Photometric Determination of Vanadium with Diphenylcarbazone in High-Purity Iron
Abstract Generated abstract
A photometric procedure is presented for determining trace vanadium in especially high-purity iron using diphenylcarbazone, a sensitive reagent whose application is limited by interference from iron and several accompanying elements. The method combines extraction of most iron and molybdenum from 6 N hydrochloric acid with diethyl ether, oxidation of vanadium, alkaline precipitation of residual interfering metals, and measurement of the vanadium, diphenylcarbazone complex at 536 nm. Tests on pure iron samples gave a stated sensitivity of 5 x 10^-5 percent vanadium, a relative error within about 30 percent, and an analysis time of approximately 4 hours.
Full Text
PHOTOMETRIC DETERMINATION OF VANADIUM WITH DIPHENYLCARBAZONE IN HIGH-PURITY IRON
V. B. Sokolovich, G. E. Gomboeva
(Presented by the Scientific-Methodological Seminar of the Faculty of Chemical Technology)
Among the large number of photometric reagents for vanadium, one of the most sensitive and comparatively accessible is diphenylcarbazone [1, 2, 5].
According to the literature, the determination of vanadium with diphenylcarbazone is interfered with by iron, chromium, and, as our investigations have shown, Mo, as well as Mn, Ti, and Al in amounts 10 times greater than the vanadium content.
We established a method for satisfactory separation from iron and accompanying elements, consisting in the extraction of molybdenum and the major amount of iron with diethyl ether from a 6 N hydrochloric acid solution, followed by precipitation of the residues of iron, manganese, titanium, and part of the chromium with alkali.
Using diphenylcarbazone, a procedure was developed for the photometric determination of vanadium in high-purity iron with a sensitivity of \(5 \cdot 10^{-5}\%\), a relative error not exceeding 30%, and a time expenditure of 3–4 hours per determination.
Twice-distilled water, chemically pure and analytical-grade reagents, and a 0.1% acetone solution of diphenylcarbazone were used in the work. The initial standard vanadium solution containing \(1000\ \mu\text{g}\) per ml was prepared by dissolving ammonium vanadate in caustic soda. Its titer was established by the gravimetric method with cupferron [3].
A working standard solution containing \(1\ \mu\text{g}\) of vanadium per ml was prepared immediately before use by appropriate dilution of the initial standard solution.
Course of Analysis
An iron sample of about 0.5 g is placed in a glass (preferably quartz) beaker, treated with 10 ml of especially pure 7.8 N hydrochloric acid, covered with a watch glass, and heated for 10–15 min. After complete decomposition of the sample, 15 drops of nitric acid (1:1) are added to oxidize iron to the trivalent state, and the solution is heated almost to boiling for about 10 min to remove nitrogen oxides. The solution is cooled and transferred to a separatory funnel; the beaker is rinsed with 5 ml of the same acid. The resulting solution is approximately 6 N with respect to hydrochloric acid.
From the hydrochloric acid solution, iron, molybdenum, and others are extracted with diethyl ether in the form of chloride complexes. The extraction is repeated three times with 20 ml portions of ether, with three minutes of shaking. After the third extraction the aqueous layer is drained into a beaker, slightly heated for about 15 min in an organic-glass hood under a heat lamp or on a hot plate with a closed coil to remove traces of ether. After removal of the ether, 0.05 N potassium permanganate solution is added dropwise to the hot solution until a stable brown coloration appears, and it is left for three minutes to oxidize vanadium to the pentavalent state. The excess permanganate is reduced with a freshly prepared 3% solution of sodium nitrite, which is added carefully dropwise until the permanganate is decolorized. The solution is heated; iron remaining after extraction, some chromium, as well as manganese and other elements are precipitated with 8 ml of 30% sodium hydroxide solution. The precipitate is filtered off through a small ashless blue-ribbon filter and washed with hot bidistillate.
The filtrate is collected in a 50 ml volumetric flask and, after cooling, is brought to the mark with bidistillate. Then two 10 ml aliquots are taken from the prepared solution. One is placed in a 50 ml volumetric flask, the other in a 50–100 ml beaker. One drop of methyl red indicator is added to the beaker, and the solution is titrated with acetic acid (1:7) until the color of the indicator changes to red, which corresponds to pH = 5.
Into the volumetric flask with the second aliquot are introduced the amount of acetic acid consumed in titrating the first aliquot and 10 ml of 0.1% acetone solution of diphenylcarbazone. The contents of the flask are diluted to the mark with bidistillate and thoroughly mixed. After 10–15 min, the optical density of the vanadium complex with diphenylcarbazone is measured on an FEKN-57 in cuvettes with a 50 mm layer thickness, using green light filter 5 with a transmission maximum at 536 mµ. The comparison solution is bidistillate.
In parallel, a portion of the standard vanadium solution and a blank test are carried through all stages of the analysis.
The vanadium content is calculated by the formula
\[ \% V=\frac{C_v (D_x-D_0)\cdot 10\cdot 10^2}{(D_{\text{st.}}-D_0)\cdot 10^6}, \]
where \(C_v\) is the vanadium content in the portion of the standard solution, in µg;
\(D_{\text{st.}}\) is the optical density of the vanadium complex with diphenylcarbazone in the standard solution;
\(D_x\) is the optical density of the vanadium complex with diphenylcarbazone in the solution being analyzed;
\(D_0\) is the optical density of the blank-test solution;
10 is the conversion factor to a gram sample.
Table 1
Results of the photometric determination of vanadium with diphenylcarbazone in samples of pure iron
| Measured quantity | \(n\) | \(\bar{x}\cdot 10^{-3}\) | \(S_x\cdot 10^{-3}\) | \(S_{\bar{x}}\cdot 10^{-3}\) | \(\alpha\) | \(\tau\) | \(\varepsilon\cdot 10^{-3}\) | Experimental result | Relative error |
|---|---|---|---|---|---|---|---|---|---|
| \(V,\ \%\) | 16 | 1.15 | 0.65 | ±0.162 | 0.95 | 2.131 | ±0.345 | \(1.49—0.81\cdot 10^{-3}\) | ±29.55 |
| \(V,\ \%\) | 16 | 1.16 | 0.65 | ±1.162 | 0.95 | 2.131 | ±0.345 | \(1.50—0.82\cdot 10^{-3}\) | ±29.31 |
The experimental data obtained in the determination of vanadium in samples of pure iron, and the results of their treatment by the method of mathematical statistics, are presented in Table 1.
Conclusions
A procedure has been developed for the photometric determination of vanadium in especially high-purity iron with diphenylcarbazone.
Sensitivity: \(5 \cdot 10^{-5}\%\).
The relative error of the determination is within 30%.
The duration of the analysis is about 4 hours.
Literature
-
I. M. Goltsberg, G. L. Koval, G. A. Klemeshev. Collected Works of the Ukrainian Scientific Research Institute of Metals. Vol. 11, p. 387, Kiev, 1965.
-
New Methods of Analysis at Metallurgical and Metalworking Plants. Metallurgiya Publishing House, Moscow, p. 46, 1964.
-
Z. S. Mukhina, E. I. Nikitina et al. Methods of Analysis of Metals and Alloys. Oborongiz, Moscow, p. 118, 1959.
-
J. Morrison, G. Freiser. Extraction in Analytical Chemistry. GKhI, Leningrad, p. 131, 1960.
-
P. P. Korostelev. Preparation of Reagents for Chemical-Analytical Work. Nauka Publishing House, Moscow, p. 90, 1964.