title: The use of octadecyl-bonded microparticulate silica in the separation of free and bound fractions during saturation analysis of vitamin D metabolites.
abstract: The use of octadecyl-bonded microparticulate silica to separate free and bound fractions during the saturation analysis of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D has been investigated. A slurry of octadecyl-bonded silica in an appropriate incubation buffer was prepared and used in parallel with a conventional dextran-coated charcoal suspension in several assay procedures. Standard curves, non-specific binding and plasma values were compared. A competitive protein binding assay for 25-hydroxyvitamin D and two radioreceptor assays and one radioimmunoassay for 1,25-dihydroxyvitamin D were investigated. In most cases the octadecyl-bonded silica preparation gave the more favourable results; its action was rapid, time- and temperature-independent, and it produced low non-specific binding and higher B0 values in all the assays examined. It was in our hands easier to use than dextran-coated charcoal. The use of octadecyl-bonded silica is recommended as an efficient agent for the separation of free and bound fractions in the saturation analysis of vitamin D metabolites.
authors.affiliation: Department of Chemical Pathology, London Hospital Medical College, UK.
authors.forename: R D
authors.initials: RD
authors.lastname: Coldwell
authors.forename: J
authors.initials: J
authors.lastname: Nolan
authors.forename: D J
authors.initials: DJ
authors.lastname: Trafford
authors.forename: E B
authors.initials: EB
authors.lastname: Mawer
authors.forename: H L
authors.initials: HL
authors.lastname: Makin
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002112:Calcifediol / Q000302:isolation & purification / Q000493:pharmacokinetics; D002117:Calcitriol / Q000302:isolation & purification / Q000493:pharmacokinetics; D002417:Cattle; D002606:Charcoal; D002642:Chick Embryo; D003600:Cytosol / Q000378:metabolism; D003911:Dextrans; D006801:Humans; D011485:Protein Binding; D011869:Radioligand Assay; D012822:Silicon Dioxide; D013696:Temperature; D013950:Thymus Gland / Q000378:metabolism; D014807:Vitamin D / Q000302:isolation & purification* / Q000493:pharmacokinetics
chemical_list: D003911:Dextrans; C026679:octadecylsilica; D014807:Vitamin D; D002606:Charcoal; D012822:Silicon Dioxide; D002117:Calcitriol; D002112:Calcifediol