Crosslinked Carboxymethyl Starch Based Solid Phase Extraction Combined with Direct Slurry Sampling Graphite Furnace Atomic Absorption Spectrometry for Determination of Trace Cr(III) and Cr(VI)in Water
A new method of solid phase extraction(SPE),using crosslinked carboxymethyl starch(CCMS) as adsorbent,combined with direct slurry sampling graphite furnace atomic absorption spectrometry(ss-GFAAS) has been developed for the speciation of trace Cr(Ⅲ) and Cr(Ⅵ) in environmental water samples.Various influencing factors on the separation and preconcentration of Cr(Ⅲ) and Cr(Ⅵ),such as the acidity of the aqueous solution,sample volume,adsorption time and effects of other ions,have been investigated systematically.Cr(Ⅲ) could be selectively retained by CCMS at pH 6.0 within 15 min,then the retained Cr(Ⅵ) on the CCMS was separated and the slurry of the precipitate prepared in 0.1% agar suspension was directly injected into the graphite furnace for the determination of Cr(Ⅲ).Total chromium was determined after the reduction of Cr(Ⅲ) to Cr(Ⅵ) by 1 mL 1% hydroxylamine hydrochloride,and Cr(Ⅲ) concentration was calculated by subtracting Cr(Ⅲ) from total chromium.The detection limit for Cr(Ⅲ) was 0.044 μg/L with an enrichment factor of 50,and the relative standard deviation(RSD) was 10.4%(cCr(Ⅲ) =1.0 μg/L,n=11).The proposed method has been applied to the speciation of chromium in water samples with satisfactory results.To validate the method,the proposed method was also applied to the determination of Cr(Ⅲ) and Cr(Ⅵ) in environmental water reference materials and the results obtained were in good agreement with the certified value.