Due to the ease of use and portability of fluorometers, a colorimetric or fluorometric method can be employed on site (i.e., in the laboratory where APIs are purified), eliminating the need to transport synthetic samples. We developed a high throughput method for quantifying trace palladium in APIs by fluorescence or color (Scheme 1). In this method, resorufin allyl ether (RAE) undergoes palladium-catalyzed allylic C-O bond cleavage (Tsuji-Trost type reaction) to produce fluorescent, magenta resorufin in its anion form. The correlation between the resorufin concentration and fluorescence signals with our instrument (see the experimental procedure section for detail) is shown in Figure . The reaction is accelerated by tri(2-furyl)phosphine (TFP) and sodium borohydride (NaBH4). The roles of TFP are two-fold: first, it binds to palladium to form catalytically active fluorescence intensities (entry 2.3). However, in the 0-0.8 nM palladium range (the first three columns), the solutions changed from yellow to purple, making it difficult to visibly distinguish the magenta color from the purple color. We were also aware that too many parameters, such as time and the concentrations of NaBH4, NaOH, and H2O, varied in entries 2.1, 2.2, and 2.3. When the NaBH4 concentration was 50 mM from the beginning (entry 3), all the solutions turned purple (Figure ). Because the observations above were not easily interpreted, we redesigned an experiment so that only the NaOH concentration would vary (entry 4 and Figure ). Both the lower and higher NaOH concentrations decelerated the deallylation reaction. We initially thought that at lower NaOH concentrations, NaBH4 degraded rapidly and thus was unable to reduce air-oxidized palladium species. At higher NaOH concentrations, once again the reactions turned purple. If the method can tolerate only a narrow range of NaOH concentrations, that would make the method difficult to employ. As we discuss below, this was not the case.