Abstract:
In this work, a flow injection (FI)-spectrophotometric system coupled with on-valve separation, using suitable adsorbent, for the sequential determination of caffeine and total polyphenols (PP) was developed. Adsorbent adsorbs polyphenols, not caffeine. Caffeine was therefore analyzed prior to PP that would be eluted later by a solvent. Caffeine in the purified water stream was measured at 273 nm. Then PP was analyzed based on Folin Ciocalteu (FC) assay, the formation of a blue complex (max= 760 nm.) in alkaline. The study adsorbent between Polyvinylpyrrolidone (PVP) and Polyvinylpolypyrrolidone (PVPP), which the appropriate adsorbent for this work is PVP. To optimize the system, the effects of type of PVP-conditioning solvent and type of PP eluent on the PP-adsorption efficiency and caffeine recovery were studied. It was found that using the mixture of methanol: water: acetic acid (20:79:1) provided PP-adsorption efficiency of 91%, higher than using purified water (70%) and methanol (64%), respectively, and caffeine recovery of 98-100% was obtained. To elute PP from PVP adsorbent, 70% methanol was selected with the PP recoveries of 69-114%. The developed system was used to determine caffeine and PP in 5 different known-concentration mixtures. The results showed good accuracy with %recovery of caffeine and PP ranged 100-112% and 96-116%, respectively, and acceptable precision (% RSD < 6%).