Ascorbic acid concentration

Absorption, Transport, and Excretion. The vitamin is absorbed through the mouth, the stomach, and predominantly through the distal portion of the small intestine, and hence, penetrates into the bloodstream. Ascorbic acid is widely distributed to the cells of the body and is mainly present in the white blood cells (leukocytes). The ascorbic acid concentration in these cells is about 150 times its concentration in the plasma (150,151). Dehydroascorbic acid is the main form in the red blood cells (erythrocytes). White blood cells are involved in the destmction of bacteria. 

Ascorbic acid is photosensitive and unstable in aqueous solution at room temperature. During storage of foods, vitamin C is inactivated by oxygen. This process is accelerated by heat and the presence of catalysts. Ascorbic acid concentration in human organs is highest in adrenal and pituitary glands, eye lens, liver, spleen, and brain. Potatoes, citrus fruits, blade currants, sea buckthorns, acerola, rose hips, and red paprika peppers are among the most valuable vitamin C sources [1,2]. 

BENZIE i FFand STRAIN J J (1999) Ferric reducing/antioxidant power assay Direct measure of total antioxidant activity of biological fluids and modified version for simultaneous measurement of total antioxidant power and ascorbic acid concentration, Meth Enzymol, 299, 15-27. 

Sobala, G.M., Crabtree, J., Dixon, M.F., Schorah, C.J., Taylor, J.D., Rathbone, B.J., Heatley, R.V. and Axon, A.T.R. (1991a). Acute Helicobacter pylori infection clinical features, local and systemic immune response, gastric mucosal histology and gastric juice ascorbic acid concentrations. Gut 32, 1415-1418. 

The IrIV anion, [Ir(H20)Br5], oxidises ascorbic acid at 20.0 °C.51 This reaction is first order with respect to ascorbic acid concentration and first order with respect to the Irlv anion. Comparison of hexabromo-, hexachloro, aquopentachloro-, and di-aquotetracholoiridium(IV) reactions with ascorbic acid shows that replacing a halide ion with a water molecule increases the standard reduction potential of the IrIV complex and increases the rate of reaction. 

Kolb E et al. (1991) Ascorbic acid concentration in plasma, in amniotic and allantoic fluids, in the placenta and in 13 tissues of sheep fetuses and newborn lambs. Dtsch Tierarztl Wochenschr. 98(11) 424 127. 

Fig. 35.5 Kinetic data for Cu(II) ion-catalyzed (0.785 x 10 M) oxidation of ascorbic acid in acetate buffered PVP solution (0.4%) at pH = 4.5 [Ascorbic acid concentrations (A 2.85, B 5.67,...

It seems reasonable that susceptibility and resistance of different plant species and different varieties within a species should depend on concentrations of endi enous antioxidants. The results of such studies do not give a clear picture Hanson et al. concluded that the range of susceptibility in petunia varieties depended on the ascorbic acid concentration, but Menser found that the ascorbic acid content of tobacco varieties was not related to ozone susceptibility. Ozone resistance of plants can be conferred by application of antioxidants. In the... 

Hanson, G. P., L. Thome, and C. D. Jativa. Ozone tolerance of petunia leaves as related to their ascorbic acid concentration, pp. 261-266. In H. M. Englund and W. T. Beery, Eds. Proceedings of the Second International Clean Air Congress. Held at Washington. D.C., Dec. 6-11, 1970. New York Academic Press. 1971. 

Glucose False negatives may occur when the urine contains small amounts of glucose (75-125 mg/dl) and/or ascorbic acid concentrations of 50 mg/dl or more. Sensitivity may also be decreased by the presence of ketone bodies. 

Bilirubin A false negative may occur when the sample contains ascorbic acid concentrations of 25 mg/dl or more. The yellow/orange-to-red color produced by the presence of indican (indoxyl sulfate) is also problematic. 

A more conventional mechanism appears to be operative in the photopolymerization of ethyl acrylate [178] and methyl methacrylate [179] in aqueous solution, sensitized by fluorescein and Erythrosin, respectively. Ascorbic acid is the reducing agent in both cases and it is observed that the reaction does not proceed in the absence of buffer, usually phosphate buffer pH 6. Polymer formation starts after an induction period but its dependence on light intensity and ascorbic acid concentration has not been determined. The rate of photopolymerization is proportional to the monomer concentration and to the square root of the light intensity, dye, and ascorbic acid concentration. The authors report the order with respect to the monomer as 3/2. However, from our analysis of the data for fluorescein, which are more... 

However, no independent evidence is presented for the existence of this complex. In our view a simpler explanation for the lack of reaction in unbuffered solution is that the nondissociated form of ascorbic acid is a chain terminator. At the typical concentrations employed, 1-10 mM, more than 90% of ascorbic acid (pK = 4.1) is not dissociated when dissolved in pure water. At pH 6.0 only 1% is present as the protonated form. Furthermore, in their study of the photopolymerization of methyl methacrylate initiated by acriflavine-ascorbic acid, Lenka and Mohanty [180] report the rate of polymerization reaches a maximum when the ascorbic acid concentration is approximately 10 mM. The decrease in polymerization rate at higher concentrations suggests ascorbic acid participates in chain transfer and/or termination reactions. 

Some studies have suggested that ascorbic acid concentrations are lower in the leukocytes and platelets of oral contraceptive users (183) however, this has not been confirmed (184). 

Dehydroascorbic acid appears to have a diabetogenic effect and ascorbic acid causes increased excretion of glucose. High ascorbic acid concentrations can delay the insulin response to a glucose challenge and prolong postprandial hyperglycemia (170). 

One report has described low plasma ascorbic acid concentrations during indometacin treatment, and a case of hyperglycemia has been reported (489). 

The calibration graph based on the decrease in steady-state current was rectilinear in the L-ascorbic acid concentration range from... 

The ascorbic acid concentration is high in immature fruit, and it decreases as the fruit ripen and increase in size, according to Harding et al. (17). 

The change in the ascorbic acid concentration of juice during acid reduction processing is illustrated in Figure 7. 

Olusi, S.O., Ojutiku, O.O., Jessop, W.J., and Iboko, M.I. Plasma and white blood cell ascorbic acid concentrations in patients with bronchial asthma. Clin Chim Acta, 92,161-166, 1979. 

K3. Kar Man Choy, C., Benzie, I. F. F., and Cho, P., Ascorbic acid concentration and total antioxidant activity of human tear fluid measured using the FRASC assay. Invest. Ophthalmol. 41, 3293— 3298 (2000). 

In reconstructed human epidermis the presence of vitamin C was required to normalize stratum corneum lipids, which was accompanied by an improvement of skin barrier formation.36 Interestingly the ascorbic acid concentration in the skin of atopic dermatitis37 and psoriatic patients38 measured in vivo by microdialysis was significantly lower than in healthy subjects. In psoriasis there was no significant difference in lesional versus nonlesional skin. There has also been demonstrated a decrease of ascorbic acid concentration in skin with increasing age.39... 

Leveque, N. et al., High iron and low ascorbic acid concentrations in the dermis of atopic dermatitis patients, Dermatology, 207, 261, 2003. 

Leveque, N. et al., Decrease in skin ascorbic acid concentration with age, Eur. J. Dermatol., 12, XXI-XXII, 2002. 

Acrylic acid and its sodium salt have been polymerized in the presence of hydrogen peroxide and ascorbid acid 61). Ascorbid acid is not oxidized at pH values lower than 7. The decomposition kinetics for hydrogen peroxide is dependent on H202 and ascorbic acid concentrations. 

Two kinetic equations have been established depending on ascorbic acid concentration. Although the theoretical mechanism is in a good agreement with experimental values at low concentrations of the acid, the calculated kinetic parameters (such as the reaction yields) are far from the experimental results described in Fig. 3.1. A mechanism has been suggested for the polymerization of various monomers initiated by Fenton s reagent (H202/Fe2+)4I,43) ... 

Figure 26. Dependence of the specific rate constant upon developing agent (ascorbic acid) concentration [107].

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