Chromatographic experiments

A typical column chromatography experiment is outlined in Figure 12.4. Although the figure depicts a liquid-solid chromatographic experiment similar to that first used by Tswett, the design of the column and the physical state of the... 

The nature of the stationary and mobile phases in a particular chromatographic experiment determines the efficacy of component separation in a... 

An advantage of Hquid chromatography is that the composition of the mobile phase, and perhaps of the stationary phase, can be varied during the experiment to provide greater efficacy of the separation. There are many more combinations of mobile and stationary phases to effect a separation in Ic than one would have in a similar gas chromatographic experiment, where the gaseous mobile phase often serves as Httle more than a convenient carrier for the components of the sample. 

The following polyvitamin prepai ations were analyzed Kal tsid (OAO Comfort Plus , Russia), Asvitol (OAO INC Marbiofarm , Russia), Pikovit (KRKA, d.d. The New Place, Slovenia), Yeast with vitamin C (000 EKKO Plus , Russia). Chromatographic experiment has been carried out using Silufol UV-254 (Kavalier, Czech Republic) and acetone - ethyl acetate - acetic acid - ethanol (3 5 1 1) - CTAB (2T0 M) as a mobile phase mixture. The linearity calibration plot, built in coordinate S = f (IgqAC), is valid in the interval 5-25 p.g. Correctness of the determination has been checked by photometry. The obtained results for the ascorbic acid determination are presented below. 

Distinctions have to be made among the solvent for shipment, eluent for the chromatographic experiment, and the solvent for long-term storage. 

A liquid chromatographic experiment resulted in the same retention time for the electroactive compounds A and B. Which electrochemical detection scheme would offer a selective detection of the two coeluting analytes Explain your selection. (E = +0.43 V Eg = +0.77 V.)... 

Different dependencies are obtained at the two pressures and for the different flames. First, consider the difference owing to pressure change in the light of the linear dependence of ion formation rate on additive concentration that is obtained in gas chromatographic experiments. It has been demonstrated that at high pressures the principal ion loss mechanism is dissociative recombination. Thus, with n+ = ne-, we can write... 

The model, therefore, predicts the elution behavior of solutes during a chromatographic process over a swollen gel as the stationary phase as a function of solute size and of the gel nanomorphology. On the reverse, from the elution behavior of solutes of known molecular size it is possible to extract the polymer chain concentration from chromatographic experiments, where an unknown swollen gel is the stationary phase. This is the basis of the ISEC, which is so often mentioned through this chapter [16,17,105,106]. 

Thiols are easily oxidized to disulfides in solution, but this reaction occurs only very slowly at most electrode surfaces. However, use can be made of the unique reaction between thiols and mercury to detect these compounds at very favorable potentials. The thiol and mercury form a stable complex which is easily oxidized, in a formal sense it is mercury and not the thiol which is actually oxidized in these reactions. For the LCEC determination of thiols a Au/Hg amalgam electrode is used Using a series dual-electrode both thiols and disulfides can be determined in a single chromatographic experiment... 

In this study, chromatographic experiments were 10 times faster with the monolithic column and results were equivalent to those obtained with the silica-based columns. This approach could be further optimized with faster gradient since flow rate should be increased by a factor 3 or 7 compared to conventional Cig supports [61, 62] and gradient time reduced by the same factor [63] to fully exploit the potential of monolithic supports. 

FIGURE 17.3 Schematic experimental setup of a 2D chromatographic experiment. 

In the second type of chromatographic experiments chiral crown ethers of type [284] covalently attached to silica were equilibrated with solutions of racemic ammonium salts or amino-acid ester salts solubilized by addition of 18-crown-6 or alcohols in chloroform or dichloromethane (Table 66). The... 

For quantitative analysis by either the external or internal standard methods, HPLC requires the use of calibration solutions that are injected under identical conditions. Thus to fully identify quantitative effects, calibration solutions plus standard solutions need to be analysed for each experiment in a ruggedness test. As duplicate determinations are required for the estimation of standard errors a single experiment can consist of up to six chromatographic experiments as shown below. 

Compound 74 undergoes decarboxylation to give 2-furaldehyde, as evidenced by the results of chromatographic experiments.110 However, the fact that 74 is decarboxylated102,110,118 at less than 2% of the rate for D-galacturonic acid under comparable conditions indicates that it is essentially an end product in the reaction, and not an intermediate, either in the production of 2-furaldehyde or in the decarboxylation reaction. Although mechanistic studies have not been reported for this conversion, the obvious structural relationships between 74 and its precursors suggest that 74 is formed by mech-... 

Chromatography and thermodynamics. Thermodynamic relationships can be applied to the distribution equilibria defined in chromatography. /C(= Cs/Cm), the equilibrium constant defining the concentration C of analyte in the mobile phase (M) and stationary phase (S) can be determined from chromatographic experiments. If the temperature of the experiment is known, it is possible to determine the variation of the standard free energy AG° for this transformation ... 

In general, it should be stated that for very long molecules the adsorption proceeds as a phase transition. Therefore, in order to work with long molecules (M > 105) at critical conditions, careful chromatographic experiments are necessary. In the case of oligomers, no such problems arise. 

The completion of a chromatographic experiment calls for a means to detect the presence of solutes in the collected fractions. The detection method used will depend on the nature of the solutes. Smaller molecules such as lipids, amino acids, and carbohydrates can be detected by spotting fractions... 

Most liquid chromatographic experiments performed with PAD employ alkaline mobile phases or use postcolumn addition of base to get the electrode at the appropriate pH for the formation of the oxide. The exceptions to this are the detection of carbohydrates and alcohols in acidic media and the detection of sulfur compounds. The oxidation of carbohydrates and alcohols is not oxide catalyzed, and since they exhibit a stronger adsorption to piatinum than gold, they can be determined under acidic conditions. Sulfur compounds are adsorbed at oxide-free surfaces, and the kinetics for detection are favorable even at pH values below 7. 

The usefulness of the LSER approach hinges on the similarity of the partitioning coefficients obtained from the sensing experiments (Ks) and the gas chromatographic experiments (Kqc)- In other words, it is assumed that the relationship Ks Kgc holds. This is how LSER is used for evaluation of a new sensing material. First, the coefficient Kqc is obtained from the tabulated database or experimentally. Second, the multiple linear regression technique (see Chapter 10) is used to obtain the best fit for the sensor test data, and the individual coefficients in (2.3) are evaluated. This approach has been used successfully in evaluation of multiple materials for gas sensors (Abraham et al., 1995 Grate et al., 1996). 

Contrast the difference in interaction of the mixture of vapors with the solid phase used in a gas chromatographic experiment and in a direct sensing application. 

The transfer process is completely independent from the NMR measurements. This means that the samples can be prepared for the NMR measurements while the NMR spectrometer is used for other purposes. It is even possible to perform the chromatographic experiments in a separate laboratory. 

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