Resolution and selectivity

Resolution between peaks is dependent on the retention characteristics of each component (k), the ability of the stationary phase to selectively retain the components (a) and the overall efficiency of the column (N). The equation derived below was first developed by Purnell in 1959 to accurately relate the degree of separation attainable in a GC column in terms of the separating capability and efficiency [13-15], 

The equation is important in column design, for example, to achieve a given separation in the minimum column length and analysis time. Resolution is a function of the square root of N so large changes in N are required to have a marked effect. Efficiency may be improved by increasing column length but 

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Using the data from Problem 1, calculate the resolution and selectivity factors for each pair of adjacent compounds. For resolution, use both equations 12.1 and 12.21, and compare your results. Discuss how you might improve the resolution between compounds B and C. The retention time for an unretained solute is 1.19 min. 

Linked or longer columns for greater resolution and selectivity... 

FIGURE 9.1 Comparison of resolution and selectivity with increased speed. L = column length. dp= particle size. (Courtesy of Waters Corp.)... 

In view of the future development of sensors driven by increasing demand for accuracy and precision, and by the opening of new fields close to the biological area (which is oriented toward nano-biosensor fabrication), it appears even more important to properly use the most relevant sensor keywords, such as response curve, sensitivity, noise, drift, resolution, and selectivity. 

FIGURE 10 Effect of flow rate on the chiral resolution of lorglumide on ovomucoid CSP using phosphate buffer (13mM)-acetonitrile (74 26, v/v, pH 6.3) as the mobile phase (O) resolution and ( ) selectivity factors. (From Ref. 60.)... 

Photochemical methods offer a convenient tool to study intra- and interprotein ET because of their time resolution and selectivity. Various mechanistic and design approaches based on photochemistry of metal complexes have been undertaken. Most of the studies on protein electron transfer processes have been done for hae-moproteins using among others ruthenium complex as a photosensitizer, modified haemoproteins in which haem iron is substituted by another metal (mainly Zn), and CO-bonded haem proteins [6,7],... 

Reproducibility between different batches of the sorbent High capacity in terms of dynamic loading in preference to static loading of the desired components) in the feedstock High resolution and selectivity under linear and partial overload chromatographic conditions... 

S. D. West, The prediction of reversed-phase HPLC retention indices and resolution as a function of solvent strength and selectivity,/. Chromatogr. Set. 25 (1987), 122-129 and S. D. West, Correlation of retention indices with resolution and selectivity in reversed-phase HPLC and GC, J. Chromatogr. Set. 27 (1989), 2-12. 

Its rapid analysis time, low sample and solvent volume requirements, high resolution, and selectivity will continue to attract researchers who are involved in separation analysis. 

The rapid advancement in peptide research over the past 25 years must be attributed, in part, to the effectiveness of high-performance liquid chromatography (HPLC), particularly reversed-phase chromatography, in the separation and analysis of peptides. The resolution and selectivity of this technique allows peptides to be effectively isolated and purified from closely related substances. It also separates most or all of the components of complex biological mixtures such as tryptic digests of proteins. 

Demonstration of adequate resolution and selectivity between drug substance and known or unknown impurities. 

The resolution and selectivity in ICP emission comes primarily from the monochromator. As a result, a high-resolution monochromator can isolate the analyte spectral line from lines of concomitants and background emission. It can thus reduce spectral interferences. In atomic absorption spectrometry, the resolution comes primarily from the very narrow hollow cathode lamp emission. The monochromator must only isolate the emission line of the analyte element from lines of impurities and the fill gas, and from background emission from the atomizer. A much lower resolution is needed for this puipose. 

One of the more impressive advantages of LC/MS is that less resolution and selectivity are required from the LC separation. For assay methods involving complex matrices such as plasma, the separation of analyte from matrix components is not as critical, so the separation can be much shorter. Assay methods requiring 15 to 20 min with LC/UV or fluorescence can be shortened to only a few minutes. Methods that previously required large numbers of theoretical plates and long (25-cm) analytical columns can now be implemented with less resolution and shorter (1- to 15-cm) columns. 

Good resolution and selectivity, too long analysis time resulting in poor efficiency and band broadening... 

The derivatised glucose can act as a chiral site and result in diastereomeric interactions with enantiomers which together with the steric fit requirements within the cavity and the different interactions with the cellulose strands provides the basis for enantioselective interaction and subsequent resolution. The acetate, benzoate and phenylcarbamate glucose ester give superior resolution and selectivity compared with the parent material. Hydrophobic mobile phases are most commonly encountered though aqueous based eluants can be used with many versions of these materials. These stationary phase packings have been used to separate a wide range of pharmaceutical compounds [80]. 

Laser micropyrolysis gas chromatography-mass spectrometry A laser microprobe is used to target selectively microscopic samples of toner, for subsequently GC-MS detection. Fused toners are directly analyzed in situ avoiding the traditional separation of toner from the paper substrate. This method offers a high spatial resolution and selectivity but further studies may be necessary to improve its reproducibility. 

The term column switching in liquid chromatography is used if two or more columns are connected to form a network. Column switching is a technique that changes the direction of flow of the mobile phase by valves, so the effluent from a primary column passes to a secondary column for a defined period of time as illustrated in Fig. 2. The objectives of column switching are to increase the chromatographic resolution and selectivity, to enrich trace amounts of sample, to protect sensitive detectors such as electrochemical detectors from contamination by coextractives, to prevent destabilization of the chromatographic equilibrium of the column by coextractives, and to achieve further objectives or a combination of... 

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