title: Rapid flow injection spectrophotometric determination of monofluorophosphates in toothpastes after on-line hydrolysis by alkaline phosphatase immobilized on a cellulose nitrate membrane.
abstract: A new, rapid flow injection (FI) method is reported for the spectrophotometric determination of monofluorophosphate (MFP) ions in toothpastes. MFP ions are hydrolyzed on-line by alkalinephosphatase (APase) immobilized on a cellulose nitrate membrane, prior to injection in the FI system. The yielded orthophosphate ions are determined spectrophotometrically (lambda(max) = 690 nm) using the molybdenum blue approach. The chemical and FI variables that affected the enzymatic reaction were studied and optimized. A study of interferences was also carried out. The proposed method is very precise (s(r) = 0.7% at 1.0 x 10(-4) mol l(-1) MFP, n = 12), fast (sampling rate of 72 h(-1)) and allows the determination of MFP ions in the range of 4.0 x 10(-5) to 6.0 x 10(-4) mol l(-1) with a satisfactory 3sigma detection limit of 4.0 x 10(-6) mol l(-1). The application of the proposed FI method to toothpaste samples yielded accurate results (e(r) < 2.0%) compared with a potentiometric reference procedure.
authors.affiliation: Department of Chemistry, Aristotle University of Thessaloniki, Greece.
authors.forename: P D
authors.initials: PD
authors.lastname: Tzanavaras
authors.forename: D G
authors.initials: DG
authors.lastname: Themelis
mesh_terms: D002327:Cariostatic Agents / Q000032:analysis*; D005459:Fluorides / Q000032:analysis*; D006801:Humans; D006868:Hydrolysis; D010710:Phosphates / Q000032:analysis*; D013053:Spectrophotometry / Q000379:methods; D014100:Toothpastes / Q000737:chemistry*
chemical_list: D002327:Cariostatic Agents; D010710:Phosphates; D014100:Toothpastes; C012980:fluorophosphate; D005459:Fluorides