Mobile phase composition determining

A computer program was compiled to work out the ray-tracing of UV detector of high performance capillary electrophoresis at the investigation of 5 and 6 (98MI59). The capacity factor of 5 at different temperature and at different mobile phase compositions was experimentally determined in bonded-phase chromatography with ion suppression (98MI15). 

Morita et al. [69] optimized the mobile phase composition using the PRISMA model for rapid and economic determination of synthetic red pigments in cosmetics and medicines. The PRISMA model has been effective in combination with a super modihed simplex method for fadhtating optimization of the mobile phase in high performance thin layer chromatography (HPTLC). 

Experimental variables such as temperature, flow rate, sample concentration and mobile phase composition can cause changes in the elution volume of a polymer [439,457,460-464]. Chromatographic measurements made with modem equipment are limited more by the errors in the absolute methods used to characterize the molecular weight of the calibration standards than any errors Inherent in the measurements themselves, since the determination of molecular weights by SEC is not an absolute method and is dependent on calibration [462]. The Influence of temperature on retention in SEC is not very great, since no strong sorptive interactions are involved in the retention mechanism. Temperature differences between the column and solvent delivery... 

To exemplify the determination of log P employing /iPLC, a single cartridge was used to generate a standard curve for four known compounds and analyze a fifth (unknown) compound.31 Retention times were determined for the four known compounds (acetanilide, benzophenone, naphthalene, and diphenylamine) and standard (uracil) at five different isocratic mobile phase compositions (Table 6.5). 

Mobile Phase Compositions Employed for jUPLC Determination of Log P... 

For HPLC-EC measurements, however, the precise value is of minor interest, as the optimum working electrode potential is determined via experiments (see Chapter 2). Potential stability is the measure of real importance for analysis. The mobile phase composition (including [Cl ]) is a constant for a certain analysis i.e. the reference potential is constant for a certain analysis. 

Again, experiments as described in Experimental Determination of Optimum Detection Potential and Estimation of Detection Limit will help to determine the optimum mobile phase composition with respect to both separation and detection. The pH variations may strongly influence both the background current and the analyte electrolysis current (signal), see Figure 4-2. Therefore mobile phases should preferably be buffered. 

In this experiment, a mixture of methyl, propyl, and butyl paraben (structures shown in Figure 13.14) in methanol solvent will be separated by reverse phase HPLC. Mobile phase compositions of varying polarities will first be tested to see which one gives the optimum resolution of this mixture, and following this, a standard curve for methyl paraben will be constructed and its concentration in this solution determined. 

Part A Determination of the Optimum Mobile Phase Composition... 

Normal-phase TLC has been employed for the control of the synthesis of some new reactive azo dyes containing the tetramethylpiperidine fragment. The chemical structure of the basic molecule and the substituents of the new derivatives are shown in Fig. 3.16. The new derivatives were characterized by their RF values determined in different mobile phases. Compositions of mobile phases were n-propanol-ammonia (1 1, v/v) for dye 1.2 (Rp = 0.84) n-propanol-ammonia (2 1, v/v) for dyes 1.3 (RF = 0.50) and 1.4 (RF = 0.80) and n-heptane-diethyl ether (1 1, v/v) for dyes 1.5 (RF = 0.80) and 1.6 (RF = 0.76). The results indicated that together with other physicochemical methods such as IR and H NMR, normal-phase TLC is a valuable tool for the purity control and identification of new synthetic dyes [96],... 

In gradient elution, the mobile-phase composition in the region of the analyte at any point in time determines an isocratic value of k, which defines the... 

Untreated silica column can be advantageously used for HPLC preseparation of PAHs from triglycerides. The capacity of a silica column to retain fat (for columns of the same particle size) depends on the column size, the mobile phase composition, as well as the type and by-products (free acids and polymerized material) of the fat injected [706,713]. Off-line HPLC-HPLC, employing silica column (250 X 4.6 mm i.d., 5 pm of particle size) for sample preparation before RP-HPLC and spec-trofluorometric detection, was successfully applied for PAH determination in edible oils [659,691] and fish [714]. After PAH elution, the silica column needs to be backflushed with dichloromethane to remove the fat. The entire sample preparation step can be automated by using a backflush valve and a programmable switching valve box [691]. 

In RPC separation of peptides, the fundamental structural properties of the amino adds within the sequence and the relative accessibility of the nonpolar amino add residues to a large measure determine the overall selectivity that can be achieved with a defined RPC systemJ20-23 As a consequence, peptides typically elute from RPC sorbents in the order of their relative hydrophobicities, for a pre-selected mobile-phase composition, pH, and temperature. However, the relative hydrophobicities of different peptides are also conditional on the solvation environment in which they are placed. The exposure or greater accessibility of previously sequestered polar or hydrophobic amino acid side chains in polypeptides with well-developed secondary structures will thus significantly affect the relative binding affinities of these peptides to hydrocarbonaceous-bonded phase surfaces. 

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