Elimination of sulfide interference by sodium hypochlorite solution in the cold vapor atomic absorption spectrometric determination of mercury using tin(II) reduction in alkaline medium

An addition of sodium hypochlorite solution effectively eliminated the interference by sulfide in the cold vapor atomic absorption spectrometric determination of mercury using tin(II) reduction in alkaline medium. Mercury ranging from 0.01 to 0.5 μg could be determined within ±10% error in 100 mL of sample solution containing 10 mg of sulfide by the addition of 1 mL of 10.4%(w/v) sodium hypochlorite solution. The proposed method is rapid (5 min per determination) and has good reproducibility (3.0%).     

Rapid determination of total mercury in treated waste water by cold vapor atomic absorption spectrometry in alkaline medium with sodium hypochlorite solution

Addition of a sodium hypochlorite solution (9.2% (w/v)) was effective to reduce a sulfide interference in determination of organic mercury, including methylmercury and phenylmercury, as well as a previously reported determination of inorganic mercury by cold vapor atomic absorption spectrometry (CVAAS) in an alkaline medium. Total mercury ranging from 0.17 to 33 μg L⁻¹ in 15 mL of sample solutions containing up to 200 mg L⁻¹ of sulfide can be determined without any serious interference by sulfide when 1 mL of the sodium hypochlorite solution was added after dilution of the sample solution to 25 mL. The proposed method was simple and rapid because no digestion processes were required for the determination of total mercury; the time required for the determination was only about 5 min. The proposed method was applicable to the analysis of treated waste water.     

Cold vapor atomic absorption spectrometric determination of mercury using sodium tetrahydroborate reduction and collection on gold

Summary Sodium tetrahydroborate(III) is equivalent to or better than tin(II) chloride as a reducing agent for mercury in cold vapor atomic absorption spectrometry using collection on gold. Concentrations of copper, silver, nickel, iodide, antimony, arsenic, bismuth and selenium typically found in water or waste water do not interfere. Prerequirements for satisfactory performance are that the gold is at a temperature below 100C during collection of mercury and that the gas from the reaction flask is washed with sodium hydroxide and dried with magnesium perchlorate. All determinations were carried out in 5 mol l^–1 hydrochloric acid and in the presence of 200 mg l^–1 iron(III). Detection limits (3) of 0.15 ng absolute, and of 15 ng l^–1 or 3 ng l^–1, using 10 ml or 50 ml solution, respectively, are obtained. The analytical curve is linear to 40 ng, and the relative standard deviation in the optimum working range is better than 2%.

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Kaltdampf-Atomabsorptionsspektrometrische Bestimmung von Quecksilber mit Reduktion durch Natrium-Tetrahydroborat und Sammeln auf Gold

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Dedicated to Prof Dr. W. Fresenius on the occasion of his 75th birthday     

On-line high-performance liquid-chromatographic separation and cold vapor atomic absorption spectrometric determination of methylmercury and inorganic mercury

A reversed-phase high-performance liquid chromatography (HPLC) method with cold vapor atomic absorption spectrometry (CV-AAS) detection is developed for mercury speciation. In this paper, the efficiency of tetrabutylammonium bromide reagent and sodium chloride in a methanol-water mixture as mobile phase is evaluated for HPLC separation of methylmercury and inorganic mercury coupled with on-line CV-AAS determination. Both mercury species are separated on a reversed-phase C(18) column. Several parameters (e.g. composition and flow-rate of mobile phase) are investigated for the optimization of HPLC separations. CV-AAS technique parameters are also studied for their effect on sensitivity (sodium borohydride and sodium hydroxide concentrations in the reducing agent, reducing agent flow-rate, length of the reduction coil and nitrogen flow-rate). Quantitative recoveries for both inorganic mercury and methylmercury are obtained from a spiked natural water sample.     

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.     

Routine,high-sensitivity,cold vapor atomic absorption spectrometric determination of total mercury in foods after low-temperature digestion

A cold vapor atomic absorption spectrometric method was developed for the subnanogram-per-gram determination of total Hg in a wide variety of foods. Foods were weighed into 50 mL polypropylene centrifuge tubes and dried without charring at 55 degrees C in a circulating oven. Samples were then digested at 58 degrees C with HNO3, HCl, and H2O2. After matrix modification with solutions of 2% Mg(NO3)2, 0.01% Triton X-100, and Cu(II) at 10 microg/mL, samples were analyzed by using a CeTAC Technologies M-6000A dedicated Hg analyzer. Based on a 2 g sample weight, the detection limit of the method over 12 batches averaged 0.30 ng/g wet weight and ranged from 0.03 to 0.6 ng/g. Recoveries of Hg added to 17 different foods, analyzed in a routine manner, averaged 97%, and individual recoveries ranged from 77 to 107%. Accuracy was confirmed by analysis of 7 biological reference materials from the National Research Council of Canada and the National Institute of Standards and Technology. Stabilization of low concentrations of Hg in solutions containing no sample was required to prevent loss of Hg from blanks. In a comparison of NaCl, potassium dichromate, and Au(II), chloride was much more effective for stabilization than the other two, and HCl was used for subsequent stabilization.     

Demethylation of methylmercury during inorganic mercury determination by the magos cold vapor atomic absorption technique

Previous animal experiments suggested that the Magos cold vapor atomic absorption spectroscopic (CVAAS) method might overestimate the concentrations of inorganic mercury (I-Hg) in the presence of methylmercury (MeHg). In the present study it is shown that this error is due to a fast degradation of MeHg during the formation of the analytical signal. For brain samples, about 5% of the total amount of MeHg in the reaction vessel is degraded to I-Hg. Speciation of Hg in aqueous solution of MeHg chloride, after purification with ionexchange chromatography using the Magos method, showed that about 9% was I-Hg. Analysis by NMR of MeHg chloride and MeHg hydroxide showed that less than 1% was in the form of I-Hg. The absolute magnitude of the error in the CVAAS method is dependent on the amounts of SnCl₂ and MeHg in the reaction vessel; however, the ratio of I-Hg to total (T-Hg) is shown to be independent of the amount of MeHg (25.5–255 ng as Hg) in the reaction vessel. A procedure for corrections is proposed, based on the results from these studies and empirical data from speciation analyses of brain tissue from MeHg-exposed rats and rabbits.     

Determination of mercury in carbon black by cold vapor atomic absorption spectrometry

Recently, a new color additive, D&C Black No. 2, a high-purity furnace black in the general category of carbon blacks, was listed as a color subject to batch certification by the U.S. Food and Drug Administration. A simple procedure was developed to determine mercury (Hg) in D&C Black No. 2, which is limited by specification to not more than 1 ppm Hg. The method uses partial acid digestion followed by cold vapor atomic absorption and was developed by modifying a method used for other color additives. The carbon black samples are treated with a mixture of nitric and hydrochloric acids and heated by microwave in sealed Teflon vessels. The resulting solutions, which are stable to Hg loss for at least 1 week, are diluted and analyzed for Hg using cold vapor atomic absorption spectrometry. Validation was performed by spiking carbon black samples with inorganic Hg (HgNO3) at levels from 0.1 to 1.5 microg/g, and by analyzing 2 standard reference materials. At the specification level of 1 ppm Hg (1 microg Hg/g), the 95% confidence interval was +/-0.01 ppm Hg (0.01 microg Hg/g). The method developed in this study gave good results for very difficult-to-analyze materials, such as coal standard reference materials and carbon black. By eliminating volatility and adsorption factors through the formation of HgCl4(-2) complexes, one can avoid using extremely hazardous acids such as HF and HClO4.     

Determination of mercury in gasoline by cold vapor atomic absorption spectrometry with direct reduction in microemulsion media

The determination of Hg in gasoline by cold vapor atomic absorption spectrometry, after direct aqueous NaBH₄ reduction in a three-component (microemulsion) medium, was investigated. Microemulsions were prepared by mixing gasoline with propan-1-ol and 50% v / v HNO₃ at a 20 : 15 : 1 volume ratio. A long-term homogeneous system was immediately formed this way. After reduction, the Hg vapor generated in a reaction flask was transported to an intermediate K₂Cr₂O₇/H₂SO₄ trap solution in order to avoid poisoning of the Au–Pt trap by the gasoline vapors. A second reduction step was then conducted and the generated Hg vapor transported to the Au–Pt trap, followed by thermal release of Hg⁰ and atomic absorption measurement. Purified N₂ was used as purge and transport gas. After multivariate optimization by central composite design calibration graphs showed coefficients of correlation of 0.9999 and a characteristic mass of 2 ng was obtained. Typical coefficients of variation of 5% and 6% were found for ten consecutive measurements at concentration levels of 1 and 8 μg L⁻¹ of Hg²⁺, respectively. The limit of detection was 0.10 μg L⁻¹ (0.14 μg kg⁻¹) in the original sample. A total measurement cycle took 11 min, permitting duplicate analysis of 3 samples per hour. The results obtained with the proposed procedure in the analysis of commercial gasoline samples were in agreement with those obtained by a comparative procedure. Gasoline samples of the Rio de Janeiro city have shown Hg concentrations below 0.27 μg L⁻¹.     

Study of interference in the flame atomic absorption spectrometric determination of lithium by using factorial design

The severe interference of a number of metallic ions found in brines, marine sediments and sea water in the determination of lithium is demonstrated. Calcium, iron and sodium significantly depressed the absorption signal on lithium in an air/acetylene flame. Aluminium, magnesium and strontium up to 1500, 1000 and 200 μg/mL, respectively, showed no interference in the determination of lithium under the same conditions. Potassium produced some suppression of the lithium signal at levels in excess of 1500 μg/mL. Experimental data were examined using the factorial design method. Interference was demonstrated in two synthetic samples (models of “brine” and “marine sediments” ) and natural marine sediment. It was possible to eliminate all interferences using a higher temperature (nitrous oxide/acetylene flame). In addition, by using the standard addition method the interference disappeared, which confirmed the interference as a proportional systematic error.     

Study of interference in the flame atomic absorption spectrometric determination of lithium by using factorial design

The severe interference of a number of metallic ions found in brines, marine sediments and sea water in the determination of lithium is demonstrated. Calcium, iron and sodium significantly depressed the absorption signal on lithium in an air/acetylene flame. Aluminium, magnesium and strontium up to 1500, 1000 and 200 μg/mL, respectively, showed no interference in the determination of lithium under the same conditions. Potassium produced some suppression of the lithium signal at levels in excess of 1500 μg/mL. Experimental data were examined using the factorial design method. Interference was demonstrated in two synthetic samples (models of “brine” and “marine sediments” ) and natural marine sediment. It was possible to eliminate all interferences using a higher temperature (nitrous oxide/acetylene flame). In addition, by using the standard addition method the interference disappeared, which confirmed the interference as a proportional systematic error. Received: 4 December 1998 / Revised: 3 March 1999 / Accepted: 6 March 1999     

Determination of mercury by continuous flow cold vapor atomic fluorescence spectrometry using micromolar concentration of sodium tetrahydroborate as reductant solution

Systematic experiments were conducted to evaluate and compare the analytical figures of merit of two reducing agents (SnCl2 and NaBH4) in a continuous flow cold vapor atomic fluorescence mercury analyzer. It was found that sodium tetrahydroborate can efficiently reduce Hg2+ in various environmental samples at a concentration as low as 10 microM (ca. 3.8 x 10(-5)% w/v). Most commonly encountered transition metals (Fe2+, Fe3+, Zn2+, Cu2+, Ni2+, Pb2+ and Cr3+) did not interfere with total Hg determination. No interference from hydride-forming elements (Se4+, Sb3+ and As3+) was observed. Interference caused by Mn2+ and Ag+ could be readily removed by dilution and by using appropriate modification of the reaction matrix. A higher concentration of NaBH4 (0.1 M) is stable for I month when stored in the NaOH matrix (0.2 M) and at low temperature (4 degrees C). A working solution of NaBH4 can be freshly prepared by dilution. With NaBH4, the whole continuous flow system is kept clean much more easily as no precipitate is formed, which in turn considerably reduces memory effects, simplifies analytical operation and reduces the chemical cost six-fold.     

Automated microwave digestion of certifiable color additives for determination of mercury by cold vapor atomic absorption spectrometry

A procedure using an automated microwave flow digestion technique was developed and validated for the digestion of samples of certifiable color additives before mercury determination by cold vapor atomic absorption spectrometry. Recovery studies were performed by spiking most of the color additives subject to batch certification by the U.S. Food and Drug Administration with inorganic mercury (HgNO3) and with organic mercury (CH3HgCl). Successful recoveries of 72-113% Hg added at the 1 microg/g level were obtained. A method detection limit of 0.2 microg Hg/g was estimated from a Hg-spiked FD&C Yellow No. 6 sample. At the specification level of 1 ppm Hg (1 microg Hg/g), the 95% confidence interval was +/- 0.2 ppm (0.2 microg Hg/g).     

On-line microwave sample pretreatment for the determination of mercury in blood by flow injection cold vapor atomic absorption spectrometry

A method for on-line treatment of whole blood in a microwave oven and determination of mercury by flow injection cold vapor atomic absorption spectrometry was developed. After dilution of the whole blood and addition of oxidant, all further treatment and measurement were performed automatically, on-line. Recoveries of five mercury compounds were complete. Good agreement between measured and recommended values of mercury in whole blood reference materials was obtained. Measured mercury values also agreed with results from other accepted methods. Sample throughput was about 45 measurements/hr. Detection limit (3s) in diluted sample was 0.1 μg/l corresponding to 1μg/l Hg in whole blood. The RSD value at 0.5 μg/l Hg in the diluted sample was 6–7% (11 measurements and 0.5 ml sample volume). Mercury concentrations between 1 and 150 μg/l in whole blood can be measured using this method. For three replicate measurements, 0.5 ml of whole blood is required.     

Annotation paper Interference by volatile nitrogen oxides in the determination of mercury by flow injection cold vapor atomic absorption spectrometry

The determination of mercury by the title method with sodium tetrahydroborate as reducing agent can be interfered with by volatile nitrogen oxides which inhibit the reduction of mercury by scavenging the reducing agent. The nitrogen oxides are formed as reduction products of nitric acid during sample decomposition. The interference effect was encountered in the determination of mercury in sewage sludge digests, and the main symptom was poor reproducibility of the shape of the mercury peak. The area of the mercury peak is more resistant to the interference than the peak height. The nitrogen oxide interference did not cause any systematic error in the mercury determination when calibration was done by standard addition. The interference can be easily remedied by purging the sample with argon.     

Comparative study of copper(II) and cadmium(II) salts as catalytic reagents in the determination of mercury by continuous-microflow cold vapour atomic absorption spectrometry

A continuous-microflow method with cold vapour atomic absorption spectrometric detection was used for the determination of mercury. A comparison of copper(II) and cadmium(II) salts as catalytic reagents is described in detail It was found that in the presence of at least 80 mg 1^?1 of copper(II) salt a similar signal was obtained for both inorganic mercury [mercury(II) chloride]and organic mercury [methylmercury(II) chloride]. With a cadmium(II) salt at least 100 mg 1^?1 were required.     

Speciation of mercury in soils and sediments by thermal evaporation and cold vapor atomic absorption

Evaporation studies of mercury in several chemical compounds, soils, and sediments with a high content of organic matter indicate that a quantitative release is possible at temperatures as low as 400°C. The desorption behaviour from a gold column is not influenced. Only from samples with a thermal prehistory, such as brown coal ash, did mercury evaporate at higher temperatures. Qualitative conclusions can be derived about the content of metallic mercury as well as mercury associated with organic matter or sulfide. A comparison of the analytical results obtained by using the evaporation technique or by dissolving using a mixture of conc. HCl and HNO₃ shows good agreement; the advantages of the evaporation technique are obvious at very low mercury concentrations.     

Speciation and simultaneous determination of mercury species in dolphin liver by liquid chromatography with on-line cold vapor atomic absorption spectrometry

Summary An interface for coupling liquid chromatography with atomic absorption spectrometry is described and fully evaluated. Inorganic, methyl and ethyl mercury are separated as cysteinato complexes by isocratic elution on a reversed-phase column. Protein bound mercury is released from dolphin liver homogenate by acid hydrolysis. Inorganic and methyl mercury are simultaneously determined by direct on-column injection of liver hydrolysate previously subjected to a simple centrifugation step. No sample clean-up, solvent extraction or chemical derivatization step is required. Detection limits are in the order of 200 ng/g of tissue. The method is highly selective for Hg species: no spurious peak was observed even with complex samples such as liver hydrolysate. A sampling rate of 12 samples/h was achieved.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday