Detectors used in high performance liquid chromatography
Detector plays a very important role in High-performance liquid chromatography (HPLC) to detect the compound from the sample solution. there are multiple types of detectors are used in HPLC as per their uses.
There are 11 types of detectors used in HPLC :
- Refractive index detectors
- Ultraviolet detectors
- Fluorescent detectors
- Transport detectors
- Electrochemical detectors
- Electric conductivity detectors
- Liquid light scattering detectors
- “Advanced detectors”
- Aerosol based detectors
- Chiral detectors
- Pulsed Amperometric detectors
Let’s understand detectors used in high-performance liquid chromatography:
- Refractive Index detectors: A solute’s ability to modify the RI of the mobile phase is required for detection. The detector can be very useful for detecting non-ionic compounds that don’t absorb in the UV region or fluoresce. Christiansen effect detectors, interferometer detectors, and thermal lens detectors are all types of RI detectors.
- UV detectors: These are the most common detectors used in HPLC. Most organic compounds absorb in the visible or ultraviolet range of the spectrum. All of them are based on Beer-Lambert law. There are two types of UV detectors: single wavelength and multi-wavelength. Detectors of this type are of two types: Dispersion detectors and Diode Array Detectors (DADs). Detector for separation of carboxylic acids and fatty acids. In traditional medicine, DAD is used to identify poisons.
- Fluorescence detectors: In terms of sensitivity, specificity, and selection, these detectors are the best available today. The flow cell can detect a single molecule. UV detectors have a sensitivity 10 to 1000 times higher than strong UV absorbing materials. There are 3 types: single wavelength: has a sensitivity of ~ 1 X 10 exp-9 g/ml. This is a multivariable FL detector. The most sensitive optical technique is the laser-induced FL detector. LIFD is typically used with Capillary Electrophoresis.
- Transport detectors: Moving wires, chains, and discs. The transport detector extracts the solute from the mobile phase and places it on its metal surface.
- Electrochemical detectors: These detectors detect substances that can be oxidized or reduced. At the surface of the electrode, a reaction occurs. The generation of electrons results in the production of a signal. There are two types of detectors: dynamic detectors and equilibrium detectors. A dynamic or amperometric approach used in multi-electrode array detectors that allow simultaneous detection of several analytes using each electrode in the array at a different potential. This detector detects and separates neuroactive substances. Equilibrium detectors measure the conductance of flowing streams, which change with solutes and are recorded by these devices.
- Electrical conductivity detector: This detector used to determine alkali and alkaline earth cations.
- Liquid light scattering detectors: The operation of these detectors is based on the measurement of scattered light. There are two types. Scattering of laser light at a low angle, and scattering of laser light at multiple angles. Large molecules can be measured simply and accurately with LALLS. In MALLS, the intensity of scattered light depends on the particle’s size, shape, material, orientation, and internal structure.
- Advanced detectors: LC-MS is extremely sensitive. The technique is used to identify chemicals of specific masses i.e. complex mixtures. Typically used in bioanalysis and drug development. Eg. Study of pharmacokinetics, peptide mapping, glycoprotein mapping, and decomposition of natural products.
- Aerosol-based detectors: These include: Evaporative Light Scattering Detectors (ELSD) Charged Aerosol Detectors (CAD) and Nano Quantity Aerosol Detectors (NQADs). ELSD is used to analyze compounds such as caffeine, carbohydrates, lipids, surfactants, polymer blends, and copolymers. A CAD model can be applied to virtually any non-volatile or semivolatile compound, such as pharmaceuticals, lipids, proteins, steroids, surfactants, carbohydrates, polymers, and oligosaccharides. Ibuprofen, estradiol, and other well-known drugs are all tested by CAD. Drug impurities, degradation products, & expedients can be found using NQAD. NQAD is applicable to the analysis of non-volatile & semi-volatile compounds such as amino acids, carbohydrates, cations, and
- Chiral Detectors: It can be used to detect asymmetric carbon atoms in optically active compounds. The two detection techniques are optical rotary dispersion and circular dichroism. ORD detectors are used to test compounds such as amino acids, analgesics, diuretics, vitamins, and flavors such as camphor, orange oil, and lemon oil. CD detectors distinguish enantiomers. CD detectors can detect chiral compounds with UV absorption in the range of 220-420nm. UV+CD signals enable optical purity determination without chiral separation. Circular dichroism can be used to measure compounds such as flavanone, sugar, trans-stilbene oxides, and pindolol.
- Pulsed Amperometric detectors: An important application of the PAD technique is the separation & detection of polar aliphatic compounds that have poor detection properties & require derivatization for optical measurements. Compounds containing amine, alcohol or sulfur moieties as well as carbohydrates can be detected using PAD.
These are a total of 11 types of Detectors used in high performance liquid chromatography as per their uses in pharmaceuticals and other industries.
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