by What are detectors in chromatography
A chromatography detector is a device used in GC or LC to detect components of the mixture being eluted off the chromatography column. 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 UV absorption) and thus affords greater analyte recovery.
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A chromatography detector is a device used in gas chromatography (GC) or liquid chromatography (LC) to detect components of the mixture being eluted off the chromatography column.
The detector is a critical component in the chromatograph. The detector translates and provides information gathered by the chromatograph in a format usable to the technician. This information can then be stored and used by recording devices and computers, allowing technicians to analyse the data and make crucial decisions.
The important characteristics of chromatography detectors are as follow:
- Sensitivity
- Linear range
- Preferably Non-destructive
- Adequate stability and reproducibility
- Good range of temperature
- High reliability
- Low noise
- Small peak value to avert peak broadening and the resultant loss of resolution
- Short response time with an independent flow rate
Detectors used in gas chromatography
There are a few different kinds of gas chromatography detectors used in gas chromatography. Below are some of the most common.
- Thermal Conductivity Detector (TCD).
- Flame Ionization Detector(FID).
- Thermo Iconic Detector.
- Flame Photometric Detector.
- Ultraviolet Detector..
- Radio Flow Detector.
Thermal Conductivity Detector
The thermal conductivity detector (TCD) is a general detector that can be used for both organic and inorganic compounds. It produces a signal by measuring the thermal conductivity of the carrier gas/analyte mixture leaving the GC column.
Flame Ionization Detector (FID)
Flame-ionization detection (FID) is a good general detector for organic compounds in GC that detects the amount of carbon in a sample. After the column, samples are burned in a hot, hydrogen-air flame. Carbon ions are produced by the combustion.
The flame ionization detector, or FID, is perhaps the most popular of all gas chromatography detectors. FIDs are widely appreciated for their steadfast dependability and sensitivity when detecting organic vapours.
The FID is the most common detector used in gas chromatography. The FID is sensitive to and capable of detecting compounds that contain carbon atoms (C), which accounts for almost all organic compounds. However, the FID is not sensitive to carbon atoms with a double bond to oxygen, such as in carbonyl groups and carboxyl groups (CO, CO2, HCHO, HCOOH, CS2, CCl4, etc.).
Thermo Iconic Detector
Thermo ionic detectors, or TIDs, are not as widely used as FIDs and TCDs. These detectors are used to gauge and measure the presence of compounds featuring phosphorous or nitrogen atoms.
Flame Photometric Detector
This analytical discrimination gives the pulse flame photometric detector the ability to selectively, and sensitively detect some analytes co-eluting in the presence of others.
Similar to thermo iconic detectors, flame photometric detectors (FPDs) are used for select applications. These devices detect components with phosphorous or sulfuric atoms.
Ultra Violet Detector
Analytes arrive in the flow cell and are exposed to VUV light from a deuterium lamp. Specially coated reflective optics paired with a back-thinned charged coupled device (CCD) enable the collection of high quality VUV absorption data.
Radio Flow Detector
Radio flow detectors measure the radioactivity of the effluent. This detector can be destructive if a scintillation cocktail is continuously added to the effluent
Detectors used in HPLC
Like gas chromatography, there are many different kinds of HPLC chromatography detectors.
Different types of HPLC detectors are used to generate a signal proportional to the amount of sample mixture that emerges from the HPLC column, allowing for quantitative sample analysis.
Some common detectors used in HPLC chromatography are:
- Ultraviolet Detector.
- Photodiode array detector.
- Fluorescence Detector.
- Refractive Index Detector.
- Radio Flow Detector.
- Chiral Detector.
Ultraviolet Detectors
UV detectors are used with high performance liquid chromatography to detect and identify analytes in the sample. A UV visible HPLC detector uses light to analyze samples. By measuring the sample’s absorption of light at different wavelengths, the analyte can be identified. HPLC UV detectors can be used by any lab using HPLC, including genomic, biology, and biochemistry laboratories, to analyze nucleic acids, proteins, and to do toxic and therapeutic drug testing. Two types of HPLC UV detectors are single and variable wavelength detectors. Single wavelength detectors measure the samples absorption of a single wavelength, while variable wavelength detectors measure absorption of multiple wavelengths and are therefore more sensitive. When deciding on a HPLC UV detector, consider whether a single wavelength will be sufficient or if a variable wavelength detector is needed. The wavelength range that can be used and the sensitivity of the detector should also be factored into the decision.
Photodiode array detector:
A common type of detector in HPLC is the photodiode array (PDA) detector, sometimes called a diode array detector (DAD). With a PDA detector, researchers can gather information about the sample separations’ identity, quantity, and purity as they exit the HPLC column. PDA is the broadly used detector in HPLC to record absorbance in the range of the ultraviolet and visible (UV-VIS).
Fluorescence Detector
Fluorescence detectors irradiates the effluent with a light of set wavelength and measure the fluorescence of the effluent at a single or multiple wavelengths.
Refractive index detector (RI or RID)
RI detectors monitor the difference in RI between the column eluent containing analyte and a reference stream containing mobile phase only. These detectors are the closest to universal detectors in HPLC because any solute can be detected as long as its RI is different from that of the mobile phase.
Radio Flow Detector
Radio flow detectors measure the radioactivity of the effluent. This detector can be destructive if a scintillation cocktail is continuously added to the effluent.
Chiral Detector
Chiral detectors continuously measure the optical angle of rotation of the effluent. They’re used only when chiral compounds are being analysed.
