What is rate theory in chromatography?
The rate theory provides a more realistic explanation of the processes that take place inside a chromatographic column. It takes into account the time taken by the solute to equilibrate between the stationary and mobile phase unlike the plate model which assumes that the equilibration is infinitely fast.
How does flow rate affect gas chromatography?
A high flow rate reduces retention times, but a poor separation would be observed as well. Like above, the components have very little time to interact with the stationary phase and are just being pushed through the column. A longer column generally improves the separation.
Which are the theories of gas chromatography?
Gas chromatography is often used to determine the purity of an unknown substance or to separate out the components of an unknown mixture so that each of the different parts can be analyzed. It is a technique that can be used to detect samples in very small quantities.
What does a van deemter plot tell you?
The van Deemter equation is a hyperbolic function that predicts that there is an optimum velocity at which there will be the minimum variance per unit column length and, thence, a maximum efficiency. …
What is the difference between plate theory and rate theory?
The key difference between rate theory and plate theory is that rate theory describes the properties of a chromatographic separation via comparing the rate of analyte that elutes through the column, whereas plate theory describes the properties of chromatographic separation via determining the number of hypothetical …
What does a resolution of 1 mean in chromatography?
Equation (1) indicates that the resolution is the difference between peak retention times divided by the average peak width. In a peak with Gaussian distribution, the peak width is W = 4 σ (where σ is the standard deviation) and the peak FWHM is W0. 5h = 2.354σ.
How does carrier gas and flow rate affect column efficiency and resolution?
If the carrier gas velocity increases, the longitudinal diffusion term decreases so that the column efficiency increases, but at the same time, the mass transfer resistance term increases, which in turn reduces the column efficiency.
How do you calculate Van deemter?
The equation H=f(u), the van Deemter equation, is shown in Figure 6. One sees that H has a minimum at an optimum flow velocity that can be determined empirically or by knowledge of A, B, and C (which in many cases is not difficult).
What are the three terms that make up the van deemter equation?
The Van Deemter equation is governed by three cumulative terms: (A) eddy diffusion, (B) longitudinal diffusion, and (C) mass transfer. A loss in peak efficiency can be observed as a wider analyte band, and therefore, these three terms can also be viewed as factors that contribute to band broadening.
What is rate theory and plate theory of chromatography?
The key difference between rate theory and plate theory is that rate theory describes the properties of a chromatographic separation via comparing the rate of analyte eluted through the column, whereas plate theory describes the properties of chromatographic separation via determining the number of hypothetical plates …
What is the rate theory of chromatography?
The Rate Theory of Chromatography• In the rate theory, a number of different peak dispersion processes were proposed and expressions were developed that described • the contribution of each of the processes to the total variance of the eluted peak • the final equation that gave an expression for the variance per unit length of the column.
What is a Gasgas chromatograph?
gas chromatograph (GC) is an analytical instrument that measures the content of various volatile components in a sample. The analysis performed by a gas chromatograph is called gas chromatography.
What is the mobile and stationary phase in chromatography?
Like for all other chromatographic techniques, a mobile and a stationary phase are required for this technique. The mobile phase (=carrier gas) is comprised of an inert gas i.e., helium, argon, or nitrogen.
What is the difference between GPLC and gas chromatography?
Technically, GPLC is the most correct term, since the separation of components in this type of chromatography relies on differences in behavior between a flowing mobile gas phase and a stationary liquid phase . The instrument that performs gas chromatography is called a gas chromatograph.