Colour changes of chemical indicators-VI: metallochromic indicators for direct chelometric titrations of zinc

Eriochrome Blue SE, Eriochrome Red B, Naphthylazoxine 6S, SNAZOXS, and Zincon have been studied in order to find optimum conditions for their use as metallochromic indicators in direct visual chelometric titrations of zinc. The sharpness of the indicator transitions has been investigated by means of photometric titrations and the colour quality has been specified with the aid of the C.I.E. chromaticity systems. Zincon and Eriochrome Blue SE have been found to be the most convenient for visual titrations of zinc.     

Photometric titrations with indicators

Various types of photometric titration curves are discussed. If a metal M is titrated conipleximetrically using a metal indicator and the absorbance is plotted vs. the titrant consumed, the inflection point appears at a pM value defined by the equation 3 pM_infl = pM_trans + 2 pM_eqThis expression is valid when M combines in a 1 : 1 ratio with the complexing agent and the indicator and when the indicator concentration is small compared to the total metal concentration.The difference between the pM values at the inflection and equivalence points can be calculated from the equation ΔpM = pM_infl — pM_eq = $\text{1}\text{3}$(pM_trans — pM_eq) = $\text{1}\text{6}$log(C_MK²_MI/K_MY)If the inflection point is taken as the equivalence point, the error arising can be calculated from ΔpM, or more simply, read from a diagram.If transmittance, instead of absorbancc, is plotted as a function of the titrant volume, the inflection point depends on the added amount of indicator. However, at high transmittance values, i.e., at low indicator concentrations, the inflection point of a transmittance curve occurs practically at the same volume of added titrant as the inflection point of an absorbance curve. Rules are given for applying an indicator correction for the amount of metal bound to the indicator at the end-point.The derived equations and discussions can also be applied to acid-base titrations.     

Studies on metallochromic indicators--II. Zincon and its mercury and zinc complexes as indicators in EDTA titrations

Zincon has been found to be an excellent indicator in the titration of mercury(II) with EDTA at pH 5.5-7. Moreover the mercury(II)-Zincon and zinc-Zincon systems have been found to be suitable indicators in the direct EDTA titrations of Pb(2+), Cd(1+) and Ca(2+). Interference studies of a number of cations and anions have been made. Chloride and bromide can be tolerated in the titration of mercury(II), up to equivalent concentrations.     

The use of Omega Chrome Black Blue G in chelatometric titrations

Summary The reactions of Omega Chrome Black Blue G with a large number of cations is studied. This study has shown in many cases high sensitivity limits of detection of metals. It also showed that this dye can be used as an indicator for EDTA titrations of zinc, cadmium, manganese and lead. It is also a suitable indicator for the step wise titration of calcium and magnesium in blood serum and water.     

On the use of the mercury electrode in chelatometric potentiometric titrations

Summary Information is given on the applicability of the mercury electrode in chelatometric potentiometric titrations. The influence of ternary complex formation, the formation of precipitates on the electrode and possible errors, due to the asymmetric shape of the titration curves are discussed.

---

Über die Verwendung der Quecksilberelektrode bei chelatometrisch-potentiometrischen Titrationen

Zusammenfassung Einige Betrachtungen werden angestellt über die Anwendung der Quecksilberelektrode für komplexometrische Titrationen mit potentiometrischer Endpunktsanzeige. Der Einfluß der Bildung ternärer Komplexe, die Bildung von Niederschlägen auf der Elektrode und die Fehler infolge der Asymmetrie der Titrationskurven werden besprochen.

     

A new selective metallochromic reagent for the detection and chelatometric determination of calcium

A new reagent, Calcichrome, which gives a highly sensitive colour reaction with calcium ions in alkaline solution, has been synthesised. Neither barium, strontium nor magnesium react with the reagent, which is therefore proposed as a selective spot-test reagent for calcium. In addition, Calcichrome may be used as a metallochromic indicator for the accurate complexometric titration of calcium in the presence of at least twelve-fold amounts of barium. Trans-1:2-diaminocyclohexane-N:N:N':N'-tetra-acetic acid is used as titrant since it is the only complexan available which is sufficiently selective in its reactivity towards calcium and barium.     

Precise chelatometric titrations of zinc, cadmium, and lead with molecular spectroscopy.

Spectral data during a chelatometric titration were utilized for determining an equivalence point of the titration. Three-dimensional titration data were analyzed by fitting to a theoretical equation that was derived from equilibrium equations among a metal ion, an indicator and EDTA. The equation with optimized parameters successfully explained the three-dimensional titration data. This method was applied to EDTA titration systems of zinc, cadmium and lead with xylenol orange (XO) as an indicator. These systems were analyzed while taking the formation of 1:1 and 2:1 metal-indicator complexes into account. By this method, an accurate equivalence point was determined as well as stability constants and molar absorption spectra of metal-indicator complexes in each titration system. Moreover, the comparability among the concentrations of the metal standard solutions prepared from pure metals (Zn, Pb, and Cd) was also confirmed by the proposed evaluation method.     

Redox indicators in titrations with dichloramine-B

Naphthidine, dimethylnaphthidine, dimethylnaphthidinedisulphonic acid, o-dianisidine, Quinoline Yellow, diphenylbenzidine and Amaranth are proposed as indicators in titrations of arsenic(III), iron(II), antimony(III), hydroquinone, hydrazinium sulphate, phenylhydrazine hydrochloride, semicarbazide hydrochloride and ascorbic acid with dichloramine-B. They give a very sharp colour change at the equivalence point. Arsenic(III) and iron(II) are suggested for standardization of dichloramine-B solutions. A potentiometric method for the determination of arsenic(III) and semicarbazide hydrochloride is described.     

Redox indicators in titrations with chloramine-T

Naphthidine, 3,3'-dimethylnaphthidine disulphonic acid, o-dianisidine, di-phenylbenzidine, quinoline yellow, amaranth, methyl red, methyl orange, rhodamine-B and erioglaucine-A are examined as indicators in macro-and micro-titrations of arsenic(III), antimony(III), ascorbic acid, hydroquinone, metol, hydrazinium sulphate, isonicotinic acid hydrazide, semicarbazide hydrochloride and phenylhydrazine hydrochloride with chloramine-T. The indicators give sharp colour changes under optimal conditions. Transition potentials are reported.     

Critical study of metallochromic indicators for calcium

The visual clarity of the colour changes at the end-points in the compleximetric titration of calcium is discussed for the metallochromic indicators, arsenazo-III, calcein, calcon, eriochrome blue black B, methylthymol blue, murexide, phthalein complexone, and thymolphthalein complexone. The colour changes were specified with the help of CIE chromaticity diagrams. The sharpness of the colour changes of the indicators was studied by varying the optical (or colour) concentration. Thymolphtalein complexone and phthalein complexone are shown to be the most appropriate indicators for the visual titration of calcium with EDTA.     

pH-stat techniques in titrimetric analysis: IV. pH-stat monitoring of chelatometric titrations

The theory of pH-stat chelatometric titrations recently developed [Anal. Chim. Acta 456 (2002) 313] is experimentally substantiated here. The titrations of four representative doubly charged cations having different behaviour (copper, zinc, calcium, magnesium) are taken as examples. Copper is titratable between pH 3 and 5, zinc between 3 and 6, calcium between 6 and 10, and magnesium between 7 and 10. The shapes of the titration plots agree well with the theory, accounting for simultaneous equilibria involving proton exchange. The technique yields accurate and precise results, which compare favourably with those of other instrumental techniques, in particular photometric titrations.     

New metallochromic indicators for compleximetric titration of calcium

Seven o,o'-dihydroxyazo dyes were synthesized and tested as metallochromic indicators for calcium: 1-(2-hydroxy-3-sulfo-5-chloro-1-phenylazo)-2-hydroxy-3-naphthoic acid (I), 1-(2-hydroxy-3-sulfo-5-chloro-1-phenylazo)-2-naphthol-3,6-disulfonic acid (II), 1-(2-hydroxy-6-sulfo-1-naphthylazo)-2-naphthol-3,6-disulfonic acid (III), 2,2'-dihydroxy-1, 1'-azonaphthalene-3,3', 6,6'-tetrasulfonic acid (IV), 1-(2-hydroxy-3-carboxy-1-naphthylazo)-2-naphthol-3,6-disulfonic acid (V), 1-(2,3-dihydroxy-1-naphthylazo)-2-naphthol-3, 6-disulfonic acid (VI), 1-(2,3-dihydroxy-6-sulfo-1-naphthylazo)-2-naphthol-3,6-disulfonic acid (VII). The acid dissociation constants and the formation constants of the calcium and magnesium chelates of these dyes were determined. The rate of the decomposition of these dyes and their calcium chelates in alkaline solutions was also examined. From the results of photometric and visual titrations of calcium in the presence of magnesium, indicators III and IV provide the sharpest end-points and the best stability in alkaline solutions.     

Performance comparison of five metallochromic indicators for barium

The color transitions produced by certain metallochromic indicators used in the complexometric determination of Ba (with EDTA) were studied using tristimulus chromaticity theory. Metalphthalein, thymolphthalein complexone, methylthymol blue, antipyryl-o-arsenazo I, and antipyryl-p-arsenazo I were the indicators studied. The results obtained indicate that, of the indicators considered here, the most suitable for visual titration of Ba with EDTA are metalphthalein and thymolphthalein complexone.     

N-substituted phenothiazines as indicators in titrations with chloramine-T

Trifluoperazine dihydrochloride, butaperazine dimaleate, promethazine hydrochloride, diethazine hydrochloride, prochlorperazine maleate and chlorpromazine hydrochloride have been studied as redox indicators in titrations of hydroquinone, metol and ascorbic acid with chloramine-T. The end-points obtained are sharper than with conventional indicators. The molar absorptivities of the oxidized indicators are reported. Simple but accurate methods for the determination of hydroquinone and metol are described.     

Multiparametric curve fitting-IV Computer-assisted estimation of successive dissociation constants and of molar absorptivities from absorbance-pH curves by the DCLET program

The program DCLET evaluates the dissociation (or protonation) constants and molar absorptivities (HjL) of all light-absorbing species (HjL), (j = 0,..., J) of a polyprotic acid (HjL) by a non linear regression of the function A = f(pH; pK (a), (HjL)), i.e., by multiparametric curve fitting. The three specific subroutines DATADC, UBBEDC, SKRDC described form part of the general program ABLET. The goodness of fit is tested by statistical examination of the residuals. Heuristic or algorithmic strategies of minimization may be used, and experimental or synthetic data may be processed. By examining the effects on the results of varying the density and distribution of points of a synthetic data set, it is possible to improve the planning of experiments, and by introducing parametric weight, to improve the sensitivity of a particular parameter in a model.     

Application of chemiluminescent indicators in EDTA titrations

The chemiluminescent indicators lucigenine and luminol are readily applicable to end-point detection in the EDTA titration of cadmium, zinc and nickel ions. Back-titration with copper(II) gives reproducible results. The end-point is indicated by the disappearance of the green chemiluminescence of lucigenine, or by the appearance of the bluish luminescence of luminol.     

A thermometric titration study of the interaction of Co2+ with metallochromic indicators

A thermometric titrimetry study of the interaction in aqueous solution of Co²⁺ with xylenol orange, eriochrome black T and catechol violet at a specified pH, has revealed in each case a linear reaction heat/[Co²⁺] relationship, thereby suggesting the potential of metallochromic indicators for the determination of macro trace levels of cobalt in water. The relevant complexation enthalpies are rationalized in terms of a combination of ligand steric effect, cobalt-ligand bond energies and chelate effect.     

Some observations on screened indicators for the direct chelatometric titration of calcium

The screening of five common metallochromic indicators used in the complexometric determination of Ca was studied using tristimulus chromaticity theory. Calcon-tartrazine-Orange II (6.8 + 1 + 4.6, w/w), thymolphthalein complexone-Orange II-tartrazine (14.22 + 1.22 + 1), Arsenazo III-Remazol Brilliant Blue-tartrazine (25.2 + 8.9 + 1), phthalein complexone-tartrazine-Remazol Brilliant Blue (2.47 + 1 + 1.1), and methylthymol Blue-Orange II-tartrazine (13 + 2.9 + 1) are proposed for the titration of calcium against Na₂ EDTA. The clarity and accuracy of titration are improved.     

Specification of colour changes of metallochromic indicators in the titration of bismuth with EDTA

The quality of the colour changes at the end-point in the complexometric titration of bismuth(III) with EDTA, using the indicators Hemotoxylin, PAN [1-(2-Pyridylazo)-Naphthol-2], PAR [4-(2-Pyridylazo)-Resorcinol], Xylenol Orange and Thoran is studied by means of the CIE 1931 trichromatic system, using specific colour discrimination (SCD) and colour difference (DeltaE*). The indicators are arranged in order of colour change quality. Of the indicators studied, Hemotoxylin is recommended as the most suitable for this titration.     

N-substituted phenothiazines as redox indicators in titrations with chloramine-T and chloramine-B

Profenamine hydrochloride, fluphenazine dihydrochloride, trifluopromazine hydrochloride, cyamepromazine maleate, perphenazine dihydrochloride and mepazine hydrochloride are proposed as redox indicators in the titration of hydroquinone, metol and ascorbic acid with chloramine-T and chloramine-B in sulphuric, hydrochloric and acetic acid media. They give a sharp reversible colour change at the equivalence point. A simple but accurate method for the determination of hydroquinone, metol and ascorbic acid is described. The conditional potentials and molar absorptivities of the indicators and redox potential of chloramine-B are reported.