A new graphical method based on stoichiometric dilution for the classification of binary complexes with mole ratio 1:1.

A simple approach to the treatment of spectrophotometric data obtained by stoichiometric dilution is presented for complexes of the type M(m)B(n) and m/n = 1. The values of m and n are obtained by matching the slope of a straight line with a mathematically predicted value. The method can be applied to moderately strong complexes, the concentration of which can be determined by absorbance measurements, and allows calculation of the formation constant as well.

Spectrophotometric study on the reactions of iron(II) and iron(III) with Bromopyrogallol Red and hexadecyltrimethylammonium bromide.

Bromopyrogallol Red (BPR) combines with iron(III) in the presence of hexadecyltrimethylammonium bromide (CTMAB) to form an intensely blue complex having a molar absorptivity of 5.20 x 10(4)l. mole(-1).cm(-1) at 635 nm. The complex contains three molecules of BPR co-ordinated to an iron(III) ion, and two molecules of CTMAB associated with each BPR molecule, giving the overall formula (CTMAB)(6)(BPR)(3)Fe(III). Iron(II) also reacts with BPR and CTMAB in the presence of dissolved oxygen to form the iron(III) complex. No oxidizing or reducing agents are required for the determination of total iron in mixtures of iron(III) and iron(II), and Beer's law is followed from 0.05 to 0.5 ppm iron (1.00-cm cells). Of nine metal ions tested at the 1-ppm level, only manganese(II) and vanadium(V) interfere. Copper(II), cobalt(II), zinc, lead, nickel, aluminium and chromium(III) produce little or no interference when present at 100 ppm concentration.

Mixed-ligand complexes of iron and hydroxy-1,10-phenanthrolines.

The half-wave potentials of all of the possible tris-complexes formed between iron(II) and 1,10-phenanthroline (A), 4-hydroxy-1,10-phenanthroline (B), and 4,7-dihydroxy-1,10-phenanthroline (C) have been measured at a rotated platinum electrode. Values on the hydrogen scale are 1.06 V for A(3)Fe(II), 0.78 for A(2)B, 0.58 for A(2)C, 0.60 for AB(2), 0.39 for B(3), 0.39 for ABC, 0.21 for AC(2), 0.22 for B(2)C, 0.06 for BC(2), and -0.10 for C(3) at pH 11.0, 25 degrees , and ionic strength 0.2. Half-wave potentials of the parent binary complexes are constant from pH 9 to 13 and are equal to the conditional reduction potentials. The mixed complexes are stable from pH 10 to 12, and form a redox indicator system with a continuous range of accessible potentials from -0.10 to +1.06 V vs. NHE.

Effect of pH on the conditional reduction potential of the tris(1,10-phenanthroline)iron(III,II) couple.

The half-wave potential for reduction of tris(1,10-phenanthroline)iron(II) at a rotated platinum electrode is constant from pH 0 to 11. The value is 1.06 V at 25.0 degrees and ionic strength 1.0 and is equal to the conditional reduction potential of the tris(1,10-phenanthroline)iron(III,II) couple, as demonstrated by cyclic voltammetry.

Spectrophotometric determination of iron in highly alkaline solution with 4-hydroxy-1,10-phenanthroline.

4-Hydroxy-1,10-phenanthroline forms a stable tris-chelate with iron(II) in the range of alkalinity from pH 10 to 2M sodium hydroxide, with molar absorptivity 1.19 x 10(4) l.mole(-1).cm(-1) at 545 nm. The determination of iron is performed by adding the phenanthroline, stannous chloride, and iron-free sodium hydroxide to the sample to give pH > 13; stannite is the active reductant. Beer's law is obeyed over the iron concentration range from 1 x 10(-5) to 8 x 10(-5)M. Advantages over existing methods are the use of stannous chloride instead of sodium dithionite, which avoids the problem of turbidity, and the stability of the iron(II) chelate towards oxidation by air. The conditional reduction potential at pH 11 for the iron(III)/iron(II) complex couple is 0.39 V.

Iron (III) derivatives of 4,7-dihydroxy-1,10-phenanthroline.

The chemistry of the iron (III) derivatives of 4,7-dihydroxy-l,10-phenanthroline has been studied in detail. Oxidation of the intensely red tris(4,7-dihydroxy-l,10-phenanthroline) iron (II) ion results in a grey compound, tris(4,7-dihydroxy-l,10-phenanthroline)iron(III), which is stable below pH 10. Above pH 10 the grey compound is partially converted into an amber compound in which the ratio of phenanthroline to iron is 2:1. The amber compound is the conjugate base of a purple 2:1 compound with pK(a) = 9.77. The visible absorption spectra of the three species at various pH values are reported. For 4,7-dihydroxy-1,10-phenanthroline pK(3), as determined by ultraviolet absorptometry, is 12.62 +/- 0.2.

Tris(4,7-dihydroxy-1,10-phenanthroline)iron(II) as a low-potential oxidation-reduction indicator: determination of hydrosulphite.

The formal reduction potential of the tris(4,7-dihydroxy-1,10-phenanthroline)iron(III,II) couple is -0.06 V in the pH range 10-13, not -0.11 V as reported earlier. The couple forms an excellent visual oxidation-reduction indicator for the titration of sodium hydrosulphite with potassium ferricyanide in alkaline solution.

Location of end-points in high-precision coulometry.

A computer has been used to fit a cubic equation to experimental data obtained in the region of the end-point in high-precision coulometric titrations of 4-aminopyridine and tris(hydroxy-methyl) aminomethane. For these weak bases, the two end-points (points of inflexion calculated by setting the second derivative equal to zero) obtained by choosing first time, and secondly pH, as the independent variable, are in good agreement.

On the properties of Calcein Blue.

A satisfactory method for the preparation of Calcein Blue has been devised. Elemental analysis, equivalent weight by neutralization, and the NMR spectrum show the compound to be 4-methylumbelliferone-8-methyleneiminodiacetic acid.0.25H(2)O. The ultraviolet absorbance and fluorescence have been studied as a function of pH and, combined with potentiometric titration and solubility date, have yielded for the acid dissociation constants the values pK(1) = 3.0, pK(2) = 6.9, and pK(3) = 11.3. These acid functions are identified respectively as carboxyl, phenol, and ammonium ion, the free Calcein Blue being a zwitter-ion. Calcein Blue fluoresces in both acidic and basic solution when excited at a suitable wavelength. The fluorescence of the doubly-charged anion formed on the neutralization of the phenol group, when excited at 360 nm, reaches a maximum at pH 9, and decreases to zero with the neutralization of the ammonium ion; the wavelength of maximum emission is 455 nm. In the presence of calcium, the fluorescence increases with alkalinity up to pH 9 and then remains constant. The calcium derivative is a 1:1 compound, formation constant 10(7.1). The fluorescence of Calcein Blue at all pH values is quenched by copper(II). The calcium derivative is changed on standing in highly alkaline solution, presumably by ring opening, to another fluorescent material; thus Calcein Blue, although satisfactory as an indicator, is not useful for the direct fluorometric determination of calcium.

Spectrophotometric determination of dissolved oxygen with tris(4,7-dihydroxy-1,10-phenanthroline)iron(II).

Tris(4,7-dihydroxy-1,10-phenanthroline)iron(II) reacts rapidly and quantitatively with dissolved oxygen in alkaline aqueous solution. In ammoniacal solution, the reaction is accompanied by the disappearance of the intense red colour of the iron(II) compound, which gives way to the pale gray, slightly-dissociated ion tris(4,7-dihydroxy-1,10-phenanthrolinefiron)(III). By measurement of the absorbance of a solution containing the ferrous compound before and after the injection of an oxygen-containing solution, the concentration of dissolved oxygen in the sample can be accurately determined in the range 1-20 ppm.