Kyoji Tôei

Spectrophotometric determination of phosphate in river waters with molybdate and malachite green

On the basis of the coloration formed with molybdate and malachite green in aqueous solution, trace amounts of phosphate were determined. The molar absorptivity was 7.8 × 104 l mol–1 cm–1 at 650 nm. The absorbance of the reagent blank was about 0.02, and its relative standard deviation was less than 10%. The recommended concentration range of phosphorus was 0.1–5 µg and the limit of detection was 0.01 µg of phosphorus. The sample solution was acidified with sulphuric acid and heated in a water-bath above 90 °C for 40 min, and subsequently it was coloured with molybdate and malachite green. The colour was stabilised by adding poly(vinyl alcohol). The method was applied to the determination of parts per billion (109) amounts of phosphorus in river and tap waters; the relative standard deviation was less than 4% and the recovery was 95–101%.

A conductometric method for colloid titrations

Abstract A negative or positive colloid sample solution can be directly titrated, respectively, with a polycationic (poly-N, N-diallyldimethylammonium chloride) or polyanionic (potassium polyvinylsulfate) titrant to a conductometric end-point. With the conventional toluidine blue indicator method a positive colloid solution is titrated directly with a polyanionic titrant, but a negative colloid solution must be treated with an excess of a polycationic titrant, which is back-titrated with the polyanionic titrant. For positive colloid solutions, both indicator and conductometric methods are suitable; for negative colloids the conductometric method is preferable because of its constant titration vlues over a range of pH values.

The gas chromatographic determination of selenium(IV) and total selenium in natural waters with 1,2-diamino-3,5-dibromobenzene

Abstract The total selenium and selenium(IV) contents in sea water and river water can be determined directly by a gas chromatographic method with l,2-diamino-3,5-dibromobenzene without preconcentration. The reagent reacts only with selenium(IV) to form a 4,6-dibromopiazselenol; other oxidation states of selenium must therefore be converted to the tetravalent state for total selenium determinations. The piazselenol formed can be extracted quantitatively into 1 ml of toluene from 500 ml of sample water. A method is proposed for the determination of selenium(IV) and total selenium in natural waters at levels as low as 2 ng l -1 . Coastal sea water and river water in Japan contain 8–30 ng of Se(IV) and 20–50 ng of total Se per liter.

Solvent extraction-spectrophotometric determination of phosphate with molybdate and malachite green in river water and sea-water

Molybdophosphate, formed between orthophosphate and molybdate in sulphuric acid solution, is extracted into a mixture of toluene and 4-methylpentan-2-one (1:3 v v ) with Malachite Green as counter-ion. A single extraction with equal phase volumes gives an apparent molar absorptivity for phosphate of 2.3 x 10(5) l.mole(-1).cm(-1) at 630 nm; the absorbance of the reagent blank is 0.03. With an organic to aqueous phase-volume ratio of 1:10, the molar absorptivity is 2.5 x 10(5) l.mole(-1).cm(-1) and the absorbance of the reagent blank 0.08. By the proposed method, ng ml levels of phosphorus can be determined, and the detection limit is about 0.1 ng ml . The standard deviation and relative standard deviation for the determination of phosphorus in tap water (4.3 ng ml ) are 0.05 ng ml and 1.1%, respectively. The method can also be applied to the determination of phosphorus in river water and sea-water.

Extractive spectrophotometric determination of non-ionic surfactants in water

The solvent extraction of non-ionic surfactants with potassium chloride and tetrabromophenolphthalein ethyl ester potassium salt has been studied, and a method developed for determining trace amounts of non-ionic surfactants in water spectrophotometrically. Various non-ionic surfactants of general type RO(CH(2)CH(2)O)(n)H (where R is an alkyl or alkylphenyl group and n is the number-average degree of polymerization) are extracted quantitatively into o-dichlorobenzene from the water sample, and reacted in the organic phase with tetrabromophenolphthalein ethyl ester potassium salt to give a coloured product, the absorbance of which is measured at 620 nm.

Fluorometric determination of nitrite in natural waters with 3-aminonaphthalene-1,5-disulphonic acid by flow-injection analysis

Nitrite in river and sea-water was determined fluorometrically by flow-injection analysis. In acidic medium, nitrite was reacted with 3-aminonaphthalene-1,5-disulphonic acid (C-acid) to form the diazonium salt, which was converted into the fluorescent azoic acid salt in an alkaline medium. The carrier stream, into which the sample solution was injected, was distilled water. The reagent solution stream, which contained C-acid, EDTA and hydrochloric acid, was mixed with the carrier stream in a 13-m length of Teflon tubing (bore 0.5 mm) maintained at 90 degrees in a thermostatic bath. After passing through the mixing coil, the stream was mixed with an alkaline solution. The fluorescence intensity (excited at 365 nm) was measured at 470 nm. The detection limit (S N = 3) was 1 x 10(-9)M (14 ng 1 . nitrite-nitrogen) and the RSD of 10 injections of 10(-6)M nitrite was 0.4%. Analyses can be done at a rate of up to 45 hr .

o-Diketonedioxime compounds as analytical reagents for the spectrophotometric determination of nickel

Sixteen dioxime compounds, including six new compounds, were synthesized and their reactions with nickel, cobalt, iron(II, III) and copper ions were examined. The nickel chelates of the glyoxime derivatives show hardly any absorption in the visible region, and are therefore unsuitable as color reagents. The nickel chelates of the benzildioxime derivatives can be extracted into organic solvents and provide a selective color reaction, so that useful extraction-spectrophotometric methods are possible. The metal complexes of quinonedioximes are extracted into some organic solvents, and the complexes have relatively large molar absorptivities in the visible region, but the reagents are not selective. However, the molar absorptivity of the ternary complex, Ni2+-reagent-zephiramine, with 1,2-naphthoquinonedioxime-4-sulfonic acid was 2.03·104 at 480 nm, and that of the nickel complex of 9,10-phenanthrenequinonedioxime was 2.49·104at 456 nm. The compositions of the nickel-dioxime complexes were examined spectrophotometrically.

Determination of ultramicro amounts of selenium by gas chromatography

4-Chloro-o-phenylenediamine reacts with selenous acid at pH 0-1 to form 5-chloropiaselenol, which is then extracted into 1 ml of toluene. The toluene layer is injected into an electron-capture detector gas Chromatograph. From the peak height selenium is determined, the minimum amount detectable being about 0.04 mug.

Determination of ultramicro amounts of selenium by gas chromatography with electron-capture detection

Formation of piazselenols by the reaction of Se(IV) with 1,2-diaminobenzene and its derivatives, followed by solvent extraction and gas chromatography with electron-capture detection, provides the most sensitive means of determining selenium. By suitable chemical manipulation, the method can be used for Se(-II), Se(O), Se(IV) and Se(VI). Applications to a wide variety of samples are reviewed.

Gas-chromatographic determination of ultramicro amounts of selenium in pure sulphuric acid.

Ultramicro amounts of selenium in pure sulphuric acid are converted into selenous acid with a bromine-bromide redox buffer solution. The selenous acid reacts quantitatively with 4-nitro-o-phenyl-enediamine to form 5-nitropiaselenol which can be extracted into toluene. The extract is very sensitive to electron-capture detection in gas chromatography, and the sensitivity is higher than that of 5-chloro-or 4, 5-dichloro-piaselenol. The calibration curve (peak heights) is linear up to 0.15 mug of selenium in 1 ml of toluene. Pure sulphuric acid, commercially available, contains 10(-6)