3.3. Caffeine RM purity assignment
Measurement of the caffeine RM purity % was carried out by two different analytical techniques, as illustrated in Figure 8. The first was HPLC (M1) with a Zorbax-Eclipse-XDB-C18 column using diode array detection. Caffeine (0.01 g) from each of the randomly selected RM vials was dissolved in ultrapure water, and 1 mL of that diluted solution was injected into the HPLC system. Measurements for each vial were performed under the same repeatability conditions. The mean of each set of measurements was calculated, which is given in Table 1. The second technique was UV/Vis spectrophotometry (M2), where sample was prepared by dissolving 0.0183 g sample of each of the selected five vials in 50 mL of 0.1N HCl. The same protocol of measurements carried out by HPLC was followed using the UV/Vis spectrophotometer.