Direct Determination of Ultratrace Cadmium in Spinach by Electrothermal Vaporization Atomic Fluorescence Spectrometry Using On-line Atom Trap of Tungsten Coil

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A novel solid sampling method of detecting cadmium in spinach by electrothermal vaporization atomic fluorescence spectrometer(SS-ETV-AFS) was established,which made use of a tungsten-coil as a Cd trap at room temperature to remove matrix interferences and foam graphite as a electrothermal vaporizer and a sample boat.In our wok,it was proven that the foam graphite vaporizer had a stable performance and different sample boats had no difference for testing;there was good homogeneity and representativeness for fresh spinach sample grinded with liquid nitrogen,16.3mg was calculated by the Pauwels equation as the minimum sample mass which satisfied microsampling of SS-ETV-AFS.After optimization,the ashing(50 W for 50 s then 70 W for 80 s) and evaporating(70 W for 30 s) procedures were separated,and 600 mL/min Ar/H2(9∶1,V/V) was chosen as the carrier gas.Under the optimized conditions,the limit of detection was 0.2 μg/kg;the recovery was 90.1%-106.1%,the relative standard deviation was less than 10%,and the analysis time was within 5 min.There was no interference from the other elements and organic matrix,and there was no significant difference(p0.05) between the methods of SS-ETV-AFS and microwave digestion graphite furnace atomic absorption spectrometer.