Surfactant-sensitive

A ring test proved that surfactant-selective electrodes are suitable for quantitative determination of anionic surfactants including alkanesulfonates [21]. The precision of this method, however, does not yet correspond to the state-of-the-art of the two-phase titration. Therefore, further development is needed to enhance the reproducibility and competitiveness of surfactant-sensitive titration. 

Progress in the application of Arsenazo 111 reagent in analytical chemistry has recently been discussed [1]. A review of systems based on ternary and multicomponent complexes recently developed for spectrophotometric determination of elements have been presented [2]. The use of mixed ligand, surfactant sensitized, ion-association, flotation, derivative and FIA techniques has been discussed. 

Spectroscopic evidence for association through the sharing of carboxylate cations has been reported (37) (the phenomenon is discussed in Chapter 15) for surfactant-acrylic acid copolymer interactions. This dependence on surface carboxylate groups (Figure 17) is not observed in cellulose ether or in HEUR 200 formulations. This observation is made in reviewing all of the data, and probably reflects only the extreme surfactant sensitivity of HEUR 200. 

The effect of hardness ions on surfactant activity is further illustrated in Figure. 4. Surfactant activity was monitored by means of a surfactant sensitive electrode as a function of hardness. The increase in potential in each curve between 900 and lOOOppm Ca indicates a reduction in activity. Only the sodium silicate maintained the surfactant activity at a constant level up to nearly 900ppm of Ga. The other alkalis resulted in a decrease in surfactant activity at about 400ppm. 

There are a number of reviews available for surfactants in specific industries [S7], and for specific surfactant classes. References [SJ-90] discuss methods for the determination of anionic surfactants, which are probably the most commonly encountered in the petroleum industry. Most of these latter methods are applicable only to the determination of sulfate- and sulfonate-functional surfactants. Probably the most common analysis method for anionic surfactants is Epton s two-phase titration method [9J, 92] or one of its variations [93, 94], Related, single-phase titrations can be performed and monitored by either surface tension [95] or surfactant-sensitive electrode [84, 85, 96-98] measurements. Grons-veld and Faber [99] discuss adaptation of the titration method to oleic phase samples. 

A promising method for quantitation of anionic process surfactants is by cationic surfactant (e.g., Hyamine) titration monitored by a surfactant-sensitive electrode. The basic approach is described in references [76, 77, S9-92]. This technique has found application in the analysis of formulated products in the cosmetic [9J ] and pharmaceutical [90] industries and may... 

Titrations of anionic, cationic and amphoteric surfactants with surfactants of opposite charge, using a surfactant-sensitive electrode. Titrations of cationic and amphoteric surfactants, and metal complexes of nonionic surfactants, with tetraphenylborate. 

Potentiometric titration with surfactants of opposite charge using a surfactant-sensitive electrode... 

Surfactant-sensitive electrodes are commercially available, and they are also easily made in the laboratory. They can be used to detect the end-point in titrations of anionic and cationic surfactants with surfactants of opposite charge. They are used in exactly the same way as a glass electrode in acid-base titrations, or a silver-silver chloride electrode in titrations of chloride with silver nitrate. The main advantages of potentiometric as opposed to two-phase titration are ... 

The construction of surfactant-sensitive electrodes presents no difficulty, and three types are described here. The first type is a concentration cell, the second is a conductor coated with a membrane containing a surfactant salt, and the third is a conductor coated with a membrane not containing a surfactant salt. Many other electrodes have been described in the literature over the last 20 years or so, but most if not all of them are of one of these basic types. 

With all types of surfactant-sensitive electrodes, high concentrations of electrolyte tend to depress the potential jump at the end-point, and some product types require separation of the surfactant from the product matrix. 

Pipette 25 ml into a 100 ml beaker. Insert a surfactant-sensitive electrode and a reference electrode. Add lOmlM hydrochloric acid. If necessary add water until the electrode tips are immersed. 

Pipette 25 ml into a 100 ml beaker, insert surfactant-sensitive and calomel electrodes and commence stirring. 

It is to be expected that other types of surfactant-sensitive electrodes can be used with equal or greater success, and it would not be surprising if the two-phase methods, e.g. that of Cross (section 7.1.3) could also be used, although the author is unaware of any published evidence. 

The concentration of the surfactant were determined by titration with cetylbenzyldimethylammonium chloride, which forms water-insoluble complexes with the anionic surfactant. Potentiometric titrations were carried out with a Titroprocessor 672 (Metrohm, Switzerland) using a surfactant-sensitive electrode [7]. The cationic polymer was analyzed by polyelectrolyte titration with poly-(ethylensulfonate) (PES). The equivalence point of the polyelectrolyte complexation reaction was indicated either by streaming potential (PCD 2, Mutek GmbH, FRG) [8] or, for lower concentrations of the cationic polymer, by a color change due to the cooperative binding of a metachromic dye on the excess chromotrope titrant [9, 10]. Brilliant Yellow was used as dye indicator. 

CIO-14 alkyl benzenesulfonic acid surfactant, sensitive-skin prods. PEG-30 glyceryl soyate Proielan AG 8 STEPAN-MILD BSB STEPAN-MILD LSB... 

The product is acidified and titrated with sodium tetraphenylborate in aqueous solution using a surfactant-sensitive electrode or other electrode for end point detection, as described in Chapter 16. The addition of gum arabic to the titration vessel smooths the titration curve by preventing the deposition of the cationic/ tetraphenylborate precipitate on the electrode. 

Schulz, R., Potentiometric titration of nonionic surfactants with the surfactant-sensitive electrode (in German), SOFW-Jour., 1996,122,1022,1024-1028. 

One research group advocates an electrochemical method, indirect tensammetry, for determination of nonionics in environmental samples. This is based on the decrease in the size of the amperometric peak of ethyl acetate in the presence of surfactants. Sensitivity is gained by preliminary extraction or sublation of the sample, or use in conjunction with the BiAS test (132,133). 

InvestigatiOTis of surfactant-sensitive potentiometric electrodes began in the 1970s. Since surfactant ion-selective electrodes have been developed by Gavach and Seta, the development of potentiometric surfactant sensors is an area of interest. Several excellent articles " "" review the use of different types of electrodes for surfactant analysis. When compared with other analytical methods, ion-selective electrodes (ISEs) are simple, relatively inexpensive, robust, durable, and ideal for their use in field environments. Some other advantages involve that they can be used very rapidly, that they allow cmitinuous monitoring, and that they are not affected by turbidity or color of a sample. 

Madunic-Cacic D, Sak-Bosnar M, Matesic-Puac R (2011) A new anionic surfactant-sensitive potentiometric sensor with a highly lipophilic electroactive material. Int J Electrochem Sci 6 240-253... 

Matesic-Puac R, Sak-Bosnar M, Bilic M, Grabaric S (2005) Potentiometric determination of anionic surfactants using a new ion-pair-based all-solid-state surfactant sensitive electrode. Sens Actuators B Chem 106 221-228... 

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