The Determination of Free Chlorine

Abstract

A number of reagents have been proposed for determination of free chlorine or chloramine in water. Phelps suggested the use of 0tolidine in acetic acid (1) and Ellms and Hauser devised a method for estimation of chlorine based upon the use of o-tolidine in hydrochloric acid (2). The starch iodide test has been used for some time by certain workers. More recent suggestions are the use of dimethylp-phenylenediamine hydrochloride as a reagent for chlorine (3) and methyl orange for the estimation of chlorine in the absence of chloramine.The chief interfering substances in the accurate determination of chlorine by o-tolidine have been found to be manganese, nitrites and iron (1,5,6,7,8). At an earlier date Boruff and Buswell showed that there was no interference from nitrites and iron under the conditions necessary for making the o-tolidine test for free chlorine (9). But with the present general use of chloramine instead of chlorine longer reaction time must be allowed for the development of full color. Where this long reaction time is used, nitrites and iron, as well as manganese, interfere in the test. Obviously, the o-tolidine reagent is not entirely satisfactory and attempts have been made to adapt the reagent to the purpose by making corrections or eliminating the cause of interference either mechanically or chemically (4).In the o-tolidine test, each of the following would exert an effect: concentration of chlorine, oxidation potential of the chlorine or chloramine, pH and HCl concentration, concentrations of manganese and iron and the degree of oxidation of each, concentration of nitrite, concentration of the reagent and reaction time. With these things in mind work has been carried on in an attempt to find a reagent which would eliminate part of the difficulties experienced with 0tolidine. This investigation has been divided into three parts, involving (I) the application of the principle of oxidation-reduction potentials to the problem (II) nitrite interference in the o-tolidine test and (III) the nature of o-tolidine reactions. 1645

Note on the Determination of Chlorine

“…It was concluded that, since the color produced by Cl, or NH2Cl was so unstable, the reagent was not more advantageous than the 30 per cent o-tolidine reagent. This agrees with conclusions from earlier studies made in this laboratory (3).…”

Electrically-polarized nanoscale surfaces generate reactive oxygenated and chlorinated species for deactivation of microorganisms

“…HOCl is known to form from H2O2 in the presence of Cl ─ and copper ions (70). In the presence of o-tolidine, the ENM0V and ENM3V treated solutions turned yellow due to formation of holoquinone (97), confirming the presence of HOCl in the solution (Fig. 5I and tables S6 ─ S7).…”

Colorimetric Determination of Chlorine Residuals up to 10 ppm. With Ortho‐tolidine

“…When the ratio of acid to ortho-tolidine becomes less than 100: 1, the color decreases That low concentrations of ortho-tolidine favor the formation of the holoquinone has been pointed out by Tarvin, Todd and Buswell (12). From the oxidation-reduction standpoint this is plausible.…”

“…Dragt (15) showed that, as the pH is lowered, the effect of iron interference is lessened. Scott (28,31), Tarvin, Todd and Buswell (12) and others have recommended the use of more ortho-tolidine, ortho-tolidine in additional acid or ortho-tolidine and additional acid to eliminate the interference of iron. This recommendation appears in Standard Methods as a modification of the usual procedure, which specifies the use of 1 m!.…”

“…, Tiedeman(21), Enslow(22,23),Rudolfs and Gehm (20), Tarvin, Todd and Buswell(12), McCarthy(18),Lea (26),Cox (27), Scott (28), Almquist (13), Buswell and Boruff (29), Harral and Jaffe(17) and others recommended the use of more ortho-tolidine reagent or an increase in its acid strength. An A.W.W.A.…”