Development of "One drop solvent concentration method"for Highly Sensitive Micro Analysis

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A simple and effective concentration method into micro volume of solvent has been developed. After solvent extraction, one drop of high boiling-point solvent is added to the separated organic phase, and the extracting solvent with low boiling-point is removed by evapolation. Thus, the analyte is concentrated into the residual micro volume of high boiling-point solvent.The proposed method has been successfully applied to the concentration of cobalt (II) ion with the enrichment factor of 1000 and introduced to ion-pair reversed-phase HPLC.Separtion of excess reagent from the analyte is required to obtain the large enrichment factor without precipi-tation in the final water-miscible solvent. The cobalt (III)-2,2'-dihydroxyazobenzene (DHAB,H_2L) complex, [CoL_2]^-, is extracted into chloroform as the ion-pair with tetrabutylammonium ion following removal of excess DHAB by extraction of its neutral species, H_2L.To the separated organic phasemicro volume of dimethylsulfoxide (DMSO,boiling point : 189 C) is added and the low boiling-point solvent, chloroform, is removed by evaporation to concentrate the analyte in the residual DMSO.The undesired depressiveeffect of the organic solvent on HPLC peak profiles was eliminated by using a suitable injection solution of 1 : 1 DMSO-water. When the startingaqueous sample volume of 100 cm^3 and 0.1 cm^3 of DMSO were used, the detection limit reached 3*10^<-11> mol dm^<-3> (1.8 ppt).