The effect of drop volume on extraction efficiency was investigated. It was found that the absorbance of cadmium increased with the increasing of the drop volume from 10 to 25L. How-ever, increasing the drop volume in SDME usually resulted in the release of the micro drop. In order to enhance the adhesion force of the microdrop, a rolled PTFE tube was attached to the tipof syringe needle. When volume larger than 25L was used, the drop became unstable and was easily released from the tipof the rolled PTFE tube connected to the syringe needle. Considering the sampling volume of spectrophotometer, the subsequent dilution could not avoid. To weaken the negative effect for enhancement factor, four parallel extractions were employed, and the lager drop size of 25Lwas used for all extractions. Fig. 3.Selection of the type of extractant