Photocolorimetric Determination of Trace Cobalt in Oils of Western Siberia
Abstract Generated abstract
A photocolorimetric procedure is described for determining trace cobalt in oils from Western Siberia using nitroso-R salt, which forms a water-soluble cobalt complex stable in mineral acid. Oil ash residues are dissolved, buffered, treated with citric acid and nitroso-R salt, boiled with nitric acid, and measured at 530 nm against a calibration series containing 0.5 to 3.0 micrograms of cobalt. The method was applied to individual samples and aliquots from oils from fifteen Western Siberian fields, with reported cobalt contents on the order of 0.86 to 4.10 x 10^-5 percent and associated statistical errors.
Full Text
Photocolorimetric Determination of Traces of Cobalt in Oils of Western Siberia
E. A. Guber, Yu. A. Karbainov, L. S. Dyadik, N. A. Grigorieva
(Submitted by the scientific seminar of the Department of Analytical Chemistry)
The most sensitive, selective, and readily available reagents for the photometric determination of cobalt are 1-nitroso-2-naphthol, 2-nitroso-1-naphthol, and nitroso-R salt [1—7], which form orange-red complexes with cobalt salts.
For the quantitative determination of Co in oils, nitroso-R salt was used in this work. This reagent forms a water-soluble cobalt complex that is stable in the presence of mineral acids. This makes it possible to determine Co in a mixture with other elements whose complexes are destroyed under the indicated conditions [8].
Course of Analysis
The ash residue of the oil, dissolved in hydrochloric acid (1:1), is transferred into 50 ml beakers, and the solution is evaporated almost to dryness. To the moist residue are added 5 ml of bidistilled water, 1 ml of citric acid, 1.24 ml of phosphate-borate buffer (pH = 8), and 1 ml of nitroso-R salt. The contents of the beaker are covered with a watch glass, boiled for 1 min, 20 drops of concentrated HNO₃ are added, and it is boiled again for 1 min. After cooling in the dark, the solution is transferred into a 10 ml volumetric flask, brought to the mark with bidistilled water, and photometered in a cuvette with a layer thickness of 20 mm using green light filter No. 5 (FEK-N-57) at \(\lambda = 530\) mµ. Bidistilled water serves as the reference solution. A blank test is run in parallel.
Table 1
Dependence of the optical density of the solution on the cobalt content
| No. | Co, µg | Optical density |
|---|---|---|
| 1 | 0.5 | 0.018 |
| 2 | 1.0 | 0.040 |
| 3 | 1.5 | 0.063 |
| 4 | 2.0 | 0.082 |
| 5 | 2.5 | 0.108 |
| 6 | 3.0 | 0.132 |
| 7 | 0 | 0.010 |
The cobalt content in the sample being analyzed is found from the calibration graph (Table 1).
Experience showed that comparable results are obtained provided that individual oil samples of about 3 g are analyzed, or that a sample of about 10—12 g of oil is subjected to analysis, from which 3—4 aliquot portions are taken for the determination of cobalt.
The analysis of oils was carried out both from individual samples and from aliquot portions. By the method described, an analysis of oils was performed
fifteen fields of Western Siberia. The results of the analysis are given in Table 2.
Table 2
Cobalt content in oils of Western Siberia
| No. | Field | Well No. | Number of measurements | Arithmetic mean, \(x \cdot 10^5\) | Error of the arithmetic mean | Student parameter | Absolute deviation | Experimental result, \(x \cdot 10^5\%\) |
|---|---|---|---|---|---|---|---|---|
| 1 | Ubinskoye | 305 | 8 | 1,72 | 0,036 | 2,36 | 0,085 | 1,72±0,08 |
| 2 | Ubinskoye | 315 | 9 | 2,05 | 0,143 | 2,31 | 0,33 | 2,05±0,33 |
| 3 | Ubinskoye | 324 | 4 | 0,86 | 0,035 | 3,18 | 0,111 | 0,86±0,11 |
| 4 | Ubinskoye | 328 | 4 | 2,24 | 0,03 | 3,18 | 0,33 | 2,24±0,33 |
| 5 | Ubinskoye | 346 | 4 | 2,24 | 0,03 | 3,18 | 0,095 | 2,24±0,09 |
| 6 | Kartopinskoye | 8 | 8 | 3,24 | 0,218 | 2,36 | 0,514 | 3,24±0,514 |
| 7 | Tolumskoye | 13 | 7 | 2,95 | 0,15 | 2,45 | 0,367 | 2,95±0,37 |
| 8 | Luginetskoye | 162 | 4 | 2,23 | 0,027 | 3,18 | 0,086 | 2,23±0,09 |
| 9 | Severnoye | 205 | 5 | 1,79 | 0,095 | 2,78 | 0,264 | 1,79±0,26 |
| 10 | Severnoye | 206 | 8 | 3,84 | 0,195 | 2,36 | 0,459 | 3,84±0,46 |
| 11 | Severnoye | 207 | 4 | 4,10 | 0,205 | 3,18 | 0,651 | 4,10±0,65 |
| 12 | Vartovskoye | 330 | 9 | 2,65 | 0,05 | 3,31 | 0,116 | 2,65±0,12 |
| 13 | Samotlorskoye | 324 | 5 | 2,83 | 0,109 | 2,78 | 0,303 | 2,83±0,30 |
| 14 | Yu.-Cheremshanskoye | 335 | 9 | 2,71 | 0,109 | 2,31 | 0,252 | 2,71±0,25 |
| 15 | Megionskoye | 514 | 7 | 2,08 | 0,049 | 2,45 | 0,111 | 2,08±0,11 |
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