Polarography of Thiocyanate Ion. Complex Ion Formation with Mercury(II) Ion

Abstract

ions. Because chromium is the only element listed which is normally found associated with vanadium in analytical samples, such as steels, the problem is not too serious.The interference of iron, due to the color of the ferric ion, can be easily eliminated by the addition of fluoride ion, as shown in Table V. Care must be taken to avoid a large excess of fluoride, as large quantities of this ion interfere.The interference of organic acids, if any are present, can easily be removed by destroying the organic material with nitric acid. CONCLUSIONSThe proposed 3-tungstovanadic acid method is very sensitive, exceeding the sensitivity of the well-known method based upon tungstovanadophosphoric acid. In addition, the results obtained are precise and accurate. Chromium, the most serious interference, must be completely removed. Interference of iron is eliminated by complexation with fluoride.Because of the necessity of removing chromium, if present, the determination of vanadium by this method may be lengthy, but no more so than by other standard colorimetric methods under the same conditions. A minor disadvantage is the rather narrow pH range that must be maintained. As pH meters are now commonplace, this requirement is not a serious defect.

Complex Ion Formation of Mercury(II) and Thiosulfate Ion

“…If only one complex exists in solution, it has been shown (4,8,9) that a plot of log (i/id-i)' vs. E¿,e. for a given polarogram should produce a straight line of reciprocal slope 2.303 RT/nF for some value of j in the formula MXj.…”

“…The (at E1/2) S.C.E. (at Em) X 10"28 1.98 X values of j and the concentration of thiosulfate at the electrode surface were estimated by an approximation procedure outlined previously (8). The values of F2(X) were obtained from the graphical procedure of Leden (7) and DeFord and Hume (8) employing the latter authors' definition of F"(X) including activity coefficients.…”

“…Values of F0{X) are calculated from Equation 2 of (8) employing the data in Table II, and in turn, the values of Total mercury concentration = 1 X 10-3M…”

“…The procedure employed in determining polarograms and half-wave potentials was identical with that employed in another study (8) using a polarographic cell described elsewhere (ID-Stock solutions were prepared from redistilled water with chemicals of reagent grade. The sodium thiosulfate stock solutions were prepared from Merck reagent grade crystals and were standardized volumetrically with potassium iodate solution using the procedure of Kolthoff and Sandell ( ).…”