Chromatography calculation examples

Riviello et al. made a careful comparison of conductivity changes in cation chromatography between direct- and suppressed conductivity detection [7]. The calculation example is outlined in Fig. 7.5. The change in conductivity, AG, is actually slightly greater with non-suppressed conductivity. Flowever, the noise is much higher in the non-suppressed detection mode. Noise may be defined as the random signal that... 

Dipole interact ions,. tee Electrostatic forces Dispersion forces (energies), 44-47 on alumina, 245 in gas-solid adsorption, 243-245 Displacement chromatography, 34-36 Distribution coefficient A, lOi-ll calculation (examples), 385-396 correlation between different adsorbent batches, 148-149... 

The ratio of the content of a fatty acid in position 2 of the triacylglycerides to its total content (E factor, E = enrichment) is independent of the origin of the plant oil. After hydrolysis of the fat with pancreatic lipase, separation of the 2-monoglycerides, and their methanolysis, the concentration in position 2 is determined by gas chromatography and the E-factor calculated (examples for linoleic acid are shown in Table 14.25). Adulteration of olive oils with ester oils is shown by an increased E-factor for palmitic acid (cf. 3.3.1.4). 

Paper Chromatography. This example is based on safety handling of laboratory chemicals, but is useful in lecture. Students are asked to calculate the overall gas composition in a laboratory room where solvent is left uncapped. Students have a room volume to work with, assume full evaporation, and assume no loss of solvent from the room. If 24 students, each given 50.0 ml of acetone, all forget to cap their beakers of solvent, then what is everyone s exposure This can be as difficult as the instructor likes Students can be asked to use/calculate evaporation rate, vapor pressure, volatility depending on the instructor s approach. The easiest example is to assume full evaporation within the lab session and complete build-up. The conversion of liquid to gas and the volume occupied allows the student to calculate ppm. The calculated ppm value is then compared to acceptable limits. This exercise can generate a lot of discussion about air quality, be sure to make students use calculations to prove their points ... 

Example 12 Calculation of Band Profiles in Displacement Chromatography Au equimolar mixture of two compoueuts (couceutra-tious cf = = 1 arbitrary iiuit) is separated with a displacer with couceutratiou... 

Time, wavelength and added volume in the above-mentioned examples are the domains of the measurement. A chromatogram is measured in the time domain, whereas a spectrum is measured in the wavelength domain. Usually, signals in these domains are directly translated into chemical information. In spectrometry for example peak positions are calculated in the wavelength domain and in chromatography they are calculated in the time domain. Signals in these domains are directly interpretable in terms of the identity or amount of chemical substances in the sample. 

Before releasing a process column for chromatography, it is advisable to perform some test to measure efficiency, such as calculating height equivalent theoretical plates (HETP), both to forestall any problems in the column bed and to provide a benchmark by which to measure column reproducibility and predict degradation of the bed or material. Examples of compounds that are relatively innocuous for use in pharmaceutical applications are 1% NaCl (for gel filtration), concentrated buffer solutions (for ion exchange), and benzyl alcohol and parabens for reverse phase LC.10... 

A quantitative analysis of the structure-retention relationship can be derived by using the relative solubility of solutes in water. One parameter is the partition coefficient, log P, of the analyte measured as the octanol-water partition distribution. In early work, reversed-phase liquid chromatography was used to measure log P values for drug design. Log P values were later used to predict the retention times in reversed-phase liquid chromatography.The calculation of the molecular properties can be performed with the aid of computational chemical calculations. In this chapter, examples of these quantitative structure-retention relationships are described. 

It seemed possible to correlate the elution order in reversed-phase liquid chromatography with the octanol-water partition coefficient, logP. For example, the partition coefficients calculated by Rekker s method showed a... 

Measurements of binary vapor-liquid equilibria can be expressed in terms of activity coefficients, and then correlated by the Wilson or other suitable equation. Data on all possible pairs of components can be combined to represent the vapor-liquid behavior of the complete mixture. For exploratory purposes, several rapid experimental techniques are applicable. For example, differential ebulliometry can obtain data for several systems in one laboratory day, from which infinite dilution activity coefficients can be calculated and then used to evaluate the parameters of correlating equations. Chromatography also is a well-developed rapid technique for vapor-liquid equilibrium measurement of extractive distillation systems. The low-boiling solvent is deposited on an inert carrier to serve as the adsorbent. The mathematics is known from which the relative volatility of a pair of substances can be calculated from the effluent trace of the elutriated stream. Some of the literature of these two techniques is cited by Walas (1985, pp. 216-217). 

The synthesis of the transactinides is noteworthy from a chemical and a nuclear viewpoint. From the chemical point of view, rutherfordium (Z = 104) is important as an example of the first transactinide element. From Figure 15.1, we would expect rutherfordium to behave as a Group 4 (IVB) element, such as hafnium or zirconium, but not like the heavy actinides. Its solution chemistry, as deduced from chromatography experiments, is different from that of the actinides and resembles that of zirconium and hafnium. More recently, detailed gas chromatography has shown important deviations from expected periodic table trends and relativistic quantum chemical calculations. 

This method amounts to a complete resolution of the type described in Section 19-3D, but on an analytical scale. For example, assume that you have a partially resolved compound, A, consisting of unequal amounts of the enantiomers Aand A. By reaction with a second chiral enantiomerically pure substance, B+, A is converted to a mixture of diastereomers A+B+ and A B+. Because these diastereomers are chemically and physically different, the mixture usually can be analyzed by gas-liquid chromatography (Section 9-2A). If the reaction of B+ with A+ and A was quantitative, the relative areas of the two peaks eluting from the column correspond to the ratio of the diastereomers A,.B+/AJB+, and thus to the ratio of enantiomers A+/A, from which the enantiomeric purity of the partially resolved mixture can be calculated. 

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