Determination of total mercury in coal fly ash by gold amalgamation cold vapour atomic absorption spectrometry

A method for the determination of total mercury in coal fly ash by gold amalgamation cold vapour atomic absorption spectrometry (CV-AAS) was optimized. Most of the experiments were performed on NBS SRM 1633a Coal Fly Ash with a certified value of 160 ± 10 ng Hg g^?1. The main attention was focused on the decomposition of the sample. The efficacy of pressure decompositions in closed silica and sealed Pyrex tubes using various combinations of acids (HNO₃, HCl, HClO₄) was compared with oxidative combustion of the coal fly ash. Notwithstanding the incomplete mineralization of the sample in sealed tubes, the results obtained showed good agreement with the certified value and results obtained by neutron activation analysis (NAA), which suggests that mercury is quantitatively released from the sample into solution. Lower results were obtained using decomposition in closed (but not hermetically sealed) silica tubes owing to losses of mercury by volatilization during decomposition. Interferences from some metal ions (nickel, lead, copper, silver, palladium, zinc and antimony) were also examined. The results showed a serious depression of the mercury signal only when gold, palladium and platinum were present at higher concentrations, which never or very seldom occur in fly ash matrices, and therefore do not represent a limitation of the method.     

Utilization of pneumatic carrier facility of Dhruva reactor for trace element determination by neutron activation analysis

The pneumatic carrier facility (PCF) of Dhruva reactor is being extensively used for neutron activation analysis (NAA) studies pertaining to research work as well as routine sample analysis. It is useful for the determination of trace elements using short and medium half-lives radioisotopes produced in neutron activation with available higher neutron flux (~5 × 10¹³ cm^?1 s^?1). Solid samples placed in high density polypropylene capsule, are irradiated for 1 min duration and radioactive assay is carried out by high resolution gamma ray spectrometry. Design aspects of PCF and various applications to samples of diverse matrices using NAA are presented.     

Determination of concentration of iodine in grass and cow milk by NAA methods using reactor neutrons

Instrumental and preconcentration methods of neutron activation analysis (NAA) have been standardized for the determination of concentration of iodine in grass and cow milk samples, respectively. To study the transfer of iodine from grass to milk, known quantity of grass spiked with potassium iodide solution was fed to a cow. The spiked grass samples and milk samples, obtained from the cow after the ingestion of spiked grass, were collected. Iodine was separated from the milk samples chemically using Dowex 1X8 anion exchange resin. Spiked grass and ion exchange resin samples were neutron irradiated and radioactive assay was carried out using a 45?% relative efficiency HPGe detector coupled to an 8k channel analyzer. Iodine concentrations in spiked grass samples were found to be in the range of 1,487?C2,002?mg?kg^?1. Concentration of iodine in milk after 12?h of feeding the cow with spiked grass was 871?±?56???g?L^?1 which was reduced to 334?±?32???g?L^?1 after 48?h.     

Arsenic speciation in water and biota samples at trace levels by ion chromatography inductively coupled plasma-mass spectrometry

A sensitive, reliable, simple and rapid analytical method was developed for the determination of arsenite [As(III)], arsenate [As(V)] and arsenobetaine (AsB) species using ion chromatography combined with inductively coupled plasma-mass spectrometry (IC-ICP-MS). Inorganic and organic arsenic species were separated with an anion exchange column (Dionex AS9) and a 50 mM sodium bicarbonate mobile phase (pH 10) at a flow rate of 1.0 mL min^?1. %RSD values were found to be lower than 5.1% for all arsenic species. The limits of detection (LOD) obtained for As(III), As(V) and AsB were 16.5 ng L^?1, 14.1 ng L^?1 and 6.2 ng L^?1, respectively. The developed analytical method was tested using AsB certified reference material (NMIJ CRM 7901-a), and spring water certified reference material (UME CRM 1201) for accuracy check. This method was applied for the quantitative determination of arsenic species in different water samples and chicken samples as a solid matrix.     

Total and inorganic mercury determination in fish tissue by flow injection cold vapour atomic fluorescence spectrometry

A simple and reliable method for Hg determination in fish samples has been developed. Lyophilised fish tissue samples were extracted in a 25% (w/v) tetramethylammonium hydroxide (TMAH) solution; the extracts were then analysed by FI-CVAFS. This method can be used to determine total and inorganic Hg, using the same FI manifold. For total Hg determination, a 0.1% (w/v) KMnO₄ solution was added to the FI manifold at the sample zone, followed by the addition of a 0.5% (w/v) SnCl₂ solution, whereas inorganic Hg was determined by adding a 0.1% (w/v) L-cysteine solution followed by a 1.0% (w/v) SnCl₂ solution to the FI system. The organic fraction was determined as the difference between total and inorganic Hg. Sample preparation, reagent consumption and parameters that can influence the FI-CVAFS performance were also evaluated. The limit of detection for this method is 3.7 ng g^?1 for total Hg and 4.3 ng g^?1 for inorganic Hg. The relative standard deviation for a 1.0 µg L^?1 CH₃Hg standard solution (n = 20) was 1.1%, and 1.3% for a 1.0 µg L^–1 Hg²⁺ standard solution (n = 20). Accuracy was assessed by the analysis of Certified Reference Material (dogfish: DORM-2, NRCC). Recoveries of 99.1% for total Hg and 93.9% inorganic Hg were obtained. Mercury losses were not observed when sample solutions were re-analysed after a seven day period of storage at 4°C.     

Robust microwave-assisted extraction protocol for determination of total mercury and methylmercury in fish tissues

A rapid and efficient closed vessel microwave-assisted extraction (MAE) method based on acidic leaching was developed and optimized for the extraction of total mercury (Hg), inorganic mercury (Hg²⁺) and methylmercury (CH₃Hg⁺) from fish tissues. The quantitative extraction of total Hg and mercury species from biological samples was achieved by using 5 mol L⁻¹ HCl and 0.25 mol L⁻¹ NaCl during 10 min at 60 °C. Total Hg content was determined using inductively coupled plasma mass spectrometry (ICP-MS). Mercury species were measured by liquid chromatography hyphenated with inductively coupled plasma mass spectrometry (LC-ICP-MS). The method was validated using biological certified reference materials ERM-CE464, DOLT-3, and NIST SRM-1946. The analytical results were in good agreement with the certified reference values of total Hg and CH₃Hg⁺ at a 95% confidence level. Further, accuracy validation using speciated isotope-dilution mass spectrometry (SIDMS, as described in the EPA Method 6800) was carried out. SIDMS was also applied to study and correct for unwanted species transformation reactions during and/or after sample preparation steps. For the studied reference materials, no statistically significant transformation between mercury species was observed during the extraction and determination procedures. The proposed method was successfully applied to fish tissues with good agreement between SIDMS results and external calibration (EC) results. Interspecies transformations in fish tissues were slightly higher than certified reference materials due to differences in matrix composition. Depending on the type of fish tissue, up to 10.24% of Hg²⁺ was methylated and up to 1.75% of CH₃Hg⁺ was demethylated to Hg²⁺.     

Determination of Inorganic and Organic Thiophosphates with Ion-Selective Membrane Electrodes

Abstract

The conditions for the determination of sodium thiophosphate and sodium S-(2-amino-ethyl)-thiophos-phate in the presence of phosphate ion using ion-selective membrane electrodes are described. Both thiophosphates (inorganic and organic) are hydrolyzed in acidic medium. The phosphate ion is determined with Pb(II) using a Pb²⁺ – selective membrane electrode.

Cysteamine is determined by potentiometric titration with Hg(I1) using a Ag⁺/S^2? – crystal membrane electrode or by direct potentiometry with a Cu²⁺ selective membrane electrode. The results were verified by the iodination method.     

Determination of inorganic and methylmercury in fish by cold vapor atomic absorption spectrometry and inductively coupled plasma atomic emission spectrometry

Simple and rapid analytical procedures for the determination of Hg²⁺ and methylmercury in fish were proposed after careful optimization of chemical and instrumental parameters for Hg measurement by cold vapor (CV)/hydride generation (HG) atomic absorption spectrometry (AAS) and CV/HG inductively coupled plasma atomic emission spectrometry (ICP-AES). Quantitative extraction of Hg species avoiding any inter-species conversion was achieved by fast microwave assisted solubilization of fish tissue with relatively low amount of tetramethylammonium hydroxide (TMAH) or 6 mol L^− 1 HCl. After careful optimization of chemical parameters selective determination of Hg²⁺ in the presence of excess of methylmercury is attained by using continuous flow CV AAS, 1% m/V SnCl₂ as reductant and 0.1 mol L^− 1 HCl as reaction medium. Simple calibration curve prepared with aqueous standard of Hg²⁺ is recommended for its quantification. Both Hg²⁺ and methylmercury could be determined simultaneously with equal sensitivity by CV/HG ICP-AES directly in the diluted TMAH solution obtained after extraction with 1% m/V NaBH₄ as reductant. Quantification of the sum of Hg²⁺ and methylmercury against calibration curve prepared with aqueous standard of methylmercury is suggested. It should be mentioned that batch hydride generation system with quartz tube heated in air/acetylene flame could also be used for simultaneous determination of both Hg species in fish extracts, with standard additions calibration. The validity of the developed analytical procedures for selective determination of Hg²⁺ and methylmercury (by difference between the total Hg and Hg²⁺) is confirmed by the analyses of certified reference material DOLT-1 and reference material IMEP-20. Very close agreement between certified values and analytical results was found.     

Determination of mercury and methylmercury in hair samples by neutron activation

Mercury and methylmercury in hair samples were determined by neutron activation analysis. Samples were digested in 10M NaOH, and methylmercury was then isolated by solvent extraction with toluene. The isolated methylmercury was then absorbed onto cysteine paper. The dried cysteine paper was activated for six hours in a TRIGA reactor and methylmercury was analysed via 279.2 keV of²⁰³Hg. Methylmercury and total mercury in some standard reference materials were also analysed, and the results were in good agreement with those reported in the literature. Results for hair samples showed that the methylmercury concentration ranged 14–40% of the total mercury. Gas chromatogram showed that methylmercury was only present in the samples analysed. In samples where methylmercury and other organic mercury are presented, the NAA method is good for the determination of the total organic mercury only.     

Oxidation processes at mercury electrodes for tetraphenyllead and related compounds in dichloromethane

Two oxidation waves are observed at mercury electrodes for tetraphenyllead in dichloromethane. The mechanisms of the oxidation processes have been investigated by dc and differential pulse polarography. The first wave is a broad two-electron step and represents the summation of a number of processes related to mercury exchange and halide abstraction. The exchange reactions are as follows: 2 Φ₄Pb + Hg→2Φ₃Pb⁺ + Φ₂Hg+2e^? 2 Φ₃Pb⁺ + Hg→2Φ₂Pb²⁺ + Φ₂Hg+2e^? Dichloroethane and HgCl₂ are identified as products of controlled potential electrolysis experiments as well as Φ₂Hg and Φ₂PbCl₂ implying that the coordinatively unsaturated Φ₃Pb⁺ and/or Φ₂Pb²⁺ react with the solvent dichloromethane and abstract chloride. The second oxidation process is the two electron step. Φ₂Hg+Hg→2 ΦHg⁺ + 2e^?Tetraalkyllead compounds (tetramethyl, tetraethyl, tetrabutyl) also give rise to related electrode processes at mercury electrodes and polarographic techniques may form the basis of a method for their analytical determination if separated chromatographically prior to detection.     

Determination of mercurial species in fish by inductively coupled plasma mass spectrometry with anion exchange chromatographic separation

This work demonstrated the feasibility of mercury speciation analysis by anion exchange chromatographic separation with inductively coupled plasma mass spectrometry detection. For the first time, by complexing with the mobile phase containing 3-mercapto-1-propanesulfonate into negatively charged complexes, fast separation of inorganic mercury (Hg²⁺), monomethylmercury (MeHg), ethylmercury (EtHg) and phenylmercury (PhHg) was achieved within 5 min on a 12.5-mm strong anion exchange column. The detection limits for Hg²⁺, MeHg, EtHg and PhHg were 0.008, 0.024, 0.029 and 0.034 μg L⁻¹, respectively. The relative standard deviations of peak height and peak area (5.0 μg L⁻¹ for each Hg species) were all below 3%. The determined contents of Hg²⁺, MeHg and total Hg in a certified reference material of fish tissue by the proposed method were in good accordance with the certified values with satisfactory recoveries. The relative errors for determining MeHg and total mercury were −2.4% and −1.2%, respectively, with an acceptable range for spike recoveries of 94–101%. Mercury speciation in 11 fish samples were then analyzed after the pretreated procedure. The mercury contents in all fish samples analyzed were found compliant with the criteria of the National Standards of China.     

New Developments in Activation Analysis for Material and Environmental Sciences

Activation analysis in general and mainly reactor neutron activation analysis (NAA) has been used extensively for measuring trace elements in high purity materials, particularly semiconductor materials. The advantages of NAA in determination of trace elements differ from one semiconductor material to another. For all of them the inherent properties of activation analysis especially those of non contamination with the reagents, low blanks and high sensitivity are the reasons for the choice of NAA as the main analytical procedure. These inherent properties are essential for analysis of high-purity materials where concentrations of ppb's and sub ppb's have to be measured. NAA is specially suitable for the determination of trace elements in silicon due to the very short lived very low activity induced by neutron reaction in silicon. This enables easy instrumental (i.e. without chemical separations) determination of trace elements in silicon. In the HFR reactor at Peten, Netherlands, a special facility was constructed for irradiation of silicon samples of Philips, in which silicon wafers of up to 15 cm diameter can be irradiated with 4 × 10¹³n. cm^?2. sec^?1 and the irradiation is done for 72–96 hours. using large Ge(Li) detectors (100 to 150cc) and long counting time (8–16 hours) they measured 22 elements in concentrations below ppb and 10 others between ppb and 300 ppm. Trace elements in germanium have been determined both instrumentally after very long decay time (100 days) or after short decay time removing the activities from the matrix by chemical separation. Trace elements in GaAs are determined only after chemical separtion. Several other semiconductor material such as Sc, Te, GaP and CuInS₂ were also determined by NAA. Some trace elements cannot be determined by neutron activation. Carbon, nitrogen and oxygen are determined by activation with protons, alphas or ³He particles. Boron and hydrogen are determined by prompt emission induced by charged particle activation, which gives not only the total concentration but also the depth profile. Carbon, nitrogen, oxygen and phosphorus were also determined by prompt proton activation analysis. The environmental samples studied by activation analysis can be divided into three categories: atmospheric aerosols, water samples and solid wastes. NAA of atmospheric aerosols have been used for their posible toxicological hazards, their source identification and for studies of atmospheric transport processes.     

Hydride generation atomic absorption spectrometry for the quantification of germanium in iron meteorites

A simple and inexpensive hydride generation atomic absorption spectrometric procedure was developed for the quantification of germanium in iron meteorites. The final procedure involved dissolving the meteorite in nitric acid, dilution with water, addition of citrate to buffer the solution and complex the iron and liberation of germanium hydride with sodium tetrahydroborate. The hydride was collected in a liquid air trap and fed into a nitrogen-hydrogen-air-entrained flame. The limit of detection (2σ) was 0.03 μg g^?1 in the original meteorite and the r.s.d, was 3.9% for ten replicate analyses of the Toluca meteorite. The germanium content of this meteorite was 246 αg^?1, the same as that obtained by neutron activation analyses (NAA). Analyses of nine iron meteorites afforded values in agreement with those previously obtained by NAA.     

Solid-phase extraction of Hg(II) on creatine modified activated carbon and determination by ICP-OES in water samples

A new sorbent was successfully prepared by immobilizing creatine on activated carbon and then used for separation/preconcentration of trace Hg(II) prior to detection by inductively coupled plasma optical emission spectrometry (ICP-OES). Experimental conditions including pH, sample flow rate and volume, eluting variables and tolerance limit of interfering ions were evaluated and established. At pH 1.0 and flow rate of 2.5?mL?min^?1, Hg(II) was adsorbed quantitatively on the column, then quantitatively eluted by 2.0?mL 0.1?mol?L^?1 nitric acid solution; other transition metal ions did not interfere with the determination of Hg(II). An enrichment factor of 100 was obtained for Hg(II). The maximum adsorption capacity was 49.5?mg?g^?1. Under the optimal conditions, the value of the detection limit (3σ) was 0.06?ng?mL^?1, and the relative standard deviation (RSD) calculated was lower than 3.0% (n?=?8). The methodology was validated by analyzing certified reference materials and successfully applied to the determination of trace Hg(II) in natural water samples with satisfactory results.     

Challenges and successes in the use of neutron activation analysis procedures for value assignment of animal serum and bovine liver Standard Reference Materials

Analyses for value assignment in the renewal Standard Reference Materials^® SRM 1598a Animal Serum and SRM 1577c Bovine Liver included extensive characterization by neutron activation analysis (NAA). Conventional instrumental NAA procedures were complemented by pre-irradiation chemical separations for the determination of Al, V, Mn, and Cu, radiochemical separations for the determination of Ag, As, Cd, Cr, Cu, Mo, Sb, and Se, and the use of (anti-) coincidence gamma-ray spectrometry systems for the instrumental determination of Ag, Cr, and Hg. The previous materials, SRMs 1598, 1577, and 1577b, were analyzed together with the new materials for quality control.     

Critical comparison of two standard digestion procedures for the determination of total mercury in natural water samples by cold vapour atomic absorption spectrometry

Two pretreatment procedures for total mercury determinations in natural water samples were compared. The first, the Swedish Standard method (DP1), involves digestion of water in the presence of concentrated nitric acid at 120°C and under pressure for 30 min. In the West German Standard method (DP2), small volumes of nitric and sulphuric acids, permanganate and peroxodisulphate are added to the sample, and digestion proceeded at 50°C in an ultrasonic bath. Mercury was determined after both digestion procedures using a modified cold vapour atomic absorption spectrometric method, in which mercury generated on addition of a reducing agent is collected and subsequently atomized in a platinum-lined graphite furnace. The efficacy of the two digestion procedures was tested using various standard organic mercury compounds and it was found that only DP2 provided quantitative recoveries. Purification of the reagents required by DP2 was achieved using a mercury-selective ion-exchange resin, Chelite S, resulting in blank levels below 1.5 ng Hg l^?1. Both methods were applied to the determination of total mercury in an unpolluted marsh water sample, giving 2.0 ng Hg l^?1 (DP1) and 2.7 ng Hg l^?1 (DP2). The West German Standard digestion procedure (DP2) is recommended for the determination of total mercury in natural water samples.     

Nonextractive Trace Level Simultaneous Determination of Mercury(II) and Zinc(II) in Environmental Samples with 2‐(5‐Bromo‐2‐pyridylazo)‐5‐diethylaminophenol and Cetylpyridinium Chloride

Abstract

A simple, rapid, selective, and sensitive method for the derivative spectrophotometric determination of Hg(II) and its simultaneous determination in the presence of Zn(II) using 2‐(5‐bromo‐2‐pyridylazo)‐5‐diethylaminophenol in the presence of cetylpyridinium chloride, a cationic surfactant, has been developed. The molar absorption coefficient and analytical sensitivity of the 1∶1 Hg(II) complex at 558 nm (λ_max) are 5.78×10⁴ L mol^?1 cm^?1 and 0.67 ng mL^?1, respectively. The detection limit of Hg(II) is 1.40×10^?2 ng mL^?1, and Beer's law is valid in the concentration range 0.05–2.40 µg mL^?1. Overlapping spectral profiles of Hg(II) and Zn(II) complexes in zero‐order mode interfere in their simultaneous determination. However, 0.10–2.00 µg mL^?1 of Hg(II) and 0.065–0.650 µg mL^?1 of Zn(II), when present together, can be simultaneously determined at zero cross point of the derivative spectrum, without any prior separation. The relative standard deviation for six replicate measurements of solutions containing 0.134 µg mL^?1 of Hg(II) and 0.620 µg mL^?1 of Zn(II) is 1.72 and 1.47%, respectively. The proposed method has successfully been evaluated for trace level simultaneous determination of Hg(II) and Zn(II) in environmental samples.     

Simultaneous determination of inorganic As(III), As(V), Sb(III), Sb(V), and Se(IV) species in natural waters by APDC/MIBK-NAA

A solvent extraction preconcentration as well as separation method involving ammonium pyrrolinedithiocarbamate (APDC) and 4-methyl-2-pentanone (MIBK) in conjunction with neutron activation analysis (NAA) was developed for the simultaneous measurement of low levels of inorganic arsenic, antimony and selenium species in natural waters. Several critical factors affecting the APDC/MIBK-NAA method were studied in detail including the selection of chelating agent, solvent, aqueous pH for the extraction of six species as well as a few organoarsenic species as representatives for organic species, the stability of the complexes in organic phase, phase volume ratios for extraction and back-extraction steps, and the reduction of the species from higher to lower oxidation state. The detection limits for arsenic, antimony and selenium were found to be as low as 0.026, 0.010 and 0.12 μg L^?1, respectively. Trace amounts of As(III), As(V), Sb(III), Sb(V), and Se(IV) in different types of natural water sample and two water certified reference materials were measured using the APDC/MIBK-NAA method.     

Voltammetric Quantification of Zn and Cu,Together with Hg and Pb,Based on a Gold Microwire Electrode,in a Wider Spectrum of Surface Waters

The simultaneous determination of Zn and Cu by anodic stripping voltammetry (ASV) is prone to errors due to the formation of Cu‐Zn intermetallic compounds. The main aim of this work was to study the possibility of simultaneous determination of Zn and Cu, together with Hg and Pb, using a mercury‐free solid gold microwire electrode. The multi‐element detection was carried out by differential pulse anodic stripping voltammetry (DPASV), in a chloride medium (0.5 M NaCl) under moderate acid conditions (HCl 1.0 mM) in the presence of oxygen, where the gold microwire electrode was used as stationary or vibrating working electrode during the deposition step. Under these conditions, no formation of Cu‐Zn intermetallic compounds were found for concentrations usually determined in surface waters. In addition, quantification of Zn and Cu, together with Hg and Pb, can be performed in a wide range of concentrations (about two orders of magnitude) using the same sample, in a very short period of time. The detection limits for Cu, Hg, Pb and Zn, using a vibrating electrode and 30 s of deposition time, were 0.2 µg L^?1 for Hg, 0.3 µg L^?1 for Pb and 0.4 µg L^?1 for Zn and Cu, respectively. The proposed DPASV methods were successfully applied to the determination of Cu, Hg, Pb, and Zn in a certified reference fresh water, river, tap and coastal sea waters. These results proved the applicability and versatility of the proposed methods for the analysis of different water matrices and showed that a gold microwire electrode is a suitable choice to determine simultaneously Zn and Cu.     

Determination of 135Cs in nuclear power plant wastes by ICP-MS and k 0-NAA

A radiochemical method for the determination of ¹³⁵Cs in radioactive wastes has been adopted/developed. For the separation of cesium from other elements ammonium-molybdophosphate precipitation and cation exchange chromatography were used. The chemical yield of the method was about 60–100 %. ¹³⁵Cs was measured by two methods. In neutron activation analysis (NAA), Cs was irradiated with reactor neutrons. ¹³⁶Cs was detected by gamma spectrometry, wherefrom the activity/mass of ¹³⁵Cs was calculated according to the k ₀-standardization technique. The Cs containing fractions were measured by inductive coupled plasma mass spectrometry, as well. NAA and ICP-MS techniques were comparatively evaluated and a good agreement between the results was found. The activity concentration of ¹³⁵Cs in a couple of waste samples originating from VVER-440 type nuclear reactors was in the range of 1–5 Bq L^?1 (20–120 ng L^?1) while ¹³⁷Cs activity concentrations varied between 0.1 and 1 MBq L^?1.