Dieter Klockow

Determination of sulfur dioxide in air on the basis of the catalyzed autoxidation of Co(II) in an azide medium

A method used for the determination of S(IV) in precipitation was adapted for measurements of SO2 in air. A solution containing tris(hydroxymethyl)-aminomethane (TRIS) and sodium azide is used to trap SO2 during 30 min at an air flow of 15–40 L/h−1. The addition of a solution containing perchloric acid, CO2+ and Mn2+ leads to a formation of a mixture of azido-cobaltate(III) complexes (pH 5.2–5.4 for the final HN3/N3−-buffer), proportional to the total [S(IV)] in the absorption solution. Spectrophotometric measurement is performed at 365 nm with a slope of (3.07±0.03)×104 L·mol−1·cm−1 of the calibration curve. Detection limit is 8×10−8 M in the working solution with 5 cm light path cuvettes. This results in a relative detection limit of 2.8 μg SO2/m3 under the sampling conditions chosen. Interference of oxidants and H2S is avoided by inserting in the sampling train a cartridge containing FeSO4·7H2O and silver wool upstream of the absorber. Oxides of nitrogen do not interfere. The method provides results comparable with those obtained with a coulometric monitor based on the I2/I− system.

The sulfur(IV)–cobalt(II)–azide system and its application to the investigation of the decomposition of sulfur hexafluoride under electrical discharges

A wet chemical procedure is described that is suitable for investigating the degradation of sulfur hexafluoride (SF6), used as an insulating medium in high-voltage and ultra-high-voltage power equipment. It is based on the alkaline hydrolysis of SIV species present in aged SF6 and subsequent spectrophotometric determination of sulfite through its capability to accelerate the autoxidation of CoII to CoIII in aqueous azide solution. Results showing the ageing of SF6 as a function of time are presented.

The Catalytic Cycle of Oxidation of Iodide Ion in the Oxygen/Nitrous Acid/Nitric Oxide System and Its Potential for Analytical Applications

Abstract The oxidation of iodide to iodine by nitrous acid in aqueous acidic medium takes place catalytically in the presence of dissolved oxygen and can be followed spectrophotometrically at 288 and 352 nm. An indirect molar absorptivity for nitrite on the basis of I3 − formation can be as high as 8.5×105 L mol−1 cm−1 at 288 nm. Analytical curves were established. The iodine released in the catalytic cycle can also be titrated with thiosulfate. The reaction is pseudo–second‐order in oxygen consumed, with t1/2=15.7 min at 25°C. A rate determining step could be the NO · O2 as the activated species. Measurements of the iodine formed at catalytic conditions was used to determine nitrite in meat extracts and NOx in car exhausts.