Novel Enzymatic Potentiometric Approaches for Surfactant Analysis

Abstract

1IntroductionSurfactants form au nique class of organic compounds which generally consist of ah ydrophilic head group and ah ydrophobic chain (or tail) [1].T he hydrophobic part is usually hydrocarbon chain (C 8 -C 18 ), while the hydrophilic group may be carboxylates,s ulfates, sulfonates (anionic), polyoxyethylenated chains (nonionic) or quaternary ammoniums alts in case of cationic surfactants [1][2][3].Thew orldwide production of surfactants was about 13 million metric tonsi n2 008;7 0% of them represent anionico nes.S urfactants are mainly employed in formulation of detergents,p ersonal-care products, paints,p esticides and textile industry [4][5][6].A fter application, surfactants are discharged into waste treatment units and then dispersed into the environment causings erious toxic effects on aquatic organismsw hen discharged with massive quantities [7][8][9].Thew idespread applications of surfactants and their environmental impacts were reflected on the development of reliable,r apid and accurate procedures for surfactanta nalysis [10][11][12][13][14][15][16][17].T wo-phaset itrationi st he most populara nalytical method for ionic surfactants in water samples [18]. Thet arget surfactant is extracted into organic solvent via formation of lipophilic ion-pair with suitable titrant in presence of an ionic dye which colors the organic layer differently at the end point. Formation of emulsion during titration,t oxicity of the chlorinated organics olvent and lack of efficiency for short chain surfactanta re the main drawbacks of such method [14].P otentiometric approaches using ion selective electrodes (ISEs) are promising option for analysis of surfactants,offering simple measuring protocol and sample pre-treatment. Surfactant potentiometric sensors are usually used as titration end-point indicator electrodes;a lthough some direct potentiometric surfactant sensors have also been reported [13,17,19,20].Liquid and PVC membranes electrodes [21,22] are inconvenient as they are mechanically complicated with difficulty of miniaturization and short lifetime. Solid-state electrodes were reported referring to an ew type of ISEs in which the internal reference elementw as in direct contact with the electroactive membrane [13,20,[23][24][25]. Elimination of the internal reference solution leads to certain advantageous such as simplicity,m iniaturization and ability to operatea th igher pressuree nvironment where the PVC membrane can be damaged.C arbon paste electrodes (CPEs) were introduced as end-point indicator electrode for potentiometric titration of surfactants [19,20] with very short response time in addition to the ease of fabrication and regeneration. However,d esigns and shapes of the aforementioned sensors were inconvenient for every purpose such as flow injection analysis or portable analyzers where the measuring unitsr equired sensors of special constructions and size.Thep ractical and economic interests have been driven the development of various kindso fd isposal electrochemical sensors based on screen-print...

Potentiometric Sensing

“…As this compound is composed of a hydrophobic cation and anion, it does not seem to possess ion-exchanger properties and so its function is unclear, other than decreasing the resistance of the membrane phase. Khaled et al demonstrated an enzymatic approach for surfactant analysis . As the surfactants are known to inhibit the activity of some cholinesterase enzymes, the authors used this characteristic to determine the surfactant concentration.…”

“…Khaled et al demonstrated an enzymatic approach for surfactant analysis. 187 As the surfactants are known to inhibit the activity of some cholinesterase enzymes, the authors used this characteristic to determine the surfactant concentration. The enzymatic activity of acetylcholinesterase was measured by monitoring the hydrolysis of acetylcholine with a disposable acetylcholine potentiometric sensor.…”

Flow-Through Acetylcholinesterase Sensor with Replaceable Enzyme Reactor

“…Starting from chemical warfare detection [ 12 , 13 ], AChE biosensors have found a large application in the determination of organophosphate and carbamate pesticides inhibiting enzymes [ 14 , 15 , 16 ]. Due to a wide variety of species exerting the anticholinesterase effect, AChE biosensors were proposed as indicators of general pollution of the environment [ 17 ] and for detection of heavy metals [ 18 ], surfactants [ 19 ], fluorides [ 20 ] and organic solvents [ 21 , 22 ] exerting a non-specific inhibitory effect. Recently, AChE biosensors were also successfully utilized for the determination of reversible inhibitors, e.g., anti-dementia drugs [ 23 , 24 ] and aflatoxins [ 25 , 26 ].…”