The buffer, tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid (TES), and analytes, atenolol, mesityl oxide, and naproxen may be replaced. Ideally, the lab should include two positively charged analyte and a neutral marker to require the student to use critical thinking and laboratory skills to qualitatively and quantitatively assess a sample. The cations 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 ascorbic acid and tolmetin (negative charge at pH 7). Before asking students to use different chemicals, we recommend you perform the experiments outlined in Learning Module II with your substitute set.