Determination of some organic thio-compounds by precipitation of mercuric sulphide from mercury(II) ammine complexes-I Determination of thioacetamide and thioacetanilide

A gravimetric method based on precipitation of mercuric sulphide has been developed for determining thioacetamide and thioacetanilide. Concentrated nitric acid is added to 0.1M mercuric nitrate, the solution is made alkaline with concentrated ammonia solution, and thioacetamide (dissolved in water) or thioacetanilide (dissolved in alcohol) is added, and the mixture is boiled. The method has good accuracy, and takes about 40 min.     

Adsorptive stripping voltammetric determination of thiourea and thiourea derivatives

Adsorptive stripping voltammetry of thiourea, α-naphthylthiourea and diphenyl-thiourea is discussed. In perchlorate solution, these compounds are adsorbed at the hanging mercury drop electrode at positive potentials (or at open circuit) and can be stripped in a cathodic scan. Detection limits are 2.5 ng l^?1 for thiourea, 80 ng l^?1 for α-naphthylthiourea and 50 ng l^?4 for diphenylthiourea. The method is applicable in the determination of thiourea in cattle-feed and in the direct analysis of urine.     

重铬酸钾滴定法测定废杂铜中的铁含量

研究了废杂铜中铁含量的测定方法.试料采用盐酸、硝酸、高氯酸溶解,加入过量氨水生成氢氧化铁沉淀与铜、铬等干扰元素分离,沉淀用热盐酸溶解后,用氯化亚锡还原至溶液呈浅黄色,重铬酸钾滴定法测定铁含量.探讨了溶样方式、氯化铵用量、氨水过量的体积、硫磷混酸用量对测定结果的影响.对4个废杂铜样品中的铁含量进行测定,测定结果的相对标准...     

Rapid determination of copper in plants by neutron activation analysis

A rapid and simple neutron-activation analysis method has been developed for the determination of copper in plant leaves. Irradiated samples are dissolved in a mixture of fuming nitric acid, 70% perchloric acid and concentrated sulphuric acid in the presence of copper carrier solution. The copper in the resulting solution is extracted as copper cupferronate into chloroform and back-extracted into concentrated ammonia solution. The copper is precipitated as sulphide with 3% aqueous thioacetanude solution and the precipitate is dissolved in nitric acid. The induced activity of copper-64 in the resulting solution is counted with a 400-channel analyser. The photopeak of the annihilation energy of copper-64 at 0.51 MeV is compared with that of a copper standard processed in the same manner. After counting, the chemical yield of the separated copper is found by re-irradiating aliquots of the copper nitrate solution and comparing the induced activity of coppcr-66 at 1.04 MeV with that of another standard processed in a similar manner. The time required to complete the analysis, including the second irradiation and all radioactivity measurements, is about 25 min. The accuracy of the method was checked by analysing a biological standard of known copper content. The proposed method was successfully applied to the determination of copper in the leaves of 10 different plants (copper content 4-30 ppm).     

Ultraviolet spectrophotometric determination of copper in copper ores by flow-injection analysis

A flow-injection analysis (FIA) method for the ultraviolet spectrophotometric determination of copper in copper ores is described. The ore samples are dissolved in concentrated perchloric acid, the excess acid is neutralized with ammonia solution, and the resulting solution is used for the determination of copper. The UV-FIA system is based on the reaction of copper (II) ions with pyrophosphate and subsequent measurement of the absorbance of the dipyrophosphatocuprate (II) complex at 240 nm. The main factors which control the formation of this complex and the FIA variables influencing the system are discussed. The calibration graph is linear from 2-50 ppm copper. At a sampling rate of about 70 samples h(-1) with 50 mul sample injections, precision was about 1% relative standard deviation. Results obtained compare well with those obtained by atomic absorption spectrometry.     

Spectrophotometric determination of pentaerythritol tetranitrate (PETN) in waste water from lead styphnate primer plants

An accurate spectrophotometric method is proposed for the determination of pentaerythritol tetranitrate (PETN) in waste water from lead styphnate primer plants by use of phenoldisulphonic acid. The waste water is filtered through a sintered glass crucible and the PETN is determined in the filtrate and the residue. In the determination of PETN in the filtrate, sodium hydroxide is added and the PETN is extracted with methylene chloride (in alkaline solution, styphnate and TNT are not extracted). The methylene chloride solution is then evaporated to dryness, the residue is treated with a solution of phenoldisulphonic acid in sulphuric acid, water and ammonia are added, and the yellow colour is measured. In the determination of PETN in the residue, the PETN is dissolved in acetone, an aliquot of the acetone solution is treated with water and sodium hydroxide, the PETN is extracted with methylene chloride and the colour is developed as above. Various factors affecting the determination were investigated. The solubility of PETN in water was studied.     

Ion-exchange recovery of palladium(II) from multicomponent chloride solutions

Ion-exchange sorption of palladium(II) from both concentrated aqueous hydrochloric acid solution containing Fe(III), Sn(II), Zn(II), and Cu(II) and weakly acidic concentrated aqueous ammonium chloride solution containing Zn(II) and Cu(II) was studied. The Purolite S920, Purolite S924, and Purolite S984 macroporous resins with the thiourea, thiol, and polyethylenepolyamine functional groups, respectively, were used as sorbents. Strongly basic Purolite A500 anion exchanger was also tested. The desorption of palladium(II) with aqueous ammonia, hydrochloric acid, and acidified aqueous thiourea was examined.     

An atomic absorption spectrophotometric method for the determination of trace amounts of zinc in canned juices after ion exchange separation

An atomic absorption spectrophotometric method is described for the determination of microgram quantities of zinc in canned juices. After sample digestion in concentrated nitric acid, the solution is evaporated till near dryness, and then a solution of 2 M HCl is added to form tetrachlorozincate (II) ion. This acid solution, containing the zinc complex is passed through an ion-exchange column (anion exchange resin, chloride form, which is preconditioned by passing 1 M HCl solution). Zinc is eluted from the column with 0.01 M HCl solution. After evaporation to dryness, the residue is dissolved in 1% (v/v) HNO3, and then atomized into an air-acetylene flame. The limit of detection of the method is 0.15 micrograms ml-1 Zn. The analytical aspects of the proposed method, including the standard addition technique are discussed.     

The determination of nitrogen in nitrocellulose

A method for the determination of nitrogen in nitrocellulose has been developed. The sample is dissolved in concentrated sulphuric acid and a salicylic acid solution is added. The nitrosalicylic acid formed is reduced at room temperature with an excess of titanous chloride solution and the excess is estimated by titration with ferric alum. Statistically designed experiments were used to establish the conditions necessary for accurate results. The procedure is more rapid than the usual nitrometer method and gives results of high precision; e.g. on a mean result of about 13.8% nitrogen, the standard deviation is 0.014.     

微波消解-氢化物发生-原子荧光光谱法测定中药材中痕量砷

采用微波消解法用硝酸-过氧化氢(3+1)溶液消解样品,以硫脲及抗坏血酸混合溶液作为预还原剂,利用氢化物发生-原子荧光光谱法测定中药材当归、丹参、甘草、三七和黄芪中痕量砷的含量。在盐酸(3+97)溶液中加入溶于20g.L-1氢氧化钾溶液中的10g.L-1硼氢化钾溶液使与溶液中砷离子反应生成氢化物。分析中采用载气流量为800mL.min-1。砷的质量浓度在12μg.L-1以内与其对应的荧光强度呈线性关系,方法的检出限(3s/k)为0.020μg.L-1。应用此法对国家标准物质人发(GBW 09101)进行分析,测定值与认定值一致。     

火焰原子吸收光谱法测定粗铜中痕量铋、锑

粗铜样品经硝酸溶解,所得样品溶液中的铜离子在过量氨水中生成可溶性铜氨络离子,而铋、锑则以氢氧化铁和氢氧化镧作载体共沉淀,实现了富集铋、锑并与铜分离。基于此提出了原子吸收光谱法同时测定粗铜中的微量铋、锑。对浓盐酸的用量,硝酸铁和硝酸镧的加入量等试验条件进行了优化。铋的质量浓度在10 mg.L-1以内、锑的质量浓度在5 mg.L-1以内分别与其吸光度呈线性关系,检出限(3s)分别为0.06,0.04 mg.L-1,相对标准偏差(n=10)均小于2.0%。     

Titrimetric determination of silicon dissolved in concentrated HF-HNO3-etching solutions

The wet chemical etching of silicon by concentrated HF-HNO₃ mixtures in solar and semiconductor wafer fabrication requires the strict control of the etching conditions. Surface morphology and etch rates are mainly affected by the amount of dissolved silicon, that is continuously enriched in the etching solution with each etching run. A fast and robust method for the titrimetric determination of the total dissolved silicon content out of the concentrated etching solution is presented. This method is based on the difference between the two equivalence points of the total amount of acid and the hydrolysis of the hexafluorosilicic anion. This approach allows a silicon determination directly from the etching process in spite of the presence of dissolved nitric oxides in the etching solution. The influences of different acid mixing ratios and of the etching solution density depending on the silicon content is considered and discussed in detail.     

Determination of thiourea and its methyl derivatives by hypoiodite oxidation, and iodine monochloride end point; iodine bromide end point in the titration of thiourea with iodate

Summary Procedures have been described for the quantitative determination of thiourea and its methyl derivatives, wherein iodate, permanganate, and ceric sulphate have been used as direct titration solution, either following preoxidation by alkali hypoiodite via (ICI + KOH) or in case of thiourea, by iodine bromide method. Apart from using standard oxidants the methods have an added advantage of a high conversion factor due to oxidation of sulphur to sulphate. Alternative physical methods of detecting the end point is an added feature of these procedures.The authors wish to express their grateful thanks to Dr. S. S. Joshi, D. Sc. (London), for his kind interest in the work.     

Complexometric determination of some toxic mixtures of ions using bromo-cresol orange with visual endpoint indication

A rapid and simple general complexometric method was presented for the determination of lead, cadmium and thallium or mercury or arsenic(V) in laboratory synthesized mixtures similar to those of some ores, minerals and alloys of such metals. The precision and accuracy attainable in successive titrations of Pb(2+), Cd(2+) and Tl(3+) or Hg(2+) or AsO(3-)(4) (As(5+)) with 0.05 and/or 0.01 mol 1(-1) solutions of disodium ethylenediaminetetraacetate (Na(2)EDTA) and standard Pb(NO(3))(2) of the same concentration using Bromo-Cresol Orange (BCO) as a new metallochromic indicator with visual endpoint indication were studied. For the analysis of a three component mixtures of the aforementioned ions, Tl(3+) was at first directly titrated with Na(2)EDTA at pH 0.5-1 (HNO(3)) using BCO as indicator. At the thallium endpoint an excess of Na(2)EDTA was added and the pH was adjusted at pH approximately 4.8 using hexamine-HNO(3) buffer (solution A). The excess EDTA was back-titrated with standard solution of Pb(NO(3))(2). 1,10-Phenanthroline (1,10-phen) was added to release the EDTA combined with Cd(2+), while thiosemicarbazide (TSC) was used to liberate the EDTA from the mercury-EDTA chelate. To determine AsO(3-)(4) ion in such type of mixtures the pH of (solution A) was raised to a value of 10 using ammonia buffer. Excess standard Mg(2+) solution was added and the formed precipitate of MgNH(4)AsO(4) was separated, dissolved and its magnesium content equivalent to AsO(3-)(4) was determined complexometrically using Eriochrome Black-T (EBT) indicator. The interference caused by different anions, cations and organic acids was investigated. A comparison of the indicators BCO and Xylenol Orange (XO) for successive titration of the studied metal ions was carried out. The proposed successive titration method was applied successfully to some real samples of ores, minerals and alloys of the studied metal ions and the results were satisfactory and agreed with those obtained by AAS.     

Neutron activation determination of rheumium in rocks and ores after preliminary extraction with pyridine

A simple neutron-activation method for the determination of rhenium based on a preliminary extractive separation of the latter from molybdenum and tungsten is described. The sample is decomposed with sodium peroxide, a small amount of water is added and the resulting pulp is extracted with pyridine. The extract is evaporated to dryness, the residue is dissolved in water and the solution is passed through a column packed with Dowex 50WX8 in H⁺ form to eliminate the metal impurities. The HReO₄ passed, after neutralization with ammonia, is evaporated to dryness in penals, which then are irradiated with thermal neutrons.     

A New Simple Voltammetric Method for Thiourea and Thiourea Dioxide Determinations

Abstract

Linear sweep voltammetry at glassy carbon or other carbon materials is shown to be a simple, highly sensitive, and relatively versatile analytical method for the determination of thiourea and thiourea dioxide. Using the first one-electron oxidation peak occurring at ～0.6V, thiourea can be determined directly in a variety of electrolytes from concentrated acids to solutions of pH ～5. The thiourea dioxide determination is based on the two-electron oxidation peak which appears in a number of electrolytes at ～1.2V.     

Masking agents in the determination of selenium by hydride generation technique

The effects of several masking agents in the determination of selenium by hydride generation was studied using a continuous flow hydride generator coupled with atomic absorption spectrometry. A miniature argon hydrogen diffusion flame was employed as the atomizer. The effects of masking agents (KI, NaSCN, thiourea, -cysteine, 1,1,3,3 tetramethyl-2-thiourea) were studied both in the absence and in the presence of selected interfering species (Cu, Ag, Au, Ni, Co, Pd, Pt and Fe) and using different addition strategies of the masking agents to the reaction system: in batch mode, either to sample or NaBH₄ reducing solution; in on-line mode, to the sample either before or after the HG step). The combined effect of some masking agents was also investigated. The addition mode of the masking agent to the reaction system could play a decisive role in the control of interfering processes both in the absence and in the presence of concomitants. The addition of NaSCN to the reducing solution of NaBH₄ produced a moderate catalytic effect, similar to the one obtained in the presence of KI, and improved the tolerance limits for Cu, Ni, Co and Pd. Linearity of calibration graphs was unaffected by the on-line addition of 1,1,3,3 tetramethyl-2-thiourea to sample solution, while under similar conditions thiourea produced dramatic curvature of calibration graphs. The combined use of KI (added to reducing solution) and 1,1,3,3 tetramethyl -2-thiourea (added on-line to the sample) exhibited masking properties comparable but not superior to those of thiourea, except for Pt and Pd for which good tolerance limits were achieved. In the absence of KI in the reductant solution the masking efficiency of 1,1,3,3 tetramethyl-2-thiourea was considerably lowered. The addition of some masking agents such as thiourea, -cysteine and 1,1,3,3 tetramethyl thiourea on-line to reaction solution after the NaBH₄+KI reduction step, could be highly effective in the control of Cu and Ag interferences. The method was applied to determination of trace of selenium in pure copper standard reference materials.     

硝酸铅滴定法测定延期药中氧化铜

以硝酸和H2O2对延期药中铅化合物和氧化铜完成溶解,通过硫脲释放,采用硝酸铅滴定法测定延期药中的氧化铜。加入30 mL HNO3溶液(1+8)和15 mL六次甲基四胺控制样品溶液为pH 5～6。结果表明,方法的回收率为98.8%～99.9%,测定结果的相对标准偏差为0.12%～0.2%(n=6)。该方法准确可靠,可用于延期药中氧化铜分析。     

Spectrophotometric determination of bismuth in copper and cartridge brass by the iodide method

An improved spectrophotometric method is proposed for the determination with iodide of trace amounts of bismuth in copper and cartridge brass. The sample is dissolved in nitric acid and the bismuth is separated from the copper by an ammoniacal precipitation in the presence of iron(III) hydroxide as a gathering agent. The hydroxide precipitate is dissolved in hydrochloric acid, sulfuric acid is added, the solution is evaporated to a few ml, hydrobromic acid is added to volatilize the antimony and tin, and the solution is evaporated to fumes of sulfuric acid. The bismuth iodide color is then developed with a composite potassium iodide—sodium hypophosphite reagent. Factors affecting the bismuth iodide color are investigated.     

Determination of silver, bismuth, cadmium, copper, iron, nickel and zinc in lead- and tin-base solders and white-metal bearing alloys by atomic-absorption spectrophotometry

A simple atomic-absorption spectrophotometry method is described for the determination of silver, bismuth, cadmium, copper, iron, nickel and zinc in lead- and tin-base solders and white-metal bearing alloys, with use of a single sample solution. The sample is dissolved in a mixture of hydrobromic acid and bromine, then fumed with sulphuric acid. The lead sulphate is dissolved in concentrated hydrochloric acid. The method is particularly suitable for the determination of silver and bismuth, which are co-precipitated with lead sulphate. The other elements can also be determined after removal of the lead sulphate by filtration.