Electrometric titrations

Titration methods using adsorption indicators, based on the precipitation of insoluble iodides, have also been proposed (81—84). The sensitivity of these methods is less than that for the thiosulfate titration. Electrometric titration of the reaction between iodine and thiosulfate (85) was not found to be practicable for routine deterrninations of minute quantities of iodine. 

Electrometric titrations with two polarizable electrodes involving chelating agents. K. Stulik and F. Vydra, Chelates Anal. Chem. 1969, 2, 93-115 (70). 

Electrometric titration shows the purity to be at least 95%. The product does not melt below 300°. 

Three pKa values have been reported for leucovorin (free acid) they are 3.1, 4.8, and 10.4, as determined by electrometric titration.6 The first two values are attributed to the glutamyl carboxyls, and 10.4 is assigned to the hydroxyl group at the 4 position,8 by comparison to model compounds. 

ELECTROMETRIC TITRATIONS (2) in a closed system with standard NaOH — then subtract... 

Selenious acid readily decomposes potassium permanganate, but analytical results are untrustworthy in the presence of more than a limited quantity of sulphuric acid.1 The oxidation should be carried out at 50° C., a known quantity of 0-lN potassium permanganate being used and the excess determined either by means of standard oxalic acid solution or by electrometric titration with ferrous sulphate. In the presence of tellurium, the latter is also oxidised and should be determined in a separate sample by oxidation with potassium di-chromate, which does not oxidise the selenium, and the necessary deduction can then be made.2... 

A method involving electrometric titration depends on the volumetric reduction of selenious acid to selenium by means of titanium sulphate. The method is rapid and accurate5 if the solution is in cold concentrated hydrochloric acid saturated with sodium chloride. The presence of the latter is important, for it ensures rapid and uniform coagulation of the selenium hydrosol and increases the sharpness in the change of voltage at the end-point. The use of the hydrochloric acid in the cold eliminates the otherwise almost inevitable loss of selenium by volatilisation. Under these conditions any tellurium which may be present is unreduced and only has the effect of modifying the nature of the end-point.6... 

For suitable cell combinations for the electrometric titration of arsenites with permanganate, see Lang, Zeitsch. Elektrochenu, 1926, 32, 454 also Hall and Carlson, J. Aimer. Ghent. Soc., 1923, 45, 1615. 

Seleninoacetic acid, SeOgH.CH2.CO2H,1 is obtained as indicated above and isolated in the form of its barium salt, which contains two molecules of water, the parameters of the crystals being a b c = 1 276 1 1 555. The values of kx and k2 for the acid by electrometric titration are 2 50 x 10 3 and 3 74 x 10 6 respectively. The free acid melts with decomposition at 99° C. The diquinine salt contains seven molecules of water and melts at 122° C. (decomp.), six molecules of water being lost on heating in vacuo. 

Guanidine is a strong monoacid base, indistinguishable from potassium hydroxide in an electrometric titration. There is considerable evidence 5 which indicates that the charge of the guani-donium ion resides upon its carbon atom. 

G. Bredig,1 and R. Bach concluded that while the first acidic function is nearly the same as that of ammonium hydroxide, the second acidic function of the base is so weak in aq. soln. that the corresponding salts are almost completely hydrolyzed. T. Curtius and H. Schulz said that a dihydrate exists in aq. soln. because the cryoscopic data gave a mol. wt. of 68. These data, however, can be interpreted on the basis either of a monohydrate or of a dihydrate. All this, does not decide whether hydrazine is a monoacidic or a diacidic base. E. C. Gilbert also found that in the electrometric titration of a 0-lM-soln. of hydrazine hydrate... 

Fig. 61. — Electrometric Titration of Solutions of Hydrazine with Acids.

The acid liberated during hydrolysis is neutralized continuously with concentrated alkali, using either indicators or—more conveniently—electrometric titration (6, 7). 

Stulik, K., and F. Vydra Electrometric Titrations with Two Polarised Electrodes. Determination of Inorganic Compounds and of Water by Means of Karl Fischer Reagent. Chem. Zvesti 21, 274 (1967). 

One of the developments in electrometric titrations has produced at least one instrument for the determination of chloride which is simple, rapid, and accurate. For those institutions large enough to run many chloride determinations and with chloride allowed as an emergency test, the acquisition of such an instrument would be readily justified. Future development in electrometric methods might increase the importance of any of these instruments, particularly if it were adapted to more than one clinically important test. 

HPLC-RT correlation, shake flask-electrometric titration, Slater et al. 1994)... 

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