What is mass transfer in chromatography?

What is mass transfer in chromatography?

Mass transfer, the C term, is the movement of analyte, or transfer of its mass, between the mobile and stationary phases. Through this type of diffusion, increased flows have been observed to widen analyte bands, or lower peak efficiencies.

What are the 4 principles of chromatography?

Four separation techniques based on molecular characteristics and interaction type use mechanisms of ion exchange, surface adsorption, partition, and size exclusion. Other chromatography techniques are based on the stationary bed, including column, thin layer, and paper chromatography.

Why is diffusion a problem in chromatography?

Why is longitudinal diffusion a more serious problem in gas chromatography than in liquid chromatography? Diffusion coefficients of gases are 10^4 times greater than those of liquids. Therefore, longitudinal diffusion occurs much faster in gas chromatography than in liquid chromatography.

What is the general elution problem?

The General Elution Problem There is a problem which arises in all types of chromatography, when samples of widely differing retention properties are present in the same sample. If the elution conditions are correct for the early eluting compounds, the late ones will remain in the column too long.

What is mass transfer effects?

Mass transfer is the net movement of mass from one location, usually meaning stream, phase, fraction or component, to another. Mass transfer occurs in many processes, such as absorption, evaporation, drying, precipitation, membrane filtration, and distillation.

How does size affect chromatography?

The distance a sample travels can depend on the size or the polarity of the molecules involved. Larger molecules take longer to move up the chromatography paper or TLC plate, whereas smaller molecules are more mobile.

What are the two general elution problems?

The general elution problem arises whenever chromatograms are obtained on samples that contain species with widely different partition ratios. When conditions are such that good separations of the more strongly held species are realized, lack of resolution among the weakly retained species is observed.

How do you solve general elution problems?

This is termed the general elution problem. A simple solution is to increase the column temperature during the course of the separation. The well-resolved, highly volatile solutes are removed from the column at the lower temperatures before the low-volatility solutes leave the origin at the column inlet.

Which is an example of a mass transfer process?

Other mass transfer operations include distillation, humidification, liquid-liquid extraction, adsorption and ion exchange, and so on. The common denominator in mass transfer processes is that species fluxes occur within a phase when there are compositionvariations within that phase.

What is the contribution of film mass transfer?

The film mass transfer contribution to the external mass transfer is characterized by the film mass transfer coefficient, kf, which represents a characteristic time constant for protein transport through a boundary layer of thickness, δ, surrounding a chromatography particle.

When to discuss external mass transfer in preparative protein chromatography?

When discussing external mass transfer in the case of preparative protein chromatography, two phenomena should be considered.

How are external mass transfer rates related to equilibrium?

External mass transfer rates are generally correlated in terms of a linear driving force expressions, where t is time, kf the external mass coefficient, and c * the equilibrium value of c. Mass transfer rates in packed beds have been measured extensively, and the subject has generated considerable controversy in the literature.