[Determination of trace chromium in rock samples by graphite furnace-AAS after microsphere phase separation...

A new method for the determination of trace chromium in geological samples by graphite furnace atomic absorption spectrometry (GFAAS) with microsphere phase separation extraction was developed. With the existence of cosolvent of ethanol and solvent of 1-amylalcohol, the diphenylcarbazide reacted with Cr to form a complex in a homogenous phase. Then the complex was separated out with microsphere from the homogenous phase after a little water was added in the system. The operating conditions for phase separation and the heating program of graphite furnace were experimented and optimized. The interference of co-existent ions was studied. The results indicated that the microsphere phase separation extraction can be used to separate and extract the analyte, and also the microsphere can be used as the matrix modifier in the heating program of graphite furnace. As the cosolvent, the dosage of ethanol was about 0.2-0.5 times of the volume of water with the existence of 0.2-1.5 mL 1-amylalcohol. Under the optimum conditions, the linear range of the method was 0-10 microg x L(-1) and the detection limit was 0.057 microg x L(-1) with the relative standard deviation (RSD) of 3.3% (n=11). The concentration factor was 10 with 15 mL of water and 1.5 mL of 1-amylalcohol. The method has been applied to determine the concentration of Cr in geological samples and the analytical results are in agreement with the certified values.