomposition of MeHg⁺ into Hg²⁺. Hg²⁺ and MeHg⁺ cations were completely recovered from the water with a preconcentration factor of 200. The relative standard deviation obtained for eight replicate determinations at a concentration of 0.3 g L^–1 was 1.8%. The procedure was applied to analysis of water samples, and the accuracy was assessed via recovery experiment.     

Determination of biogenic amines in wine after clean-up by solid-phase extraction

Summary A suitable method for the determination of 16 biogenic amines in wine has been developed. The method involves clean-up of wine samples using ion-exchange cartridges and a preconcentration step, under controlled vacuum, before derivatization of the amines by treatment with phthalaldehyde (PA) and reversedphase HPLC with gradient elution and fluorimetric detection. Linearity of response was obtained for all the biogenic amines from 100 g L^–1 to mg L^–1. Limits of detection for the amines were similar for all PA-derivatives (25–50 g L^–1) and the quantitation limits were about 0.1 mg L^–1. After clean-up and preconcentration, the concentration levels increased 10-fold for all amines except putrescine and cadaverine, which gave poor recovery by this method unlike the rest which gave recoveries of almost 90%. The overall process was successfully applied to identify and quantify biogenic amines in several red wines from the Tarragona region.     

Flow Analysis of Transition Metals by Thermal Lensing

The conditions for the flow determination of Al(III), Bi(III), Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Mn(II), Nd(III), Ni(II), Pb(II), Pr(III), and Zn(II) by reaction with Xylenol Orange in aqueous solutions at pH 4.5 and the determination of Cd(II), Co(II), Cu(II), Fe(II), Ni(II), Pb(II), and Zn(II) by reaction with 4-(2-thiazolylazo)resorcinol in water–ethanol mixtures (5 : 1) at pH 5.0 using an injected sample volume of 80 L were proposed. The limits of detection were n × 10^–8–n × 10^–7 mol/L; the linearity ranges in the calibration graphs were of about three orders of magnitude; the relative standard deviation was of 3–7%.     

Determination of Heavy Metal Ions in Chinese Herbal Medicine by Microwave Digestion and RP-HPLC with UV-Vis Detection

A new method for the simultaneous determination of heavy metal ions in Chinese herbal medicine by microwave digestion and reversed-phase high-performance liquid chromatography (RP-HPLC) has been developed. The Chinese herbal medicine samples were digested by microwave digestion. Lead, cadmium, mercury, nickel, copper, zinc, and tin ions in the digested samples were pre-column derivatized with tetra-(4-chlorophenyl)-porphyrin (T₄-CPP) to form the colored chelates which were then enriched by solid phase extraction with C₁₈ cartridge and eluted from the cartridge with tetrahydrofuran (THF). The chelates were separated on a Waters Xterra RP₁₈ column by gradient elution with methanol (containing 0.05molL^–1 pyrrolidine-acetic acid buffer salt, pH=10.0) and THF (containing 0.05molL^–1 pyrrolidine-acetic acid buffer salt, pH=10.0) as mobile phase at a flow rate of 0.5mLmin^–1 and detected with a photodiode array detector in the range of 350–600nm. In the original samples the detection limits of lead, cadmium, mercury, nickel, copper, zinc and tin are 4ngL^–1, 3ngL^–1, 6ngL^–1, 5ngL^–1, 2ngL^–1, 6ngL^–1, and 4ngL^–1, respectively. This method was applied to the determination of lead, cadmium, mercury, nickel, copper, zinc and tin in Chinese herbal medicine samples with good results.     

Using enzymes isolated from diverse sources to determine metal ion cofactors

Oxidoreductases and hydrolases isolated from different sources (horseradish and peanut peroxidases, alcohol dehydrogenases from bakers yeast and horse liver, and alkaline phosphatases from Escherichia coli, chicken and seal intestine) were used to determine their metal ion cofactors: Fe(III), Zn(II) and Mg(II), respectively. Studying the effects of the metal ion cofactors on the catalytic activity of the enzymes of different origin showed that the extent of their inhibition, activation, or reactivation of their apoenzymes depended on the structure and accessibility of the enzyme active site, which varies among the biocatalysts isolated from different sources. The developed procedures are based on the inhibiting (Zn(II)) or activating (Mg(II)) effects of the metal ions on the catalytic activity of the enzymes, or on reactivating effects (Fe(III) and Zn(II)) on the apoenzymes. The procedures are characterized by high sensitivity and selectivity; the detection limits of Fe(III) using horseradish peroxidase, Zn(II) using alcohol dehydrogenase from bakers yeast, alkaline phosphatase from seal intestine and its apoenzyme, and Mg(II) using alkaline phosphatase from chicken intestine equal 10 ng L^–1, 20 ng L^–1, 3 g L^–1, 8 g L^–1 and 0.2 g L^–1, respectively.Presented at the 8th Symposium Kinetics in Analytical Chemistry, Rome, Italy, 5–8 July 2004.     

Adsorptive stripping voltammetric determination of cobalt in the presence of dimethylglyoxime and cetyltrimethylammonium bromide

A sensitive procedure for determination of micro-traces of Co(II) by adsorptive stripping voltammetry is proposed. The procedure exploits the enhancement of the cobalt peak obtained by use of the system Co(II)–dimethylglyoxime–piperazine-1,4-bis(2-ethanesulfonic acid)–cetyltrimethylammonium bromide. Using the optimized conditions, a detection limit (based on the 3 criterion) for Co(II) of 1.2×10^–11 mol L^–1 (0.7 ng L^–1) was achieved. The calibration plot for an accumulation time of 30 s was linear from 5×10^–11 to 4×10^–9 mol L^–1. The procedure was validated by analysis of certified reference materials and natural water samples.     

2,3-Dihydroxypyridine-loaded cellulose: a new macromolecular chelator for metal enrichment prior to their determination by atomic absorption spectrometry

New macromolecular chelators have been synthesized, by loading 2,3-dihydroxypyridine (DHP) on cellulose via linkers -NH-CH₂-CH₂-NH-SO₂-C₆H₄-N=N- and -SO₂-C₆H₄-N=N-, and characterized by elemental analysis, TGA, IR, and CPMAS ¹³C NMR spectra. The cellulose with DHP anchored by the shorter linker had better sorption capacity (between 69.7 and 431.1 mol g^–1) for Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II), and Fe(III)) than the other (51.9–378.1 mol g^–1); the former was therefore studied in detail as a solid extractant for these metal ions. The optimum pH ranges for quantitative sorption (recovery 97.6–99.8%) on this matrix were: 7.0–9.0, 6.0–9.0, 3.0–8.0, 6.0–8.0, 6.0–9.0, 6.0–7.0, and 2.0–6.0 respectively. Desorption was quantitative with 0.5 mol L^–1 HCl and 0.5 mol L^–1 HNO₃ (for Pb). Simultaneous sorption (at pH 7.0) of all metal ions other than Fe(III) was possible if their total concentration did not exceed the sorption capacity (lowest value). The recovery of seven metal ions from their mixture at pH 6.0 was nearly quantitative when the concentration level of each metal ion was 0.2 g mL^–1. The optimum flow rate of metal ion solutions for quantitative sorption of metal onto a column packed with DHP-modified cellulose was 2–7 mL min^–1, whereas for desorption the optimum flow rate for the acid solution was 2–4 mL min^–1. The time needed to reach 50% of the total loading capacity (t_1/2) was <5 min for all the metal ions except Ni and Pb. The limit of detection (blank+3s) was from 0.70 to 4.75 g L^–1 and the limit of quantification (blank+10s) was between 0.79 and 4.86 g L^–1. The tolerance limits for NaCl, NaBr, NaI, NaNO₃, Na₂SO₄, Na₃PO_4, humic acid, EDTA, Ca(II), and Mg(II) for sorption of all metal ions are reported. The column packed with DHP-anchored cellulose can be reused at least 20 times for enrichment of metal ions in water sample. It has been used to enrich all the metal ions in pharmaceutical and water samples before their determination by flame AAS. RSD for these determinations was between 1.1 and 6.9%.     

Chromotropic acid,a fluorogenic chelating agent for aluminium(III)

Complexation of aluminium(III) with the fluorogenic ligand chromotropic acid (4,5-dihydroxynaphthalene-2,7-disulfonic acid) has been revisited with the aim of using enhancement of the fluorescence intensity as an analytical tool. Complexation at the optimum pH4 was shown to lead to a 1:1 complex with a stability constant log ₁₁₀=18.4±0.7. The fluorogenic effect was thoroughly investigated. Nearly selective excitation of the chelate rather than the ligand could be achieved at wavelengths longer than 360 nm. For analytical purposes the main interfering ion was Ga³⁺. The strongest competing ligand was shown to be citric acid. Competitive complexation by acetate or formate ions can also make their use in a buffer at the usual concentration, 0.2 mol L^–1, questionable, whereas a 10^–2 mol L^–1 formic acid buffer was shown to be a good alternative. The calibration plot showed that the dependence of response on Al(III) concentration was linear up to 500 g L^–1; the detection limit was 0.65 g L^–1 (3SD _blank, n=10, SD=±1.4% at 10 g L^–1 and ±0.8% at 100 g L^–1). The analytical procedure was successfully applied to several samples of tap water and the results were in good agreement with those from AAS determination.