Surfactants precipitation test

When we introduced phase behavior tests earlier, we mentioned aqueous stability tests. The main objective of aqueous stability tests is to eliminate the surfactant precipitation problem. As we already know, the solubility of surfactant decreases with salinity. During aqueous stability tests, the surfactant solution becomes opaque up to some salinity, showing the surfactant starts to aggregate or even precipitate. When divalent or multivalent ions exist in the solution, the salinity needed to start precipitation is much lower. 

Several alkaline chemicals have been employed for various aspects of enhanced oil recovery. Two of the most favorable alkaline chemicals tested and used in tertiary oil recovery are sodium orthosilicate and sodium hydroxide. Comparing their characteristics, both chemicals react with acids in crude oil to form surfactants, precipitate hardness ions and change rock surface wettability. One difference between the two chemicals is that the interfacial properties for sodium orthosilicate systems are less affected by hardness ions (13), hence slightly lower interfacial tensions would occur. Lower Interfacial tensions can aid in in-situ emulsion formation. 

The use of polyethylene glycol ethers in a process in which a high viscosity emulsion is formed on contact with residual crude oil has also been tested as a means of plugging thief zones using surfactants (248-250). Precipitation of sodium pectate when fresh water solutions contact brine has been proposed as a method of plugging high permeability zones (251). 

Knowledge of drug properties, especially solubility in surfactants or as a function of pH, is essential. One could anticipate precipitation of the drug as the pH changes in solution, or if release from the dosage form leads to supersaturation of the test media. Be aware that preparation of a standard solution may be more difficult than expected. It is customary to use a small amount of alcohol to dissolve the standard completely. A history of the typical absorptivity range of the standard can be very useful to determine if the standard has been prepared properly. 

Surfactants have been used to solubilise lipases in organic solvents (Okahata and Mori, 1997). One method starts with mixing aqueous solutions of the surfactant and the enzyme. The enzyme-surfactant complex precipitates and can subsequently be dissolved in organic media. Several surfactants have been tested and especially good results have been obtained with dialkyl glucosyl glutamates. In one case it was shown that the complex consisted of one enzyme molecule surrounded by approximately 150 surfactant molecules. 

Dilution tests should be performed for a drug-surfactant solution to determine whether precipitation of the drug occurs on dilution. Readers can refer to the Chapter 9 Solubilization Using Cosolvent Approach for the dilution test methods. 

C) for several months. The precipitated agarose, from which the glycopeptide surfactant had been extracted, retained its capacity to form gels and these were later used in decompression tests (see below). 

Add -5 ml of 1 % sample surfactant solution into a mixture of 10 ml methylene blue solution and. 5 ml chloroform in a test tube shake vigorously then allow it to stand until two layers are formed. If the chloroform layer (bottom layer) shows blue, add another 2-3 ml of the surfactant solution. Shake well and leave for layers to form. The chloroform shows as dark blue and the water layer is almost colourless. This is a positive result of the existence of anionic surfactant in the sample solution. This test is suitable for alkylsulphate and alkylbenzolsulphonate surfactants. Soap cannot be tested because it would precipitate in the strong acidic medium. 

When the hydrogen atom of the hydroxyl group on C6 of cellulose is partially substituted with a hydroxyethyl (-CH CH OH) group in a reaction with ethylene oxide under alkaline condition, hydroxyethyl cellulose (HEC) is produced. So far there are no known testing methods for HEC detection. However, if one wants to distinguish CMC from HEC, an ion tolerance test can be conducted. CMC is anionic and can be precipitated from an aqueous solution with a cationic surfactant. Since HEC is non-ionic, its aqueous solution is compatible with cationic surfactants. Based on the same ionic tolerance principle, a high salt concentration can precipitate CMC, not HEC. 

The ionic type of a dye sample can be determined by using ionic surfactants. The anionic dyes can be precipitated by cationic surfactants and vice versa. If a colorant sample would not be affected by either cationic or anionic type of surfactants, it could be a disperse dye with non-ionic dispersants. The surfactant test should be carried out at room temperature and a surfactant solution is added into the dye solution dropwise with the help of a magnetic stirrer. The mixture should then be allowed to stand for 30-60 min for precipitation to develop. Precipitation is the positive indication of the opposite type of ion for dyes in relation to the ionic... 

To begin this simulation, we first need to set up an EQBATCH model. The difference between a phase behavior model and a flow model of an alkaline-surfactant system is that the matrix does not exist in the phase behavior test tube thus, there is no ion exchange on the matrix in the phase behavior model. Therefore, in the phase behavior model, we define 6 elemenfs and 14 fluid species based on Example 10.4 and remove Ihe calion exchanges only on fhe malrix. In particular, we keep fhe solid species Ca(OH)2(s) and CaC03(s). Af leasl one advantage is that we can ensure that there should not be any solid precipitation in the model, or any precipitation should be consistent with the observation in the test tube. The rest of the procedures to set up the EQBATCH model are similar to those in Example 10.4. 

Aqueous stock solutions of selected anionic surfactants were prepared if alcohol was to be added, it was incorporated in the stock surfactant solution. These surfactants were desalted and deoiled. Aqueous NaCl solutions were also prepared. Surfactant (or surfactant/alcohol) and NaCl solutions were mixed in 10 ml screw-capped test tubes in the proportions necessary to give the desired final concentration of each constituent. After thorough mixing, the test tubes were set aside and observed periodically for clarity and/or precipitation. The results are summarized in Table I. 

Equivalent conductivities were first measured of the systems containing 0.014 and 0.025 wt% surfactant (0.35 and 0.62 mM) to shed light on why they threw precipitates months after they had been prepared, tested, and classified as single-phase. The results at these and higher concentrations are given in Figure 5, where data for sodium dodecyl sulfate (28) (which were confirmed to within 10% at low concentrations, 5% at concentrations higher than 5 mM) and for sodium chloride are plotted for comparison. 

As a solution-based materials synthesis technique, the microemulsion-mediated method [10-18] offers the unique ability to effect particle synthesis and particle stabilization in one step. The solubilized water droplets serve as nanosize test tubes, thus limiting particle growth, while the associated surfactant films adsorb on the growing particles, thereby minimizing particle aggregation. The purpose of this chapter is to review the literature on the microemulsion-mediated synthesis of metal hydroxides and oxides the definition of a metal is extended here to include the semimetal silicon. Since metal oxides are frequently produced by decomposing metal salts, aspects of the literature on microemulsion-derived metal salts are also considered. In principle, any previously established aqueous precipitation chemistry can be adapted to the microemulsion synthesis technique. Accordingly,... 

Rapid form dissociation and precipitation of known forms of the parent celecoxib was observed in 0.1 N HCl, SGF, 0.02 N HCl, pH 6.5 phosphate buffer and pH 6.5 phosphate buffer with sodium dodecyl sulfate (SDS). The initial dissolution rate was found to be superior for the co-crystal versus the stable form of the parent compound, but rapid conversion to aggregated crystalline celecoxib made this co-crystal a poor candidate for direct use as a dosage form. This initial dissolution advantage was exploited further by formulating the co-crystal with PVP-K30 and the ionic surfactant SDS. Using this combination of excipients, the co-crystal was repeatedly observed to precipitate as a poorly crystalline mixture of metastable celecoxib form 4 and amorphous material. Although the co-crystal was not tested in vivo, the in vitro performance improvements are consistent with improvements observed in other celecoxib formulations with demonstrated in vivo advantages over Celebrex . 

It should be mentioned that the standard method API RP 42 has drawbacks [9]. For example, it does not take into account loss of surfactant due to adsorption on the rock surface [S, 9]. Once the concentration of the surfactant in the injected acid decreases due to adsorption or phase separation (precipitation), acid-oil sludge will form [32], Rietjens [41] recommended performing acid sludge tests using flow systems (coreflood experiments) to overcome some of the problems encountered with the API RP 42 procedure. 

Oftentimes a prehminaiy step applied before many analytical methods is the isolation of the polymer. The isolation of polyacrylamides from the other components of the media in which they were prepared (eg, aqueous solution or inverse emulsion, with attendant surfactants and oil) is often readily accomplished by precipitation in short-chain alcohols or acetone. The individual solubilities of formulation components should be tested if there is any doubt. Experience shows that anionic copolymers are often best precipitated in the alcohols, and cationic copolymers in acetone (homopolyaminoesters are soluble in methanol). Since acrylamide is soluble in these organic solvents, it will also be separated from the polsrmer in this procedure. 

Fatty acids and soaps dominate the nonsulflde flotation. These collectors also tend to be nonse-lective because almost all minerals can be floated. The use of appropriate activators or depressants alleviates the problem to some extent. The lack of selectivity is often related to the tendency of fatty acids to form a precipitated phase with dissolved multivalent ions. The more tolerant ether carboxylic acids have been tested in some cases. Amines are used invariably for silicate minerals. Other collectors such as sulfates, sulfonates, phosphonic acids, hydroxamates, and some amphoteric surfactants have gained little importance. 

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