Detectors play a vital role in gas chromatography, detecting components as they’re eluted off the column from the sample. There are several different types of detector, each with their own benefits and certain drawbacks.
But which one is the most commonly used? Here’s the answer you’re looking for…
Flame ionization detector (FID)
A flame ionization detection is the most commonly used method for gas chromatography. Broadly speaking, the instrument is used to measure analytes within a gas stream.
It comprises a hydrogen flame, which heats the analyte to ionize it. When it loses an electron, the flame becomes more electrically conductive, which triggers a signal that’s measured by the detector.
How are flame ionization detectors used?
Because they can be used with any gas stream, flame ionization detectors aren’t just applied to gas chromatography. They can be used on their own for gas monitoring and measurement, including landfills and emissions monitoring. That said, gas chromatography systems are their most common accompaniment.
When an FID measures a chemical, it’s typically displayed in terms of methane. In other words, what quantity of methane would produce this response? The quantity of the chemical can then be calculated using the response factor of that chemical, based on its own elemental composition and the amount of current it produces.
Generally speaking, hydrocarbons’ response factors are the same as their molecule’s total carbon atoms. That’s because more carbon atoms equals a higher current.
FID pros and cons
Pros
As the most commonly used detector for gas chromatography, it’s no surprise that FIDs have numerous benefits. Firstly, there’s the cost – they are pretty low-cost both in terms of purchasing and ongoing operation.
When working with an FID, there’s no need for difficult maintenance either. The equipment simply needs cleaning and the FID jet needs replacing if it’s damaged in any way or can’t maintain a flame. Thankfully, said damage doesn’t occur often. FIDs are relatively sturdy and durable.
Finally, they have a good range for both detection and linearity. As such, FIDs can be used to measure very low and very high levels of inorganic substances.
Cons
All that said, they do have some disadvantages too. First and foremost, FIDs are destructive detectors. That means they transform the column effluent, in this case by burning it. As such, they can’t be used for preparatory work.
On top of that, FIDs can’t detect inorganic substances like carbon monoxide and carbon dioxide. However, those substances can sometimes be detected using a methanizer, which reduces them to methane, allowing the FID to detect them.
More on flame ionization detectors
Want to read about FID in action? The article ‘Group-Type Analysis in Jet Fuel and Diesel by Flow Modulated GCxGC-FID’ discusses the use of gas chromatography with flame ionization detection for fuel analysis.
A chromatography detector is a device that detects and quantifies separated compounds as they elute from the chromatographic column. These detectors are integral to various chromatographic techniques, such as gas chromatography,[1] liquid chromatography, and high-performance liquid chromatography,[2] and supercritical fluid chromatography[3] among others. The main function of a chromatography detector is to translate the physical or chemical properties of the analyte molecules into measurable signal, typically electrical signal, that can be displayed as a function of time in a graphical presentation, called a chromatograms. Chromatograms can provide valuable information about the composition and concentration of the components in the sample.
Detectors operate based on specific principles, including optical, electrochemical, thermal conductivity, fluorescence, mass spectrometry, and more. Each type of detector has its unique capabilities and is suitable for specific applications, depending on the nature of the analytes and the sensitivity and selectivity required for the analysis.
There are two general types of detectors: destructive and non-destructive. The destructive detectors perform continuous transformation of the column effluent (burning, evaporation or mixing with reagents) with subsequent measurement of some physical property of the resulting material (plasma, aerosol or reaction mixture). The non-destructive detectors are directly measuring some property of the column eluent (for example, ultraviolet absorption) and thus affords greater analyte recovery.
Destructive detectors
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In liquid chromatography:
In gas chromatography:[9]
In all types of chromatography:
Non-destructive detectors
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Non-destructive detectors in liquid chromatography:[23]
Non-destructive detectors in gas chromatography:[30]
References
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