Bruno Jaselskis

Spectrophotometric determination of micro amounts of hydrazine and hydroxylamine alone and in the presence of each other

Hydrazine and hydroxylamine alone or in the presence of each other are determined at concentrations of 1-10 microg/25 ml with a relative precision of 3-0.8% by using iron(III) in the presence of Ferrozine.

Voltammetric determination of hydrazine and hydroxylamine

Hydrazine or hydroxylamine when present at concentrations of 0.32–5.7 mg 1–1 are readily determined in an acetate buffer at pH 5.0 by voltammetry using a rotating platinum electrode and measuring the current plateau at 0.85 V versus S.C.E. In mixtures, hydrazine and hydroxylamine are determined by measuring the plateau current before and 5 min after the addition of acetone. Amounts of hydrazine and hydroxylamine are obtained either algebraically or graphically. In this manner, the amounts can be determined with a relative standard deviation of better than 2% when present alone. In mixtures the relative standard deviation varies from 2 to 5% depending on the amount present.

Spectrophotometric determination of nitrate and nitrite in natural water and sea-water.

Nitrate and nitrite in natural waters are determined spectrophotometrically by passage through an amalgamated zinc reductor at pH 3.4 into iron(III)-Ferrozine solution. Interference by high levels of nitrite is eliminated by treatment with azide. Levels as low as 0.2 mug ml (expressed as nitrogen) can be determined with a precision of +/- 3%.

Determination of the fatty-acid composition of soybean oil by high-pressure liquid chromatography

A method for determining the fatty-acid composition of soybean oil by using high-pressure liquid chromatography (HPLC) is discussed and compared with the determination using gas chromatography. The oil is saponified and an aliquot is treated directly to form the p-bromophenacyl esters of the fatty acids, which are separated by gradient-elution HPLC. It is shown that glycerol does not interfere with the esterification, thus obviating the solvent extraction previously used to isolate fatty acids from biological samples.

Ultratrace molybdenum determination in biological samples by graphite-furnace atomic-absorption spectrometry

A method is described for molybdenum determination in human serum at sub-ng/ml levels by graphite-furnace atomic-absorption spectrometry. Sample preparation involves a nitric acid digestion, chelation with benzohydroxamic acid and extraction into hexanol. A detection limit of 0.1 ng/ml and a characteristic concentration of 0.18 ng/ml for 1% absorption can be achieved. The effectiveness of the method has been demonstrated by analysis of unspiked and spiked human serum, standard reference materials, and comparison with the results obtained by inductively-coupled plasma atomic-emission spectroscopy.

Chemical reduction and spectrophotometric determination of silver, copper and nickel

Silver(I), copper(II) and nickel(II) can be reduced to the metallic state by formaldehyde at pH 11, chromium(II) in 2.5M sulphuric acid, and borohydride at pH 5.5-6.0, respectively. Reoxidation of these metals with iron(III) in the presence of Ferrozine enables their determination at concentration below 1 mug/ml by measurement of the absorbance of the iron(II)-Ferrozine complex at 562 nm, with a precision better than 3%. The apparent molar absorptivities for silver, copper and nickel are 2.78 x 10(4), 5.56 x 10(4) and 5.58 x 10(4) l.mole(-1).cm(-1), respectively. The average thickness of silver films on glass surfaces can be determined in the way.

Proton nuclear magnetic resonance determination of hexamethylenetetramine in the presence of formaldehyde and urine

A new proton NMR method has been developed for micro-amount determination of aqueous hexamethylenetetramine (HMT) alone, in the presence of large amounts of formaldehyde, and in urine. The method is based on the direct determination of HMT in [2H3]acetonitrile containing anisole as the internal reference standard. HMT is determined in the range 5–50 µg using a 5 mm NMR tube.

Spectrophotometric determination of formaldehyde.

A new spectrophotometric method for the determination of micro amounts of formaldehyde in aqueous and methanol solutions is based on the oxidation of formaldehyde by hydrous silver oxide at pH 11-12.5 and oxidation of the metallic silver produced, with iron(III) in the presence of Ferrozine. The absorbance of the resulting iron(II)-Ferrozine complex at 562 nm is proportional to the amount of formaldehyde and corresponds to an apparent molar absorptivity of 5.58 x 10(4) 1.mole(-1).cm(-1).

Differential pulse polarographic determination of orthophosphate in aqueous media

The determination of orthophosphate in aqueous media by differential pulse polarography is described. It is based on determination of the molybdenum in 12-phosphomolybdic acid. High sensitivity is achieved by measuring the polarographic wave due to the catalytic reduction of perchlorate or nitrate in the presence of molybdenum(VI). The method is suitable for samples as small as 3.5 ml which contain as little as 9 ng of phosphorus per ml. The average relative deviation is 3.0% at the 0.045 mg/l. phosphorus level and 1.6% at the 1.2 mg/l. level. Results for the analysis of EPA quality-control water and real surface-water samples are reported.

Titrimetric determination of some organic acids by xenon trioxide oxidation.

Aqueous xenon trioxide in acidic or neutral solutions oxidises carboxylic acids quantitatively to carbon dioxide and water. Micro and semimicro amounts of carboxylic acids may be determined by the iodometric titration of the excess of xenon trioxide remaining in the reaction mixture. The optimum time and temperature for the reaction depend on the structure of the acid ; dicarboxylic and hydroxy-carboxylic acids react faster than corresponding monocarboxylic acids. Oxalic and polyhydroxy acids are oxidised within 20 min at room temperature while acetic, maleic, succinic, malonic acids require 2 hr at 40 degrees . Carboxylic acids in amounts less than 100 mug are determined with a coefficient of variation of 4%, which decreases to 1 % for amounts over 250 mug.