Ammonia ascorbic acid with

Add cautiously (FUME CUPBOARD), and with constant stirring, 10 mL of the ammonium citrate solution this will prevent the precipitation of metals when, at a later stage, the pH value of the solution is increased. Then add 10 mL of the 20 percent ascorbic acid, and adjust to pH 4(BDH narrow-range indicator paper), by the cautious addition of concentrated ammonia solution down the side of the beaker while stirring continuously. Then add lOmL of the 50 per cent potassium cyanide solution (CAUTION ) and immediately adjust to a PH of 9-10 (BDH indicator paper) by the addition of concentrated ammonia solution. 

In order to concentrate the lead extract, remove the lead from the organic solvent by shaking this with three successive 10 mL portions of the dilute hydrochloric acid solution, collecting the aqueous extracts in a 250 mL beaker. To the combined extracts add 5 mL of 20 per cent ascorbic acid solution and adjust to pH 4 by the addition of concentrated ammonia solution. Place the beaker in a fume cupboard, add 3 mL of the 50 per cent potassium cyanide solution and immediately adjust the pH to 9-10 with concentrated ammonia solution. Transfer the solution to a 250 mL separatory funnel with the aid of a little de-ionised water, add 5 mL of the 2 per cent NaDDC reagent, allow to stand for one minute and then add 10 mL of methyl iso butyl ketone. Shake for one minute and then separate and collect the organic phase, filtering it through a fluted filter paper. This solution now contains the lead and is ready for the absorption measurement. 

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.)... 

To measure hardness, the sample is treated with ascorbic acid (or hydroxylamine) to reduce Fe3+ to Fe2+ and with cyanide to mask Fe2+, Cu+, and several other minor metal ions. Titration with EDTA at pH 10 in NH3 buffer then gives the total concentrations of Ca2+ and Mg2+. Ca2+ can be determined separately if the titration is carried out at pH 13 without ammonia. At this pH, Mg(OH)2 precipitates and is inaccessible to EDTA. Interference by many metal ions can be reduced by the right choice of indicators.21... 

Hodge et al. (45) discussed mechanisms for formation of methyl furanones and related substances from Amadori compounds. They have been produced by heating D-ribose and D-ribose phosphate with ammonia (46 47). Hicks and Feather (48) demonstrated that the Amadori compound 1-benzylamino-l-deoxy-D-threo-pentulose dehydrates to 4-hy-droxy-5-methyl-3(2H)-furanone and it has also been identified as a degradation product of L-ascorbic acid. This compound is believed to be formed from ribose-5-phosphate, and gained prominence when it was isolated from beef by Tonsbeck et al. (49). It became more apparent as a precursor of meat flavor when Van den Ouweland and Peer (50) reacted it and its thio analog with HaS to produce a number of sulfur compounds, some of which had meaty odors. 

Assay Dissolve about 700 mg of sample, accurately weighed, in 50 mL of water, add 1 g of ascorbic acid, 10 mL of ammonia-ammonium chloride buffer TS, and 5 drops of eriochrome black TS, and titrate with 0.05 M disodium EDTA to a deep blue color. Each milliliter of 0.05 M disodium EDTA is equivalent to 22.26 mg of C12H22MnOi4. 

Amino acids are quickly deaminated by L-ascorbic acid, leading to browning reactions (66). In the presence of oxygen, iron, and ascorbic acid or DHA, the amino acids gave ammonia, carbon dioxide, and an aldehyde with one carbon less than the original acid (67,68). The aldehydes are isolated as dimedone derivatives and are useful for identification of the amino acids. In the presence of copper and UV light, the deamination is increased. The red color 69-73) formed upon reaction of DHA with amino acids was used for their detection. Recent studies (74-78) of the reaction of DHA with amino acids led to the isolation of a product that changes readily to a novel, stable, free radical species... 

Patents have also been obtained on ascorbic acid as the active principle for the removal of chlorine from water, making the water palatable for drinking (723,724,725). The addition of ascorbic acid (1 g) and sodium bicarbonate (0.5 g) to chlorinated water (15 L) will result in a palatable water according to a U.S. patent (723), City tap water treated with chlorine-ammonia (726) was observed to cause hemolytic anemia in patients in dialysis units of a hospital. Confirmation of this condition was obtained in in vitro tests in which the suspected water damaged red blood cells. Ascorbic acid addition to the treated water reduced the anemia problem in the patients in subsequent time periods. 

To a solution in dilute HCl, containing not more than 10 pg of Al, add 1 ml of ascorbic acid solution, and adjust the pH of the solution with ammonia to 2. After 5 min, dilute the solution with water to 15 ml, and add 2.5 ml of CAS solution and 1 ml of 20% sodium acetate solution. Adjust the pH of the solution with ammonia to 6.0 0.2, dilute with water to 25 ml in a standard flask, and measure the absorbance of the solution at 545 nm, against a reagent blank as reference. 

Place a sample solution in dilute HCl (pH 1-2, 10-15 ml), containing not more than 5 pg Al, in a small beaker and add 10 mg of ascorbic acid. After 5 min add -2 ml of CAS solution, and adjust the pH to 5.3 0.2 with dilute ammonia solution. Dilute to volume in a 25 ml standard flask, mix, and measure the absorbance of the solution at 620 nm vs. a reagent blank solution. 

Separation of Tl with dithizone. To the acidic sample solution, containing not more than 40 pg of Tl, add 1 ml of 2% ascorbic acid solution. After 3 min, add 3 ml of 10% sodium citrate solution, ammonia to make the pH 9-10, 2 ml of 10% KCN solution, and water to 20-25 ml. Extract Tl with three portions of the dithizone solution, shaking for 2 min with each portion. Add 5 drops of cone. H2SO4 to the combined chloroform extracts in a beaker, and evaporate off the chloroform. Then heat more intensely and add cone. HNO3 dropwise to mineralize the organic residue. Evaporate some of the sulphuric acid. Cool the residue and dissolve it in 10-15 ml of2MHCl. 

Determination of Sn. Acidify the alkaline solution, containing not more than 30 pg of Sn, with 3 ml of HCl (1+1) and decolorize (reduce iodine) by adding dropwise 2% ascorbic acid solution. Add 2.5 ml of the PV solution and 5 ml of 20% sodium acetate solution. Adjust the pH to 3.8 0.1 with ammonia. Transfer the solution to a 25-ml standard flask, dilute to the mark with water, and mix thoroughly. After 30 min, measure the absorbance of the solution at 552 nm against a reagent blank. 

To the acid sample solution containing not more than 50 pg of Ti, add 1 ml of 2% ascorbic acid solution and heat the solution. Add to the cooled solution 1 ml of chromotropic acid solution, adjust the pH to 2 with ammonia, and add 5 ml of the buffer. Dilute to volume with water in a 25-ml standard flask and stir well. After 10 min, measure the absorbance at 460 nm, using a reagent blank as reference. 

Masking can be achieved by precipitation, complex formation, oxidation-reduction, and kinetically. A combination of these techniques may be employed. For example, Cu " can be masked by reduction to Cu(I) with ascorbic acid and by complexation with I . Lead can be precipitated with sulfate when bismuth is to be titrated. Most masking is accomplished by selectively forming a stable, soluble complex. Hydroxide ion complexes aluminum ion [Al(OH)4 or AlOa"] so calcium can be titrated. Fluoride masks Sn(IV) in the titration of Sn(II). Ammonia complexes copper so it cannot be titrated with EDTA using murexide indicator. Metals can be titrated in the presence of Cr(III) because its EDTA chelate, although very stable, forms only slowly. 

To show that the source of the amino acids in our experiments was not the result of the reaction of the various nitrogen species produced in the reaction with ascorbic acid, we reacted ascorbate individually and in combination with ammonia, hydrazine, nitrite, and nitrate. Very low traces of amino acids were produced in these reactions, indicating that the amino acids detected are in fact produced from the electric discharge reaction. While ascorbic acid is not likely to have been an abundant prebiotic species, oxidation could have been inhibited by other available chemical species such as sulfides and reduced metal ions. 

Alditol-l-yl)-2-aryl-5-carboxamido-l,2,3-triazoles (674) were prepared from dehydro-L-ascorbic acid 2-arylhydrazone-3-oximes (494) by heating with acetic anhydride and then treating with ammonia (77MI8 82MI13 83MI8 93MI1) (Scheme 179). 

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