title: Determination of gallic acid with rhodanine by reverse flow injection analysis using simplex optimization.
abstract: A reversed flow injection (rFI) system was designed and constructed for gallic acid determination. Gallic acid was determined based on the formation of chromogen between gallic acid and rhodanine, resulting in a colored product with a λmax at 520 nm. The optimum conditions for determining gallic acid were also investigated. Optimizations of the experimental conditions were carried out based on the so-call univariate method. The conditions obtained were 0.6% (w/v) rhodanine, 70% (v/v) ethanol, 0.9 mol L(-1) NaOH, 2.0 mL min(-1) flow rate, 75 μL injection loop and 600 cm mixing tubing length, respectively. Comparative optimizations of the experimental conditions were also carried out by multivariate or simplex optimization method. The conditions obtained were 1.2% (w/v) rhodanine, 70% (v/v) ethanol, 1.2 mol L(-1) NaOH, flow rate 2.5 mL min(-1), 75 μL injection loop and 600 cm mixing tubing length, respectively. It was found that the optimum conditions obtained by the former optimization method were mostly similar to those obtained by the latter method. The linear relationship between peak height and the concentration of gallic acid was obtained over the range of 0.1-35.0 mg L(-1) with the detection limit 0.081 mg L(-1). The relative standard deviations were found to be in the ranges 0.46-1.96% for 1, 10, 30 mg L(-1) of gallic acid (n=11). The method has the advantages of simplicity extremely high selectivity and high precision. The proposed method was successfully applied to the determination of gallic acid in longan samples without interferent effects from other common phenolic compounds that might be present in the longan samples collected in northern Thailand.
authors.affiliation: Alpha Flow Analysis Group, Department of Chemistry and Center of Excellent for Innovation in Chemistry (PERCH-CIC) Together with Materials Science Research Center, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand.
authors.forename: Wilaiwan
authors.initials: W
authors.lastname: Phakthong
authors.affiliation: Department of Pharmaceutical Science, Faculty of Pharmacy, Chiang Mai University, Chiang Mai 50200, Thailand; Science and Technology Research Institute, Chiang Mai University, Chiang Mai 50200, Thailand.
authors.forename: Boonsom
authors.initials: B
authors.lastname: Liawruangrath
authors.affiliation: Alpha Flow Analysis Group, Department of Chemistry and Center of Excellent for Innovation in Chemistry (PERCH-CIC) Together with Materials Science Research Center, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand; Science and Technology Research Institute, Chiang Mai University, Chiang Mai 50200, Thailand. Electronic address: scislwrn@gmail.com.
authors.forename: Saisunee
authors.initials: S
authors.lastname: Liawruangrath
mesh_terms: D017022:Flow Injection Analysis / Q000379:methods*; D005707:Gallic Acid / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D057230:Limit of Detection; D010636:Phenols / Q000737:chemistry*; D012236:Rhodanine / Q000737:chemistry*; D029631:Sapindaceae / Q000737:chemistry*; D013053:Spectrophotometry
chemical_list: D010636:Phenols; D005707:Gallic Acid; D012236:Rhodanine
keywords: Gallic acid; Reversed flow injection analysis; Rhodanine; Simplex optimization