ascorbic-acid and isobutyl-alcohol

This study proposes modifications to the conventional Folin-Ciocalteu (FC) spectrophotometric method for individually determining ascorbic acid (AA) in complex matrices in the presence of other phenolics and potential interferents. The conventional FC assay in the aqueous phase,which normally measures total water-soluble phenolics and other antioxidants, has recently been modified by incorporating isobutanol (iso-BuOH) in the solvent mixture for the simultaneous determination of lipophilic and hydrophilic antioxidants in foods.. Interference effects of other flavonoids and phenolics to individual AA assays were overcome by preliminary extraction–removal as their La(III) chelates into ethyl acetate (EtAc). The pH of the medium was adjusted to 3.0 in order to prevent conversion of AA into over-oxidation products further beyond the dehydroascorbic acid stage, as encountered in the conventional FC assay carried out at pH 10. This pH does not permit most phenolics to ionise, rendering their oxidation difficult.. Both methods (conventional and iso-BuOH-modified FC at pH 3, with and without La(III)/EtAc pre-extraction) were applied to the determination of ascorbic acid in pharmaceutical tablets and orange juice, showing good agreement with HPLC results. The proposed spectrophotometric methods with their low cost, simplicity, reliability, versatility and accuracy offer novelty to the determination of AA in complex matrices.

Topics: Antioxidants; Ascorbic Acid; Beverages; Butanols; Chelating Agents; Citrus sinensis; Flavonoids; Humans; Hydrogen-Ion Concentration; Hydrophobic and Hydrophilic Interactions; Ions; Lanthanum; Oxidation-Reduction; Pharmaceutical Preparations; Phenols; Reproducibility of Results; Spectrophotometry; Tablets

The Folin-Ciocalteu (FC) method of performing a total phenolics assay, originally developed for protein determination, has recently evolved as a total antioxidant capacity assay but was found to be incapable of measuring lipophilic antioxidants due to the high affinity of the FC chromophore, that is, multivalent-charged phospho-tungsto-molybdate(V), toward water. Thus, the FC method was modified and standardized so as to enable simultaneous measurement of lipophilic and hydrophilic antioxidants in NaOH-added isobutanol-water medium. Optimal conditions were as follows: dilution ratio of aqueous FC reagent with iso-BuOH (1:2, v/v), final NaOH concentration of 3.5 × 10(-2) M, reaction time of 20 min, and maximum absorption wavelength of 665 nm. The modified procedure was successfully applied to the total antioxidant capacity assay of trolox, quercetin, ascorbic acid, gallic acid, catechin, caffeic acid, ferulic acid, rosmarinic acid, glutathione, and cysteine, as well as of lipophilic antioxidants such as α-tocopherol (vitamin E), butylated hydroxyanisole, butylated hydroxytoluene, tertiary butylhydroquinone, lauryl gallate, and β-carotene. The modified FC method reliably quantified ascorbic acid, whereas the conventional method could not. The modified method was reproducible and additive in terms of total antioxidant capacity values of constituents of complex mixtures such as olive oil extract and herbal tea infusion. The trolox equivalent antioxidant capacities of the tested antioxidant compounds correlated well with those found by the Cupric Reducing Antioxidant Capacity reference method.

Topics: alpha-Tocopherol; Antioxidants; Ascorbic Acid; Benzene Derivatives; beta Carotene; Butanols; Flavonoids; Indicators and Reagents; Lipids; Molybdenum; Sodium Hydroxide; Tungsten Compounds; Vitamin E

A simple and accurate method for determination of vitamin C (ascorbic acid (AsA) and dehydroascorbic acid (DHA)) using 4,5-dimethyl-o-phenylenediamine (DMPD) was investigated. It was found that DMPD is a useful fluorescent reagent. The reaction product of DMPD with DHA showed strong and stable fluorescence (Ex; 360 nm, Em; 440 nm). Fluorometric derivatives were extracted with isobutanol or n-butanol. Extraction with isobutanol was superior to that with n-butanol in terms of specificity, since fluorometric derivatives of keto acids were extracted with n-butanol, together with DHA. The fluorescence intensity of DMPD derivatives was absolutely stable in isobutanol for at least 24 h. The sensitivity of determination of vitamin C was improved by removing several non-fluorometric compounds coexisting in the samples. The derivative derived from AsA was easily separated from those of keto acids by an HPLC method. The determination of vitamin C in natural products was thus improved by extraction and the HPLC method.

Topics: 1-Butanol; Ascorbic Acid; Butanols; Chromatography, High Pressure Liquid; Dehydroascorbic Acid; Phenylenediamines; Reproducibility of Results; Spectrometry, Fluorescence

Topics: Adenine Nucleotides; Adenosine Triphosphate; Ascorbic Acid; Benzene; Butanols; Colorimetry; Diphosphates; NAD; Nucleotides; Organophosphates; Phosphates; Research