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The buffer, tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid (TES), and analytes, atenolol, mesityl oxide, tolmetin may be replaced. Ideally, the lab should include one positively charged analyte, one negatively charged analyte and a neutral marker in order to demonstrate migration order experimentally. The cation and anion we chose to work with maintained charge at pH 7. We selected TES as the running buffer because it buffers at pH 7 and provides a low background current. You may choose other systems, for example riboflavin (net neutral charge at pH7), ascorbic acid (negative charge at pH 7), and thiamine (net positive charge at pH 7). In this case phosphate buffered at pH 7, may be used as a background electrolyte. Before asking students to use different chemicals, we recommend you perform the experiments outlined in Learning Module I with your substitute set.