Determination of lanthanum in food and water samples by Zeeman-effect atomic absorption spectrometry using graphite tube lined with tungsten foil.

A sensitive, selective method for the determination of lanthanum in food and water samples by atomic absorption spectrometry using a graphite tube lined with tungsten foil is described. The atomization of lanthanum from the tungsten surface gives better analytical sensitivity, a lower atomization temperature and negligible memory effects. The characteristic mass and detection limit of the method were 8.1 x 10(-9) and 7.85 x 10(-9) g, respectively. The precision (relative standard deviation in the range 5.9-9.9%), accuracy and interferences of the method were also investigated. The method can be used directly for the determination of trace amounts of lanthanum in food and water without pre-dissociation of the matrices. The results obtained by this method are in good agreement with those obtained from inductively coupled plasma atomic emission spectrometry.     

Determination of rare earth impurities in cerium dioxide and oxalate by X-ray fluorescence technique

A method for the determination of lathanum, praseodymium, neodymium and samarium oxides in cerium dioxide has been developed. The sample in the oxalate form is mixed with the binding material (boric acid) in the ratio 1∶1 pressed to form a double layer pellet over a boric acid backing pellet and irradiated by X-rays from a tungsten tube. The secondary X-rays are dispersed with a LiF (200) crystal in a Philips PW 1220 semiautomatic X-ray fluorescence spectrometer. The intensity of fluorescent X-rays is measured by a flow proportional counter. The minimum determination limit is 0.01% for lanthanum and samarium oxides and 0.02% for praseodymium and neodymium oxides. The precision at each concentration of the standards and theoretical minimum determination limit for each element have been calculated.     

Kinetic spectrophotometric determination of acetaldehyde in medical ethanol

A novel method has been introduced for the determination of trace amounts of acetaldehyde in medical ethanol based on its inhibition effect on the reaction between piperidine and sodium nitroprussiate. The reaction is monitored by a spectrophotometric technique, measuring a decreasing rate of absorbance at 560 nm during a fixed time of 60 s. The method allows for the determination of acetaldehyde in the range of 2.5–55 ppm. The limit of detection is 0.5 ppm and the relative standard deviation for 16 determinations of 30.0 ppm acetaldehyde is 0.038, while it is 0.173 in the common simple spectrophotometric method. The reliable results make the proposed method applicable to the determination of acetaldehyde in medical ethanol. The text was submitted by the authors in English.     

Flame emission inhibition titration procedure for the determination of traces of titanium

Calcium atomization inhibition titration followed by release with lanthanum is applied to the determination of titanium (0.05–1 μg ml^-1). The detection limit is 15 ng ml^-1. The effect of some interfering ions that form involatile calcium compounds is examined.     

Molybdenum(VI)-hydroxylamine complexes

Summary Hexavalent molybdenum reacts with PAR [4-(2-pyridylazo)-resorcinol] and hydroxylamine to form a ternary complex which is intensely red coloured. This reaction is made the basis of a sensitive spectrophotometric determination of molybdenum in tungsten metal and tungsten trioxide. The method proposed is compared with the thiocyanate method to prove its superior accuracy. The standard deviations is 5 ppm at a 200 ppm level. The limit of determination as calculated from the deviation of the blank is 2 ppm.

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Zusammenfassung Sechswertiges Molybdän reagiert mit PAR [4-(2-Pyridylazo)-resorcin] und Hydroxylamin unter Bildung eines ternären, intensiv rot gefärbten Komplexes. Diese Reaktion bildet die Grundlage eines empfindlichen spektralphotometrischen Verfahrens zur Bestimmung von Molybdän in Wolfram-Metall und Wolframtrioxid. Verglichen mit der Thiocyanatmethode ergibt das vorgeschlagene Verfahren die richtigen Werte. Die Standardabweichung beträgt 5 ppm bei einem Gehalt in der Größenordnung von 200 ppm. Die Erfassungsgrenze, berechnet aus der Streuung des Blindwertes, beträgt 2 ppm.

     

共沉淀分离-氢化物发生-原子荧光光谱法测定高纯偏钨酸铵中痕量铋

提出了以氢氧化镧为共沉淀剂,对高纯偏钨酸铵中痕量杂质元素铋进行共沉淀分离富集后以HG-AFS进行测定的方法。在强碱性环境中进行两次共沉淀,能使铋元素定量分离回收,偏钨酸铵残留量降至很低水平。选择了适宜的反应条件以及仪器的最佳工作条件,考察了钨基体对被测元素的干扰。铋的检出限0.020 ng/mL,测定下限0.012μg/g,相对标准偏差4.6%,回收率在92.8%~108.4%之间,方法适用于高纯偏钨酸铵中痕量铋的测定。     

Atomic-absorption determination of rhodium in chromite concentrates

Rhodium is determined in chromite concentrates by atomic absorption after concentration either by co-precipitation with tellurium formed by the reduction of tellurite with tin(II) chloride or by fire assay into a gold bead. Interelement interferences in the atomic-absorption determination are removed by buffering the solutions with lanthanum sulphate (lanthanum concentration 1%). Substantial amounts of Ag, Al, Au, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ho, Hg, K, La, Mg, Mn, Mo, Na, Ni, Pb, Te, Ti, V, Y, Zn and platinum metals can be tolerated. A lower limit of approximately 0.07 ppm Rh can be determined in a 3-g sample.     

Alkali- und erdalkalispurenanalyse in Wolfram und wolfram-verbindungen nach wolframmatrixabtrennung an DEAE-sephadex

A new column-chromatographic method is described, for the separation of tungsten on DEAE-Sephadex, enabling trace amounts of alkali and alkaline earth metals in tungsten to be determined quantitatively by AAS without matrix interference. Mean relative S.D. for < 50 ppm Na, K, Mg, are 5–10%, and for < 50 ppm Ca 10–20%, and for >50 ppm, 2–5% and 5-10% respectively, Limits of detection in tungsten are 10 ppm Na and K, 1 ppm Mg, and 20 ppM Ca. Time for a determination is about 90 min. By appropriate changes in pH and other conditions, the method can be used for the separation of molybdenum from traces of alkali metal ions.     

Trace determination of carbon and oxygen in tungsten by spark-source mass-spectrography

A high pumping-speed vacuum system, incorporating a mechanical cryo-pump, was designed and built to attach to the source of a spark-source mass-spectrometer to reduce the partial pressure of carbon- and oxygen-containing gases. Pressures in the 10(-10) mmHg range were obtained, which provide a suitable environment for the determination of carbon and oxygen in tungsten. The effect of the partial pressure of CO on carbon and oxygen determination has been studied and characterized. A determination limit of 1 ppm has been achieved for these elements in tungsten.     

Catalytic spectrophotometric determination of tungsten using the malachite green-Ti(III) redox reaction and a thiocyanate activator

Thiocyanate was found to have a highly activating effect on the tungsten-catalyzed reaction of malachite green with Ti(III). A highly sensitive, selective and simple method was developed for the determination of tungsten based on this effect. The reaction rate was monitored spectrophotometrically by measuring the change in absorbance at 616 nm using a fixed time method. The effect of different parameters was studied and optimum conditions were established. The calibration graph was linear in the range of 1.2-10 and 10-80 ngml(-1). The detection limit was 0.15 ngml(-1) and relative standard deviation for ten replicate measurements of 1.2 ngml(-1) of tungsten was 1.8%. The proposed method was applied successfully for the determination of tungsten in hot spring waters.     

电感耦合等离子体原子发射光谱法测定钼镧合金中镧元素

采用盐酸-硝酸溶解钼镧合金样品,建立电感耦合等离子体原子发射光谱法（ICP-AES）测定钼镧合金中镧元素的分析方法,给出影响测量结果的不确定度分量。选择379.478nm为镧的分析谱线,通过基体匹配法消除基体钼的干扰。在优化条件下对钼镧合金样品进行测定,线性相关系数在0.999以上,定量下限为0.048%,测定结果的相对标准偏差（RSD,n=11）小于3%,回收率为93.00%~105.00%。该方法快速、准确,可以满足实际生产中钼镧合金样品的测定要求。     

Determination of tungsten in ores by energy dispersive X-ray fluorescence analysis

The possible determination of tungsten in low grade ores from Northern India, Rajasthan State has been explored by energy dispersive X-ray fluorescence analysis /EDXRF/ technique using radioisotope based excitation of W L X-rays and high resolution Si/Li/ detector system. Finely powdered ore has been diluted with optimal quantity of cellulose and converted into pellets to make it suitable for X-ray analysis after homogenization. The experiments have shown the minimum detectable limit of 33 ppm in diluted matrix. The results are compared with the spectrophotometric stannous chloride-thiocyanate method. EDXRF appears to be encouraging for routine and precise analysis of tungsten in low grade ores.     

Solvent extraction, spectrophotometric and inductively coupled plasma atomic emission spectroscopic (ICP-AES) determination of lanthanum(III) with crown hydroxamic acid

A new crown hydroxamic acid, 5,14-N,N'-hydroxyphenyl-4,15-dioxo-1,5,14,18-tetraaza hexacosane (NHDTAHA) for the extraction and spectrophotometric determination of lanthanum(III) is described. Lanthanum(III) forms a yellow coloured complex with NHDTAHA, which is extracted with chloroform, having molar absorptivity 7.7 x 10(3) 1 mol(-1) per cm at 372 nm. The system obeys Beer's law in the range 1.2-20 ppm of lanthanum. The extract is directly aspirated for ICP-AES measurements, the limits for estimation are 5-140 ppb of lanthanum. Lanthanum has been determined in monazite sand and standard samples.     

微波等离子体炬原子发射光谱法测定铁增敏效应

针对在低功率下工作的微波等离子体炬原子发射光谱法(MPT-AES)存在对一些元素检测灵敏度较低和抗基体干扰能力弱的问题,以氩气为载气和工作气,研究了表面活性剂及镧盐对MPT-AES测定铁的增敏效应,考察了铁测定的工作条件和共存元素对铁测定的影响.实验结果表明,非离子表面活性剂对铁的测定有抑制作用,而阳离子表面活性剂和镧盐对铁的测定有增敏作用,其中镧盐增敏效果最好.以镧盐为增敏剂,不仅可提高MPT-AES测定铁的灵敏度,还可增加共存元素的允许量.当体系中镧浓度为0.500 mg/m L时,至少可使40倍的锌,30倍的钴,20倍的镍、锰,15倍的钙,10倍的镁、铜和钠不影响铁的测定.与不加镧时相比,铁的发射强度提高了2.4倍,检出限由原来的27.5×10~(-3)μg/m L下降为8.5×10~(-3)μg/m L.将本方法应用于原油样品中铁的测定,所得结果与火焰原子吸收光谱法测定结果一致.     

Catalytic adsorptive stripping voltammetry determination of ultra trace amount of tungsten using factorial design for optimization

A highly sensitive procedure is presented for the determination of ultra-trace concentration of tungsten by catalytic adsorptive stripping voltammetry. The method is based on adsorptive accumulation of the tungsten-pyrocatechol violet complex onto a hanging mercury drop electrode, followed by reduction of the adsorbed species by voltammetric scan using differential pulse modulation. The reduction current is enhanced catalytically by chlorate. The influence of variables was completely studied by factorial design analysis. Optimum analytical conditions for the determination of tungsten were established. Tungsten can be determined in the range 0.06–12.0 ng/mL with a limit of detection of 0.02 ng/mL. The influence of potentially interfering ions on the determination of tungsten was studied. The procedure was applied to the determination of tungsten in one sandwich polyoxometalate and some synthetic samples similar to alloy compounds with satisfactory results.     

Determination of rare earths in lanthanum oxide by inductively-coupled plasma emission derivative spectrometry

Rare-earth elements (REE) at ppm levels in lanthanum oxide can be determined without prior separation and preconcentration by use of high-resolution inductively-coupled plasma emission derivative spectrometry (ICPEDS). The calibration graphs are all linear and pass through the origin, even in the presence of large amounts of lanthanum, except those for dysprosium, holmium and ytterbium. The detection limit for each REE is 1-10 mug g in lanthanum oxide. Investigation of various physical and/or spectral interferences shows that good selectivity is obtained by ICPEDS.     

Determination of platinum, palladium, and gold in a silver assay bead by atomic absorption spectrophotometry

Summary A procedure is given for the atomic absorption determination of platinum, palladium and gold in silver beads. Interferences by coexisting ions usually found in the parting solution could be eliminated by addition of 1% of lanthanum. The lowest working ranges in which it is possible to obtain results comparable in accuracy to those from a good spectrophotometric determination are estimated for each metal. (1 ppm Pd, 1 ppm Au, 5 ppm Pt). The results of several determinations using the proposed procedure to analyse silver assay beads are given.

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Bestimmung von Platin, Palladium und Gold in dokimastischen Silberperlen durch Atomabsorptions-Spektrophotometrie

Zusammenfassung Störungen durch in der Scheidelösung vorhandene Begleitionen konnten durch Zusatz von 1% Lanthan verhindert werden. Die unteren Grenzen für eine genaue Bestimmbarkeit wurden festgelegt (1 ppm Pd, 1 ppm Au, 5 ppm Pt) und Ergebnisse mehrerer Beleganalysen mitgeteilt.

     

Improvement of the sensitivity of molybdenum and tungsten determination in niobium and tantalum

A more sensitive dithiol method is described for determination of as little as 0.5 ppm molybdenum and tungsten in high-purity niobium and tantalum. The increased sensitivity is achieved by taking a much larger sample and extracting the bulk of the Nb or Ta into isobutyl methyl ketone. Selective extraction then separates Mo and W.     

Determination of molybdenum and tungsten at trace levels in rocks and minerals by solvent extraction and X-ray fluorescence spectrometry

Separation by solvent extraction followed by X-ray fluorescence spectrometry has been used for determination of molybdenum and tungsten in rocks and minerals. Samples are decomposed either by heating with a mixture of hydrofluoric acid and perchloric acid or by fusion with potassium pyrosulphate, followed by extraction of molybdenum and tungsten with N-benzoylphenylhydroxylamine in toluene from 4-5M sulphuric acid medium. The extract is collected on a mass of cellulose powder, which is dried in vacuum, mixed thoroughly and pressed into a disc for XRF measurements. The method is free from all matrix effects and needs no mathematical corrections for interelement effects. The method is suitable for determination of molybdenum and tungsten in geological materials down to ppm levels, with reasonable precision and accuracy.     

Reactions of metallochromic indicators on micelles-III Spectrophotometric determination of minute amounts of lanthanum with xylenol orange

Xylenol Orange in the presence of cetylpyridinium bromide is proposed for the spectrophotometric determination of minute amounts of lanthanum(III). A deep blue complex, La[(XO)(CP)(2)](2), whose molar absorptivity is 92,000 at 625 mmu is formed. Beer's Law is obeyed within the limits of 0.08 and 0.8 ppm. The effects of pH, reagent concentration, interfering ions and time of standing are described.