Ragnar Bye

Interferences from bivalent cations in the determination of selenium by hydride-generation and atomic-absorption spectrometry: a discussion of the claim that the metal ions are reduced to the metallic state by sodium borohydride.

The cause of interference by bivalent cations in the determination of selenium by hydridegeneration and atomic-absorption is still the subject of debate. It is suggested that these ions react with sodium borohydride to produce the metal borides and not, as generally supposed, the elemental metals. The metal borides are known to be highly reactive and could cause decomposition of the selenium hydride before it reaches the detection unit.

Critical examination of some common reagents for reducing selenium species in chemical analysis.

In an attempt to resolve apparently conflicting statements in the literature, a study has been made of the action of various reductants on selenium(VI) and selenium(IV). Chloride in hot non-oxidizing acid medium will reduce Se(VI) to Se(IV) but not further. Sulphur dioxide will reduce Se(IV) to Se, but has no effect on Se(VI). Hydrazinium salts reduce both Se(VI) and Se(VI) to Se, but hydroxylammonium salts reduce only Se(IV) to Se. Hydrogen peroxide partially reduces Se(VI) to Se(IV) but not further. If chloride is also present [to reduce Se(VI) to Se(IV)], sulphur dioxide or hydroxylammonium salts can then reduce the Se(IV) to Se, and this combined effect has led to some confusion in interpretation of experimental observations.

Determination of selenium by hydride generation atomic absorption spectrometry: elimination of interferences from very high concentrations of nickel, cobalt, iron and chromium by complexation

The use of an alkaline sample solution for the determination of Se by the hydride generation technique offers the possibility of eliminating the interference from very high concentrations of Ni2+, Co2+, Fe3+, and Cr3+. In order to achieve this, complexing agents were employed to mask the interfering metal ions. After addition of the masking agent, the pH was adjusted to 12–13 with NaOH, and sodium tetrahydroborate was finally added in order to reduce selenite to selenide ions. The selenium hydride was generated by acidifying the solution with HCl in a flow system. Ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid (DTPA) were found to be effective masking agents for Ni2+ and Co2+; the interference from up to 8000 mg l–1 of Ni2+ or Co2+ was eliminated. Tartrate was found to be a suitable masking agent for Fe3+ and Cr3+ up to 5000 mg l–1. Accurate results were obtained for the National Institute of Standards and Technology Standard Reference Materials 671 Nickel Oxide and 364 Low-alloy Steel, using combinations of DTPA and tartrate as masking agents. The detection limits were 0.1 µg g–1 for the Nickel Oxide and 0.3 µg g–1 for the Low-alloy Steel.

Chemical and biological characterization of pectin-like polysaccharides from the bark of the Malian medicinal tree Cola cordifolia

The bark of Cola cordifolia used in Malian traditional medicine contains unusual types of polysaccharides with immunomodulating activities. We report for the first time on the structure of a polymer designated CC1P1 having the repeating structure [2→)[α-D-Gal(1→3)]α-L-Rha(1→4)α-d-GalA(1→] as determined by NMR and GC/MS. α-Linked Gal is unusual in pectins. The Mw of 135 kDa was determined by SEC-MALLS. CC1P2 (1400 kDa), another polymer, having the same backbone, but this was substituted with α-4-OMe-GlcA, α-2-OMe-Gal and α-Gal as terminal units. CC1P1 shows a high complement-fixing activity, IC₅₀ being 2.2 times lower than the positive pectin control PMII (IC₅₀ appr. 71 μg/mL) while IC₅₀ of CC1P2 is 1.8 times lower. The simple structure of CC1P1 did not activate macrophages, while CC1P2 (100 μg/mL) showed the same potency as the positive controls PMII (100 μg/mL) and LPS (500 ng/mL). No cytotoxicity was detected.

Determination of arsenic and tellurium by hydride generation atomic spectrometry: minimizing interferences from nickel, cobalt and copper by using an alkaline sample solution

An alkaline sample solution in combination with the complexing agent diethylenetriaminepentaacetic acid (DTPA) was employed to minimize interference from Ni and Co in the determination of As and Te by hydride generation inductively coupled plasma atomic emission spectrometry. Tetrahydroborate was also added to the sample solution, before the hydride was generated by acidification with HCl in a continuous-flow system. The masking method was used for the determination of As and Te in the reference material NIST SRM 899 Nickel Alloy. For the determination of As in a copper sample, the interference from Cu was removed by precipitation of the hydroxide and filtration. The precipitation method was used for the determination of As in the reference material NIST SRM 398 Unalloyed Copper V; hydride generation atomic absorption spectrometry was employed to determine the concentration of As.

Optimal conditions for the reduction of selenate to selenite by hydrochloric acid

SummaryThe rate of reduction of Se(VI) to Se(IV) by hydrochloric acid was studied as a function of the acid concentration, temperature and reaction time. The reaction product Se(IV) was measured with the hydride generation-atomic absorption technique. The results show that for 10 mol/l HCl a complete reduction is achieved within 15 min at 60°C. The activation energy of the apparent first-order reaction was calculated from the results, and a value of 83 kJ mol−1 was obtained.

Reduction of gaseous phase interference in hydride generation using inductively coupled plasma atomic emission instead of flame heated quartz tube atomic absorption spectrometry: determination of selenium in nickel alloys and low-alloy steels

Selenium was determined in nickel and steel alloys by hydride generation in combination with both atomic absorption spectrometry (AAS)(heated quartz tube) and inductively coupled plasma atomic emission spectrometry (ICP-AES). A serious depression of the Se signal was observed when AAS was used for the determination, although the interference from Ni, Co, Cr, Fe and Cu was effectively masked with complexing agents. The depression was reduced when ICP-AES was used instead of AAS, indicating a gaseous phase interference. The interference may be caused by the presence of hydrides of Sn and As. For the determination of Se in nickel alloys and low-alloy steels, the detection limit was lowered by a factor 1.5–3 when ICP-AES was used instead of AAS. Several standard reference materials (nickel alloys and low-alloy steels) were analysed for Se.

The masking effect of iron(III) on the interference from nickel and copper in the determination of tellurium by hydride generation/atomic absorption spectrometry

Abstract Iron(III) can minimize the serious interferences from copper(II) and nickel(Il) on the determination of tellurium by hydride generation/atomic absorption spectrometry. The optimal concentrations were found to be 1 g l −1 and 2 g l −1 Fe (III) in 4.0 mol l −1 HCl in presence of nickel (II) and copper (II), respectively. The signals were only 25 % lower in a solution of 1.6 g 1 −1 Ni(II) than for a nickel-free solution. For copper (II), reasonable sensitivity was retained in the presence of 100 mg l −1 Cu(II).

Iron(III) as releasing agent for copper interference in the determination of selenium by hydride-generation atomic absorption spectrometry

Abstract Iron(III0 has a very effective releasing effect on the depressive interference from copper(II) on the determination of selenium by hydride-generation atomic absorption spectrometry. In solutionwith 100 mg 1 −1 Cu(II), 10 μg 1 −1 Se(IV) and 2.0 mol l −1 HCl, the absorbance obtained was much higher when 8 g 1 −1 Fe(III) was added than for any earlier releasing agent.

Atomic absorption spectrometry of selenium in an argon-hydrogen flame after electrochemical preconcentration

Abstract Different methods of atomization of selenium from a platinum wire filament are described, including electrothermal heating of the filament and atomlzation in an argon-hydrogen flame. A combination of these approaches proved to give the best sensitivity and detection limit. The selenium was preconcentrated on the filament by electrolysis prior to the atomic absorption measurements to eliminate chemical interferences and improve the sensitivity of the method. The detection limit was 0.5 μg l -1 for a 5-min electrolysis, and 0.2 μg l -1 when the electrolysis time was 30 min.