Common detector types

Detectors usually refer to devices that measure changes in the effluent composition of a column and its amount. Used to distinguish, record, or indicate changes in a variable in the environment, such as temperature, pressure, charge, electromagnetic radiation, nuclear radiation, particles, or molecules. Common detectors are the following:

1. Thermal Conductivity Detector The thermal conductivity detector (TCD) is a concentration detector, ie the detector response is proportional to the component concentration in the carrier gas. Its basic principle is based on the fact that different substances have different thermal conductivity coefficients and they respond to almost all substances. They are currently the most widely used universal detectors. Because the sample is not destroyed during the test, it can be used for preparation and other identification techniques.

2. Hydrogen Flame Ionization Detector The hydrogen flame ionization detector (FID) uses organic matter to form a ion stream by chemical ionization under the action of a hydrogen flame, and is detected by measuring the intensity of ion current. The detector has high sensitivity, wide linear range, non-demanding operating conditions, low noise and small dead volume. It is a commonly used detector for organic compound detection. However, the samples are destroyed during the test, and generally only those organic compounds that burn in the hydrogen flame and generate a large amount of carbocations can be detected.

3. Electron capture detector Electron capture detector (ECD) is the ability to capture electrons using electronegative substances and is detected by measuring electron flow. ECD has the characteristics of high sensitivity and good selectivity. It is an exclusive detector and is the most effective detector for the analysis of trace amounts of negatively charged organic compounds. The more electronegative the element, the higher the sensitivity of the detector. It contains halogen, sulfur, oxygen, carbonyl, amino groups. And other compounds have a high response. Electron capture detectors have been widely used in the determination of organochlorine and organophosphorus pesticide residues, metal complexes, organometallic polyhalogens or polysulfide compounds. It can use nitrogen or argon as the carrier gas, the most commonly used is high purity nitrogen.

4. Flame Photometric Detector The flame photometric detector (FPD) has relatively high sensitivity and selectivity for sulfur-containing and phosphorus-containing compounds. The detection principle is that when phosphorus and sulfur-containing substances are burned in a hydrogen-rich flame, a characteristic spectrum is emitted, and the intensity of the characteristic light is measured by a photomultiplier through an interference filter.

5, Mass Spectrometer Detector Mass Spectrometer Detector (MSD) is a quality, universal detector, and its principle is the same as mass spectrometry. It not only gives the chromatograms (total ion chromatograms or reconstructed ion chromatograms) that can be obtained with a general GC detector, but also gives the corresponding mass spectrum for each chromatographic peak. The automatic search of the standard library by the computer can provide the information of the compound analysis structure, so it is an effective tool for qualitative GC analysis. Often referred to as chromatography-mass spectrometry (GC-MS) analysis, it combines the high resolution of chromatography with the structural identification capabilities of MS.