Cascade system for rapid on-line dilutions in flow-injection analysis.
A system for on-line dilutions in flow-injection analysis (FIA) is described. The system requires two flow-through pumps (peristaltic) and a conventional rotary injection valve. No precision timing or computer-controlled valves are required. The "cascade" dilution technique is demonstrated by the determination of 0-1.7M chloride. Viscosity effects are studied for samples with viscosities of 1-150 relative to water. Sample-zone volume reduction by splitting streams is combined with dilution by merging streams to achieve effective dilution factors of nearly 500. The reciprocal mole fraction is proposed as a variable for the characterization of open flow-injection systems and compared with the dispersion coefficient. An equation is included to predict this factor as a function only of the flow-rates used in the system. The cascade dilution system yields reproducible dilution factors with relative standard deviations of less than 3%, with sampling rates up to 100/hr.
Whitman
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Center for Process Analytical Chemistry, Department of Chemistry, BG-10, University of Washington, Seattle, WA 98195, U.S.A.
Christian
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