The detector is the module of the hplc system used to identify analytes eluted from the column. It transforms the effluents into the electrical signal and is recorded by the system. There are different detectors that are used in LC analysis as shown below..
• UV/VIS and PDA Detector:
UV/VIS and PDA detectors are used as absorbance detectors, UV/VIS measures the ability of analytes to absorb light at a particular wavelength in the UV/VIS range, and the PDA monitors the absorbance of analytes at various different wavelengths. Detects all compounds that have an absorbance greater than zero; this is the advantage of PDA and analytes without UV activity cannot be detected. The types of UV/VIS detectors available are as follows.
1-Fixed Wavelength Detector:
Absorbance monitor at a single wavelength and that does not allow to modify/change it called fixed wavelength detector. This is a cheap and simple detector, but it detects limited types of compounds.
2-Variable Wavelength Detector:
2-Variable Wavelength Detector: Monitors a single wavelength at any one time, but any wavelength in the UV range can be selected. This type of detector is more sensitive than the fixed wavelength detector, it ranges from 190 to 900 nm and is used for a wide range of compounds.
• Refractive Index Detector:
The refractive index is the universal detector in HPLC due to its detection capabilities. RI detectors measure the refractive index of the column solvent (analytes) passing through the flow cell. It is based on the two main ones, one is deviation and the other is reflection type refractometer. Some advantages of a refractive index detector are as follows.1. Detects low to air bubble and dirt in cell.2. Covers the entire range of the refractive index.3. Detect everything with RI different from solvent, RI has low sensitivity.
• Mass Detector (LC-MS):
It is a combined analytical chemistry technique for the physical separation of liquid chromatography with mass spectroscopy. This is an important technique for providing structural information about analytes and also for calculating the low detection limit of molecular components. It combines the best sensitivity with the highest identification capacity.
• Fluorescence Detector:
The fluorescing compound can be measured by fluorescence detectors. Fluorescence detectors have better sensitivity than UV/VIS detectors due to their high sensitivity to selective groups of compounds at defined lambda maxima. High light intensity is required to detect analytes.
• Electrochemical Detector:
The electrochemical detector is used to measure the electrochemical properties of analytes based on electrochemical oxidation. It is a simple, convenient and sensitive detector. There are three electrodes that work for detection, that is, a working electrode, an auxiliary electrode and a reference electrode.
• Conductivity Detector:
This type of detector is used in ion chromatography to determine the electronic resistance in proportion to the concentration of ions present in solutions.
• Light Scattering Detector:
Light scattering detection does not require analytes to have chromophores. the light scattering method will not work with volatile analytes. Full is used for the detection of high molecular weight analytes; also works with the gradient method. Nebulization, mobile phase evaporation, and detection are the steps involved in a light scattering detector.
• Infrared Detector:
For the absorbance, there are two types of the detector are available, the wavelength scanning detector provides by semicircular filter wedges, between the wavelengths ranges 4000 to 960 cm–1. It is used to a limited extent only for non-polar lipid analysis with the specific absorbance between the 1650 to 1860 cm–1. The other type is the Fourier transform, it is more sophisticated.
