Ion-exchange resms

Formamide deionized by stirring for 30 mm with 10% (w/v) of a mixed-bed ion exchange resm (e.g, Bio-Rad AG 501-X8,20-50 mesh, Bio-Rad, Hercules, CA), filtering twice through Whatman (Clifton, NJ) no 1 paper and storing smgle-use aliquots at -80°C... 

You may already be familiar with ion-exchange resms and we will start with them. They are commonly based on the co-polymer of styrene and 1,4-divinyl benzene we discussed earlier. The polymerization is carried out in an emulsion in water so that the organic molecules are in tiny droplets. The resulting polymer forms as more or less spherical beads of less than a millimetre in diameter. They can be put through a series of sieves to ensure even sizes if required. The surface of each bead bristles with benzene rings (attached to the polymer backbone) that can be sulfonated in the para position just like toluene. 

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