Plate number, micellar

Chromatographic efficiency seems to be linked to the additive-to-surfactant concentration ratio in the micellar mobile phase. The plate numbers increase with this ratio but reach a maximum level (e.g., at pentanol/SDS = 6 and acetonitrile/CTAC= 12). - The organic solvent/surfactant ratio affects the exchange rates of the solute between micelle/stationary and aqueous phases. It also controls the extent of the surfactant coverage and the fluidity of the organic layer on the stationary phase. 

Armstrong and Nome [1] extended to micellar media the classic model of Martin and Synge, and Herries et al. [8]. The model describes the situation that a solute experiences in an ideal system formed of a number of identical plates, where partitioning equilibria take place. The transitions that can occur in the three environments that exist in a micellar chromatographic system i.e., the aqueous phase, the micelles and the stationary plmse) were considered (Fig. 5.1). The mass fraction of solute in each environment and each theoretical plate was obtained from P m and Pws The P s coefficient was not included in the model, since it can be obtained by combination of the two former (P g Pws/Pwm)-... 

Figure 6.4 shows the efficiency enhancement for benzene and EAQ obtained with 5% v/v alcohol additions to a 0.285 M SDS micellar phase. The stationaryphase is a classical C18 phase (dp = 5pm). The X-axis is the log PwM value of the alcohol, a parameter almost proportional to the alcohol carbon number [27], In pure SDS solution, the benzene and EAQ efficiencies were respectively 1400 and 49 plates (HETP, 14 dp and 410 dp). The maximum efficiencies, 3400 and 1100 plates (5.5 dp and 18 dp). 

Sdf Assembly Measurements in Solution The critical micelle concentration (CMC) is the characteristic solution concentration at wiiich solubilized single molecules aggregate into micellar structures. A number of parameters, including osmotic pressure, conductivity, turbidity and surfiice tension e q>erience dramatic changes at the CMC. One method of determining the CMC involves surfiice tension measurements using a Wilhelnty plate. The CMC of various F-terminated cellulose ester oligomers and of xylans were determined in THF and water, reflectively. 

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