A New Method for Low‐Temperature Decomposition of Chromites and Dichromium Trioxide using Bromic Acid Evaluated by Chromium Isotope Measurements

Abstract

In recent years, routine application of the stable isotope determination of chromium (Cr) in environmental and health protection research has led to the search for simpler chromite decomposition techniques. As the range of Cr isotope abundance ratios in nature is very narrow, conventional chromite decomposition techniques are no longer suitable, due to the relatively high risk of contamination during laboratory procedures. We have developed a protocol for the decomposition of chromites based on oxidation by bromic acid at room temperature. The procedure takes 15 d and requires two doses of bromic acid during the reaction period (day 1 and 8), due to the limited stability of the reagent. Chromium extracted by alkaline oxidative fusion and by bromic acid decomposition yielded statistically indistinguishable d 53 Cr values, measured by multi-collector inductively coupled plasma-mass spectrometry following addition of a 50 Cr-54 Cr double-spike.

High‐Precision Measurement of Stable Cr Isotopes in Geological Reference Materials by a Double‐Spike TIMS Method

“…During the measurement of Fe, Cr, Pb and Cu isotopes using TIMS, organic matter is considered a significant interference (Kuritani and Nakamura , Johnson and Bullen , Yamakawa et al , Chrastný et al ). The organic matter in samples is most likely derived from the exchange resin or colloidal silica.…”

“…The organic matter in samples is most likely derived from the exchange resin or colloidal silica. Previous work used ultraviolet radiation, H 2 O 2 or HClO 4 treatment to eliminate organic residues originating from the column resin (Kuritani and Nakamura , Johnson and Bullen , Yamakawa et al , Chrastný et al ). During our experiment, the beam current of 52 (Cr + ) increased smoothly and was stable over 10 × 10 −11 A when 0.5 μg of pure Cr isotope reference materials NIST SRM 979 and NIST SRM 3112a were measured.…”

“…The organic component in samples is highly persistent after the repeated drying of samples with drops of nitric acid at elevated temperature or adding H 2 O 2 (Kuritani and Nakamura , Johnson and Bullen , Yamakawa et al , Chrastný et al ). Both H 2 O 2 and HNO 3 were tried many times to eliminate organic matter after Cr purification with different temperature/time conditions (for the repeated digestion of a BHVO‐2 sample with 1 µg Cr).…”

“…The residual of the oxidising reagents (SO 4 2− ) can severely inhibit the Cr + signal during TIMS measurements, but this residual is difficult to remove (Ball and Bassett ). In addition, the high ionisation potential of Cr and the inhibition effect of the Cr + signal from organic matter during instrument measurements are the main reasons impeding the acquisition of high‐precision isotope ratio results in compositionally complex geological materials during TIMS measurements (Johnson and Bullen , Yamakawa et al , Chrastný et al , Li et al ).…”

Isotope evidence of hexavalent chromium stability in ground water samples

“…The method used is adopted from Bullen (2007), Chrastný et al (2014), and Farkaš et al (2013). First of all, the anion exchange columns were treated in the laboratory for field work.…”