Determination of Trace Chromium in Geochemical Samples by Graphite Furnace Atomic Absorption Spectrometry

This article described the application of the ZEEnit 600 graphite furnace atomic absorption spectrophotometer on determination of trace chromium in geochemical samples. The HClO₄ was added during digestion to oxidize both Cr(Ⅱ) and Cr(Ⅲ) to Cr(Ⅳ), which avoid the analysis error caused by the different absorbencies of Cr(Ⅱ) and Cr(Ⅲ). The atomization temperature of Cr was reduced to 2100℃ by the technique of longitudinal heating at maximum speed in graphite furnace. The addition of ascorbic acid as matrix modifier improved the sensitivity and precision of the measurement, meanwhile increased the service life of graphite furnace. The linear range is from 0 to 200 ng/mL and the correlation coefficient is 0.9980 with background correction by using inverse Zeeman effect. The detection limits of the method is 0.05 μg/g (dilution factor is 2500), the precision of the method (RSD) is 2.11%-5.96%. The method has been validated by the national standard materials. The measured results were consistent with the certified values, and the results were accurate and reliable.