Titration photometric

Let us examine some batch results. In trials in which 5 mL of a dye solution was added by pipet (with pressure) to 10 mL of water in a 25-mL flask, which was shaken to mix (as determined visually), and the mixed solution was delivered into a 3-mL rectangular cuvette, it was found that = 3-5 s, 2-4 s, and /obs 3-5 s. This is characteristic of conventional batch operation. Simple modifications can reduce this dead time. Reaction vessels designed for photometric titrations - may be useful kinetic tools. For reactions that are followed spectrophotometrically this technique is valuable Make a flat button on the end of a 4-in. length of glass rod. Deliver 3 mL of reaction medium into the rectangular cuvette in the spectrophotometer cell compartment. Transfer 10-100 p.L of a reactant stock solution to the button on the rod. Lower this into the cuvette, mix the solution with a few rapid vertical movements of the rod, and begin recording the dead time will be 3-8 s. A commercial version of the stirrer is available. 

The shape of a photometric titration curve will be dependent upon the optical properties of the reactant, titrant, and products of the reaction at the wavelength used. Some typical titration plots are given in Fig. 17.23. 

Discussion. Salicylic acid and iron(III) ions form a deep-coloured complex with a maximum absorption at about 525 nm this complex is used as the basis for the photometric titration of iron(III) ion with standard EDTA solution. At a pH of ca 2.4 the EDTA-iron complex is much more stable (higher stability constant) than the iron-salicylic acid complex. In the titration of an iron-salicylic acid solution with EDTA the iron-salicylic acid colour will therefore gradually disappear as the end point is approached. The spectrophotometric end point at 525 nm is very sharp. 

Determination of iron(III) in the presence of aluminium. Iron(III) (concentration ca 50 mg per 100 mL) can be determined in the presence of up to twice the amount of aluminium by photometric titration with EDTA in the presence of 5-sulphosalicylic acid (2 per cent aqueous solution) as indicator at pH 1.0 at a wavelength of 510 nm. The pH of a strongly acidic solution may be adjusted to the desired value with a concentrated solution of sodium acetate about 8-10 drops of the indicator solution are required. The spectrophotometric titration curve is of the form shown in Fig. 17.23. 

Further details of photometric titrations will be found in Refs 25 and 26. 

The basicities were determined by photometric titrations in ethanol relative to thjrmol blue [(log AT)rei = 0] (Liining and Muller, 1989). 

Micro amounts of sulfur in polymer are usually determined by oxygen flask combustion, sodium peroxide fusion in a metal bomb followed by titration [30], pyroluminescence [36] or ICP-AES. An oxygen flask combustion photometric titration procedure capable of determining total sulfur in polymers in amounts down to 50 ppm was reported. The repeatability of the sulfur determination in polyolefins in the oxygen flask is 40% at 50 ppm level, improving to 2% at the 1 % level [21]. Crompton [31] has also combined Schoniger flask combustion with a colorimetric procedure for the determination of phosphorous in polymers in various concentration ranges (0.01 to 2%, 2 to 13%). 

BASIS OF MANUAL PHOTOMETRIC TITRATION. The determination of anionic surfactants by a photometric titration employs a cationic indicator to form a coloured complex with the surfactant which is insoluble in water but readily soluble in chlorinated solvents (1 ). The end point of the titration occurs when there is a loss of colour from the organic phase. A considerable improvement in this technique is achieved by the use of a mixture of anionic and cationic dyes (4 ), for example disulphine blue and dimidium bromide (Herring s indicator (3)). The sequence of colour changes which occurs during the two phase titration of an anionic surfactant (AS) with a cationic titrant (CT) using a mixed indicator consisting of an anionic indicator (AD) and cationic indicator (CD) is summarised in Scheme 1 ... 

CHOICE OF FILTER FOR AUTOMATED PHOTOMETRIC TITRATION. At the end of a photometric titration using the above two indicators the colour of the chloroform phase changes from pink to blue. To choose a filter to detect this end point the visible spectra of the separated chloroform layers of surfactant titrations were recorded before, at and beyond the end point, see Figure 2. At 580 nm there was a greater change in absorbance than at 440 nm, thus the 580 nm filter was preferred. 

FIGURE 2 Visible spectra of chloroform layers, before, at and beyond the end point of photometric titration... 

A typical photometric titration of SDBS against hyamine at low salinity is shown in Figure 3. It was noted, however, that the titration curve was "V" shaped and not the anticipated step curve. The turbidimetric titration of SDBS against hyamine afforded a curve, Figure 4, very similar to that for the photometric titration. 

FIGURE 3 Typical photometric titration of SDBS against Hyamine at low salinity... 

Molecular Fluorescence Spectroscopy Photometric Titrations Analytical Applications of Interferometry Vol. 9 Ultraviolet Photoelectron and Photoion Spectroscopy... 

Jagner [28] has also described a semi-automatic titration for high-precision determination of chlorine in seawater, where it has been used for the potentiometric determination of total halides (silver electrode) and alkalinity (glass electrode), and for the photometric titration of total alkaline-earth metals. Several titrations can be effected simultaneously. 

Matthews and Riley [99] preconcentrated iodide by co-precipitation with chloride ions. This is achieved by adding 0.23 g silver nitrate per 500 ml of seawater sample. Treatment of the precipitate with aqueous bromine and ultrasonic agitation promote recovery of iodide as iodate which is caused to react with excess iodide under acid conditions, yielding I3. This is determined either spectrophotometrically or by photometric titration with sodium thiosulfate. Photometric titration gave a recovery of 99.0 0.4% and a coefficient of variation of 0.4% compared with 98.5 0.6% and 0.8%, respectively, for the spectrophotometric procedure. 

Sulphate has been determined in seawater by photometric titration with hydrochloric acid in dimethyl sulfoxide [223]. The sample (5 ml) is slowly added to dimethyl sulfoxide (230 ml) and titrated with 0.02 M hydrochloric acid (standardised against sulfate) with bromo-cresol green as indicator. Since borate, carbonate, and bicarbonate interfere, a separate determination of alkalinity is necessary. 

Jagner and Kerstein [654,655] used computer-controlled high-precision complexiometric titration for the determination of the total alkaline earth metal concentration in seawater. Total alkaline earths were determined by photometric titration using EDTA with eriochrome Black as indicator. The method yielded 63.32 (xmolekg-1 for the total alkaline earth concentration in standard seawater of 3.5% salinity. The precision was about 0.01%. 

The DL 40GP can handle potentiometric, voltammetric or photometric titrations. 

A concave base must be concave and basic. Therefore, the basicities (and acidities, respectively) of concave bases and acids have been determined. Because most concave acids and bases are not soluble in water, the measurements had to be performed in an organic solvent. A photometric titration versus thymol blue in ethanol was chosen [31]. 

The relative reactivity of these tyrosine residues toward acetyl imidazole can be correlated with the plf values established by spectro-photometric titration (40). Of the 50 tyrosine residues in the native enzyme, approximately 6 are titrated with a pX value close to 8.4, 7-8 other residues show pJC values of 9.0-9.2, and the remainder are not titratable below pH 10. In the presence of low concentrations of FDP, sufficient to saturate the four substrate binding sites (see below), the pK values for four of the low pJC residues are shifted from 8.4 to 9.7 the other two low piiC values are shifted only slightly, to 8.7. This accounts for the protection by FDP in the reaction with imidazole. Titration of tyrosine residues in the enzyme which has been acetylated in order to lose its sensitivity to AMP confirms that the acetylated residues are those with lowest p.K (40). 

S70> Headridge, J. B. Photometric Titrations. Oxford Pergamon Press 1961. 

Flaschka. H, Photometric Titrations. Microchemical Techniques International Symposium, Pennsylvania, 1965. London Butterworths 1965. 

Other reported procedures with minor modifications and use of different indicators have been also reported (156-165). A method was also described for determination of camphor in dilute solutions by photometric titration using bromophenol blue as the indicator (l66). 

Hydroxyl- amine Oximation Elemental analysis, photometric, titration Sensitivity depends highly [83,89] on detection mode ... 

Solvent Isopropanol-hep tane-H2 SO4 Titration-semiautomatic Titration-photometric Titration-manual colorimetric Milk Cream, whole milk powder Milk, cream Driessen et al. (1977) Evers et al. (2000) Deeth et al. (1975),... 

Among the methods listed here, the amperometric determination has evoked the most interest.151160 172-181 Potentiometric measurements149182 183 also confirm the findings of these methods, although the equilibrium concentrations of free iodine are lower by one order of magnitude than those determined by photometric titration. For the reaction... 

A photometric titration of selenium and S20eF2 established the oxidation state of the yellow species as + conductometric measurements showed that two fiuorosulfate ions are produced per four selenium atoms and the molecular weight of Se was established by cryoscopy. The absorption spectrum of the yellow 804 solution in HSOgF is shown in Fig. 4. 

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