Detection ascorbic acid

Figure 3. Simultaneous analysis for ascorbic acid and dehydroascorbic acid with the use of a gradient analysis HPLC method. The minimum detectable quantities were 10 ng/ injection for ascorbic acid and 500 ngl injection for dehydroascorbic acid (80) column, LiChrosorb NH2, 10 fxm mobile phase, 0.005M KH2PO4, pH 3.5 and CHsCN detection, ascorbic acid, 268 nm and dehydroascorbic acid, 228 nm. (Reproduced, with permission, from Hewlett-Packard.)...

PiWisVsOga ) with QPVP-Os can be used to detect ascorbic acid in the presence of dopamine iron-substituted POMs (PiWiyOgiFe ) with QPVP-Os formed multilayer films that give remarkable catalysis effects on H2O2, Br03, and N02 reactions. 

Qian et al. [31] deposited a similar polymer via the LbL technique, alternating with Au NPs, resulting in the ability to detect ascorbic acid Havens et al. [32] linked a [Os(bipy)2]Cl residue to a PVP-polyvinylpyrimidine copolymer finally anchored, through an amidic bond, to a defect of a multiple-wall CNT, trapped inside a hydrogel. This is able to swell in aqueous solvent, becoming accessible to species in solution (see Fig. 3.4). Electrocatalytic action with respect to ascorbic acid was exploited in a complete analytic work, based on amperometric measurements at a fixed potential. 

Ascorbic acid and dehydroascorbic acid have been determined by reversed-phase h.p.l.c., post-column reduction of dehydroascorbic acid to ascorbic acid with dithiothreitol, reaction of excess reagent with JV-ethylmaleimide, and electrochemical detection. Ascorbic acid and its 2-phosphate were determined by h.p.l.c. on an aminopropyl bonded-phase silica column. Dehydroascorbic acid could also be determined by the increase in the ascorbic acid content after reduction with dithiothreitol The method was applied to raw apple and potato to which these compounds are added to prevent browning. ... 

The wavelength of 254 nm was also used for detecting ascorbic acid from mice plasma and testis (44). The pH of the mobile phase was 3.1. The detection limit was carefully determined as 174 ng/mL for plasma and testis ascorbic acid. 

Biolodcal Applications Biosensors diagnosis of diabetes detecting ascorbic acid, uric acid, glucose, glomerular deposits ... 

Electrochemical methods of analysis (electroanalysis) have made progress by laser-assisted techniques [44, 92-94]. They were useful to detect ascorbic acid at a carbon electrode in flow injection [44]. Capabilities of pulsed laser beam illumination of gold and platinum disk electrodes were tested with the well-known redox couples toluidine blue, iodide, ferricyanide, ruthenium hexammine and ferrocene (see Fig. 4.10) [92]. Laser-activated voltammetry proved useful for selective removal of impurities from glassy carbon- and boron-doped diamond surfaces [93]. 

Pastes made of carbonaceous materials with ionic liquids acted also as heated electrochemiluminescence sensors. A mixture of multi-wall carbon nanotubes with an ionic liquid was used in connection with lucigenine to detect ascorbic acid which influences the luminescence of the latter [68]. Another example was a carbon/ionic liquid paste electrode where Ne-isopentenyl-adenine was detected using its enhancement action on the electrochemiluminescence of ruthenium bipyridyl [69]. 

Polybithiophene film coated on indium tin-oxide (ITO) glass plate was used to detect low levels of ascorbic acid based on changes in the UV-visible absorption characteristics of the doped polymer. To further investigate the influences of substituents on polybithiophene, both PDCBT and PDBOBT were used to detect ascorbic acid and the performance of these sensors were evaluated. 

Because of the time and expense involved, biological assays are used primarily for research purposes. The first chemical method for assaying L-ascorbic acid was the titration with 2,6-dichlorophenolindophenol solution (76). This method is not appHcable in the presence of a variety of interfering substances, eg, reduced metal ions, sulfites, tannins, or colored dyes. This 2,6-dichlorophenolindophenol method and other chemical and physiochemical methods are based on the reducing character of L-ascorbic acid (77). Colorimetric reactions with metal ions as weU as other redox systems, eg, potassium hexacyanoferrate(III), methylene blue, chloramine, etc, have been used for the assay, but they are unspecific because of interferences from a large number of reducing substances contained in foods and natural products (78). These methods have been used extensively in fish research (79). A specific photometric method for the assay of vitamin C in biological samples is based on the oxidation of ascorbic acid to dehydroascorbic acid with 2,4-dinitrophenylhydrazine (80). In the microfluorometric method, ascorbic acid is oxidized to dehydroascorbic acid in the presence of charcoal. The oxidized form is reacted with o-phenylenediamine to produce a fluorescent compound that is detected with an excitation maximum of ca 350 nm and an emission maximum of ca 430 nm (81). 

Chromatographic methods, notably hplc, are available for the simultaneous deterrnination of ascorbic acid as weU as dehydroascorbic acid. Some of these methods result in the separation of ascorbic acid from its isomers, eg, erythorbic acid and oxidation products such as diketogulonic acid. Detection has been by fluorescence, uv absorption, or electrochemical methods (83—85). Polarographic methods have been used because of their accuracy and their ease of operation. Ion exclusion (86) and ion suppression (87) chromatography methods have recently been reported. Other methods for ascorbic acid deterrnination include enzymatic, spectroscopic, paper, thin layer, and gas chromatographic methods. ExceUent reviews of these methods have been pubHshed (73,88,89). 

Two techniques for sorption-spectroscopic determination of ascorbic acid have been proposed. The first one is the recovery by silica modified with tetradecyl ammonium nitrate of blue form of molibdophosphoric HPA in the presence of vitamin C. And the second one is the interaction between the ascorbic acid in solution and immobilized on silica ion associate of molibdophosphoric acid with lucigenine. The detection limits of vitamin C are 0.07 and 2.6 mg respectively. The techniques were successfully applied to the determination of ascorbic acid in fmit juices. 

In long-wavelength UV light (2 = 365 nm) ascorbic acid (hRf 45 — 50) and dehydroascorbic acid (hRf 50—55) yielded green fluorescent zones on an orange-colored background. The detection limits were less than 5 ng substance per chromatogram zone. 

The detection limit per chromatogram zone is 50—200ng for lipids [11], 200— 400 ng for antioxidants [3] and several ng for ascorbic acid. 

FIGURE 3-27 Three-dimensional chromatogram for oxidizable biological compounds at a multichannel amperometric detection system, consisting of an array of 16 carbon-paste electrodes held at different potentials. AA = ascorbic acid NE = norepinephrine DOPAC = 3,4-dihydroxyphenylacetic acid 5-HIAA = 5-hydroxyindole-3-acetic acid DA = dopamine HVA = homovanillic acid. (Reproduced with permission from reference 68.)... 

Describe the rationale of using electrodes coated with Nation films for selective detection of the cationic neurotransmitter dopamine in the presence of the common interference from anionic ascorbic acid. 

The detection limit for ascorbic acid is less than 100 ng substance per chromatogram zone [2]. 

Ascorbic acid (h/ f 50-55) appeared as a brown-red chromatogram zone that was only stable for ca. 20 min the background was yellow. The detection limit was less than 100 ng substance per chromatogram zone. 

Note Dehydroascorbic acid, the decomposition product of ascorbic acid, does not react. But it can be detected as a yellow-orange chromatogram zone (hRf 65-70) by further treatment of the chromatogram with 2,4-dinitrophenylhydrazine. This sequence... 

Irreversible reaction of [18] iodine with acetylsalicylic acid, aethaverine, amidopyrine, ascorbic acid, benzo-caine, quinine, dihydrocodeine, fluorescein, glycine, hydrocortisone acetate, isoni-azid, metamizole, papaverine, paracetamol, phenacetin, phenol-phthalein, piperazine, resorcinol, salicylic acid, salicylamide, sulfaguanidine, thymol, triethanolamine, tris buffer detection by reaction chromatography... 

The detection limits for both ascorbic acid and dehydroascorbic acid were ca. 50 ng substance per chromatogram zone. 

FIGURE 10.13 The TLC profiles of labeled peaks isolated from [U- C]ascorbic-acid-modified calf lens protein obtained from Bio-Gel P-2 chromatography. Peaks 2 to 7 were spotted on a preparative silica gel TLC plate and developed with ethanol/ammonia (7 3, v/v). The fluorescence in each lane was detected by irradiation with a Wood s lamp at 360 nm, and the pattern of radioactivity was determined by scanning the plate with AMBIS imaging system. (Reprinted with permission from Cheng, R. et al., Biochim. Biophys. Acta, 1537, 14-26, 2001. Copyright (2001) Elsevier.)... 

Figure 2 Selective electrochemical detection of a mixture on multielectrode amper-ometry. AA = Ascorbic acid, NE = norepinephrine, DOPAC = 3-4-dihydroxy-phenylacetic acid, E = epinephrine bitartrate, 5-HIAA = 5-hydroxyindole-3-acetic acid, HVA = homovanillic acid, TRP = tryptophan, 5-HT = 5-hydroxytryptamine, and 3-MT = 3-methoxytyramine (separated by RPLC). Detection was with a 4-electrode glassy carbon array, with electrode 1 at 500 m V) electrode 2 at 700 mV, electrode 3 at 900 mV, and electrode 4 at 1100 mV. Note that at electrode 1, HVA, TRP, and 3-MT are not seen. At electrode 2, only TRP is not seen. A standard calomel electrode was used as reference. (Reprinted with permission from Hoogvliet, J. C., Reijn, J. M., and van Bennekom, W. P., Anal. Chem., 63, 2418, 1991. 1991 Analytical Chemistry.)...

Feubolt, R. and Klein, H., Determination of sulphite and ascorbic acid by high-performance liquid chromatography withe electrochemical detection,. Chromatogr., 640, 271, 1993. 

There are no approved pharmacologic treatments for atrophic AMD. The Age-Related Eye Disease Study showed that a supplement containing ascorbic acid 500 mg, vitamin E 400 IU, beta carotene 15 mg, zinc oxide 80 mg, and cupric oxide 2 mg reduced the rate of clinical progression of all types of AMD by 28% in patients with at least intermediate macular degeneration. No benefit was seen in patients with earlier stages of age-related maculopathy however, the duration of the study may have been insufficient to detect this benefit.25... 

A similar study has also been conducted to determine the suitability of ascorbic acid 2-phosphate (AAP) as an alternative substrate to 4-AP for AP under identical conditions [48], Although 4-APP and AAP were suitable substrates for amperometric immunosensors, 4-APP was superior owing to its sixfold faster enzymatic reaction and lower detection potential (approximately 200-400mV). Notably, the lower detection potential for the hydrolysis product of 4-APP minimizes interferences from other species and hence improves the sensitivity of the immunosensor. 

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