Determination of traces of palladium using radioactive zinc dithizonate as a reagent

A radioreagent method for the analysis of traces of palladium using radioactive zinc dithizonate as the reagent has been developed. The method is rapid, highly selective and palladium concentration down to 2 g present in 10 ml solution can be measured.     

Determination of traces of mercury using radioactive zinc dithizonate as a reagent

A radioreagent method for the analysis of traces of mercury using radioactive zinc dithizonate as the reagent has been developed. As small as 0,2 μg of mercury can be determined using this technique. Possible interferences from most of the metals which displace zinc from zinc dithizonate can be removed by a simple separation procedure. The method was tested by analyzing the NBS reference standard SRM 1064 and our value was found to be in agreement with the value certified by NBS. This paper was presented at the South-East and South-West ACS Regional Meeting, Memphis, Tenn., October 29–31, 1975.     

Some observations on the analytical utility of a fluorometric stopped-flow method for resolution of histidine and 1-methylhistidine mixtures

The fluorescent reactions of histidine and 1-methylhistidine with o-phthaldialdehyde and 2-mercaptoethanol are exploited for the individual and simultaneous determination of these compounds by the stopped-flow technique. The instrumental setup used consists of a stopped-flow module coupled to a conventional fluorescence spectrophotometer. The parameters used for these determinations are the initial rate and the fluorescence amplitude of the kinetic curves. Linear ranges, precision, and the results of the selectivity studies are reported. An extension of the proportional-equations method is used to resolve histidine: 1-methylhistidine mixtures in ratios between 3:1 and 1:8. The method is very simple, inexpensive, and fast (only about 10 sec is required for initial-rate measurements, and about 90 sec for those of signal amplitude).     

Some further observations on polymethylsilane as a precursor for silicon carbide

Poly(methylsilanes) produced by sodium coupling of methyldichlorosilane (2:1 molar ratio) contain residual chlorine which can be removed by reduction with LiAlH₄ at low temperature. Following this reduction, the polymers contain catalytically active centers (presumed to be silyl anions) which, in THF solution, further polymerize and crosslink the polymer at room temperature, while in toluene solution they are inactive. The reduced polymethylsilane gives high yields (ca 75%) of ceramic product on pyrolysis, but the composition is rich in silicon, compared with pure silicon carbide (SiC). Addition of catalytic amounts of dimethylzirconocene (DMZ) to this polymer gives a product which pyrolyzes to a product with stoichiometry close to that of SiC. It is concluded that the DMZ has an important influence in promoting Si–C bond formation, relative to Si–Si bond formation, during the pyrolysis.     

1,4-Cyclohexanedione bisthiosemicarbazone as an analytical reagent for spectrophotometric estimation of copper

The properties and analytical possibilities of 1,4-cyclohexanedione bisthiosemicarbazone as reagent for the spectrophotometric determination of copper have been examined. Two procedures for the estimation of copper have been established.     

Precipitation reactions of thiobenzoylphenylhydroxylamine and its use as a reagent for copper

Thiobenzoylphenylhydroxylamine (TBPHA) quantitatively precipitates copper as Cu(C₁₃H₁₀NSO)₂ which can be used as a weighing form for copper; the gravimetric factor is 0.12217. Iron, aluminium, chromium and commonly accompanying elements do not interfere. Quantitative precipitation and separation of several metals from highly acidic solutions is possible. The precipitation reactions of metals with TBPHA, over a wide range of acidity and in the presence of EDTA, are tabulated. TBPHA is of little value as a colorimetric reagent.     

Studies on the use of XeF2 as digestion reagent

A digestion procedure was developed for the determination of selected elements (Al, Ba, Ca, Ce, Cd, Co, Cr, Cu, Fe, La, Mg, Ni, Sr, Pb, Zn) in sediments using XeF₂. The use of XeF₂ has some interesting features but this reagent should be handled only under dry gas which is a severe limitation of the methodology. In a first step the sediment sample (0.1 g) is dried (120 °C) and digested by XeF₂ (1.5 g) in the vapor phase (190 °C; 9 × 10⁶ Pa). Then the dry residue is dissolved in aqua regia and the solution digested at high pressure once again (aqua regia digestion). Subsequently the digested solution is diluted with sub-boiling distilled water and is ready for the analysis by ICP-MS. The sediment standard CRM 320 was analyzed to verify the procedure. A comparison of the results with those obtained by the normally used fluoric acid digestion showed that the recovery rates of each investigated element agreed within a confidence interval of 95%, except Cr. The recovery rate of Cr was lower for the XeF₂ digestion than for the fluoric acid digestion by more than 5%. Further studies were focussed on the possible digestion of SiC by XeF₂ as first step for the trace element determination. In the gaseous reaction products Si could be detected by ICP-MS which gives evidence to a decomposition of SiC. A digestion procedure for small Si samples (0.010 g) was developed. Detection limits (DL) determined for selected elements of analytical interest (Al, Ca, Cd, Cr, Co, Cu, Fe, Mg, Ni, Pb) were between 1 to 12 ng/g. For most of the elements this is an improvement in comparison to the HF vapor phase digestion. The verification of the method was carried out with GFAAS. Received: 17 February 1999 / Revised: 15 June 1999 / Accepted: 17 June 1999     

An umpolung sulfoxide reagent for use as a functionalized benzyl carbanion equivalent

N-Methyl ortho-carbamoylaryl benzyl sulfoxides can be used as synthetic equivalents for α-hydroxy, α-chloro, and α-acetammido benzyl carbanions by means of a two-step sequence involving highly diastereoselective α-C-alkylation with alkyl halides followed by displacement of the sulfinyl residue (which can be recovered and recycled) by a hydroxyl, a chlorine or an acetamido, respectively, under non-oxidative Pummerer conditions. The scope and limits of the method, including a stereoselective version of the reaction, as well as the mechanism of the process are discussed in detail.     

Determination of traces of hydrogensulfite by chemiluminescence with cerium(IV) sulfate as the reagent

Trace amounts of hydrogensulfite in aqueous solution (0.19–50 ng ml^?1 SO₂) are determined continuously with a chemiluminescence method based on a cerium(IV) sulfate reagent at pH 1.8. The intensity per unit SO₂ concentration is about 5 times that obtained with a permanganate reagent. The inhibitory effects of nitrite, transition metal ions and formaldehyde are also reduced.     

Resorcinol as a reagent for zinc

The use of the zinc-ion-catalyzed autoxidation or hydrogen peroxide oxidation of resorcinol (1,3-dihydroxybenzene) to determine zinc concentration has been examined. The nature of the reaction products involved, the conditions of reagent concentration, pH, and reaction time have been specified. The procedure will yield results with a relative average deviation of 10% over the concentration range of 0.9 ppm to approximately 8 ppm. It is an inexpensive and convenient reagent and procedure.     

Thenoyltrifluoroacetone as a reagent for cobalt

Summary An indirect method is proposed for the determination of cobalt (II) with 2-thenoyltrifluoroacetone at the milligram level. The orange cobalt-TTA chelate can be quantitatively precipitated over the p_H range 4.0–8.0. It is dissolved in acid and estimated as cobalt sulphate. Cobalt(II) can be estimated in presence of silver, mercury(II), strontium, iron(III), chromium (III), thorium, zirconium, uranium, citrate and tartrate. The method is reproducible to within ±1 per cent.     

Some observations on the solvent extraction and spectrophotometric determination of palladium using 3,4-dihydro-4,4,6-trimethyl-2(1H)-pyrimidine-thione as a selective reagent

A highly selective spectrophotometric method is described for the determination of palladium, using 3,4-dihydro-4,4,6-trimethyl-2(1H)-pyridinethione (DTPT). The intense yellow 1:2 complex is extractable in chloroform from aqueous solution of pH 5.5. The maximum absorption occurs at 420 nm, ε = 3.90 × 10⁴ liter/mol⁻¹ cm⁻¹ and the sensitivity of the determination is 0.023 μg/ml. Palladium can be determined over a range of 0.4–24.6 ppm. CN⁻ interferes in this determination and should be absent. The method is applied to the determination of palladium in hydrogenation catalysts.