Shan Xiao-quan

The reduction and elimination of matrix interferences in graphite furnace atomic absorption spectrometry

Abstract The approaches to reduction or elimination of matrix interferences encountered in graphite furnance atomic absorption spectrometry is reviewed. These techniques include matrix modification, application of active gas, and coating tubes with metallic compounds. The research work carried out in the authors laboratory is emphasized. A more universal matrix modifier, palladium, is proposed for the determination of mercury, lead, tellurium, bismuth, arsenic, thallium and indium in environmental samples.

Is palladium or palladium–ascorbic acid or palladium–magnesium nitrate a more universal chemical modifier for electrothermal atomic absorption spectrometry?

A comprehensive comparison was made between the performances of Pd, Pd–ascorbic acid and Pd–Mg(NO3)2 for the determination of Ag, As, Au, Bi, Cd, Ga, Ge, Hg, In, Mn, Pb, Sb, Se, Sn, Te and Tl in terms of charring temperatures available, characteristic mass values, background absorption, permissible interference range, capability of improving the atomization signal shapes and relative standard deviations of the determinations of trace elements in real samples. Generally, the performances of Pd, Pd–ascorbic acid and Pd–Mg are similar, except that the background absorption of the Pd–Mg modifier is 1–2 orders of magnitude greater than that of the Pd and Pd–ascorbic acid modifiers. Therefore, the need for the addition of ascorbic acid appears to be matrix-dependent, while the addition of Mg(NO3)2 is not recommended.

Selective separation and differential determination of antimony(III) and antimony(V) by solvent extraction with N-benzoyl-N-phenylhydroxylamine and graphite-furnace atomic-absorption spectrometry using a matrix-modification technique

If copper is used as a matrix modifier for the determination of antimony, the ashing temperature for antimony in aqueous solution and a BPHA-CHCl(3) extract can be raised to 1300 degrees and 1100 degrees , respectively. A selective procedure for separating antimony(III) from antimony(V) by extraction with BPHA in chloroform is described, along with the conditions for preserving trace antimony in water samples. The recommended method has been applied satisfactorily to the determination of antimony(III) and antimony(V) in various types of water at sub-ng/ml levels.

In situ concentration of metallic hydrides in a graphite furnace coated with palladium

Abstract A method has been developed for the ultrasensitive determination of arsenic, antimony and selenium by hydride generation with subsequent trapping and atomization in the graphite furnace coated with micrograms of palladium which is used as an adsorber for the hydrides. Calibrations are achieved with simple calibration graphs having sensitivities of 10.0, 13.1 and 14.7 pg/0.0044A for arsenic, antimony and selenium, respectively. The recommended method has been applied satisfactorily to the determination of arsenic, antimony and selenium in urine and various types of water samples at ng/ml levels.

Application of matrix-modification in determination of thallium in waste water by graphite-furnace atomic-absorption spectrometry

A method has been developed for the determination of thallium in waste water at the ng ml level by graphite-furnace atomic-absorption spectrometry. If microgram amounts of palladium or platinum are used as a matrix modifier, the ashing temperature for thallium can be raised to 1000 degrees , and the interference of halides and mineral acids is greatly reduced. The relative standard deviation found was 2% (9 replicate determinations) at the 8-ng ml thallium level, and the detection limit 1 ng ml .

In situ concentration of metallic hydride in a graphite furnace coated with palladium—determination of bismuth, germanium and tellurium

Abstract An analytical method for the ultrasensitive determination of bismuth, germanium and tellurium is described. Analytes were reduced to their corresponding hydrides. A graphite tube coated with palladium was used as the collection medium and atomizer. Palladium was found to be a very efficient adsorber for bismuth, germanium and tellurium hydrides. The operating conditions were optimized, and the technique has been successfully applied to the determination of these elements in geological materials and natural water samples.

Matrix modification for determination of selenium in geological samples by graphite-furnace atomic-absorption spectrometry after preseparation with thiol cotton fibre

A graphite-furnace atomic-absorption method has been developed for the determination of selenium in geological samples at or below the mug g level after decomposition of the sample with a mixture of perchloric, hydrofluoric and nitric acids and separation of selenium from the sample matrix with thiol cotton fibre. A few micrograms of palladium are added as a matrix modifier for the atomic-absorption determination. In the presence of palladium the charring temperature for selenium can be raised to 1100 degrees , and the signal enhancement is greater than with other matrix modifiers reported in the literature.

Evaluation of a sequential extraction procedure for the fractionation of amorphous iron and manganese oxides and organic matter in soils

A commonly applied sequential extraction procedure was evaluated with special emphasis on the interaction of amorphous iron and manganese oxides and organic matter in two soil samples. The results show that the fractionation was obscured by significant uncertainty. It is suggested that reduction of manganese oxides and amorphous iron oxides by NH2OH · HCl is hindered by a covering or occlusion of organic matter. Due to the presence of these components partly as a combined phase rather than discrete phases, the selective dissolution of these entities in soils by the tested method is impossible and the nominated speciation of the associated trace metals, as outlined in the procedure, appears to give ambiguous information.

Determination of alkylselenides by gas chromatography–electrothermal atomic absorption spectrometry

A method for the determination of alkylselenides by gas chromatography (GC)–electrothermal atomic absorption spectrometry is proposed. Dimethylselenide, diethylselenide and dimethyldiselenide were separated by GC, followed by introduction of the separated compounds into a graphite furnace sequentially; the compounds were then adsorbed onto the palladium coated graphite furnace wall. Sufficient time was allowed for operation of the furnace programme during the time interval between each elution peak. The sensitivities expressed as characteristic mass giving 0.0044 absorbance are 0.018, 0.012 and 0.030 ng of selenium in dimethylselenide, diethylselenide and dimethyldiselenide, respectively. The proposed method was applied to the determination of organic vapour-phase selenium evolved from soil.

COMPARATIVE CHARACTERISTIC STUDIES ON SOIL AND COMMERCIAL HUMIC ACIDS

SummaryTwo commercial and eight soil humic acids were characterized to evaluate the use of commercial humic materials in soil and environmental studies. Significant differences between commercial and soil humic acids were observed in ash content, major and micro-element constituents, E4/E6 ratio, total acidity and 13C-NMR spectroscopy; but data from stability constant and IR-spectroscopy were almost identical. The commercial materials appeared to be significantly less aromatic and more aliphatic in nature as compared with representative soil humic acids. The above discrepancies were interpreted as indicating an origin of the respective commercial product other than soil. The two commercial humic acids investigated may not originate from the same source material as evidenced by clear-cut differences in the intensity of the 13C-NMR spectra in almost all chemical shift regions. Due to the observed structural, compositional and characteristic dissimilarities, both between soil and commercial humic acids and between different commercial ones, the commercial humic products are not recommended to be used as analogues of real soil humic acids in soil and environmental studies.