Acid Oxalate Extraction

When an iron oxide such as goethite or hematite is produced from 2-line ferrihydrite, the product can be purified by selectively dissolving the re- 

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The transformation has been followed up by XRD, Mbssbauer spectroscopy, EXAFS and colorimetry. It can be monitored more conveniently, however, by the acid oxalate extraction method in which residual ferrihydrite is dissolved and the crystalline product left intact (Schwertmann Fischer, 1966). The extent of transformation at any time is given as the ratio FOo/Fet where Fe is the oxalate soluble iron (i. e. the unconverted ferrihydrite) and Fet is the total iron in the system. A plot of log (FCo/Fet) against time of aging at 100 °C is linear over 90-95 % of the reaction... 

Papaverine, C20H21O4N. This alkaloid, first obtained by Merck, occurs in the mixture precipitated by ammonia from the mother liquors of opium extract from which morphine and codeine have been separated in Gregory s process, and methods for its isolation from this mixture have been published by Hesse and others. The alkaloid may be purified by conversion into the acid oxalate, B. H2C2O4, m.p. 196° or 201-5-202°, which is nearly insoluble in alcohol. 

In a 1-1., round-bottomed flask is placed 72 g. of the crude oxazolidine in 600 ml. of water, and 201.6 g. (1.6 moles) of hydrated oxalic acid is added. The mixture is then heated under reflux for 1 hour, cooled, treated with 600 ml. of water to dissolve precipitated oxalic acid, and extracted with three 100-ml. portions of ether. The combined ethereal extracts are washed with 50 ml. saturated sodium bicarbonate solution and then dried over anhydrous potassium carbonate. Concentration of the ethereal solution gives 30-35 g. of crude aldehyde. Distillation of this material at 70-75° (1.5 mm.) gives pure o-anisaldehyde (22.8—26.3 g. 51-59%), m.p. 35.5-38° (Note 9). 

Similar considerations apply to the allotropic forms of other minerals. For example acid oxalate (pH = 3) extraction (in absence of light) is used to distinguish between... 

P.-J. Maequer pointed out in his Dictionary of Chemistry (1778) that when plants are decomposed without combustion, acidic substances such as tartar and potassium acid oxalate are produced, that plants from which these acidic substances have been removed by extraction or distillation yield much less vegetable alkali than they otherwise would that by ignition tartar can be converted almost completely to this alkali (potassium carbonate) that the alkali in vegetable ash is therefore produced by the combustion of this acidic substance that decayed wood, in which the plant acids have been destroyed by fermentation, yields scarcely any alkali (as Boerhaave had observed) and that plants containing little or no acid yield on combustion little or no vegetable alkali (5). 

Filter packs. As shown in Fig. 11.22, NH3 can be collected on impregnated filters in filter packs designed to collect particles and gas-phase nitric acid. Oxalic acid or citric acid on Whatman filters is often used to absorb the gaseous ammonia, which is then measured by extraction into aqueous solution and ion chromatography or by a colorimetric method (e.g., see Anlauf et al., 1988 and Williams et al., 1992). 

Detection of other Esters of Fixed Acids [oxalates, tartrates, succinates, citrates).—A certain quantity of the oil (if possible 10-20 c.c. or more) is saponified in the usual way, the excess of alkali being neutralised with hydrochloric acid in presence of phenolphthalein and the alcohol expelled on a water-bath. The residue is diluted with water and extracted with ether, the aqueous solution being tested for oxalic, tartaric, succinic and citric acids by the ordinary analytical methods. 

Mapara, P.M. Godbole, A.G. Swarup, R. Nagar, M.S. Extraction of uranium and plutonium from oxalate bearing solutions using phosphonic acid Solvent extraction, extraction chromatography and infrared studies, J. Radioanal. Nucl. Chem. 240 (1999) 631-635. 

Acid (pH 3) ammonium oxalate has been widely used to dissolve iron and aluminium oxides and release bound trace metals since its introduction in 1922 (Tamm, 1922) (Tamm s reagent). Typically McLaren et al. (1986) used 0.17moll-1 ammonium oxalate +0.1 moll- 1 oxalic acid. The extraction is sensitive to light (Mitchell and Mackenzie, 1954) and particularly to ultraviolet light (Endredy, 1963). Schwertmann (1964) showed that in the dark the amorphous iron oxides were mainly attacked and under ultraviolet illumination the crystalline phases were dissolved as effectively as by the dithionite reagent. Heavy metals are released, with the exception of lead and cadmium whose oxalates are poorly soluble and which coprecipitate with calcium oxalate. The use of oxalic... 

Goncharova and Khomenko [339] have described a column chromatographic method for the determination of acetic, propionic and butyric acids in seawater and thin layer chromatographic methods for determining lactic, aconitic, malonic, oxalic, tartaric, citric and malic acids. The pH of the sample is adjusted to 8-9 with sodium hydroxide solution. It is then evaporated almost to dryness at 50-60°C and the residue washed on a filter paper with water acidified with hydrochloric acid. The pH of the resulting solution is adjusted to 2-3 with hydrochloric acid (1 1), the organic acids are extracted into butanol, then back-extracted into sodium hydroxide solution this solution is concentrated to 0.5-0.7ml, acidified, and the acids separated on a chromatographic column. 

Oxalate Transfer 1 g of sample into a 125-mL separator, dissolve in 10 mL of water, add 2 mL of hydrochloric acid, and extract successively with one 50-mL portion and one 20-mL portion of ether. Transfer the combined ether extracts to a 150-mL beaker, add 10 mL of water, and remove the ether by evaporation on a steam bath. Add 1 drop of glacial acetic acid and 1 mLof a 1 20 calcium acetate solution to the residual aqueous solution. No turbidity develops within 5 min. Sulfate Dissolve 100 mg of sample in 2.7 N hydrochloric acid, and dilute to 30 to 40 mL with water. Proceed as directed in the Sulfate Limit Test under Chloride and Sulfate Limit Tests, Appendix IIIB, beginning with the addition of 3 mL of barium chloride TS. Any turbidity produced does not exceed that shown in a control containing 300 pig of sulfate (S04). 

Add CaCl2 solution (equal in volume to that of the solution) and allow to stand for several minutes. A white precipitate indicates fluoride, oxalate, phosphate, arsenate, and tartrate t a precipitate which separates on boiling for 1-2 minutes is citrate. Of these only oxalate and fluoride are insoluble in dilute acetic acid. Hence extract the white precipitate with dilute acetic acid and filter. A residue (R) insoluble in dilute acetic acid, indicates oxalate and/or fluoride. Exactly neutralize the acetic acid solution by adding sodium hydroxide solution from a dropper and testing with an indicator paper or solution (bromothymol blue or nitrazine yellow is suitable) a white precipitate indicates the presence of phosphate, arsenate, and/or tartrate. The precipitate often separates slowly. Add a little silver nitrate solution to the suspension or solution a yellow precipitate indicates the presence of phosphate a brownish-red precipitate indicates arsenate or arsenate plus phosphate. 

The largest proportion of the total Fe was removed by ammonium oxalate, which attacks the amorphic fraction of iron oxide in the sediments (23). Among the low pH extractants, hydroxylamine was the least efficient in extracting Fe. The difference between the extraction of Fe by acid and extraction by hydroxylamine was related to the crystallinity of the hydrous iron oxide. As pure iron oxides aged (and crystallized) in the laboratory, Fe solubility in hydroxylamine declined relative to solubility in acetic acid (Table III). In San Francisco Bay sediments, the ratio of hydroxylamine-soluble Fe to acetic acid-soluble Fe increased during the period of maximum runoff to the estuary (27) suggesting the proportion of the Fe in the sediments that was freshly precipitated varied seasonally. This was expected, since periods of heavy runoff are also times of maximum Fe movement from the watershed to the tributaries of the estuary ( ). 

Phosphorus Distribution. The major sediment phosphorus fraction is that extracted by hydrochloric acid (Table III). Ammonium oxalate-oxalic acid solution extracts somewhat less phosphorus than hydrochloric acid, while sodium hydroxide as well as hydroxylamine extract much less. 

In the lower reaches of the Genesee River, the results of the extractions suggest that substances other than hydrous oxides are phosphorus sinks. This is evident where the amount of sediment phosphorus extracted by hydrochloric acid steadily increases down river, while the oxalate extractable phosphorus remains relatively constant. Schwertmann (2 ) emphasized that the results of such procedures are best considered as a measure of the relative amount of a phase or, more generally, a measure of an element s reactivity in a sediment under carefully controlled conditions. Laboratory experiments (Figure 8) show that phosphorus uptake by calcium carbonate, under simulated natural conditions, proceeds slowly. The large hydrochloric acid extractable component observed at Rochester may arise from slow uptake and subsequent mineralization of dissolved inorganic phosphorus by carbonate minerals. 

Zr (a) Adsorption on silica gel. Elution of other fission products with H2SO4/ HNO3. Elution of Zr with 0.5 M oxalic acid. (b) Extraction with thenoyltrifluoroacetone (TTA) in benzene. Back-extraction with 2 M HF and precipitation as BaZrFe- Separation of Ba as BaS04. 

Many plants contain a variety of free acids such as acetic acid, citric acid, fumaric acid, malic acid, succinic acid, oxalic acid, glycohc acid, etc. They are components of citric cycle, whereas the others are intermediates in the pathway from carbohydrates to aromatic com-pounds. Following extraction, organic acids can be separated and detected with a variety of techniques. Thin layer chromatographic methods have been also employed to separate certain organic acids,as presented in Table 3. 

When other metals (M) substitute for Fe in the structure of an Fe oxide the mole ratio of substitution is given by Mt/(Mt + Fet)(mol/mol), where Mt and Fet (t = total) are expressed in mol. Fe and other metals present at the surface of the iron oxide or in separate phases must be determined separately to correct the extent of substitution. Ferrihydrite as a separate phase can be selectively dissolved an with acid oxalate solution (see p. 50). This treatment also dissolves any separate Mn or Cr oxides. Alternatively, a short extraction (30 min, 25 °C) with 0.4 M HCl removes adsorbed surface species this method is useful if the solubility of the substituting ion in acid oxalate solution is not known or if the iron oxide under consideration (for example magnetite) is soluble in acid oxalate solution. The total Fet and Mt have then to be corrected for the oxalate soluble Fe and M. 

Hot buffer extracts contained mainly types B, C and D, oxalate extracts types A, B, C and D and in acid extracts types C, D and E dominated. 

During the purification of plant acids, oxalic acid, which may be present in excessive amounts, can be precipitated out as calcium oxalate by adding calcium hydroxide solution to a concentrated alcoholic plant extract (28). 

One of the pitfalls in the interpretation of extraction results from natural sediments is caused by the fact that the presence of Fe complexed by carboxylic acid catalyzes the reduction of crystalline iron oxides such as hematite (Sulzberger et al. 1989), magnetite (Blesa et al. 1989) and goethite (Kostka and Luther 1994). In order to avoid this catalytic dissolution of well-crystallized iron oxides by Fe + during the oxalate extraction Thamdrup and Canfield (1996) air-dried the sediment in advance, thereby oxidizing FeS and FeCOj to ferrihydrite. In addition, they applied the anoxic oxalate extraction and subtracted the released amount of Fe + from the amount of Fe determined... 

Analysis.—In fatal cases of poisoning by oxalic acid the contents of the stomach are sometimes strongly acid in reaction more usually, owing to the administration of antidotes, neutral, or even alkaline. In a systematic analysis the poison is to be sought for in the residue of the portion examined for prussic acid And phosphorus or, if the examination for those substances be omitted, in the residue or final alkaline fluid of the process for alkaloids. If oxalic acid alone is to be sought for, the contents of the stomach, or other substances if acid, are extracted with water, the liquid filtered, the filtrate evaporated, the residue extracted with alcohol, the alcoholic fluid evaporated, the residue redissolved in water (solution No. 1). The portion undissolved by alcohol is extracted with alcohol acidulated wdth hydrochloric. acid, the solution evaporated after filtration, the residue dissolved in water (solution No. 2). Solution No. 1 contains any oxalic acid which may have existed free in the substances examined No. 2 that which existed in the form of soluble oxalates. If lime or magnesia have been administered as an antidote, the substances must be boiled for an hour or two with potassium carbonate (not the hydroxid), filtered, and the filtrate treated as above. In the solutions so obtained, oxalic acid is characterized by the tests given above. The urine is also to be examined microscopically for crystals of calicum oxalate. The stomach may contain small quantities of oxalates as normal constituents of certain foods. 

Karimian and Cox (1978) found no correlation between plant Mo uptake and soil Mo extracted by anion resin or acid ammonium oxalate. Lombin (1985) found better correlations for either 0.1-N NaOH or acid ammonium oxalate extraction and Mo uptake by peanuts than for anion-resin extraction and Mo uptake. Sherrell (1989) concluded that the resin method was not accurate enough for diagnosis of Mo deficiency in the pastoral soils of New Zealand, although the resin method was more useful than the ammonium oxalate method. 

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