Drawing from an arsenal of analytical techniques—many of which were the subject of the preceding four chapters—analytical chemists design methods for the analysis of analytes at increasingly lower concentrations and in increasingly more complex matrices. Despite the power of these analytical techniques, they often suffer from a lack of selectivity. For this reason, many analytical procedures include a step to separate the analyte from potential interferents. Although effective, each additional step in an analytical procedure increases the analysis time and introduces uncertainty. In this chapter we consider two analytical techniques that avoid these limitations by combining the separation and analysis: chromatography and electrophoresis.
- 12.1: Overview of Analytical Separations
- Despite the power of liquid–liquid extractions, there are significant limitations. If we have several analytes, we may need to complete a separate extraction for each analyte. A more significant limitation is that the extent of a separation depends on the distribution ratio of each species in the sample. Other important separations include chromatographic separations and electrophoretic separations.
- 12.2: General Theory of Column Chromatography
- Of the two methods for bringing the stationary phase and the mobile phases into contact, the most important is column chromatography. In this section we develop a general theory that we may apply to any form of column chromatography.
- 12.3: Optimizing Chromatographic Separations
- Now that we have defined the solute retention factor, selectivity, and column efficiency we are able to consider how they affect the resolution of two closely eluting peaks. Because the two peaks have similar retention times, it is reasonable to assume that their peak widths are nearly identical.
- 12.4: Gas Chromatography
- In gas chromatography (GC) we inject the sample, which may be a gas or a liquid, into an gaseous mobile phase (often called the carrier gas). The mobile phase carries the sample through a packed or capillary column that separates the sample’s components based on their ability to partition between the mobile phase and the stationary phase.
- 12.5: High-Performance Liquid Chromatography
- In high-performance liquid chromatography (HPLC) we inject the sample, which is in solution form, into a liquid mobile phase. The mobile phase carries the sample through a packed or capillary column that separates the sample’s components based on their ability to partition between the mobile phase and the stationary phase.
- 12.6: Other Forms of Liquid Chromatography
- In this section we turn our attention to liquid chromatography techniques in which partitioning occurs by liquid–solid adsorption, ion-exchange, and size exclusion.
- 12.7: Electrophoresis
- Electrophoresis is a class of separation techniques in which we separate analytes by their ability to move through a conductive medium—usually an aqueous buffer—in response to an applied electric field. In the absence of other effects, cations migrate toward the electric field’s negatively charged cathode.
- 12.E: Chromatographic and Electrophoretic Methods (Exercises)
- These are homework exercises to accompany "Chapter 12: Chromatographic and Electrophoretic Methods" from Harvey's "Analytical Chemistry 2.0" Textmap.
- 12.S: Chromatographic and Electrophoretic Methods (Summary)
- This is a summary to accompany "Chapter 12: Chromatographic and Electrophoretic Methods" from Harvey's "Analytical Chemistry 2.0" Textmap.
Thumbnail: Separation of black ink on a thin layer chromatography plate. Image used with permission (CC BY-SA 3.0; Natrij)}