2.6 Recovery test
Recovery test was carried out by spiking known contents of standard samples into a rhubarb decoction sample and then was then purified using the above-mentioned SPE procedure. The average recoveries were estimated by comparing the determined amount of these analytes with the amount originally added and were counted by the formula: recovery = (amount of found – original amount) / amount spiked 100%, and RSD = (SD/mean) 100%.