Analyte charge

Cole, R.B. Harrata, A.K. Solvent Effect on Analyte Charge State, Signal Intensity, and Stability in Negative Ion ESI-MS Implications for the Mechanism of Negative Ion Formation. J. Am. Soc. Mass Spectrom. 1993,4,546-556. 

The calculation thus consists of three steps (1) calculating the scattering factors of the analytical charge density functions (see appendix G for closed-form expressions), (2) Fourier transformation of the electrostatic operator, and (3) back transformation of the product of two Fourier transforms. 

In CZE, separations are controlled by differences in the relative electrophoretic mobilities of the individual components in the sample or test solution. The mobility differences are functions of analyte charge and size under specific method conditions. They are optimized by appropriate control of the composition of the buffer, its pH, and its ionic strength. 

Moreover, the only solute descriptor for ion-pair effect was the analyte charge, but it was shown that the analyte charge status did not explain (1) different experimental curves when k is plotted as a function of the stationary phase concentration of the IPR for various IPRs (2) the dependence of the ratio of the retention of two different analytes on IPR concentration (3) the dependence of the k/ ko ratio on the analyte nature if experimental conditions are the same [16,17] and (4) ion-pairing of peptides [12]. The model makers realized that the charge may have been a too-simple solute descriptor for ion-pairing because it did not exhibit the hydrophobic effect, but they did not devise a better descriptor. Section... 

The eluent pH is important for manipulating the analyte charge status and also for controlling the degree of ionization of the IPR that influences its ion-pairing attitude... 

We predict that the physico-chemical phenomenon known as ion pairing upon which IPC is based will be further exploited in different separative techniques such as CE and SEC because the modifications of analyte charge status and hydrophobicity are effective for achieving separation. 

Reversed phase liquid chromatography (RPLC) allows the separation of analytes with different hydrophobicity and polarity characteristics. It has good selectivity mobile phases used in the technique contain organic solvents and small amounts of inorganic salts [149]. The effectiveness of the process depends on the hydrophobicity of the separated analytes. Charged substances must first be transformed into neutral derivatives (e.g., by adding appropriate anti-ions into the mobile phase). 

The addition of salt or buffer to the mobile phase can also be used to manipulate retention. Retention decreases with the addition of salt. The influence of the pH of the mobile phase depends on the nature of the analyte charged forms are more polar and generally more strongly retained than uncharged forms of the analyte. 

Temperature Field strength Viscosity Molecular size/shape Electroosmotic flow Diffusion Analyte-wall interaction Current Ionic Strength Capillary diameter Capillary length Surface negative charge Analyte charge Electrophoretic mobility... 

Electrophoretic techniques are generally used for separation of charged analytes. Charged analytes move in electrolyte solutions when an electrical field is estabhshed. Separation is obtained if the charged analytes have different m ation velocity. The electrolyte solution is most commonly a mixture of weak acids and bases in water. 

In the normal-phase extraction, compounds with polar functional groups are extracted from a nonaqueous sample. Retention is based on polar interactions such as charge-based interactions, hydrogen bonding, dipole-dipole interactions, and dispersion interactions between the sorbent and the analyte. Charge-based interactions are often not required in the normal phase, since they are very strong and difficult to disrupt (Figure 9.4). 

Lawless, P.A. (1996). Particle Charging Bounds, Symmetry Relations, and an Analytic Charging Rate Model for the Continuum Regime. J. Aerosol Sci., Vol. 27, pp. 191-215. 

Table 4.5a shows the analytical charging currents of the cables... 

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