Abstract: The primary catalyst for the oligomerization of ethylene to synthesize α-olefins is an organic trivalent chromium [Cr(Ⅲ)] compound. Due to incomplete purification of raw materials, hexavalent chromium [Cr(Ⅵ)] impurities are present in the catalyst system. Excessive Cr(Ⅵ) content can disrupt the production process, reduce product yield, and cause environmental pollution. Therefore, accurately determining the Cr(Ⅵ) content is crucial for the production process.A method for detecting Cr(Ⅵ) in organic chromium catalysts was developed. Under conditions of 80–95 ℃, 2 mL of 70% (by mass fraction) sulfuric acid is used for low-temperature digestion of the organic chromium catalyst sample. In an acidic environment, Cr(Ⅵ) first undergoes a color-developing reaction with the chromogenic reagent diphenylcarbazide and then forms a complex with p-toluenesulfonic acid. Isopentyl alcohol is employed to extract Cr(Ⅵ) into the organic phase, and finally, the content of Cr(Ⅵ) is determined using spectrophotometry. The results indicate that after color development and extraction, Cr(Ⅵ) exhibits a maximum absorption peak at a wavelength of 540 nm. The optimal extraction and separation conditions for Cr(Ⅵ) are achieved with a chromogenic reagent dosage of 1 mL, a complexing agent dosage of 2 mL, an extractant dosage of 20 mL, a color development time of 5 min, and an extraction time of 20 min. The detection limit of this method for organic chromium samples is 1.000 μg/g (based on the mass of Cr element). When the mass of Cr(Ⅵ) in the tested sample ranges from 0 to 1.0 μg, the correlation coefficient of the working curve is greater than 0.999, the relative standard deviation of test results is less than 5%, and the spike recovery rate is 95%–105%.

Key words: organic chromium catalyst, digestion, hexavalent chromium, color development, extraction, spectrophotometry