Determination of Vanadium in Sea Water by Graphite Furnace Atomic Absorption Spectrometry with a Tube Coated with Pyrolytic Graphite

Abstract

The trace amount of vanadium in sea water was determined by graphite furnace atomic absorption spectrometry with a tube coated with pyrolytic graphite (see Fig.2-2) after a preconcentration treatment described as follows. Three methods were employed, an anion exchange-solvent extraction method, a chelating exchange method and a coprecipitation method. To correct the background absorption, a deuterium lamp with a higher-brilliant thermal cathod was used. The sensitivity for vanadium increased 10∼20 fold by the use of the tube coated with pyrolytic graphite (see Table 5), and the utility lifetime of the tube was greatly extended.
Vanadium (V) 4- (2-pyridylazo) resorcinol (PAR) complexes were extracted into chloroform as an ion-pair with benzyldimethyltetradecylammonium (Zephiramine) cation alternatively. But salts in sea water considerably interfered and the extraction ratio deteriorated. Then in order to separate the interfered ions, anion exchange was carried out before the extraction treatment. The sample of sea water, which was made to 0.1 N in sulfuric acid and 0.1% in hydrogen peroxide, was loaded onto the column of Dowex 1-X 4 resin (SO₄^2--form). Vanadium was then eluted from the resin with I N sulfuric acid-0.1% hydrogen peroxide or 1 N hydrochloric acid-0.1% hydrogen peroxide, and the elute was collected and evaporated to dry. A fter dissolulion of the elute in 0.2 N nitric acid, vanadium was extracted.
Secondly, a chelating exchange was conducted. The sample of sea water was adjusted to pH 5.0, and loaded onto the column of Chelex-100 resin. Vanadium was then eluted from the resin with 2 N ammonia and the elute was collected in a volumetric flask (50 ml).
The above two methods took much time, but the coprecipitation method was not so and recommended for the determination of vanadium in sea water. Vanadium was coprecipitated with iron(III) hydroxide-hydrous titanium (IV) oxide at pH 6.0. The precipitate was filtered and was digested with nitric acid-hydrogen peroxide to reduce the background absorption due to the coprecipitated organic materials. The solution was diluted to 50 ml with water in a volumetric flask.
The result ing solutions were employed to determine the vanadium concentration by the graphite furnace atomic absorption measurement. The good agreement was obserbed between the results obtained from the three preconcentration methods, and vanadium concentrations were ranged from 1.0 to 1.5 ppb in the Indian Ocean and the Pacific Ocean (see Table 3). And the trace amounts of vanadium in various kinds of the coastal sea water were determined by the coprecipitation method (see Table 4).