G. Czichocki

Novel results on the adsorption of ionic surfactants at the air/water interface — sodium-n-alkyl sulphates

Abstract Equilibrium surface tension vs. concentration isotherms of aqueous, surface-chemically pure solutions of the homologous series of sodium n-alkyl sulphates (from C7 to C14) have been evaluated using a new surface equation of state approach. All adsorption parameters (standard free energy of adsorption, interaction parameter, saturation adsorption) and the CMC reveal a pronounced even/odd effect. Surprisingly, it was found that the cross-sectional areas of the short-chain homologues decrease with increasing chain length, reaching a minimum value for C10 and C11. However the cross-sectional areas of the longer-chain homologues (Cn ≥ C12) increase again drastically with increasing chain length. This novel effect is attributed to increasing electrostatic repulsion within the adsorption layer caused by increasing Debye lengths of the stronger surface-active homologues. The good agreement between the data for the cross-sectional area of sodium-n-dodecyl sulphate, as obtained from the new surface equation of state approach, from the Gibbs equation and from crystal structure analysis, make us suggest that it is unreasonable to apply an additional factor in the Gibbs equation for ionic amphiphiles as long as the counterion is very small in comparison with the oppositely charged amphiphilic molecule.

New and effective entrapment of polyelectrolyte-enzyme-complexes in LentiKats.

Amyloglucosidase EC 3.2.1.3 was used as model for the immobilisation of enzymes in poly(vinylalcohol) hydrogel (LentiKats) lenses. The entrapment of the enzyme in PVA-hydrogel based on a two-step procedure, firstly its coupling to polyelectrolytes increased the structure level of the enzyme, and subsequently, the resulting complex was entrapped in LentiKats. The immobilised enzyme retained 45% of its original activity and lost no activity over five repeated batch runs.

Characterization of alkyl polyglycosides by both reversed-phase and normal-phase modes of high-performance liquid chromatography

Alkyl polyglycosides today represent the most important sugar surfactant. Nonionic sugar surfactants produced via different synthetic routes are mixtures of alkyl homologues, oligomers, anomers and isomers. Alkyl homologues and oligomers of alkyl mono- and diglucosides were separated by reversed-phase high-performance liquid chromatography (HPLC) with methanol-water as the mobile phase using a gradient elution. The gradient was optimized in respect to a simultaneous separation of alkyl glycosides according to their alkyl chain length and alkyl polyoxyethylene glucosides with regard to their length of the polyoxyethylene spacer. The separation of alkyl glycosides into alpha- and beta-anomers was carried out by normal-phase HPLC with isooctane-ethyl acetate (60:40, v/v)-2-propanol in the gradient mode. Light scattering detection was used. Matrix-assisted laser desorption ionization time-of-flight mass spectra of alkyl glucosides and dodecyl glucosides with oxyethylene spacer groups are presented.

Adsorption behavior of oxyethylated anionic surfactants Part 1. Adsorption equilibrium

Abstract Anionic surfactants containing one to three oxyethylene groups have been synthesized and their adsorption behavior at the water/air interface studied by measurement of their surface tension isotherms. On the basis of a long-time approximation model of the diffusion-controlled adsorption model, the equilibrium surface tension of low dilute solutions is determined. The experimental results support the theory and show that in a certain time range the approximation yields realistic equilibrium surface tension values. These values are not affected by surface active impurities. Oxyethylene groups in the anionic surfactant molecule increase surface activity. The effect of oxyethylene groups is comparable to that of methylene groups in the alkyl chain. The analysis of the adsorption isotherms suggests that at low surface pressure the oxyethylene groups are localized within the water/air interface. With increasing surface pressure an orientation change normal to the interface may occur.

Determination of dodecanol traces in sodium dodecyl sulfate

Abstract A high-performance liquid chromatography method for quantitative determination of dodecanol traces in sodium dodecyl sulfate which is more sensitive than that of lowering the surface tension in the region of the critical micelle concentration is described.

Adsorption behaviour of oxyethylated anionic surfactants - 2 - adsorption kinetics.

Abstract The adsorption kinetics of anionic surfactants containing one to three oxyethylene groups have been studied at the water/air interface by measuring the dynamic surface tensions using maximum bubble pressure and drop volume tensiometry. On the basis of a diffusion-controlled adsorption model the dynamic surface tensions are discussed. Quantitative interpretation was possible when the initial load of a bubble was considered and a non-equilibrium adsorption layer at extremely short adsorption times was taken into consideration.

Determination of trace amounts of alcohols in sodium alkyl sulphate mixtures using high-performance liquid chromatography and surface tension measurements

Abstract A method was developed for the simultaneous trace analysis of C8, C10 and C12 alkanols in sodium alkyl sulphate mixtures. The alkanols determined after derivatization with aromatic isocyanates, RNCO (R = phenyl, 1-naphthyl, 2-anthryl). In the preferred method, microbore high-performance liquid chromatography was applied with acetonitrile—water as eluent after derivatization with 1-naphthyl isocyanate at 333 K using an RP-18 5-ωm reversed-phase column. The peaks were monitored at 222 nm.

Liquid chromatography of polyisoprenes: determination of critical composition using non protic binary and acidic ternary solvent mixtures

Abstract Mixed solvent systems for the critical liquid chromatography of polyisoprenes are investigated. Under critical solvent conditions, the energetic and entropic interactions between the polymer and the stationary phase cancel each other, the free energy of interaction approaches zero and the retention time is independent of the polymer chain length. Critical conditions for polyisoprene–silica gel have been established for a non-protic binary solvent mixture [ i -octane–tetrahydrofuran (THF); critical composition at 0.88% (v/v) of THF] and a ternary system containing an acidic component [ i -octane–[0.5% (v/v) acetic acid in methyl- tert .butylether (MTBE)]; critical composition at 0.65% (v/v) of the acetic acid–MTBE mixture].

Quantitative determination of dodecanol in sodium dodecyl sulphate in the nanogram range by high-performance liquid chromatography with UV detection

Abstract The method described here has been used for the trace analysis of alkanols (carbon number in even-numbered alkyl chain C 8 –C 16 ) in alkyl sulphates, and especially for the determination of residual dodecanol in sodium dodecyl sulphate. The alkanols were determined isocratically with acetonitrile—water (78:22) after derivatization with 1-naphthylurethane at 333°K using a RP-8 10-μm reversed-phase column. The peaks were monitored at 254 and 290 nm, respectively.