Surfactant sensor

Solid-state sensors for anionic surfactants can be constructed by using polyaniline as sensing membrane [107,108], and by using polypyrrole as ion-to-electron transducer in combination with plasticized PYC as sensing membranes [53,66]. The sensors may be applied for the determination of dodecylsulfate in, e.g., mouth-washing solution and tap water [107], and for the determination of dodecylbenzenesulfonate in detergents [66,108]. Solid-state surfactant sensors allow a sample rate of 30 samples/h, when applied in flow-injection analysis [53]. 

This chapter was intended to provide an overview of different electroanalytical methods for surfactant analysis. Surfactant sensors are usually divided into poten-tiometric, voltammetric, and amperometric sensors and biosensors. While amper-ometric sensors and biosensors are very few for the determination of surfactants, potentiometric sensors are the most common due to their simplicity and versatility. 

Potentiometric surfactant sensors are usually used as titration end-point indicator electrodes, although some direct potentiometric surfactant electrodes have also been reported. All surfactant titrations are based oti the so-called antagonist reaction, where an ionic surfactant reacts with an oppositely charged ion (mainly surfactant, too) forming a water insoluble salt (ion-pair). Before the... 

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. 

Moody and coworkers and Buschmarm and coworkers were leaders in constructing efficient surfactant sensors. ISEs containing PVC membranes with ortho-nitrophenyloctyl ether (p-NPOE) as a plasticizer were suitable for the determination of amphoteric (ZS) and catirmic (CS) surfactants. At pH < 1.5, the ZS reacts as a CS and can be titrated by a bulky counter ion such as tetraphenylborate. Complexation of the ethoxylated part of nonirmic surfactants with a bivalent cation such as Ba " allows potentiometric titratirMi with tetraphenyl borate. Jones et al. " report a detection limit of 1 x 10 mol for Antarox 880. 

A sensitive potentiometric surfactant sensor was prepared based on the highly lipophilic l,3-didecyl-2-methyl-imidazolium cation in the form of its tetraphe-nylborate associate. The sensor responded fast and showed a Nemstian response for the following surfactants under investigation CPC, CTAB, and hyamine with slope values of 59.8, 58.6, and 56.8 mV decade respectively. The sensor served as an end-point detector in ion-pair surfactant potentiometric titrations using sodium tetraphenylborate as titrant. Several technical grade cationic surfactants and a few commercial disinfectant products were also titrated, and the results were compared with those obtained from a two-phase standard titration method. The results, compared to those obtained using a commercial surfactant electrode with the standard two-phase titration method, exhibited satisfactory mutual agreement. 

An alternative approach for construction of solid contact electrodes can be also applied by casting the sensitive membrane directly oti the surface of a conductor such as silver or a conductive carbon resin. Thus, two surfactant sensors were prepared using hyamine 1622 or tetradodecylammonium (TDA) as catimiic and DBS as anionic surfactant.The sensing materials were incorporated in a PVC matrix containing o-NPOE as a solvent mediator and applied on a support of a conductive resin without inner reference solution. The responses of these electrodes to DS and DBS as well as the interferences of several common inorganic anions and anionic surfactants were examined. The membranes showed good performance for use as a general potentiometric sensor responsive to anionic surfactants. 

In parallel to research considering surfactants sensors, some commercially surfactant selective electrodes have been launched into the market. Orion model 93-42, ASTEC model TSE 01 91, and Metrohm High Sense Tenside are examples with considerable long operational life time and is the most promising specimen on the market. It is stable over a wide pH range and its use permits differentiation between some detergents in mixtures simply by changing the pH of the analyzed sample. 

Sak-Bosnar M, Grabaric Z, Grabari BS (2004) Surfactant sensors in biotechnology part 1—electrochemical sensors. Food Technol Biotechnol 42 197-206... 

A recent design of the maximum bubble pressure instrument for measurement of dynamic surface tension allows resolution in the millisecond time frame [119, 120]. This was accomplished by increasing the system volume relative to that of the bubble and by using electric and acoustic sensors to track the bubble formation frequency. Miller and co-workers also assessed the hydrodynamic effects arising at short bubble formation times with experiments on very viscous liquids [121]. They proposed a correction procedure to improve reliability at short times. This technique is applicable to the study of surfactant and polymer adsorption from solution [101, 120]. 

A new generation of mesoporous silica (SG) materials obtained by sol-gel technique where polymers and ionic or non-ionic surfactant act as stmcture - directed templates is widely developed during last year s. Final materials can be synthesized as thin films and used as sensitive elements of optical and electrochemical sensors. 

Low temperature sol-gel technology is promising approach for preparation of modified with organic molecules silica (SG) thin films. Such films are perspective as sensitive elements of optical sensors. Incorporation of polyelectrolytes into SG sol gives the possibility to obtain composite films with ion-exchange properties. The addition of non-ionic surfactants as template agents into SG sol results formation of ordered mechanically stable materials with tunable pore size. 

Luo K, Shi Z, Varesi J, Majumdar A (1997) Sensor nanofabrication, performance, and conduction mechanisms in scanning thermal microscopy. J Vac Sci Technol B 15 349-360 Majumdar A (1999) Scanning thermal microscopy. Annu Rev Mater Sci 29 505-585 Manghk RM, Wasekar VM, Zhang J (2001) Dynamic and equilibrium surface tension of aqueous surfactant and polymeric solutions. Exp Thermal Fluid Sd 25 55-64... 

Microelectronic circuits for communications. Controlled permeability films for drug delivery systems. Protein-specific sensors for the monitoring of biochemical processes. Catalysts for the production of fuels and chemicals. Optical coatings for window glass. Electrodes for batteries and fuel cells. Corrosion-resistant coatings for the protection of metals and ceramics. Surface active agents, or surfactants, for use in tertiary oil recovery and the production of polymers, paper, textiles, agricultural chemicals, and cement. 

BIAlite system. Sensor Chip CMS, HBS buffer (lOmM H es, pH 7.4, 150 mM NaCl, 0.005% v/v surfactant p20 in distilled water), amine coupling kit were fi-om Pharmacia Biosensor (Uppsala, Sweden). 

The calibration curve obtained for hydrogen peroxide exhibited a detection limit of 30 pmol and ranged over three decades at least. These performances compared well with those previously obtained in non-micellar media54. The presence of surfactant compounds in the ECL measurement buffer appeared thus to have little effect on the H2O2 ECL sensor performances. In optimized conditions, the determination of free cholesterol could be performed with a detection limit of 0.6 nmol and a calibration curve ranging over two decades at least. 

Chemical sensors for liquids (like pH, surfactant concentration, water hardness)... 

Surface acoustic waves (SAWs), acoustic wave sensors and, 22 270 Surface-active agent(s), 12 33. See also Surfactant entries cmc values of, 24 121t general classification of, 24 144-153 nonionic, 10 665 organic esters as, 10 519 Surface-active molecules, 12 1 foaming and, 12 3... 

Fluorescent molecular sensors of neutral molecules and surfactants... 

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