title: Reaction-frequencymetric method: a new analytical technique for determination of submicromolar concentration levels of vitamin C.
abstract: A new analytical technique for the assay of pharmaceutical substances at low concentration levels has been proposed and applied to the determination of vitamin C as an example of its application. It is based on the chemical reaction of vitamin C with iodine in a sodium citrate-hydrochloric acid medium, followed by measurement of the frequency change of a silver-plated piezoelectric quartz crystal. The frequency change is proportional to the vitamin C concentration from 2 x 10(-7) to 4 x 10(-6) M. The method was applied to the assay of vitamin C in pharmaceutical preparations.
authors.affiliation: Department of Chemical Engineering, Hunan University, Changsha, China.
authors.forename: L H
authors.initials: LH
authors.lastname: Nie
authors.forename: S L
authors.initials: SL
authors.lastname: Tan
authors.forename: S Z
authors.initials: SZ
authors.lastname: Yao
mesh_terms: D001205:Ascorbic Acid / Q000032:analysis* / Q000737:chemistry; D002021:Buffers; D002626:Chemistry, Pharmaceutical; D002951:Citrates; D019343:Citric Acid; D006851:Hydrochloric Acid; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D007455:Iodine / Q000737:chemistry; D012996:Solutions; D013607:Tablets
chemical_list: D002021:Buffers; D002951:Citrates; D007202:Indicators and Reagents; D012996:Solutions; D013607:Tablets; D019343:Citric Acid; D007455:Iodine; D001205:Ascorbic Acid; D006851:Hydrochloric Acid