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RECEIVED for review June 30, 1986. Resubmitted May 11, 1987. Resubmitted August 12, 1987. Accepted October 14, 1987.
Tubular Donnan Dialysis-I nductively Coupled Plasma Atomic Emission Spectrometry John A. Koropchak* and Ewa Dabek-Zlotorzynska' Department of Chemistry and Biochemistry, Southern Illinois University, Carbondale, Illinois 62901-4409
The use of tubular Donnan dialysis as an on-line means of cation preconcentration can provide rapid enhancement of inductively coupled plasma atomk emission spectrometry ( ICP-AES) signals and corresponding limit of detection improvements. Fiow rate requirements of the ICP-AES sample Introduction system are compatible with those required to provide high cation enrichment factors for Donnan dialysis, especialry uslng a glass-frll nebuWzer. Intraaikai interferences are alleviated in an on-line fashion within certain mole ratio limits, which are cation dependent. Easily ionizable components in the receiver appear to normalize the matrix with regard to slgnai enhancements in the initial radiation zone of the ICP.
Donnan dialysis is a process by which ions are transported across an ion-exchange membrane as a result of an ionic strength gradient (1). If the volume of a high ionic strength receiver solution is smaller than that of a low ionic strength sample solution, enrichment of sample ions in the receiver results (2). The ion-exchange membrane employed may be flat (3) or tubular ( 4 ) . Donnan dialysis has been shown to provide essentially matrix-independent ion enrichment for samples of moderate to low ionic strength (2, 5 ) . Modest success has been reported for the application of tubular ion-exchange membranes to on-line preconcentration of cations prior to flame atomic absorption (FAA) analysis (6). More recently, detailed characterization of this approach was described, with signal enhancement factors exceeding 20 achievable within 5 min (7). Enrichment factors were shown to increase with tubing length, lower receiver pHs, and temperature (7). Easily ionizable elements (EIE) could be in-
* Author t o whom correspondence should be sent.
On leave from Department of Chemistry, Warsaw University, Warsaw. Poland.
cluded in the receiver solution for ionization suppression, further enhancing signals (7). Interferences due to counterions, such as PO4*, were also alleviated in this on-line fashion within the ionic strength limitations of Donnan dialysis (7). In order to select flow rates for the on-line tubular Donnan dialysis experiment, compromise between the low flows optimal for Donnan dialysis (
