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.     

Determination of free acidity in antimony chloride solutions

A method for the determination of free acid in antimony(III) chloride solutions is described. The total acid is determined by titration in the presence of tartrate as masking agent, and the bound acidity is calculated from the antimony content of the same aliquot, determined by titration with bromate. This method is simple and rapid compared to the earlier potentiometric techniques.     

On the use of hydrogen peroxide as a masking agent for the determination of yttrium in uranium oxide-yttrium oxide mixture

Use of hydrogen peroxide as a masking agent for uranium during the EDTA titration of yttrium in an yttrium-uranium mixture containing large amounts of uranium has been investigated. High acetate ion concentration was necessary to keep the peroxy complex of uranium in solution during the titration. It has been observed that upto 500 mg of uranium could be tolerated in the determination of yttrium with 0.5 ml of 30% hydrogen peroxide in {lM acetate medium. The precision and accuracy of the method based on 16 determinations of yttrium at 6–16 mg level in presence of 300 mg uranium has been found to be ±0.2%.     

Direct complexometric determination of magnesium in the presence of uranium, iron and aluminium

Conditions for the direct complexometric determination of magnesium in the presence of uranium, iron and aluminium are described. The method is based on the masking of uranium by hydroxylamine, and of iron and aluminium by triethanolamine. Methylthymol Blue is used as indicator for the EDTA titration of magnesium at pH 10.     

Study of interferences by transition metal ions in hydride generation atomic absorption spectrometry of antimony

The mechanism of the interference of metal ions in the hydride generation atomic absorption spectrometry (AAS) of antimony was studied. Experiments on the decomposition rate of sodium tetrahydroborate in acidic media were done in the presence of interfering metals, with and without the addition of masking agents. The results were compared with experiments on the sensitivity of AAS in the presence of the same interfering metals with and without the addition of the same masking agents. AAS experiments are described in which the product of the reaction between sodium tetrahydroborate and one of the interfering metals was present during hydride formation. This reaction product was certainly one of the causes of interference, but the contribution of the catalytic decomposition of sodium tetrahydroborate to interference is not clear.     

Masking Agents in Metal Titration with Edta Part IV - Thorium Titration in the Presence of Some Metals

Abstract

The authors studied the possible employment of various compounds containing sulfur as masking agents for divalent and trivalent metals, in the titration of thorium with EDTA. Reagents studied were thioglicolic acid, 3-mercaptopropionic acid, 2-mercaptoethanol, 2,3-dimercaptopropanol, BIS (2-hydroxy ethyl) dithlocarbamate, ethylxantate, thionalid, thiourea and thiosulfate.

The ones which proved more efficient were 2,3-dimercaptopropanol and BIS (2-hydroxyethyl) dithiocarbamate.     

A note on the determination of thorium in the presence of some bivalent metal ions

A new method for complexometric determination of thorium in the presence of bivalent metals without their masking is presented. Two aliquots of metal solution are necessary. In one the sum of the thorium and other metals is determined by DTPA titration. The second aliquot is treated with Zn(2)TTHA complex. Only thorium, forming a 1:1 complex with TTHA, displaces twice its molar amount of zinc from the complex, while other elements displace only an equimolar amount of zinc. The amount of thorium corresponds to the difference of consumption in the two titrations.     

Back titration with mercuric nitrate in alkaline medium analysis of tertiary mixtures of mercury(II) with some other metals

Summary Tertiary mixtures each containing mercury(II) were analysed by simple procedures involving combination between the recent method of back titration with mercuric nitrate in alkaline medium, and the volumetric methods which make use of masking agents as cyanide. The content of mercury(II) in most mixtures is determined potentiometrically with potassium iodide using the silver amalgam as indicator electrode. End points are attended with fair accuracy within 0.02 ml titrant and with reasonable jumps from 60 to 90 mv per 0.1 ml of mercuric nitrate solution or from 170 to 200 mv per 0.1 ml of potassium iodide solution.     

Determination of bismuth(III) by direct potentiometry and potentiometric titration, with an electrode sensitive to Bi(3+)

A liquid-state ion-exchange electrode containing the chelate bismuth(III) complex with 5-mercapto-3-(naphthyl-2)-1,3,4-thiadiazole-2-thione in tetrachloroethane is applied to the determination of bismuth(III) by direct potentiometry and potentiometric titration. The influence of various interfering cations is discussed. In the presence of potassium cyanide as masking agent, Ni(II), Co(II), Cu(II), Ag(I) and Hg(II) do not interfere in the potentiometric EDTA titration. Satisfactory results have been obtained for the determination of bismuth(III) in Wood's metal and two pharmaceuticals.     

Thiomercurimetric determination of sulphur, aliphatic and aromatic thiols and disulphides in hydrocarbon solvents, using reduction with sodium aluminium bis(2-methoxyethoxy)dihydride

A method is proposed for determination of hydrogen sulphide and aliphatic and aromatic thiols in hydrocarbon solvents by extraction with 2M potassium hydroxide and titration with o-hydroxymercuribenzoic acid in the presence of dithiofluorescein and dithizone, with selective masking with acrylonitrile. Sulphur and organic disulphides are readily converted by sodium aluminium bis(2-methoxyethoxy)dihydride in benzene solution into hydrogen sulphide and thiols, which can either be directly titrated after dilution with alcohol or separated by extraction and determined in the presence of each other.     

Rapid visual compleximetric titration of calcium in natural waters

Visual compleximetric methods for the titration of calcium in the presence of magnesium have been based either on masking the magnesium or using an indirect indicator procedure, e.g., the system Zn-EGTA-Zincon. In the proposed method these two approaches are combined. Zn-EGTA complex is added to the mixture and the zinc liberated in the calcium replacement reaction is titrated with EGTA after the magnesium has been masked with fluoride ion.     

A precise direct heterometric determination of traces of copper with diethyldithiocarbamate in excesses of metals

The most favorable conditions for the heterometric titration of copper with sodium diethyldithiocarbamate and the influence of complexing agents on the titration were investigated.Titrations of copper were carried out in the presence of large excesses (? 99. 5%) of most of the common cations. A method is presented for a precise determination of traces of copper in metals and salts.The titration time was 7–10 minutes. In most titrations the amount of copper present was determined with an error close to zero.     

Synthesis and Characterization of Star-Branched Nylon 12

Linear and star-branched polyamide 12 were prepared in the presence of mono- and multifunctional acid agents. Molecular masses and molecular mass distributions are discussed according to our model recently presented and are compared with the data obtained by Flory's model. End group titration and SEC data are discussed. Oligomerisation data confirm the general validity of our model.     

8-quinolinol-5-sulphonic acid as both indicator and masking agent--II: titration of phosphate with La(III)

The use of 8-quinolinol-5-sulphonic acid as both masking agent and indicator in the titration of phosphate with La(III) has been investigated. The reagent forms complexes with most cations in preference to the formation of their phosphate precipitates at pH 7, but the reverse is the case for the rare earths, which permits the precipitation reaction to be carried out in the presence of these other cations. Amounts of P of the order of 5 microg have been determined at a concentration of 5 ppm.     

鼓风炉渣中氧化钙的测定方法改进

在参照DHF83-B多元素快速分析仪法测定炉渣中氧化钙的基础上,对鼓风炉渣中氧化钙的测定方法进行了改进。用盐酸（1+1）溶样,三乙醇胺掩蔽残留的铁、铝、锰等元素,以钙指示剂作指示剂,于pH值大于12时用EDTA标准溶液滴定氧化钙。EDTA滴定法分析结果的相对标准偏差RSD为2.82%,与DHF83-B多元素快速分析仪法比较,其结果基本一致。该方法具有准确度好、快速简便等优点,适合用于冶炼炉渣中氧化钙含量的测定。     

Al3+对电位滴定仪测定游离酸的干扰及其消除研究

溶液中Al3+易水解,对游离酸的测定存在严重干扰。本文以NaF溶液掩蔽Al3+,用自动电位滴定仪测定含Al3+溶液中的游离酸含量,通过溶液化学分析论证了NaF溶液掩蔽Al3+的可行性。NaF掩蔽-自动电位滴定法测定含Al3+溶液中游离酸含量的精密度实验RSD小于2.0%,方法的加标回收率在98.00%～103.00%之间,与手动滴定法对比可靠性检验结果t=0.25;以上结果表明该方法具有准确度高、重复性好的优点。     

EDTA滴定法测定铟锡氧化物废靶粉中铟的含量

建立用EDTA滴定法测定铟锡氧化物(ITO)废靶粉中铟含量的方法。ITO废靶粉样品经盐酸和硝酸分解,用氢溴酸加热除锡,以冰乙酸做掩蔽剂,p H控制在2.5~3.0之间,在70~80℃下用EDTA直接滴定法测定铟的含量。该方法改进了除锡条件,优化了酸度、温度,讨论了络合掩蔽剂及其用量的选择过程。在最佳实验条件下,铟的回收率为99.4%~100.5%,测定结果的相对标准偏差小于1%(n=6)。该方法可以满足ITO靶材中常量铟的分析要求。     

Application of masking agents in minimizing interferences from some metal ions in the determination of arsenic by atomic absorption spectrometry with the hydride generation technique

The use of thiosemicarbazide and 1,10-phenanthroline as masking agents to minimize interferences from Cu, Ni, Pt, and Pd in the determination of arsenic by atomic absorption spectrometry in an argon-hydrogen flame by the hydride generation technique is reported. Little interference was observed for Cu, but the strong suppression of the arsenic signal by a 1000-fold (weight) amount of Ni and 100-fold (weight) amount of Pt or Pd was effectively eliminated with these masking agents.     

Potentiometric determination of silver(I), palladium(II) and gold(III) in mixtures by use of an iodide-selective electrode

Two procedures are proposed for the potentiometric determination of Ag(I), Pd(II) and Au(III) in binary mixtures, by titration with potassium iodide solution, and use of a commercial iodide electrode as sensor. In the first procedure, two aliquots of the mixture are titrated, at pH 2.0 ± 0.2 and 9.0 ± 0.2, adjusted with dilute sulphuric acid and ammonia solution. At pH 2.0, the titrant reacts with both metals, whereas at pH 9.0, Ag(I) is the only reactant. The second procedure utilizes titration of two aliquots of the mixture in the presence and absence of a selective masking agent. The methods have been applied to the determination of these metals in some jewellery alloys.     

头发中微量铜和锌的 5-Br-PADAP 分光光度法测定

研究了测定铜和锌时多种掩蔽剂联合掩蔽头发中的干扰离子。测定铜时用六偏磷酸钠和焦磷酸钾联合掩蔽;测锌时用柠檬酸钠、六偏磷酸黄和铜试剂联合掩蔽。在表面活性剂OP存在下,5－Br-PADAP显色,不经分离,直接在水事测定斑秃患者头发中的铜和锌。铜络合物的最高吸收峰在558nm,锌络合物的最高吸收峰在560nm,在25mL溶液中,铜在0－37．5mg/L,锌在0－238mg/L范围内符合beer定律。斑秃患者头发中锌和铜低于正常人。