title: An on-line normal-phase high performance liquid chromatography method for the rapid detection of radical scavengers in non-polar food matrixes.
abstract: An on-line method for the rapid pinpointing of radical scavengers in non-polar mixtures like vegetable oils was developed. To avoid problems with dissolving the sample, normal-phase chromatography on bare silica gel was used with mixtures of hexane and methyl tert-butyl ether as the eluent. The high performance liquid chromatography-separated analytes are mixed post-column with a solution of stable free radicals in hexane. Reduced levels of the radical as a result of a reaction with a radical scavenger are detected as negative peaks by an absorbance detector. After investigating a number of different reagents, solvents, concentrations and solution flow rates an optimized instrumental set-up incorporating a superloop for pulse-free delivery of the reagent solution is presented. Both 2,2'-diphenyl-1-picrylhydrazyl (DPPH) and 2,6-di-tert-butyl-alpha-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-p-tolyloxy (galvinoxyl) were used as stable free radicals. The method is suitable for both isocratic and gradient HPLC operation. The method has a simple experimental protocol, uses standard instruments and inexpensive and stable reagents, and accepts any hexane-soluble sample. It can also be used for semi-quantitative analysis. The method was applied to several pure, non-polar natural antioxidants, vegetable oils and lipid-soluble rosemary extract. The limits of detection varied from 0.2 to 176 microg/ml, depending on the compound tested.
authors.affiliation: Natural Products Chemistry Group, Laboratory of Organic Chemistry, Wageningen University, Dreijenplein 8, 6703 HB Wageningen, The Netherlands.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Zhang
authors.forename: Elbert J C
authors.initials: EJ
authors.lastname: van der Klift
authors.forename: Hans-Gerd
authors.initials: HG
authors.lastname: Janssen
authors.forename: Teris A
authors.initials: TA
authors.lastname: van Beek
mesh_terms: D000975:Antioxidants / Q000032:analysis* / Q000378:metabolism; D001559:Benzhydryl Compounds / Q000737:chemistry / Q000378:metabolism; D001713:Biphenyl Compounds / Q000737:chemistry / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D005504:Food Analysis / Q000379:methods*; D006586:Hexanes / Q000737:chemistry; D013058:Mass Spectrometry; D009822:Oils, Volatile / Q000737:chemistry; D000069463:Olive Oil; D010851:Picrates / Q000737:chemistry / Q000378:metabolism; D010938:Plant Oils / Q000737:chemistry*; D027542:Rosmarinus / Q000737:chemistry; D012680:Sensitivity and Specificity; D024505:Tocopherols / Q000737:chemistry
chemical_list: D000975:Antioxidants; D001559:Benzhydryl Compounds; D001713:Biphenyl Compounds; D006586:Hexanes; D009822:Oils, Volatile; D000069463:Olive Oil; D010851:Picrates; D010938:Plant Oils; C050055:wheat germ oil; C053775:rosemary oil; C004931:1,1-diphenyl-2-picrylhydrazyl; D024505:Tocopherols; C020338:galvinoxyl