Solid-Phase Microextraction
Solid-phase microextraction (SPME) is an attractive method for isolating an analyte prior to injecting it into a gas chromatograph. In one approach, which is illustrated here, a fused-silica fiber is placed inside a […]
Image and Video Exchange
Get a look at images, photos, videos, and animations that encompass many facets of teaching and learning about analytical chemistry.
Gas Chromatography Columns
Shown here is an example of a packed column for gas chromatography. This column is made from stainless steel and is 2 m long with an internal diameter of 3.2 mm. The […]
Gas Chromatograph
Photograph showing an example of a typical gas chromatograph with insets showing the heated injection ports—note the symbol indicating that it is hot—and the oven containing the column. This particular instrument is […]
Contributions to Band Broadening in Chromatography
One way to improve a separation is to decrease the height of a column’s theoretical plate. The figures here consider four contributions to plate height: variations in paths length, longitudinal diffusion, mass […]
Optimizing Separation Using a Window Diagram
The illustration below shows how the mobile phase pH in liquid chromatography affects our ability to separate a mixture of four substituted benzoic acids. The retention times in (a) suggest there are many […]
The General Elution Problem in Chromatography
Adjusting the retention factor to improve the resolution between one pair of solutes may lead to unacceptably long retention times for other solutes. For example, suppose we need to analyze a four-component […]
Tailing and Fronting of Chromatographic Peaks
The ideal chromatographic peak has a Gaussian profile, which occurs if the solute’s partition coefficient, KD, between the stationary phase and mobile phase KD = [S]s/[S]m is independent of the solute’s concentration. If this […]
Chromatographic Resolution
The goal of chromatography is to separate a mixture into a series of chromatographic peaks, each representing a single component of the mixture. The resolution between two chromatographic peaks, RAB, is a […]
Retention Time, Baseline Width, and Void Time
A solute’s chromatographic peak may be characterized in many ways, two of which are shown in this figure. Retention time, tr, is the time between when we inject the sample injection and […]
Column Chromatography
The most common method for bringing the stationary phase and the mobile phases into contact is to hold the stationary phase within a column and to pass the mobile phase through the […]
Electrophoretic Separation
In chromatography, a separation occurs because there is a difference in the equilibrium partitioning of solutes between the mobile phase and the stationary phase. Equilibrium partitioning, however, is not the only basis […]
Chromatographic Separations
As illustrated below, in chromatography we pass a sample-free phase, which we call the mobile phase, over a second sample-free stationary phase that remains fixed in space. We inject or place the […]