Ammonium Fluoride-Hydrochloric Acid Extractable

1 Ammonium Fluoride-hydrochloric Acid Extractable Phosphorus of Soils Bray s 1 Method Bray and Kurtz, 1945 (For soils with pH around 5.5 or less) 

Fluoride ion (F ) from ammonium fluoride complex with aluminium (AP +) and ferric (Fe+++) in acid solution in the form of double fluoride with consequent release of phosphorus held in the soil by these trivalent ions 

Thus in contact with aluminium and ferric phosphates, the aluminium and ferric ion concentrations are reduced and so the phosphate ion concentration is increased to maintain the solubility product at their constant levels. AIPO4 represents various hydrated and hydroxyl phosphates of aluminium, including any adsorbed or precipitated surface layers on oxides and alumino-silicates. FePO similarly, represents various hydrated and hydroxyl phosphates of iron including adsorbed or precipitated surface layers on iron oxide. 

Very short shaking period is advocated (one minute or 40 seconds for Bray 2 extractant) In fact, for an soils, there is little change in the phosphate concentration of the extract with increase of time but for some soils either more or less phosphate is extracted. Moreover, the fluoride ion has a slightly depressant effect on molybdenum blue colour development and hence its concentration must be kept constant in the test and standard. 

Note To avoid interference of fluoride, 7.5 ml of 0.8 (M) Boric acid (50g HgBOg per litre) may be added to 

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V. P. Gorodnov, A. Yu. Ryskin, and M. V. Pavlov. Increasing oil extraction from stratum—by pumping-in hydrochloric acid solution or its mixture with hydrofluoric acid or ammonium fluoride, followed by pumping aqueous solution or surfactant. Patent SU 1795092-A, 1993. 

Two typical acid extractants are the Bray (which has two forms, both of which are acidic) and the Mehlich-3. The Bray extractant is a dilute solution of hydrochloric acid and ammonium fluoride [11], The Mehlich-3 extractant is a dilute solution of acetic and nitric acids and also contains ammonium nitrate and EDTA [11], Both are designed to extract soluble, exchangeable, and easily dissolved nutrients, particularly phosphate. While the Bray extractant is designed to extract plant available phosphorus, the Mehlich-3 extractant also extracts potassium [10-12],... 

Some extremely low detection limits in chemical samples have been reported by APDC/MIBK and other dithiocarbamate extractions. Further increased concentration factors can be obtained by back-extraction into a minimum of acid. Copper in ammonium fluoride solution used in semiconductor processing has been determined down to 4.5 X 10 7% [20]. To a 40% ammonium fluoride solution (50 ml) was added ammonia solution (1ml), 50—60 /Ltg of a palladium(II) carrier solution (dissolved in 1ml) and sodium diethyldithiocarbamate (5 ml). After extraction of the copper chelate into chloroform the solvent was evaporated, the residue dissolved in concentrated nitric acid (10 drops) and water (2 ml) and this was then evaporated. The final dissolution was in concentrated hydrochloric acid (2 drops) and concentrated nitric acid (ldrop). The solution was made up to 1 ml and the determination made by standard additions using an air/ acetylene flame and the 324.7 nm copper resonance line. 

Clearly some form of sample pretreatment is required for soils and sediments. Total levels may be obtained following sodium carbonate-boric acid fusion and the dissolution in hydrochloric acid employing lanthanum as a buffer and releasing agent. If the determination of silicon is not required, it may be volatilized as silicon tetrafluoride using hydrofluoric acid, although some calcium may also be lost as calcium fluoride. For many samples, however, it may be more appropriate to determine the exchangeable cation content of the sample. Here, the sample may be shaken with an extractant solution, for example, 1 mol 1 ammonium chloride, ammonium acetate, or disodium EDTA, prior to filtration and analysis. Where final solutions contain more than - 0.5% of dissolved material, the standards should also contain the major constituents, even where no chemical interference is expected, in order to match the viscosity and surface tension and avoid matrix effects. 

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