Takashi Yoshino

Separation and acid equilibria of xylenol orange and semi-xylenol orange.

A mixture of Xylenol Orange (XO) and Semi-Xylenol Orange (SXO) was chromatographed on a cellulose column and ion-exchanged with Diaion SK-1 resin. XO and SXO in the acidic forms were titrated with sodium hydroxide to determine the basicities and the acid formation constants. The absorption spectra of XO and SXO were measured over a wide pH range, and were used for the calculation of acid formation constants, molar absorptivities, and the effect of ionic strength on the activity of XO. The purity of a commercial XO was measured by absorption spectroscopy, and it was found that the sample contained 36.3% of XO and 17.2% of SXO. Pure XO and SXO form a 1:2 and a 1:1 complex respectively with Zn(II). On the basis of these data the ionic structure of XO and SXO have been compared with those of Cresol Red and iminodiacetic acid, and discussed.

Acid equilibria of methylthymol blue and formation constants of cobalt(II), nickel(II), copper(II) and zinc(II) complexes with methylthymol blue.

Potentiometric and spectrophotometric studies on acid equilibria and reactions with Co(II), Ni(II), Cu(II) and Zn(II) for Methylthymol Blue (MTB) are described. The equilibrium constants have been calculated. MTB has been found to form 1:1 and 2:1 (mole ratio of metal to ligand) complexes, including protonated ones. The probable configuration of the complexes and the effects on the stabilities have been discussed.

Studies on methylthymol blue—I: Separation and purification of methylthymol blue and semimethylthymol blue

The metallochromic indicator Methylthymol Blue was purified chromatographically with cellulose and ion-exchange resin columns. The monosubstituted product of the reaction, Semimethylthymol Blue, was also separated and purified, and can also be used for the colorimetric determination of metals. There are not marked differences between the infrared spectra of Methylthymol Blue and Semimethylthymol Blue. The purities of Methylthymol Blue and Semimethylthymol Blue finally obtained were above 97% and 90% respectively. In acidic medium Methylthymol Blue forms 1:1 greyish blue and 1:2 pure blue chelates with copper(II) whilst Semimethylthymol Blue forms only 1:1 orange chelates with bivalent metals. The molar absorptivities at 435 mmu are 1.89 (+/- 0.03) x 10(4) for Methylthymol Blue at pH 5.00 and 1.76 (+/- 0.03) x 10(4) for Semimethylthymol Blue at pH 5.45.

Removal of chloride interference in the determination of chromium by atomic absorption spectrometry with electrothermal atomization

Abstract Two mechanisms of chloride interference are described. The first arises from coordination of chloride to chromium(III), which can be prevented by addition of a masking agent such as tetraammonium—EDTA, The other is due to chloride salts remaining at the atomization step; this can be prevented by volatilizing the chlorides or converting them to oxides before atomization.

Formation constants of zinc(II) complexes with Semi-Xylenol Orange.

A potentiometric and spectrophotometric investigation on the formation of zinc(II) complexes with Semi-Xylenol Orange (SXO or H(4)L) is reported. In an aqueous solution (mu = 0.1), three 1:1 complex species, MH(2)L, MHL(-), ML(2-), and a 1:2 complex, ML(6-)(2), seem to exist. In a strongly alkaline medium (above pH 12.5) the complexes may dissociate to give zinc hydroxide and L(4-). The formation of a hydroxy complex is not observed. The absorption maxima are at 445 nm (MH(2)L), 466 nm (MHL(-)) and 561 nm (ML(2-)), the molar absorptivities being 2.34 x 10(4), 2.42 x 10(4) and 3.14 x 10(4) 1.mole(-1) .cm(-1) respectively. The formation constants are (at 25 +/- 0.1 degrees ) log K(M)(ML) = 11.84, log K(M)(MHL) = 7.13, log K(M)(MH(2)L) = 2.70, log K(M)(ML(2)) = 16.60.

A method for removal of chloride interference in determination of aluminium by atomic-absorption spectrometry with a graphite furnace

Methods for removal of the chloride interferences in determination of aluminium by atomic-absorption spectrometry with a graphite furnace have been investigated. Two mechanisms of chloride interference have been established. The first arises from co-ordination of the chloride to aluminium. This interference can be removed by preventing the co-ordination. The other is due to co-existing chloride salts remaining until the atomization step. This interference can be removed by volatilizing the chloride or by converting it and/or aluminium chloride into another substance such as the oxides before the atomization step. The tetra-ammonium salt of EDTA is very suitable as an additive to overcome chloride interference because of its ability to co-ordinate aluminium and other cations, and also its effect when heated.

Oxygen reduction with hydroxy-1,4-naphthoquinones immobilized at carbon electrodes

Oxygen reduction with naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) has been studied by cyclic voltammetry and by flow-through electrolysis. The mechanisms of oxygen reduction were studied thermodynamically. At pH 7 the semiquinone anion is the most likely candidate for oxygen reduction among the reduced species of naphthazarin, including quinols, and the superoxide is mainly produced by this species. By flow-through electrolysis e.s.r. the semiquinone has been detected under anaerobic conditions. Its concentration depends on the potential because of disproportionation. Distribution of the semiquinone has been calculated against the potential, and the results are compared with the potential dependence of the e.s.r. intensity. The redox activity of other quinones has also been studied. Naphthazarin is the most active in oxygen reduction.

The removal of chloride interference in determination of chromate ion by atomic absorption spectrometry with electrothermal atomization

Abstract Two mechanisms of chloride interference in the atomic absorption spectrometry of chromate in a graphite furnace have been established. The first is due to chloride salts remaining at the atomization step; this can be prevented by volatilizing the chlorides or converting them to oxides before atomization. The other arises from formation of chlorochromate ions, which can be removed by addition of an organic acid. The tetraammonium salt of EDTA is very suitable for this purpose.

Equilibria of iron(III) complexes with xylenol orange and methylthymol blue

Abstract A potentiometric and spectrophotometric study of Fe(III) complexes with Xylenol Orange (XO) and Methylthymol Blue (MTB) has been made. The formation constants for the Fe(III) complexes with XO and MTB were determined. Evidence was found for the formations of 1:1 and 2:1 complexes (metal:ligand) and it was assumed that protonated and hydroxo-complexes exist in addition to the simple complex in each case. The hydroxo-complexes are stable over the pH range of 7–12. Suggestions are made concerning the probable structures of these complexes.

Electrothermal atomic absorption spectrometric determination of trace lead, copper and manganese in aluminum and its alloys without preliminary separation

Abstract Graphite-furnace atomic absorption spectrometry is used for the determination of >0.001% of lead, copper and manganese in aluminum and its alloys. The samples are dissolved in hydrochloric acid and analyzed directly after addition of a slight excess of (NH4)2 EDTA over aluminum. Sample and standard solutions must contain equal amounts of EDTA.