Tartrate precipitation prevention

Determination of azo dyes is done most satisfactorily in the presence of sodium tartrate which prevents the precipitation of the difficultly soluble dye acids (e.g., benzopurpurin, see Knecht, pages 31-32). Yellow dyes cannot be easily titrated because titanium tartrate is strongly yellow in color. 

Stabilizing wines to prevent precipitation of calcium tartrate is not easy, as the crystallization of potassium bitartrate does not indnce that of calcium tartrate, despite the fact that these two salts should logically syncrystallize as they have the same crystal systems. On the contrary, crystallization of TCa may induce that of KTH. The prevention of calcium tartrate precipitation is further complicated by the fact that the solubility of TCa (Postel, 1983) is not very temperature-sensitive. Thns, TCa is hardly three times more soluble at 20°C than at —4°C. 

In the processes described above, tartrate precipitations are prevented by eliminating the corresponding salts. It is also possible to envisage the addition of crystallization inhibitors. 

Metatartaric acid is a polyester resulting from the inter-molecular esterification of tartaric acid at a legally imposed minimum rate of 40%. It may be used at doses up to a maximum of 10 g/hl to prevent tartrate precipitation (potassium bitartrate and calcium tartrate) (Ribereau-Gayon etal., 1977). 

Yeast mannoproteins were first fonnd to have a certain inhibiting effect on tartrate crystallization in a model medium by Lubbers et al. (1993). However, these experiments used mannoproteins extracted by heat in alkaline buffers, under very different conditions from those accompanying the spontaneons enzymic release of mannoproteins dnring aging on the lees. Furthermore, the effectiveness of mannoproteins extracted by physical processes in preventing tartrate precipitation has not been established in most wines, despite demonstrations in a model medium. 

An industrial preparation (Mannostab ) has been purified from yeast-wall mannoprotein. It is a perfectly soluble, odorless, flavorless, white powder. This product has been qnite effective (Table 1.20) in preventing tartrate precipitation in... 

It should also be noted that the purified manno-protein preparation obtained by digesting yeast cell walls contains another protein fraction that has a protective effect on tartrate precipitation (Moine-Ledoux et al., 1997) (Section 1.7.7). It is perfectly possible to envisage using an industrial preparation of this protective colloid in the near future to stabilize white wines and prevent tartrate precipitation. 

Refrigeration is widely used for stabilization to prevent tartrate precipitation. This treatment alone may be adequate to ensure the stability of red wines. However, if bentonite is not used to treat white wines, prior heating is necessary to prevent protein precipitation. In some countries, equipment capable of applying both heat and cold is used. These processes give satisfactory results in stabilizing white wine with a low iron content, as they have only a limited effect on ferric casse. 

This chapter also describes several physicochemical treatments based on electrical charges in solutions. Ion exchange and electrodialysis are mainly used to prevent tartrate precipitation. These techniques are much more controversial than purely physical methods. If they are not properly used, they may produce unacceptable changes in a wine s chemical composition. This is why they are not legally permitted in all wine growing countries. Their utilization must be carefully controlled by legislation. 

One effect of heating is to dissolve crystallization nuclei, which are necessary for crystals to grow and precipitate. New wine is a supersaturated tartrate solution. The precipitation of tartrates, however, requires the presence of submicroscopic nuclei that are the starting point from which molecules build up into crystals (Section 1.5.1). Heating wine, especially when it is already in the bottle, may be sufficient to stabilize it and prevent tartrate precipitation. 

Cold stabilization is mainly used to prevent tartrate precipitation. As there are effective, less expensive treatments are available for other problems. 

The various processes using cold temperatures to prevent tartrate precipitation have been described elsewhere (Section 1.7.1 to 1.7.5). There are three major procedures ... 

Hydrogen, sodium and magnesium resins may be nsed to removed K+ and prevent tartrate precipitation. These different forms are obtained by the regeneration operation that consists of circnlating either an acid or a saline solution (sodinm or magnesium chloride) through the column to saturate the sulfonate or acid radicals (Figure 12.2) in the resin with H+, Na+ or Mg + ions. 

Virginie Moine-Ledoux for her work on the use of yeast mannoproteins in preventing tartrate precipitation (Chapter 1), as well as the stabilization processes for protein casse (Chapter 5)... 

Once the cuv e has been blended, the base wine is cold-stabilized to prevent tartrate precipitation. In some cases, it may be fined just before or after cold stabilization. 

This system has a number of advantages. It eliminates the labor costs of riddling and disgorging, as well as the time the wine is immobilized on the riddling racks. Dosage liqueur is much more evenly distributed. It is also possible to blend several batches of wine after the second fermentation to obtain the desired quality. Cold-stabilization prevents tartrate precipitation and filtration ensures that the yeasts are completely eliminated, leaving the wine perfectly clear. 

Direct Titrations. The most convenient and simplest manner is the measured addition of a standard chelon solution to the sample solution (brought to the proper conditions of pH, buffer, etc.) until the metal ion is stoichiometrically chelated. Auxiliary complexing agents such as citrate, tartrate, or triethanolamine are added, if necessary, to prevent the precipitation of metal hydroxides or basic salts at the optimum pH for titration. Eor example, tartrate is added in the direct titration of lead. If a pH range of 9 to 10 is suitable, a buffer of ammonia and ammonium chloride is often added in relatively concentrated form, both to adjust the pH and to supply ammonia as an auxiliary complexing agent for those metal ions which form ammine complexes. A few metals, notably iron(III), bismuth, and thorium, are titrated in acid solution. 

In a copper or iron kettle of 4-I. capacity is placed a solution of 200 g. of d-tartaric acid and 700 g. of sodium hydroxide in 1400 cc. of water. A 12-I. flask through which cold water is run is placed in the mouth of the kettle in order to prevent loss of water vapor, and the mixture is boiled gently over an open flame for four hours. The solution is now transferred to a 12-I. flask or crock and partially neutralized with 1400 cc. of commercial hydrochloric acid (density 1.19). To the still alkaline solution is now added just enough sodium sulfide to precipitate all the iron or copper which has been dissolved from the kettle (Note i). The filtered solution is then just acidified with hydrochloric acid, boiled to expel all hydrogen sulfide, and made very faintly alkaline to phenolphthalein with sodium hydroxide solution. To the hot solution is then added a concentrated solution of 300 g. of anhydrous calcium chloride which causes an immediate precipitation of calcium tff-tartrate and mesotartrate. 

A. Direct titration. The solution containing the metal ion to be determined is buffered to the desired pH (e.g. to PH = 10 with NH4-aq. NH3) and titrated directly with the standard EDTA solution. It may be necessary to prevent precipitation of the hydroxide of the metal (or a basic salt) by the addition of some auxiliary complexing agent, such as tartrate or citrate or triethanolamine. At the equivalence point the magnitude of the concentration of the metal ion being determined decreases abruptly. This is generally determined by the change in colour of a metal indicator or by amperometric, spectrophotometric, or potentiometric methods. 

H. 8-Hydroxyquinaldine (XI). The reactions of 8-hydroxyquinaldine are, in general, similar to 8-hydroxyquinoline described under (C) above, but unlike the latter it does not produce an insoluble complex with aluminium. In acetic acid-acetate solution precipitates are formed with bismuth, cadmium, copper, iron(II) and iron(III), chromium, manganese, nickel, silver, zinc, titanium (Ti02 + ), molybdate, tungstate, and vanadate. The same ions are precipitated in ammoniacal solution with the exception of molybdate, tungstate, and vanadate, but with the addition of lead, calcium, strontium, and magnesium aluminium is not precipitated, but tartrate must be added to prevent the separation of aluminium hydroxide. 

Discussion. Iodine (or tri-iodide ion Ij" = I2 +1-) is readily generated with 100 per cent efficiency by the oxidation of iodide ion at a platinum anode, and can be used for the coulometric titration of antimony (III). The optimum pH is between 7.5 and 8.5, and a complexing agent (e.g. tartrate ion) must be present to prevent hydrolysis and precipitation of the antimony. In solutions more alkaline than pH of about 8.5, disproportionation of iodine to iodide and iodate(I) (hypoiodite) occurs. The reversible character of the iodine-iodide complex renders equivalence point detection easy by both potentiometric and amperometric techniques for macro titrations, the usual visual detection of the end point with starch is possible. 

The use of other metal cations such as those derived from zinc, lithium, or aluminium proved less effective (136). Treatment of allyl alcohol with diethyl zinc in the presence of a catalytic amount of diisopropyl (/ ,/ )-(+ )-tartrate (DIPT) in 1,4-dioxane, however, afforded the corresponding (5/f)-2-isoxazolines with excellent selectivity er >92 8) (178). Addition of dioxane was necessary in order to avoid precipitation of the complex of zinc salts containing the DIPT moiety. Without this solvent, lower stereoselectivity was found, probably due to the precipitation mentioned above, which prevents the favorable catalytic cycle proposed (Scheme 6.32) (178). 

Auxiliary complexing agents such as NH3, tartrate, citrate, or triethanolamine may be employed to prevent metal ion from precipitating in the absence of EDTA. For example, Pb2+ is titrated in NH, buffer at pH 10 in the presence of tartrate, which complexes Pb2+ and does not allow Pb(OH)2 to precipitate. The lead-tartrate complex must be less stable than the lead-EDTA complex, or the titration would not be feasible. 

The experimental apparatus is shown in Figure 6. A concentrated basic solution of potassium antimony tartrate containing sodium borohydride is used. A sufficient amount of tartaric acid is added to prevent hydrolysis and precipitation of the resulting antimony compound. The solution is delivered with a syringe drive under the surface of a solution of 4 N sulfuric acid, and stibine is produced in the acidic medium. The net reation in the flask is... 

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