Solid-liquid extraction as a preconcentration technique in trace element analysis Extraction of trace impurities from metal chlorides

Microgram quantities of iron, cobalt, copper, zinc and cadmium are extracted with various aqueous, organic and mixed solvents from chlorides of sodium, potassium, nickel, cadmium, barium and lead prepared by evaporation of aqueous sample solutions. An ultrasonic field accelerates the extraction, and satisfactory trace recoveries and separation factors are achieved in several systems within a reasonable time. The application to a polarographic determination and a two-stage separation technique are also described.     

Further investigation on the solid-liquid extraction of trace impurities from basic bismuth nitrate

Summary The effect of heat treatment of basic bismuth nitrate on the extraction ofg quantities of iron, cobalt and zinc with a 0.07M phosphoric acid-0.12M hydrochloric acid mixture or water has been studied to optimize the extraction procedure as a preconcentration technique in trace element analysis.

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Zusammenfassung Der Effekt der Hitzebehandlung von basischem Wismutnitrat auf die Extraktion von Mikrogrammengen Eisen, Kobalt und Zink mit einer Mischung aus 0,07-m Phosphorsäure und 0,12-m Salzsäure oder auch mit Wasser wurde untersucht, um den Extraktionsvorgang zwecks Anreicherung in der Spurenanalyse zu verbessern.

     

Separation of trace impurities of131I from99Mo obtained by extraction from fission products of uranium

The radioisotope⁹⁹Mo was separated from a mixture of²³⁵U fission products in the presence of Hg²⁺ by sorption on a chromatographic column filled with Al₂O₃ and elution with 1M NH₄OH. Trace impurities of¹³¹I in the molybdenum fraction were eliminated by selective sorption on silver iodide or by repeated sorption of⁹⁹Mo on Al₂O₃.     

Flame AAS determination of dopants and trace metal impurities in single crystals of potassium titanylphosphate

A flame AAS method is used for the determination of dopants and impurities in potassium titanylphosphate (KTP) single crystals. Sample digestion using sulphuric acid and hydrofluoric acid is proposed as being the most appropriate procedure. The effect of major and minor components in the sample solution on the analytical signal is studied. The content of the dopants Cr, Mn and Ni (at a level of about 1 mg g(-1)) as well as the content of the impurities Fe, Na, Mg, W and Al (from 4 mug g(-1), depending on the trace metal) in the KTP single crystals is determined. The precision of the method is characterized by a relative standard deviation of 3-10%. The accuracy is checked by comparison with ICP-AES data for the trace element content in the KTP single crystals.     

Elemental characterization of impurities at trace and ultra-trace levels in metallurgical lead samples by INAA

The purity of several economically important metals is routinely verified by a reference material. Further, it is essential to provide a means of maintaining the consistency between laboratories and on disseminating the accurate value.This work, developed within an activity of certification promoted by EURATOM, reports the results on impurity determination (Ag, As, Cd, Ni, Sb, Sn, Te and Zn) at trace (µg g^{− 1}) and ultra-trace (ng g^{− 1}) levels in three metallurgical lead samples (99.99% of purity). Among the different analytical techniques available for the characterization, the use of a nuclear technique, i.e. Instrumental Nuclear Activation Analysis, has allowed to reach high sensitivity and to obtain accurate values for these elements.The irradiations were performed in the rotating rack (Lazy Susan) and in the central channel of the Triga Mark II reactor reaching a total integrated flux of 9.36 × 10¹⁷ n cm^{− 2} and 2 × 10¹⁹ n cm^{− 2}, respectively.The results about the determination of elements such as Ni, Sn, Te and Zn present at ultra-trace levels (ng/g), are showed and discussed. This task is very interesting for the radio-analytical and methodological implications: in fact, for analyzing them a radiochemical separation is involved and an anti-Compton gamma spectrometer is necessary due to their very low levels.     

Determination of trace level impurities in uranium compounds by ICP-AES after organic extraction

The determination was studied of Al, B, Be, Cd, Ca, Co, Cu, Mg, Mn, Mo, Pb, Si, Sn, V, Cr, Ni, and Fe as trace level impurities in uranium compounds by ICP-AES after extraction of uranium with three different mixtures of di-(2-ethyl-hexyl) phosphate (D2EHP) and tri-(2-ethyl-hexyl)-phosphate (T2EHP) in solvents like toluene, carbon tetrachloride, hexane and cyclohexane. The study was carried out in presence of different concentrations of HCl and HNO₃. A single extraction with D2EHP in cyclohexane using nitric acid as matrix was sufficient to reduce the U₃O₈ concentration from 100 g/l to 100 g/ml. The ICP-AES instrumentation applied, allowed the determination of metal concentrations ten-times lower than those usually found in nuclear grade U₃O₈. To check the efficiency of the extraction and the accuracy of the proposed method, Certified Reference Materials were used in the dissolution and extraction steps. The method described can be used for the determination of trace metals in nuclear grade U₃O₈.     

Determination of trace level impurities in uranium compounds by ICP-AES after organic extraction

The determination was studied of Al, B, Be, Cd, Ca, Co, Cu, Mg, Mn, Mo, Pb, Si, Sn, V, Cr, Ni, and Fe as trace level impurities in uranium compounds by ICP-AES after extraction of uranium with three different mixtures of di-(2-ethyl-hexyl) phosphate (D2EHP) and tri-(2-ethyl-hexyl)-phosphate (T2EHP) in solvents like toluene, carbon tetrachloride, hexane and cyclohexane. The study was carried out in presence of different concentrations of HCl and HNO(3). A single extraction with D2EHP in cyclohexane using nitric acid as matrix was sufficient to reduce the U(3)O(8) concentration from 100 g/l to 100 microg/ml. The ICP-AES instrumentation applied, allowed the determination of metal concentrations ten-times lower than those usually found in nuclear grade U(3)O(8). To check the efficiency of the extraction and the accuracy of the proposed method, Certified Reference Materials were used in the dissolution and extraction steps. The method described can be used for the determination of trace metals in nuclear grade U(3)O(8).     

Production of potassium sulfate from potassium hydrosulfate solutions using alcohols

Potassium sulfate is used to produce multicomponent fertilizers, free of chlorides. The desalting out of potassium sulfate from an aqueous solution of potassium hydrosulfate was conducted using 40 mass %, 45 mass %, or 50 mass % aqueous solutions of either methanol or propan-2-ol. Composition of the resultant precipitate was analyzed using chemical methods and XRD analysis. The results of the XRD analysis revealed that the main precipitate phase is K₂SO₄. Small amounts of K₅H₃(SO₄)₄ were detected when the desalting out was carried out from 2.5 M KHSO₄ solution using 40 mass % and 50 mass % methanol solution. When the amount of potassium bisulfate in the solution increased to 3.5 M and 3.8 M, the main phase consisted of K₃H(SO₄)₂. Generally, the desalting out process using propan-2-ol caused the formation of K₃H(SO₄)₂. Potassium sulfate was obtained only by desalting out the 2.5 M KHSO₄ solution using 50 mass % aqueous propan-2-ol. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Possibility of separating potassium and rubidium nitrates,and potassium and cesium nitrates,by zone melting in ammonium nitrate

Conclusions The mutual effect of KNO₃ and RbNO₃, and of KNO₃ and CsNO₃, during the directed crystallization of NH₄NO₃ is not manifested on the values of the equilibrium distribution coefficients. The salts pairs: KNO₃-RbNO₃ and KNO₃-CsNO₃ can be separated by zone melting in ammonium nitrate.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2808–2809, December, 1971.     

磷酸铈共沉淀分离富集硫酸钴中痕量铅及铅的原子吸收光谱测定

提出了用磷酸铈(CePO4)作为共沉淀捕集剂分离富集CoSO4溶液中的痕量Pb2+,用火焰原子吸收光谱(FAAS)测定的方法。共沉淀效率受pH、Ce(NO3)3和H3PO4溶液用量的影响。结果显示,在溶液pH3.0～4.0时,CePO4能够定量共沉淀CoSO4溶液中的Pb2+,对于20mL的样品溶液,方法的检出限为5.59×10-2mg/L,铅的标准加入回收率为98.32%,排除了基体干扰,取得了较为满意的结果。     

Extraction chromatography preconcentration of impurities from high purity lead

Summary The method of multielement preconcentration of impurities from high-purity lead utilizing an extraction Chromatographie separation in tri-n-octylamine-HCl system is developed. Unlike a well-known procedure based on precipitation of lead nitrate this method is applicable to very small samples. Being used in combination with the precipitation procedure mentioned, this method provides a considerable increase in the effectiveness of the latter.     

Sequential extraction of trace metals from sediments

With the aim of harmonizing the methodology associated with the trace metal partitioning in sediments, a group of European researchers proposed a three-step sequential extraction scheme using acetic acid, hydroxylamine hydrochloride and ammonium acetate as extracting agents. The metal content in each extract is mainly determined by AAS or ICP.In this paper, the validation of chromium determination in the extracts by AAS is described. The optimum instrumental conditions and the matrix effects of the different reagents used in the extraction scheme are studied for Cr(III) and Cr(VI) solutions by FAAS and ETAAS techniques. The effect of the concomitant species are also studied in the different extracts. The interfering effects are minimized by means of releaser agent for FAAS.The addition of 1% oxine is recommended for acetic acid and hydroxylamine extracts, whereas for step 3 the use of a releaser agent is not necessary. For ETAAS, the use of a calibration graph with pyrolytically-coated tubes gave satisfactory results.The procedure of analysis is applied to chromium partitioning in two sediments with certified total chromium content and to different sediments from Rio dos Sinos of Brazil.From the results obtained it is recommended to measure chromium contents in steps 1 and 2 by ETAAS and the content of step 3 by FAAS.     

Differential scanning calorimetry of sodium and potassium nitrates and nitrites

Differential scanning calorimetry (DSC) experiments were performed with NaNO₃, KNO₃, (Na,K)NO₃, NaNO₂ and KNO₂ over the temperature range 350–990 K. Endothermic peaks, indicative of decomposition reactions, were observed to occur in the single salts above their melting points. The equimolar mixture of sodium and potassium nitrate did not decompose in the temperature range specified. The nitrites began to decompose at 800±10 K. Sodium nitrate began to decompose at 840±10 K and potassium nitrate began to decompose at 820±20 K. These results were compared with previously reported differential thermal analysis investigations of NaNO₃ and KNO₃.     

浊点萃取-火焰原子吸收光谱法测定淡水鱼中痕量铅

采用以双硫腙为络合剂、Triton X-100为表面活性剂的新型浊点萃取体系富集淡水鱼中的痕量铅,并用火焰原子吸收光谱法对其进行测定。探讨了溶液pH、表面活性剂浓度、络合剂用量、平衡温度、平衡时间等对浊点萃取及测定灵敏度的影响,优化了实验条件。在最佳条件下测得铅的检出限为0.090μg/L,校准曲线相关系数为0.9999。该方法已用于淡水鱼中痕量铅的测定。     

Radiochemical precipitation studies for separation of iodine from tellurium and other trace impurities

Precipitation of radiotellurium, containing trace radioimpurities, has been carried out from sulfate media at different pH-values. The highest precipitation yield was achieved at the region of pH ~4–6. Quantitative uptake by the formed precipitate was noticed for (i) ⁵⁴Mn, ^110mAg and ¹²⁵Sb over all the pH-range of study (pH 1.7–9.2), (ii) for ⁶⁵Zn and ⁶⁰Co in the regions of pH ~6–8 and pH 6–8.8, respectively, and (iii) for ¹³⁴Cs in the region of pH 1.7–2.8, while its percent uptake fluctuated around 60.5 % in the region of pH 4.4–6.4. Further precipitation studies have been conducted for a mixture of ¹²⁵I and radiotellurium from sulfate, nitrate and chloride media at pH-values of 6.0 and 7.5. The highest ¹²⁵I recovery yield in the obtained supernatant was 95.0 ± 1.3 %, which was achieved with sulfate medium at pH 6.0 with percent uptake values of 5.0 ± 1.3, 98.9 ± 0.9 and 62.0 ± 4.6 % of ¹²⁵I, ^123mTe and ¹³⁴Cs, respectively, and quantitative uptake of ⁵⁴Mn, ^110mAg, ¹²⁵Sb, ⁶⁰Co and ⁶⁵Zn by the precipitated tellurium. Thereafter, the supernatant was further acidified with H₂SO₄ and boiled, after adding H₂O₂, for 3 h. >99 % of ¹²⁵I was distilled off from the acidified supernatant. The distilled of ¹²⁵I was received in 0.1 M NaOH + 1 % Na₂S₂O₃ solution, with a radionuclidic purity of >99.99 %, radiochemical purity of >99.8 % as I^? and pH ~13.     

Isothermal mass crystallization of ammonium and potassium nitrates from Tergitol NP-4-based water-in-oil microemulsions

A procedure is elaborated for preparing powders of ammonium and potassium nitrates with microsized particles and stable sols with particle sizes of 7–16 nm based on isothermal mass crystallization from Tergitol NP-4-stabilized water-in-oil microemulsions in decane. The crystallization process is studied by turbidimetry and photon-correlation spectroscopy. The isolated powders are characterized by scanning electron microscopy, while sols and microemulsions are studied by photon-correlation spectroscopy. Evaporation of water from microemulsion droplets upon stirring water-in-oil micellar solutions at 25–45°C is shown to be the reason for the salt crystallization. It is ascertained that the time of the onset of crystallization and the morphology of resulting particles depend on temperature, content of an aqueous pseudophase, and the nature of a salt. A desolubilization-emulsion hypothesis is proposed for explaining the formation of nanoparticle powders and organosols.     

Spectrographic determination of trace impurities in sulphur

Summary An emission spectrographic method for the estimation of traces of some common impurites viz., Al, Ba, Bi, Ca, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, Ti and V in high-purity sulphur is described. The impurities separated from 1-g sample, after removing sulphur as SO₂ by heating it in air at about 300° C, were dissolved in a small amount of 6M hydrochloric acid and loaded on 10 mg of carrier mixture containing 90% graphite and 10% sodium chloride in the 1/4 electrode crater. The spectra were exited in a D. C. arc carrying 13 A current for 45 seconds. Cobalt was used as an internal standard and sodium chloride as a carrier. The lowest detection limits lie in the range 0.005 to 0.05 ppm for the different elements. The precision of the method ranges from 6–19% for the elements analysed.

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Zusammenfassung Eine emissionsspektrographische Methode zur Bestimmung üblicher Spuren-Verunreinigungen in hochgereinigtem Schwefel, wie Al, Ba, Bi, Ca, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sn, Ti und V, wurde beschrieben. Die aus 1 g Schwefel, nach dessen Entfernung als SO₂ durch Erhitzen an der Luft bei etwa 300° C, abgetrennten Verunreinigungen werden in wenig 6-m Salzsäure gelöst und mit 10 mg Trägergemisch, bestehend aus 90% Graphitpulver mit 10% Natriumchlorid, in die Vertiefung einer 1/4-Elektrode eingebracht. Das Spektrum wird im Wechselstrombogen von 13 A für 45 sec angeregt. Kobalt dient als interner Standard mit Kochsalz als Träger. Die unterste Nachweisgrenze liegt bei 0,005–0,05 ppm für die verschiedenen angegebenen Elemente. Die Genauigkeit beträgt 6–19%.