The DCB Arsenazo [3 （2 Arsonophenylazo） 6 （2

6 dichloro 4 bromo） 4

5 dihydroxy naphthalene 2

7 disulfonic acid] used as complex reagent was loaded on the mixture of active carbon silica gel. Main experimental parameters were optimizied. In the buffer solution of NH 3·H 2O HCOOH at pH 4.0

La 3+

Gd 3+ could be preconcentrated in a micro column preconcentration system and was determined by ICP AES. Its enrichment factor was 10; the detection limits was at μg/L level

the sampling frequency was 8 times/h. This method has been applied to the analysis of NBS standard sample of tomato leaves and GBW08505 tea leaves with satisfactory results.