Coulometric Titration of 8-Quinolinol

Abstract

collected in proximity tu dustproducing processes, wch as those carried on in the ore preparation department, had a nirdian size (2.2 microns) greater than those in the maintenanre liuilding (1.1 microns) which is more remote from the major w u r w c of dust pollution. This gr:itl:ition i b logic-a1 nL:CEI\-E." hlarch 1:i, 1930. This rirojccr was supported by a cancer control grant from t h e Hariford Forks, General Elertrir Company, Rirhland, R'ash.4 microtitration of 8-quiriolinol with electrolytically generated bromine is dcscrihed. The use of an improved electrometric indicator circuit permits direct titration of samples containing 0.4 to 2.0 mg. of 8-quinolinol with a precision of =tO..5%, in spite of the slowness of bromination. The amount of bromine used is measured by determining the number of coulombs of electricity passed through the electrolysis cell by electrolyzing at constant current and measuring the time. 1 simple, electronically controlled ronstant current source suitahle for use in the titration is described.IIP: estimation of 8-quiiioliriol (&hydroxyquinoline, oxini,) T is important in the determination of metals that form insoluble precipitates with it. In the volumetric method. thr metal quinolate precipitate is pu ti h y a suitable procedure and the 8-quinolinol content is det ined by dissolving in acid, adding : i n excess of brominating agent, and back-titrating with arsenite or thiosulfate. A direct titrxtioii with electrolytically generated tromiric was studied and found to bc practical. In this method, t hr amount of bromine gener:ited is measured hy determining the iiumher of coulombs passed through the cell.The use of electrolytically generated bromine in analysis is well cbst:il)lishcd. It has been used for. the determination of arsenite lycols (3), mustard gas (4), thiocyanate, hydrazine, and imine (5). It is espcinlly useful for microtitrations, as the amount of bromine added is easily controlled and accurately memured for rates :is low as lo-* equivalent per second. No standard solutions are required and the method lends itself to routine use.The principal reactions occurring in the analysis are those of I)romincr formation and bromination of oxine. Formation of Br? :tt t~l~,c~tr(;tle. 2Br---+ Br? + 2e Concurrently H? is formed at cathode. 2H" + 2~-+ HZ Bromination of 8-quinolinol. C9H,0S + 2Br2 --+ (~pHaO?;Br? + 2HBr The bromination of onr mole of 8-q~iinolinol thus requires the passage of 4 f:irndays of elrctricity. A P P 4 K \ " b S Constant Current Source. The clrruit of the constant current source used in these experiment^ I-bhown in Figure 1.The output current flows through resistors R-1 and R-2, which are the input of a conventional voltage regulator circuit. The voltage regulator circuit holds the I R drop across R-1 and R-2 (.onstant and compensates for changes in the output current.

Millicoulometric Redox Titrations

“…More recently the coulometric method of measuring the current consumed in the titration has been replaced by the use of a constant-current generator (3,18), and the calculations are based on the time during which this known current is applied to the cell, so that one might more properly speak of a "chronometric" titration (SI). At the same time amperometric (S, 8, 13, 16, 19, SS) and potentiometric (4, 6, 7, 9, 17, SI) methods for the detection of the end point have found wide application.…”

Measurement of Ionic Strength of Aqueous Solutions by Electrolysis

“…The published (ethylenedinitrilo)tetraacetate titration methods (1) for the determination of magnesium, in which magnesium is determined by difference of two titrations (5), are not sufficiently accurate for magnesium oxide levels as low as 0.05% in commercial calcium phosphates and a few tenths of a per cent in commercial lime. Phosphate interference in the EDTA titration is overcome by precipitation of the phosphate with ferric ions at a pH low enough to prevent precipitation of magnesium (5).…”

“…As the striking enhancement of the color obtained with the molybdate reagent and silicate in the presence of TCA suggested that this procedure might be analytically useful, silicate was determined with both the system used for phosphate (1) and the method devised for silicate (2) with TCA present. Also, the concentration of the sulfuric acid was varied to determine the effect of intermediate concentrations.…”

A simple amperostat for coulometric titration

“…Servo mechanical systems have since been devised (e.g., 3,4) which give currents constant to better than 0.01% over long periods, although their response times are not fast. A number of electronic current regulators using vacuum tubes have also been described (e.g., [5][6][7][8][9] generally involving dc amplifiers with feedback. A common method in present electrochemical practice is to place the electrolytic cell in the feedback loop of a standard operational amplifier unit (see Fig.…”