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Solid Phase Reagents for Titrations

IP.com Disclosure Number: IPCOM000047135D
Original Publication Date: 1983-Sep-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 4 page(s) / 48K

Publishing Venue

IBM

Related People

Studebaker, JF: AUTHOR

Abstract

This article relates generally to chemical analysis of aqueous solutions and more particularly to a titration method and device for determining the concentration of metal ions and the like in a solution. Titration is widely used in chemical laboratories to determine the concentration of acids, bases, metal ions, oxidizing agents, or reducing agents in aqueous solutions. The determinations generally require some skill on the part of the analyst and often take considerable time. In the approach proposed here, the titrant solution and the soluble indicator traditionally used in titrations are replaced by solid phase reagents bound to beads. The beads are packed into cylindrical columns with transparent walls.

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Solid Phase Reagents for Titrations

This article relates generally to chemical analysis of aqueous solutions and more particularly to a titration method and device for determining the concentration of metal ions and the like in a solution. Titration is widely used in chemical laboratories to determine the concentration of acids, bases, metal ions, oxidizing agents, or reducing agents in aqueous solutions. The determinations generally require some skill on the part of the analyst and often take considerable time. In the approach proposed here, the titrant solution and the soluble indicator traditionally used in titrations are replaced by solid phase reagents bound to beads. The beads are packed into cylindrical columns with transparent walls. After a measured volume of the solution to be titrated has passed down the column, the concentration of the species being determined is calculated from the length of that part of the bead bed where the indicator has changed color. As a titrating cartridge for calcium metal ions, for example, a cartridge packed with a chelating resin like CHELEX 100* may be used (Fig. 1). Beads with a covalently bound metal ion indicator are mixed uniformly with the CHELEX 100. Polymeric beads containing a covalently bound, calcium-sensitive dye may be prepared by first diazotizing 2- amino-4-chlorophenol (Fig.
2), coupling it to J acid at alkaline pH (Fig. 3), and then coupling the azo dye thus formed to carboxymethyl cellulose by the carbodiimide reaction (Fig. 4). The resulting polymer-bound dye changes from purple to red when calcium ions are added to the surrounding solution at strongly alkaline pH. At the outset, the solution filling the cartridge of Fig. 1 is metal free. When a solution containing a metal ion is passed into the bed, metal ions are bound to both the chelating groups and the indicator. The indicator changes color along the length of the bed down to the point at which the passing solution had lost all its metal ion to the CHELEX. Where that point falls is determined by the concentration of the metal ion in the solution and the volume of solution which has passed into the column. For example, if (a) the bed contains 0.1 milliequivalent of chelating groups per ml of bed volume, (b) the total bed volume is 3.0 ml, and (c) 15 ml of a .01 M solution of CaCl2 is passed into the column, the top of the column would be the color of the metal indicator complex and the bottom 50% the color of the free indicator, as shown in Fig. 1. Similarly, 15 ml of a
.005 M solution of CaCl2 changes the color of the top 25% of the cartridge. Extension to other concentrations indicates that the column of this example may be used to measure metal ion concentration in the range .002 M - .02 M. Using a larger or smaller volume of sample extends the useful range of the cartridge to lower or higher concentrations. For lower concentrations, an alternative is to dilute the chelating beads with beads which have similar phys...