Ester ethoxylates characterization

Trathnigg, B., Hreczuch, W. 2000. Characterization of fatty ester ethoxylates by coupled chromatographic techniques. Proceedings of the 5th World Surfactant Congress. Firenze, 1 472-480. 

In addition to their poor solubility in water, alkyl phosphate esters and dialkyl phosphate esters are further characterized by sensitivity to water hardness [37]. A review of the preparation, properties, and uses of surface-active anionic phosphate esters prepared by the reactions of alcohols or ethoxylates with tetra-phosphoric acid or P4O10 is given in Ref. 3. The surfactant properties of alkyl phosphates have been investigated [18,186-188]. The critical micelle concentration (CMC) of the monoalkyl ester salts is only moderate see Table 6 ... 

These products are characterized by using the procedures (appropriately modified) for characterization of the parent compound. For example, phosphate esters of ethoxylated alcohols can be analyzed for EO content, alkyl chain length, and free alcohol by the methods described in Chapter 2 for analysis of alcohol ethoxylates. 

Ethoxylated amine Ethoxylated ester Alkyl/EO ratio Characterization of acid Other tests... 

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. 

Henrich developed a comprehensive TLC method for identification of surfactants in formulations (4). She specified two reversed-phase and four normal phase systems, with detection by fluorescence quenching, pinacryptol yellow and rhodamine B, and iodine. Prior to visualization, one plate was scanned with a densitometer at 254 nm, and UV reflectance spectra were recorded for each spot detected. Tables were prepared showing the Rf values of 150 standard surfactants in each of the six systems, along with the reflectance spectra and response to the visualizers. This system allows for systematic identification of compounds of a number of surfactant types (LAS, alcohol sulfates and ether sulfates, alkane sulfonates, sufosuccinate esters, phosphate compounds, AE, APE, ethoxylated sorbi-tan esters, mono- and dialkanolamides, EO/PO copolymers, amine oxides, quaternary amines, amphoterics and miscellaneous compounds). Supplementary analysis by normal phase HPLC aided in exactly characterizing ethoxylated compounds. For confirmation, the separated spots may be scraped from one of the silica gel plates and the surfactant extracted from the silica with methanol and identified by IR spectroscopy. 

Forming the trimethylsilyl ethers of ethoxylates of moderate MW makes them volatile enough to be analyzed even by packed-column gas chromatography. The complete molecular weight distribution can be calculated on a relative basis, with standards required for definitive work. Compounds also containing oxypropylene moieties usually cannot be distinguished from pure ethoxylates by this technique. Alkanolamides and the various esters of sorbitol, sucrose, and glycerin can be characterized by analysis of the trimethylsilyl derivatives. 

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