Therefore, although lower concentrations of NH4OAc show stronger signals, we chose 200 mM NH4OAc. With this concentration, we performed the next round of a combinatorial assay for NaOH and NaBH4 (Figure ); lower signals were observed with the combination of low NaBH4 concentration and high NaOH concentration. We also found that when the NaOH concentration was above the NH4OAc concentration, the result depended too highly on the NaBH4 concentration, which is undesirable for the reason we stated above. Therefore, we conclude that the NaOH concentration must be below the NH4OAc concentration, which is also corroborated with the photograph in Figure ; palladium-free solutions showed a purple color when the NaOH concentration was higher than NH4OAc concentration.