Abstract:

A novel method has been developed for the speciation of chromium in environmental water samples based on microemulsion extraction separation and preconcentration, and determination by doubleslotted quartz tube atom trapflame atomic absorption spectrometry(STAT-FAAS). In this method, Cr(Ⅲ) reacts with 8-hydroxyquinoline(8-HQ) yielding a hydrophobic complex, which then is extracted in the microemulsion phase, whereas Cr(Ⅵ) remained in aqueous phase. Thus, separation of Cr(Ⅲ) and Cr(Ⅵ) could be realized. Total chromium was determined after the reduction of Cr(Ⅵ) to Cr(Ⅲ) by using hydrogen peroxide as the reducing reagent. The main factors affecting the separation of Cr(Ⅲ) and Cr(Ⅵ) were optimized. The optimum conditions of the experiment are as follows, equilibration temperature and time are 80 ℃ and 10 min respectively, the pH of the system is 9.0, amounts of NH3-NH4Cl buffer and 8-HQ are 2.0 mL and 0.05 mmol, respectively, and microemulsion is made of mixture of Triton X-100, n-pentanol, n-hexane and water at mass ratio of 3.0∶15.0∶1.5∶4.0. Under the optimized conditions, the preconcentration system permitted an enrichment factor of 25 for chromium from the initial 50 mL sample solution to the final 2 mL concentrated solution; the linear concentration range was 2.5~500 μg/L for chromium. The limit of detection was 0.62 μg/L, and the relative standard deviation(n=10) was 3.8% for 10 μg/L Cr(Ⅲ) solution. The proposed procedure has been applied to the speciation of chromium in electroplating wastewater samples successfully.

Key words: Speciation determination of chromium, slotted tube atom trap-flame atomic absorption spectrometry (STAT-FAAS), microemulsion extraction, hydroxyquinoline