Absorption of ascorbic acid

Oral absorption of ascorbic acid is via an energy-dependent process that is saturable and dose-dependent. Ascorbic acid is stored in the body. Excessive amounts of consumed vitamin C, i.e. if daily intake surpasses 100 mg, are rapidly excreted in the urine. 

The turnover rates of ascorbic acid from tissues (afflux Tti) were larger than the afflux (see Table III, column headed "Tn/Ti/ ), suggesting either that the distribution equilibrium between labeled ascorbic acid and available tissue ascorbic acid has not been reached, or that part of the compartmental pool of ascorbic acid cannot be exchanged. Therefore, formal calculation of the total turnover of ascorbic acid using tissue data results in a turnover somewhat larger than that calculated using plasma data (mean value 12.5-8 mg/d). When calculated from the food intake, the turnover is 16 it 3 mg/d therefore, one must assume that the bioavailability of ascorbic acid present in the diet is not 100%. Studies on the absorption of ascorbic acid in humans have demonstrated... 

Absorption of ascorbic acid in the gut is a passive process for the rat (18), while scurvy-prone animals require an active transport system with a Na -dependent, gradient-coupled carrier mechanism that is inhibited by ouabain (19,20). A transport model is favored that fea-... 

The ultraviolet absorption of ascorbic acid in the region of 265 mji has been commonly used for the estimation of ascorbic acid in simple solutions. In complex biological materials, however, other substances absorb considerably at this wavelength. A variety of ways to overcome this difficulty have been explored, such as measuring the decrease in absorption after more or less specific destruction of the ascorbic acid with cuprous ions, or irradiation, or with ascorbic acid oxidase. The effect of pH on altering the absorption band of ascorbic acid from 245 mfi in acid to 265 m i in neutral solution has also been used to increase the specificity of the absorption measurements (D5). 

There must also be a second mechanism of ascorbic acid transport through certain specialized cells, difierent from the diffusion of dehydro-ascorbic acid followed by intracellular reduction. There are no indications that dehydroascorbic acid is involved in the renal tubular absorption of ascorbic acid, and, contrary to earlier conclusions, it appears that the concentration of ascorbic acid into the aqueous humors of the eye occurs in the form of ascorbic acid itself. 

Aspirin reduces the absorption of ascorbic acid by about one-third. Serum salicylate levels do not appear to be affected by ascorbic acid. 

TABLE 2 Maximum values of absorption of ascorbic acid solutions in ultra-violet field. 

Bodansky. O.. Wroblewski, 0.. and Markardt. B. Concentrations of ascorbic acid in plasma and white cells of patients with cancer and noncancerous chronic disease. Cancer Res.. 11 238-242.1951. Boyland, E. The selective absorption of ascorbic acid by guinea-pig tumourtissue. Biochem. J.. 30 1221-1224,1936. 

Aspirin (acetyl salicylic acid) inhibits the absorption of ascorbic acid in both... 

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). 

Iron Absorption. A very important effect of ascorbic acid is the enhancement of absorption of nonheme iron from foods. Ascorbic acid also enhances the reduction of ferric iron to ferrous iron. This is important both in increasing iron absorption and in its function in many hydroxylation reactions (140,141). In addition, ascorbic acid is involved in iron metaboHsm. It serves to transfer iron to the Hver and to incorporate it into ferritin. 

Up to 80% of oral doses of ascorbic acid are absorbed in humans with intakes of less than 0.2 g of vitamin C. Absorption of pharmacological doses ranging from 0.2 g to 12 g results in an inverse relationship, with less than 20% absorption at the higher doses. A single oral dose of 3 g has been reported to approach the absorptive capacity (tissue saturation) of the human intestine. Higher blood levels can be attained by providing multiple divided vitamin C doses per day. 

INDIRECT DETERMINATION OF ASCORBIC ACID BY ELECTROTHERMAL ATOMIC ABSORPTION SPECTROMETRY... 

In this work, a method based on the reduction potential of ascorbic acid was developed for the sensitive detennination of trace of this compound. In this method ascorbic acid was added on the Cr(VI) solution to reduced that to Cr(III). Cr(III) produced in solution was quantitatively separated from the remainder of Cr(VI). The conditions were optimized for efficient extraction of Cr(III). The extracted Cr(III) was finally mineralized with nitric acid and sensitively analyzed by electro-thermal atomic absorption spectrometry. The determinations were carried out on a Varian AA-220 atomic absolution equipped with a GTA-110 graphite atomizer. The results obtained by this method were compared with those obtained by the other reported methods and it was cleared that the proposed method is more precise and able to determine the trace of ascorbic acid. Table shows the results obtained from the determination of ascorbic acid in two real samples by the proposed method and the spectrometric method based on reduction of Fe(III). 

Fig. 22. Kinetic curves of oxygen absorption by ascorbic acid in the presence of polytpro-pionitrile). (1) in the dark (2) in red light (3), (4) in white light...

Camire (2002) showed that texturization does not seem to have a great effect on mineral retention and bioavailability. Others have reported increased retention of ascorbic acid in rice- and maize-based snacks (Hazell and Johnson, 1989 Plunkett and Ainsworth, 2007), increased iron diffusibility and absorption of iron-complexed protein (Poltronieri et al, 2000 Watzke, 1998), and no difference in iron and zinc absorption in human subjects fed textured bran-flour (Fairweather-Tait et al, 1989). 

D-Glucosone (XII), prepared from D-glucose phenylosazone (XI) by the action of concentrated hydrochloric acid, is treated in aqueous solution with potassium cyanide. The imino-D-glucoascorbic acid (XIV) which readily separates shows many of the properties of ascorbic acid. Thus it shows a strong selective absorption band in the ultra-... 

Tominaga et al. [682,683] studied the effect of ascorbic acid on the response of these metals in seawater obtained by graphite-furnace atomic absorption spectrometry from standpoint of variation of peak times and the sensitivity. Matrix interferences from seawater in the determination of lead, magnesium, vanadium, and molybdenum were suppressed by addition of 10% (w/v) ascorbic acid solution to the sample in the furnace. Matrix effects on the determination of cobalt and copper could not be removed in this way. These workers propose a direct method for the determination of lead, manganese, vanadium, and molybdenum in seawater. 

An extractive spectrophotometric procedure based on the complexation of reduced Iron(II) with 5-Chloro-7-iodo-8-hydroxyquinoline (CIHQ) for the estimation of micro amounts of vitamin C. The resulting brown colored complex was extracted into chloroform to give a reddish brown extract which shows an absorption band at 485 nm. This chelate was formed immediately and the apparent molar absorptivity and Sandell s sensitivity for vitamin C was found to be 8.5 x 105 dm3 mol"1 cm 1 and 2.072xl0 4g cm 2. Linear relationship between absorbance and concentration of ascorbic acid is observed up to 0.8 pg ml"1. Interference studies of different substances including sugars, vitamins and amino acids, metal ions and organic acids were carried out. The utility of the method was tested by analysing some of the marketed products of vitamin C... 

Absorption of iron by the individual varies with age, iron status, the amount and chemical form of the iron ingested, and with conditions in the gastrointestinal tract, only about 5—15% of iron in the diet being normally absorbed. Ferrous iron, as the sulphate, gluconate, fumarate or lactate or as ferrous ammonium sulphate, is appreciably taken up into the bloodstream from the duodenum, especially in the presence of ascorbic acid, a reducing agent. Little difference was found in the extent of their absorption between ferrous sulphate and the various chelates, but ferric ammonium citrate or polysaccharide complexes were only very poorly absorbed22)... 

The recommended procedure for the determination of arsenic and antimony involves the addition of 1 g of potassium iodide and 1 g of ascorbic acid to a sample of 20 ml of concentrated hydrochloric acid. This solution should be kept at room temperature for at least five hours before initiation of the programmed MH 5-1 hydride generation system, i.e., before addition of ice-cold 10% sodium borohydride and 5% sodium hydroxide. In the hydride generation technique the evolved metal hydrides are decomposed in a heated quartz cell prior to determination by atomic absorption spectrometry. The hydride method offers improved sensitivity and lower detection limits compared to graphite furnace atomic absorption spectrometry. However, the most important advantage of hydride-generating techniques is the prevention of matrix interference, which is usually very important in the 200 nm area. 

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