Acid ethoxylates titration

There are no truly satisfactory methods for assay of these products. They can be determined by most chromatographic methods, as discussed in later chapters. An approximation of active agent content may be made by determining the main impurities, namely free fatty acid, PEG, and water, and subtracting from 100%. Concentration of acid ethoxylates in solution can be determined by potentiometric titration with tetraphenylborate ion as described in Chapter 16. Free PEG is also determined by this titration. 

Free fatty acid cannot usually be determined by direct acid-base titration because of the presence of the alkaline catalyst from the ethoxylation or its neutralization products. The... 

Dissolve a sample containing about 0.5 meq total base in 50 mL acetic anhydride. Titrate potentiometrically, using a glass combination electrode, with 0.1 M HCIO4 in acetic acid. Titrate to the second, weak break. This value corresponds to the sum of the ethoxylated amide, ethoxylated amine, and ethoxylated ester. Dissolve a second portion of the sample, about five times as much as titrated above, in glacial acetic acid. Titrate potentiometrically with 0.1 M HCIO4 in acetic acid. This titration gives the sum of the ethoxylated amine and ethoxylated ester. Calculation ... 

Highly concentrated ether carboxylic acids with a low degree of ethoxylation even at room temperature can give an esterification reaction with the non-converted nonionic, especially with the fatty alcohol, to several percentage points. The result may be that a too low value is found for the ether carboxylate content. This mistake in analysis can be avoided by saponification of the formed ester [238]. Two hundred to 300 mg matter and ca 100 mg NaOH were weighed in a 50-ml Erlenmeyer glass, heated with 20 ml ethanol under reflux, and after cooling supplied with water to 100 ml. Afterward a two-phase titration was carried out. 

A polyvinyl acetate latex prepared by semi-continuous polymerization at 55° using a polymethacrylic acid-nonylphenol-poly-ethoxylate phosphate ester emulsifier and sodium persulfate-sodium formaldehyde sulfoxylate initiator (23). The latex was cleaned by ion exchange and serum replacement using both Nuclepore and Pellicon membranes, and the cleaned latex and serum fractions were analyzed by conductometric titration. In addition, the dried films were extracted with water and organic solvents, and the extracts were analyzed by infrared spectroscopy and thermo-gravimetric analysis. 

The bismuth active substances (BiAS) method for the determination of nonionic surfactants with barium tetraiodobismuthate (BaBil4, modified Dragendorff reagent) is used in the standardized (DIN-Norm) procedure in Germany, as well as in other countries. Ba as a hard Lewis acid forms cationic coordination complexes with the polyethoxylate chain of the nonionic surfactants, which are precipitated by [Bim in the presence of acetic acid. The orange precipitate is then dissolved with ammonium tartrate solution, and the released bismuth ions are determined by potentiometric titration with pyrrolidinedithiocarbamate solution. Waters et al. optimized the BiAS procedure by introduction of a cation/anion exchange clean-up of the sublation extracts. The BiAS procedure fails to determine ethoxylates with less than five ethoxy units because these compounds are not precipitated by barium tetraiodobismuthate. Thus, this procedure is not suitable for determination of APEO metabolites, i.e., the shorter APEO and AP. ... 

These materials are readily determined by two-phase titration (ISO 2271) or potentiometric titration with benzethonium chloride. On acid hydrolysis they yield the corresponding alcohol, a sulphate ion and a hydrogen ion, and this affords three additional approaches—determination of the increase in acidity, of the amount of fatty alcohol or ethoxylated alcohol liberated, and of the sulphate ion. The experimental procedure may be varied within limits for example ISO 2870 [5] and ASTM D 1570-89 [6] differ with respect to the identity of the acid used, duration of boiling, choice of indicator and other details. The following procedures are similar to both of those standard methods. The choice of indicator is immaterial for these particular compounds, but is of crucial importance in some other cases. 

Other methods, states that the method can be used for ethoxylated alkanolamides. The method can be applied to the ethoxylates obtained by acid hydrolysis of alkylether sulphates and sulphated alkylphenol ethoxylates and subsequent extraction with chloroform or by deionisation. The chemical process is hydrolysis of the oxyethylene groups by nascent hydriodic acid, thermal decomposition of the ethylene di-iodide formed and titration of the iodine with thiosulphate. 

As in previous chapters, this chapter deals with the analysis of cationics and amphoterics either alone, as raw materials or as fractions isolated by ion exchange or otherwise, or in formulated products. Fractions isolated by ion exchange are likely to contain other materials, analogously with anionics. Amines, ethoxylated amines and amine oxides are included in this chapter because they are bases and capable of a cationic function. They are retained as cations by ion-exchange columns and do not appear in the nonionic fraction of separated mixtures, they can be titrated with acids and, in acid solution, with sodium dodecyl sulphate, provided the ethylene oxide chains of ethoxylates are not too long. 

Ethoxylated amines with short ethylene oxide chains can be titrated with sodium dodecyl sulphate and NaTPB in acid solution, but the titrations become increasingly unsatisfactory as the chain length increases. The same is no doubt true of ethoxylated diamines. Commercial ethoxylated amines have typically 12-60 EO units, and the diamines have up to 25. 

Extraction of ethoxylated alcohol (by deionisation) gives ether sulphate Fatty acid by petroleum ether extraction and alkali titration (lower ethoxylates also extracted) gives glyceride sulphate Extraction of fatty amine and acid titration (lower ethoxylates also extracted) gives sulphosuccinamate... 

Alkylpolyglycosides acid hydrolysis and extraction of fatty alcohol. Alkanolamides and their ethoxylates acid hydrolysis, extraction of fatty acid, titration of alkanolamine or ethoxylated alkanolamine. 

Carboxylates in the acid form can be titrated potentiometrically with alkali in 97% methanol. Observed pK values range from 5.6 for a carboxylated nonylphenol 3-mole ethoxy-late to 4.1 for a 12-mole ethoxylate (142). Thus, acid number is a measure of the purity of the carboxylate. 

The determination of active agent is complicated by the presence of various impurities in the commercial product ethoxylated ethanolamine, ethoxylated ester, polyethylene glycol, fatty acid. The nonaqueous titration is rapid, but requires knowledge of the equivalent weight of the surfactant. This makes the method unsuitable for the analysis of unknown materials unless further characterization is performed. 

Ethoxylated esters of fatty acids and sorbitol, sucrose, and glycerin are widely used in food and pharmaceuticals, and their analysis is performed according to compendial methods. The specified methods are generally those listed in Section II of this chapter, as well as modifications of the above procedures applied to unethoxylated esters. Like other polyethoxy compounds, these can be determined in aqueous solution by titration with tetraphe-nylborate ion as described in Chapter 16 (124). 

If the identity of the nonionic surfactant is known and it can be separated from interfering compounds, it may be determined by the method of HI cleavage (72). The material is refluxed with hydriodic acid in the absence of oxygen, leading to decomposition of the ethoxylate chain and the formation of free iodine, which is titrated in the usual manner with sodium thiosulfate. 

Potentiometric titration of or Ca adducts of ethoxylates with tungstophosphoric acid has been demonstrated, using a tungsten wire electrode for end point detection. This is proposed for samples containing oil or solvents which would attack the PVC membrane of a surfactant-selective electrode (75). 

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