The use of neutron activation analysis in gold prospecting in small-scale mining in Ghana

A set of rock and soil samples from Dome Beposo in the Amansie-West district of Ashanti Region of Ghana, suspected to contain gold, have been analyzed using instrumental neutron activation analysis (INAA) coupled with conventional counting techniques. The identification and quantification of the elements, gold, arsenic, mercury and antimony were done using 411.8 keV photopeak of ¹⁹⁸Au, 559.1 keV photopeak of ⁷⁶As, 77.3 keV photopeak of ¹⁹⁷Hg and 564.2 keV photopeak of ¹²²Sb. The precision and accuracy of the method were evaluated using standard reference materials. The precision and bias was found to be less than 6%. The first set of samples consists of ten rocks (GS), four of which retain moderate to quite high concentrations of gold, 0.27±0.01 mg/kg, 1.58±0.09 mg/kg, 7.51±0.44 mg/kg and 8.06±0.35 mg/kg, respectively. The second set comprises two soil samples taken from the upper and bottom layers of a gold exploration pit. Gold concentrations in upper (UL) and bottom (BL) layers are 0.06±0.002 mg/kg and 0.47±0.02 mg/kg, respectively. Arsenic was found in the soils as well as the rocks, and the levels ranged from 9.3±0.5 to 274±15.6 mg/kg. Mercury and antimony were found in the rocks only. Mercury levels in the rocks ranged between 0.11±0.004 and 9.67±0.42 mg/kg whilst antimony levels ranged from 0.21±0.01 to 6.88±0.38 mg/kg. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cupel assay of gold by an activation method

The difficulties of determining gold in rocks and ores are due to two causes: low gold concentrations in rocks (Clark 1 to 4·10⁻⁷%), and non-uniform distribution of gold in ores. A method is proposed which is based on neutron activation of the lead alloy obtained by cupel melting in the procedure of determining gold by cupel assay. Samples of 50 to 100 g are used for cupel melting. Such large samples guarantee their representativeness. Discs of 2 to 3 g are cut from the lead alloy block and activated in a neutron flux of 10¹¹ to 10¹³ n·cm⁻² sec⁻¹. The gold content is determined from the photopeak of¹⁹⁸Au using a standard for comparison. The sensitivity of the method is 0.02 g/metric ton, its accuracy at a gold content in the order of 1.0 g/metric ton is 10% relative. The method is distinguished by the fact that it is fast and requires little labour.     

Limit of detection for the determination of Pt in biological material by RNAA using electrolytic separation of gold

Neutron activation analysis based on the¹⁹⁹Au indicator for platinum requires the separation of gold at high radiochemical purity. The limit of detection is strongly affected by the presence of gold; with a gold content of 50 pg/g, irradiating for 5 days at 5·10¹³ n/cm²s is needed to achieve a limit of detection of approximately 30 pg/g. In this case the nuclear interference from gold will exceed the level of platinum by several orders of magnitude and has to be determined with exceedingly high precision. Preliminary results for SRM 1577 Bovine Liver with 95% yield gave consistent results for Au, but Pt could not be detected.     

Determination of gold by atomic absorption spectrometry after extraction into the non-desulphurized fraction of crude oil distillate

The extraction of gold from aqueous chloride solutions into non-desulphurized fractions of crude oil distillates, especially paraffin oil, is described. The fraction boiling at 150–220°C exhibited optimum properties. The extraction is tested for solutions containing chlorides, dissolved chlorine and 0.1–3 M hydrochloric acid. Nitric acid should be absent. The distribution coefficient of gold varies from 400 to 900. Extracts containing ? 0.3 g l^?1 gold are stable for at least 12 months. The organic extract is sprayed into a lean acetylene/air flame with measurement at 242.8 nm (background correction). The calibration graph has linear portions over the ranges 0–2.5 and 2.5–16 mg l^?1. The limit of detection is 0.03 mg l^?1 gold in the extract (0.001 mg l^?1 in the aqueous phase). The minimum measurable concentration for gold in auriferous rocks and ores is 0.018 g per ton with 25-g samples.     

Characterization of an epithermal irradiation facility

An epithermal energy neutron irradiation facility has been used to perform instrumental activation analysis for iodine, silicon, nickel, zirconium, uranium and thorium. The facility, which is adjacent to the fuel of the University of Virginia 2.0 MW pool reactor, consists of a dry sample region surrounded by a fixed cadmium shield. A boron nitride capsule can be used to hold the sample in the cadmium facility to further enhance the reduction of thermal neutron activation. The neutron fluence rate is 2.2×10¹⁶ n·m^–2·s^–1 for fission spectrum energy neutrons (measured with Ni(n,p)Co) and 8.2·10¹⁵ n·m^–2·s^–1 for resonance energy neutrons (measured with gold).Iodine has been measured at concentrations as low as 0.1 mg/kg with 3% counting statistics in powdered infant formula and 0.15 mg/kg with 5% statistics in liquid infant formula. Silicon has been measured at concentrations of 0.2% in biological samples with counting statistics between 5 and 10% and in coal and soil at concentrations greater than 4% with better than 1% statistics. Nickel has been measured in coal and soil at the 20 mg/kg level and higher with 6% statistics. Zirconium has been determined at 600 mg/kg and greater in ceramics with counting errors less than 3%. Uranium and thorium have been measured at the 10 mg/kg level with 3% counting statistics.     

Specific Mass and Energy-Storage Properties of Carbon Electrodes Based on NORIT DLC SUPRA 50 Activated Carbon

The effect of the carbon-material specific mass on the electrochemical parameters of electrodes for supercapacitors on neutral aqueous electrolytes is studied. It is shown that the highest specific capacitance of 11 F/g is observed for electrodes with the specific mass of 1 mg/cm². These electrodes are stable at the potential scan rate from 2 to 600 mV/s, in contrast to electrodes with the specific mass of 6 mg/cm². As the power increases, the decrease in the specific energy of the electrode with the mass of 1 mg/cm² is less pronounced as compared with the electrode with the mass of 6 mg/cm². The specific energy of the former electrode is 8 W h/kg for the specific power of 20000 W/kg, whereas for the specific energy of the latter electrode is 5 W h/kg for the specific power of 2000 W/kg.

     

Trace Detection of Mercury(II) Using Gold Ultra‐Microelectrode Arrays

The electroanalytical detection of trace mercury(II) at gold ultra‐microelectrode arrays is reported. The arrays consist of 256 gold microelectrodes of 5 μm in diameter in cubic arrangements which are separated from their nearest neighbor by 100 μm. The array was utilized in nitric acid using linear sweep voltammetry where a linear response from mercury additions over the range 10 μg L^?1?200 μg L^?1 (10^?8?10^?6 M) was observed with a sensitivity and detection limit of 0.11 nC/μg L^?1 and 3.2 μg L^?1 (16 nM) respectively from using a deposition time of 30 s at ?0.2 V (vs. SCE). This methodology was explored in 0.1 and 1 M chloride media over the mercury range 10 μg L^?1?200 μg L^?1 (5×10^?8?10^?6 M) where similar sensitivities of 0.087 nC/μg L^?1 and 0.078 nC/μg L^?1 were observed with an identical detection limit. The protocol is demonstrated to be useful for the determination of mercury for analysis of environmental water samples.     

Simultaneous Detection of Copper,Lead and Zinc on Tin Film/Gold Nanoparticles/Gold Microelectrode by Square Wave Stripping Voltammetry

In this work, three heavy metals (Cu(II), Pb(II) and Zn(II)) in wide potential window were simultaneously detected on tin film/gold nanoparticles/gold microelectrode (Sn/GNPs/gold microelectrode) by the method of square wave stripping voltammetry. The Sn/GNPs/gold microelectrode was fabricated by in situ plating of a Sn film on a gold nanoparticles (GNPs) modified gold microelectrode. The influence of hydrogen overflow on stripping of Zn(II) on the gold microelectrode was reduced by modification of GNPs, which made the stripping potential of target metals shift positively. The interference of sulfhydryl groups was reduced and the selectivity of the microelectrode was improved due to the addition of Sn in the detection solution. After accumulation at ?1.4 V for 300 s in acetate buffer solution (0.1 mol L^?1, pH 4.5), the Sn/GNPs/gold microelectrode revealed a good linear behavior in the examined concentration ranges from 5 to 500 µg L^?1 for Cu(II) and Pb(II), and from 10 to 500 µg L^?1 for Zn(II), with a limit of detection of 2 µg L^?1 for Cu(II), 3 µg L^?1 for Pb(II) and 5 µg L^?1 for Zn(II) (S/N=3). When compared with a Sb/GNPs/gold microelectrode and a Bi/GNPs/gold microelectrode, the Sn/GNPs/gold microelectrode showed the best stripping performance to Cu(II), Pb(II) and Zn(II). As a new type of environment‐friendly electrode, the Sn/GNPs/gold microelectrode has potential applications for detection of heavy metals.     

固相萃取-气相色谱-串联质谱法测定乳胶儿童用品中15种N-亚硝胺及其前体物的迁移量

建立了同时测定乳胶儿童用品中15种N-亚硝胺及其前体物迁移量的固相萃取-气相色谱-串联质谱(SPEGC-MS/MS)分析方法。以人工唾液作为迁移模拟物,以Chromabond Easy固相萃取柱(填料的主要成分是极性修饰的聚乙烯-二乙烯基苯共聚物)对迁移液中的N-亚硝胺分析物进行净化,采用HP-5 MS UI色谱柱分离,MS/MS在多反应监测模式下进行定性及定量分析。15种N-亚硝胺在5~2 000μg/L范围内呈良好的线性关系,相关系数均大于0.998;方法定量限(S/N=10)为0.625~12.50μg/kg,低于欧盟2 009/48/EC指令的限量要求。在低、中、高3个添加水平的回收率为53.8%~116.2%、52.7%~105.1%和49.5%~102.9%;日内精密度分别为1.3%~14.0%(n=6),日间精密度为1.6%~7.6%(n=4)。采用本方法对婴儿奶嘴样品和气球样品进行了测定,其中4件奶嘴和7件气球样品中检出亚硝胺及其前体物,奶嘴和气球中N-亚硝胺的总检出含量分别为0.049 9~0.126mg/kg和0.515~41.2 mg/kg;N-亚硝胺前体物总检出量分别为0.026 4~0.030 0 mg/kg和0.187~12.5mg/kg。     

Bestimmung von Gold in Geweben und Blutzellen durch Kombination von Kaltveraschung und flammenloser Atomabsorption in der Graphitrohrküvette

Zusammenfassung Goldpräparate werden seit langem in der Medizin zur Behandlung der chronischen Polyarthitis verwendet. Wirkungsweise und Metabolismus der Medikamente sind noch wenig erforscht. Die Goldbestimmung in Blutzellen und Geweben bei Patienten unter Goldtherapie kann Aufschluß über Eigenschaften und Wirkungen der Goldpräparate geben. Die Hauptschwierigkeiten bei der Bestimmung von Gold in Blutzellen und Geweben liegen in niedrigen Konzentrationen, limitierten Probenmengen und Matrixinterferenzen. Eine Methode zur Bestimmung von Gold in Lymphozyten, Granulozyten, Haut und Synovialgewebe wurde beschrieben, die die genannten Probleme löst und geringen Arbeitsaufwand bei der Probenvorbereitung erfordert. Blutzellen und Gewebe werden in einem Kaltveraschungsgerät unter Einwirkung von atomarem Sauerstoff trocken verascht, anschließend wird der Goldgehalt mit flammenloser Atomabsorption in der Graphitrohrküvette unter Anwendung der Standardadditionsmethode bestimmt. Kaltveraschte Blutzellen werden in kleinen Volumina einer Lösung von Rinderserumalbumin und Trishydroxymethylaminomethan gelöst. Auf diese Weise lassen sich Konzentrationen von 0,5 pg Au/10⁴ Zellen nachweisen. Die niedrigsten, in Haut und Synovialgewebe gefundenen Goldkonzentrationen liegen bei 2g/g Trockengewicht, die Nachweisgrenze liegt bei ca. 1/10 dieser Menge.

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Determination of gold in tissues and blood-cells by cold ashing combined with graphite furnace atomic absorption spectrophotometry

Summary Chrysotherapy is used for the treatment of chronic polyarthritis for a long time. Still the mode of action and the metabolism of gold compounds is scarcely understood. The determination of gold in blood-cells and tissues of gold-treated patients can elucidate the properties and effects of gold drugs. The main analytical problems with gold determination in bloodcells and tissues are low concentrations of gold, limited sample size and matrix interferences. A method for the determination of gold in lymphocytes, granulocytes, skin and synovial tissue, that overcomes this problems and requires minimal sample manipulation is described. Samples are dry ashed by the action of atomic oxygen in a low temperature ashing apparatus prior to gold quantitation by graphite furnace atomic absorption spectrophotometry using the method of standard additions. Cold ashed bloodcells are dissolved in small volumes of a solution, containing bovine serum albumin and trishydroxymethylaminomethane, thus as little as 0.5 pg Au/10⁴ cells could be detected. For skin and synovial tissue, the lowest gold concentrations found were about 2g/g dry weight, the detection limit lying about tenfold lower.

     

Measurement of Phosphorus in Metals by RNAA

An RNAA procedure has been developed for measurement of low-level phosphorus in metals. Samples are irradiated at a neutron flux of 2.7·10¹³ n·cm^–2·s^–1 then mixed with carrier and dissolved in acid. After chemical separation and purification of the phosphorus and gravimetric determination of carrier yield, ³²P is determined using a beta proportional counter. The detection limit for a 0.1 g sample irradiated for 30 minutes is 5 g/kg. The method has been used to determine 6.4±0.6 mg/kg phosphorus in SRM 2175 refractory alloy.     

Gastroprotection of Suaveolol, Isolated from <em>Hyptis suaveolens</em>, against Ethanol-Induced Gastric Lesions in Wistar Rats: Role of Prostaglandins, Nitric Oxide and Sulfhydryls

Hyptis suaveolens is a medicinal plant that is, according to traditional medicine, considered useful in the treatment of gastric ulcers. Although its gastroprotective activity was reported, the active compounds have not been identified. Therefore, the aim of the present study was to identify at least one active compound potentially responsible for the gastroprotective activity of H. suaveolens by using a bioassay guided study with an ethanol-induced gastric ulcer experimental model in rats. The results show that the hexane extract had protective activity (close to 70% when using doses between 10 and 100 mg/kg), and that the compound suaveolol, isolated from this extract, was one of the active gastroprotective agents. This is the first report about the gastroprotective activity of suaveolol. Rats treated with this compound at 3, 10, 30 and 100 mg/kg showed 12.6, 21.3, 39.6 and 70.2% gastroprotection respectively. The effect elicited by suaveolol (at 100 mg/kg) was attenuated by pretreatment with either N^G-nitro-L-arginine methyl ester (70 mg/kg, i.p.), a nitric oxide (NO) synthase inhibitor, indomethacin (10 mg/kg, s.c.), a blocker of prostaglandin synthesis, or N-ethylmaleimide (10 mg/kg, s.c.), a blocker of sulfhydryl groups. This suggests that the gastroprotective mechanism of action of this compound involves NO, prostaglandins and sulfhydryl groups.     

Ion-chromatographic determination of fluorine in texas lignite

Summary Samples of approximately 1.0 g were taken from three Texas lignite cores and mineralized in oxygen bombs. The residue was dissolved in distilled water to a total volume of 50 ml. The resulting solutions were analyzed for fluoride by ion chromatography and with a fluoride-sensitive electrode. The results obtained with these two methods were in good agreement. The pH of solutions prepared from mineralized lignite samples must be adjusted to fall into the range 4 to 12 before fluoride is determined by ion chromatography. The calibration curve is linear to 10 mg/l F^– (in solution). Twenty g/l of F^– (in solution) corresponding to 1 mg/kg of dry lignite can still be determined. Ion chromatography has higher sensitivity for fluoride than fluoride-sensitive electrodes and provides at the same time information about other anionic species. The fluorine concentrations in the three cores varied from 10 to 140 mg/kg (dry lignite). Layers of clay interspersed between the lignite seams had higher fluorine concentrations than the lignite.

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Ionen-chromatographische Bestimmung von Fluor in Braunkohle aus Texas

Zusammenfassung Braunkohlenproben von etwa 1 g wurden in der Sauerstoffbombe mineralisiert, der Rückstand in Wasser gelöst und die Lösung mit Hilfe der Ionen-Chromatographie und mit einer fluoridsensitiven Elektrode auf Fluorid untersucht. Die mit beiden Methoden erhaltenen Ergebnisse stimmten gut überein. Vor der Ionen-Chromatographie müssen die Lösungen der mineralisierten Proben auf pH 4–12 eingestellt werden. Die Eichkurve verläuft bis 10 mg/l F^– linear. Noch 20 g/l F^– (in Lösung), entsprechend 1 mg/kg trockener Braunkohle, können bestimmt werden. Die Ionen-Chromatographie weist eine höhere Empfindlichkeit auf als fluorid-sensitive Elektroden und bietet darüber hinaus Information über andere Anionen. Die untersuchten Fluoridkonzentrationen lagen zwischen 10 und 140 mg/kg (trockene Braunkohle). Zwischengelagerte Lehmschichten wiesen höhere Fluorgehalte auf.

     

Direct determination of gold and silver in rat plasma by graphite furnace atomic absorption spectrometry with Zeeman effect background correction and its application to the pharmacological properties of a mixture of copper,gold and silver salts

Methods for determining gold and silver in rat plasma without prior mineralization are presented. They permit concentrations above 1 μg 1^?1 to be measured. They were applied to 96 rat plasma samples with gold and silver contents up to 3 μg 1^?1. In addition, the anti-inflammatory properties of a solution containing gold, silver and copper at the mg 1^?1 level were tested and demonstrated.     

Coulometric stripping potentiometry for arsenic(III)

Calibration-free determination of As^III in the presence of As^V using coulometric stripping potentiometry is described. As^III, in the concentration range 0.01-2 mg/L, is quantitatively reduced to elemental arsenic and simultaneously dissolved in gold codeposited onto a glassy carbon substrate by electrolysis for 4 minutes at −0.50 V (vs. Ag/AgCl (0.01 MCl⁻)) in 12 μL samples containing 3 M hydrochloric acid and 10 mg/L gold(III). Selectivity between arsenic(III) and (V) is achieved by proper control of the deposition potential and by minimizing the gold(III) concentration and the time between addition of gold(III) and commencement of analysis.     

Quantitative goldbestimmung in filmmaterialien mittels flammenloser atomabsorption

A graphite rod electrothermal atomizer has been used for the AAS determination of traces of gold in hydrochloric and in hydrobromic acid solutions, and also after extraction into HBr-saturated methyl isobutyl ketone. Photographic film samples were decomposed first by enzyme action then by nitric acid/peroxide oxidation, and the gold was extracted into MIBK. For 10-μl aliquots of solution the 3s limits of detection were 3 × 10^?10g for aqueous solutions, 7 × 10^?10g for MIBK, and 7 × 10^?9 g/cm² for film.     

Studies of skeletal cadmium assay and toxicity

Flameless Atomic Absorption Spectrophotometry was found to be a sensitive (2·10^–12 g detection limit), accurate but destructive method for cadmium assay in bone biopsy samples (about 30 mg dry weight). The inductively coupled plasma emission technique was poorer in sensitivity (1.2·10^–9 g) and is also a destructive method. Activation Analysis is still less sensitive (2·10^–8 g detection limit) but a nondestructive one. Cadmium was found to accumulate in bone of rats fed, for 5 weeks, 0, 50, and 100 mg Cd/l in drinking water and the bone concentrations were 0.16, 1.09, and 2.6 mg Cd/kg bone (dry wt). Histological examination of the bones showed that cadmium induced increased osteoid surface in the bone with no evidence of accompanying kidney damage. This suggests a primary effect of cadmium on bone rather than secondary effect due to kidney damage.     

Spectrophotometric determination of gold by reaction with molybdate and nile blue in the presence of PVA

A spectrophotometric method for the determination of gold has been developed, based on the reaction of gold(III) with molybdate and nile blue (NB) to form an ion-association complex in the presence of poly(vinyl alcohol). The molar absorptivity at 595 nm is 2.71 × 10⁵ l mol^–1 cm^–1. Beer's law is obeyed over the range 0–16 g of gold per 25 ml. The relative standard deviation evaluated from seven independent determinations of 0.4 g/ml of gold is 2.6%. The limit of detection is 0.011 g/ml. The molar ratio of Au to NB in the complex is established to be 1 2. Over 30 foreign ions were tested for interference; Pt(IV), Sb(III), W(VI) and SiO ₃ ^2– interfered and had to be separated from gold on polyurethane foam. The method can be applied to the spectrophotometric determination of trace amounts of gold in powdered carbon and some ores.     

Ultratrace determination of platinum in biological materials via neutron activation and radiochemical separation

A neutron activation analysis scheme based upon a radiochemical separation of the activation products has been developed. The method utilizes the inherent sensitivity of the activation reaction¹⁹⁸Pt(n, γ)¹⁹⁹Pt and counting of the daughter nuclide¹⁹⁹Au. This nuclide is radiochemically separated from interfering activities by homogeneous precipitation as elemental gold. The remaining interference of the secondary reaction¹⁹⁷Au(n,γ)¹⁹⁸ Au(n,γ)¹⁹⁹Au from gold in the samples is quantitatively assessed and corrected. During this process accurate gold concentrations in the samples are obtained at ultratrace levels. The analysis scheme is applied to gold and platinum determinations in biological Standard Reference Materials and human liver specimens. Gold and platinum are determined at concentrations of 5·10^?11 g/g, and at higher levels.     

Simultaneous determination of mercury(II), copper(II) and bismuth(III) in urine by flow constant-current stripping analysis with a gold fibre electrode

Urine samples are treated with concentrated nitric acid and potassium permanganate ar 70°C for 10 min prior to injection. The flow electrode system consists of a 10-μm diameter gold fibre working electrode, a glassy carbon reference electrode and a platinum counter electrode. In the fully automated constant-current stripping procedure, the gold fibre is first covered with a fresh gold film after which the sample is electrolyzed for 1 min prior to stripping in 0.1 M hydrochloric acid with a current of 0.1μA. The procedure is repeated on a spiked sample after which the sample analyte concentrations are evaluated and presented digitally and graphically on a printer/plotter. The results obtained for bismuth, copper and mercury in a urine reference sample were 36.9, 39.7 and 47.7 μg l^?1 with standard deviations (n=10) of 3.2, 4.2 and 2.1, respectively. The certified values for copper and mercury were 45 and 51 μg l^?1; no certified value was available for bismuth.