Ni Zhe-ming

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.

Determination of methylmercury in biological samples and sediments by capillary gas chromatography coupled with atomic absorption spectrometry after hydride derivatization and solid phase microextraction

A method for the extraction and determination of methylmercury in biological samples and sediments by solid phase microextraction (SPME) combined with capillary gas chromatography–atomic absorption spectrometry (GC–AAS) has been proposed. The methylmercury chloride was converted to its hydride form by potassium tetrahydroborate (KBH4) in a closed headspace vial prior to extraction. A laboratory-assembled SPME device including a capillary fused-silica fiber and a modified microsyringe was used throughout the experiment. The extraction is an equilibrium process that depends on the methylmercury hydride partitioning between the liquid phase and the fiber. When the equilibrium was reached, the fiber was directly transferred to a GC column by means of the microsyringe, where the analyte was thermally desorbed inside a heated injector and subsequently the column effluent was atomized by a heated stainless steel tube and detected by an on-line coupled AAS. Several factors affecting the SPME procedure such as fiber pretreatment with hydrofluoric acid, pH buffering, addition of salt and sampling time have been investigated and optimized. The reproducibility of the SPME procedure was 91% and the detection limit based on the signal equal to 3 times the baseline noise, was 26 ng. The method was applied to determination of methylmercury in biological samples and sediments.

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.

Determination of lead by hydride generation atomic absorption spectrometry with in situ, concentration in a zirconium coated graphite tube

A method is described for the determination of lead by the in situ concentration of lead hydride on a Zr coated graphite tube with subsequent detection by electrothermal atomic absorption spectrometry. The method gives a six-fold enhancement of sensitivity with respect to that using a pyrolytic graphite coated graphite tube for the sorption of lead hydride. The characteristic mass (i.e., the mass of analyte which provides a defined peak absorbance of 0.0044 A) is 52.8 pg. The relative standard deviation for ten replicate measurements is 2% at the level of 3 ng of lead. An absolute detection limit (3σ) of 242 pg is obtained. The proposed method has been applied successfully to the determination of lead in some reference materials and a tap water sample.

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.

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.

Organic mercury speciation in fish by capillary gas chromatography interfaced with atomic absorption spectrometry

SummaryA rapid method for the speciation of mercury in fish has been described. Organomercurials in benzene extract were separated by glass capillary gas chromatography and detected by atomic absorption spectrometry. Spiked alkylmercury in fish yielded 95% recovery with one single extraction with benzene. The absolute detection limit was about 1.0×10−10 g mercury. The method can be applied to the determination of 0.04 ppm of mercury in a 0.5 g sample.

Study of palladium–analyte binary system in the graphite furnace by surface analytical techniques

The mechanisms of the stabilization of Pb, Zn and As by a palladium modifier were investigated by scanning electron microscopy, X-ray diffraction spectrometry and X-ray photoelectron spectrometry. All three elements were found to form an intermetallic solid solution with excess of Pd. The concentration ratio of Pd to analyte varies with the surface depth of Pd–analyte species. Chemical shifts measured in the binding energy of Pd and analyte are insignificant. The monophase of the Pd lattice in which some Pd atoms are displaced by the analyte atoms has been identified as being dominant. It is suggested that the reduced Pd and analyte form a stable intermetallic solid solution during the ashing stage and the analyte atoms remain in the Pd lattice until the temperature is high enough to break down the lattice.