Using a Solvent Triangle to Optimize an HPLC Separation
One strategy for finding the best mobile phase for an HPLC separation is to use the solvent triangle, which allows us to explore a broad range of mobile phases with just seven […]
Illustration
Finding the Area for Overlapping Chromatographic Peaks
In a GC analysis the area under the peak is proportional to the amount of analyte injected onto the column. The peak’s area is determined by integration, which usually is handled by […]
GC-MS
The figure below provides a block diagram of a typical gas chromatography-mass spectrometer (GC–MS) instrument. As illustrated here, a three component mixture enters the GC. When component A elutes from the column, it enters […]
Electron Capture Detector
Shown here is a schematic diagram of electron capture detector (ECD) for gas chromatography. The detector consists of a β-emitter, such as 63Ni. The emitted electrons ionize the mobile phase, which is […]
Flame Ionization Detector
The schematic diagram below shows a flame ionization detector for gas chromatography. The eluent from the column mixes with H2 and is burned in the presence of excess air. Combustion of organic […]
Thermal Conductivity Detector
One of the earliest gas chromatography detectors takes advantage of the mobile phase’s thermal conductivity. As the mobile phase exits the column it passes over a tungsten-rhenium wire filament (see figure below). […]
GC Injectors
Shown here is a schematic diagram of a heated GC injector port for use with packed columns. The needle from the syringe pierces a rubber septum and enters into the top of […]
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 […]
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 […]
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 […]