Jose Aznarez

Extraction-atomic-absorption spectrophotometric determination of lead by hydride generation in non-aqueous media

A method for lead hydride generation in a non-aqueous extraction phase is proposed. The lead hydride generation is carried out in an aliquot of lead pyrrolidine-1-carbodithioate extract in chloroform, by the addition of sodium tetrahydroborate(III) solution in dimethylformamide. Lead is determined by atomic-absorption spectrophotometry at 217.0 nm. The proposed method gives improved sensitivity and eliminates interferences, which is necessary because lead hydride generation in aqueous solution occurs in the presence of oxidants such as potassium dichromate or ammonium peroxydisulphate. The method was applied to the determination of lead in BCS standard steels and air particulates. Good accuracy and precision were obtained.

Extraction-atomic-absorption spectrophotometric determination of antimony by generation of its hydride in non-aqueous media

A method for covalent hydride generation in a non-aqueous extraction phase is proposed. The hydride generation is carried out in an aliquot of metal-complex extraction solution by sodium tetrahydroborate(III) in N,N-dimethylformamide solution and anhydrous acetic acid. The proposed method gives improved sensitivity, eleminates interferences and enables hydride generation of difficult elements to be carried out. Antimony is extracted by ammonium pyrrolidine-1-carbodithioate into chloroform and after hydride generation by the proposed method, it is determined by flame AAS. The method is applied to the determination of antimony in BCS standard steels with good accuracy and precision.

Atomic absorption spectrometric determination of lead in gasolines by generation of its covalent hydride

This paper describes a method for the atomic absorption spectrometric determination of lead in gasolines by hydride generation directly in the sample diluted with N,N-dimethylformamide (DMF) and with the addition of NaBH4 solution in a 2%m/V DMF solution. The determination is carried out with an electrothermal atomiser (an electrically heated quartz tube). The gasolines were initially standardised using two ASTM methods, and the values for concentrations of lead obtained were used for studying the best conditions for the hydride generation and the calibration. Beers law is obeyed for up to 0.40 µg of lead, and the sensitivity obtained is ca. 10 ng ml–1. The method has been applied to the determination of lead in commercial gasolines, with good accuracy and precision.

Extraction-spectrophotometric determination of germanium with phenylfluorone in N,N-dimethylformamide

Germanium(IV) is extracted as GeCl4 into toluene from 9.5 M HCI solution. The spectrophotometric determination of Ge is carried out in the same extracted phase by the addition of phenylfluorone (PF) solution in N,N-dimethylformamide. The Ge(IV)-PF complex gives an absorption maximum at 525 nm with a molar absorptivity of 7.08 ± 0.02 × 104 l mol–1 cm–1. This procedure compares favourably with respect to selectivity and stability with other methods for the determination of germanium using PF. The method has been applied to the determination of germanium in lignite ashes with good precision and accuracy. The results obtained by this method are compared with those obtained by two AAS methods (extraction of GeCl4 into hexane with flame AAS and also hydride generation).

Extraction-spectrophotometric determination of niobium with 1,2,4,6-tetraphenylpyridinium perchlorate and thiocyanate

1,2,4,6-Tetraphenylpyridinium (TPP+) as the acetate or perchlorate was used as a counter ion in the spectrophotometric determination of Nb(V) by extraction into toluene of the anionic Nb(V)-thiocyanate complex from 4–6 M hydrochloric acid. The molar absorptivity of the ion-association complex, whose composition was shown to be NbOCI(SCN)3–. TPP+, was 2.82 × 104 l mol–1 cm–1 at 395 nm. Beers law was obeyed over the range 0.1–2.5 µg ml–1 of Nb(V). The method was applied to the determination of niobium in standard steels and ores (culombite type) with good precision and accuracy.1-(4′-Nitrophenyl)-2,4,6-triphenylpyridinium (nitro-TPP+) perchlorate was also synthesised and used in the spectrophotometric determination of Nb(V), but did not show advantages over TPP+. The fluorescence of TPP+ and Nb(V)-SCN–-TPP+ solutions in toluene also disappeared when nitro-TPP+ was used, owing to the paramagnetic effect of the NO2 group.

Extraction-spectrofluorimetric determination of cadmium with diethyldithiocarbamate and calcein in non-aqueous media

Abstract Cadmium (7–80 ng ml −1 ) is extracted with diethyldithiocarbamate into chloroform from aqueous media, at pH 11–12 and the fluorescent complex is developed by addition of a calcein solution in dimethylformamide. The method is applied to the determination of cadmium in waste waters, high-purity metals and zinc ores.

Extractive spectrophotometric and fluorimetric determination of boron with 2,2,4-trimethyl-1,3-pentanediaol and carminic acid

Boric acid at mug ml or ng ml level can be extracted from 1-6M hydrochloric acid into 2,2,4-trimethyl-1,3-pentanediol solution in chloroform and thus separated from many ions which interfere in the usual spectrophotometric methods. The boron is determined directly in the organic phase without back-extraction into water, by adding a solution of carminic acid in a mixture of sulphuric and glacial acetic acids (1+2 v v ) and measuring the absorbance at 549 nm. The molar absorptivity is 2.58 x 10(4) l.mole(-1).cm(-1) and Beers law is valid for the 0.05-0.4 mug ml boron range. In the fluorimetric method, 509 or 547 nm can be used as the excitation wavelength and 567 nm for emission measurement, giving a linear response in the 8-120 ng ml boron range. Both methods have been applied to determination of boron in plants and natural waters with good precision and accuracy.

Extraction-spectrophotometric determination of niobium with N-phenylbenzohydroxamic acid and 4-(2-pyridylazo)resorcinol in non-aqueous media

A method for the spectrophotometric determination of niobium(V) is proposed, in which niobium(V) is extracted with N-phenylbenzohydroxamic acid into chloroform from 5 M hydrochloric acid. The colour is then developed in an aliquot of the chloroform extract by addition of 4-(2-pyridylazo)resorcinol solution in N,N-dimethylformamide without back-extraction. The molar absorptivity at 547 nm is 3.35 × 104 l mol–1 cm–1 with a relative standard deviation of 1.0%. The proposed method permits the determination of niobium(V) at trace levels in the presence of large amounts of other ions. The method has been applied to the determination of niobium in BCS standard steels and ores (IGS standard culombites) and high accuracy and precision have been obtained.

Extraction and spectrophotometric determination of uranium in ores

An extraction - spectrophotometric method is proposed for the determination of trace amounts of uranium in ores, based on its extraction with trioctylphosphine oxide in toluene and development of colour with glyoxal bis(2-hydroxyanil)(GBH) or 1-(2-pyridylazo)naphth-2-ol (PAN) in NN-dimethylformamide in the organic extraction phase without back-extraction. The maximum absorbance with GBH as reagent occurs at 600 nm with a molar absorptivity of 1.48 (± 0.01)× 104 1 mol–1 cm–1 and with PAN as reagent at 555 nm with a molar absorptivity of 2.61 (± 0.02)× 104 1 mol–1 cm–1. Beers law is obeyed over the ranges 0.6–10.5 and 0.3–6.0 µg ml–1 of uranium(VI)(corresponding to 20–350 and 10–200 µg of uranium in the sample) at 600 and 555 nm, with GBH and PAN, respectively.The proposed method has been applied successfully to the analysis of standard and synthetic uranium ores with uranium contents of up to 0.15%.

Determination of tin in organotin compounds by hydride generation atomic absorption spectrometry in organic media

A method is described for the determination of tin in organotin compounds (RnSnX4–n: R = butyl, phenyl; X = Cl, acetate, laurate; n= 2–4; and R4Sn: R = phenyl). The compounds were initially treated with bromine in CCl4 to separate the organic radicals bonded to tin. The reaction of the organotin compounds with bromine was of particular importance because the atomic absorption signal, without pre-treatment of the sample with bromine, depended on the organometallic compound studied. Hence, when R = butyl or phenyl, no atomic absorption peak was obtained, due to the low volatility of the alkyl (or aryl) tin hydrides formed (RnSnH4–n). Hydride generation atomic absorption spectrometry followed by direct atomisation in an electrically heated quartz tube was used for the determination. A detection limit of 1.5 ng ml–1 of tin was obtained and the precision was 3% for the determination of 4 µg of tin (n= 7).