Various Types of HPLC Detectors
HPLC detectors used in analysis of different types of samples having different chemical nature.
HPLC detectors are used in the detection of the solute present within the eluent coming from the HPLC column. they’re capable of determining the identity and concentration of eluting compounds within the mobile phase. There are specific detectors which answer a selected compound and their response isn’t hooked in to mobile phase composition. However, the response of the bulk-property detectors depends on the collective changes within the composition of the mobile phase and sample.
HPLC is basically a highly improved form of column liquid chromatography. Instead of a solvent being allowed to drip through a column under gravity, it is forced through under high pressures of up to 400 atmospheres.
There is a broad range of detectors available for various sample requirements. a number of the crucial features required of a detector include sensitivity, a linear response and either a universal or selective response. Some of the desirable features required in HPLC detectors are:
1. It should have either specific or general response to compounds during a mixture.
2. Sensitivity towards solute over mobile phase.
3. It should have a response to solute and not the mobile phase.
4. It should have a coffee cell volume for memory effects minimization.
5. It should respond linearly to solute concentration.
6. Low detector noise and detection limits.
7. It shouldn’t contribute to zone spreading.
8. It should be not be suffering from temperature variation and flow .
The different sorts of detectors are categorized into two, i.e. specific and bulk property detectors.
A) Specific HPLC Detectors
1. spectroscopy HPLC Detectors
Mass spectroscopy detectors offer very high selectivity and sensitivity and their detection is predicated on molecular fragmentation by electric fields and separation supported the mass to charge ratio of fragmented molecules. New application areas are introduced by the LC-MS technique because of its advantages in terms of sensitivity and determination .
2. UV/VIS HPLC Detectors
They are of three types, i.e. fixed wavelength detectors, variable wavelength detectors and therefore the diode array detectors. UV-VIS Detectors have mostly used detectors thanks to its specific response to the category of compounds or particular compounds counting on the functional groups of eluting molecules that absorb light, although some compounds with no light absorbing groups give suitable response after post-column derivatization to introduce light absorbing entities. A beam of the electromagnetic wave is skilled the detector flow cell and thanks to this interaction, it experiences a change in intensity and therefore the measurement of this particular changes is that the basis of most optical detectors.
3. Photo Diode Array (PDA) HPLC Detectors
A large number of diodes serving as detector elements makes it possible for simultaneous monitoring of the many absorbing components at differing wavelengths, with little time and reduced cost spent on expensive solvents.
4. Fluorescence HPLC Detectors
They are most specific, sensitive and selective, and offers greater sensitivity than the UV-VIS detector. Naturally fluorescent compounds are less as compared to the sunshine absorbing compounds, a limitation solved by post-column derivatization. There are three sorts of fluorescent detectors, namely the single wavelength fluorescent detector, multi-wavelength fluorescent detector and laser-induced fluorescent detector.
B) Bulk Property HPLC Detectors
1. Electrical Conductivity HPLC Detectors
They provide reproducible, universal and high sensitivity detection of the charged species and surfactants. The detectors measure the conductivity of the mobile phase, therefore are classified as bulk property detectors. Their sensors contains the flow-through cell with few microliters of the quantity containing 2 electrodes, usually made from chrome steel , platinum or a metallic element utilized in the determination of alkali and alkali earth metals.
2. Refrective Index HPLC Detectors
There are various sorts of RI detectors which include, the Christiansen effect detector, interferometer detector, thermal lens detector and therefore the dielectric constant detector. they need limited sensitivity and detection depends on the changes in index of refraction of eluting molecules within the mobile phase. These detectors are used for detecting non-ionic compounds that neither fluoresce nor absorb within the UV region. Temperature control is required thanks to high-temperature sensitivity.
3. Electrochemical HPLC Detectors
The detectors are often classified into two, which are the equilibrium and therefore the dynamic detectors. They answer oxidizable or reducible substances and are sensitive to changes in flow or composition of the mobile phase. The reaction takes place on the surface of the electrode producing electrical signals. Their suitability will depend upon the volumetric characteristics of the solute molecules within the aqueous or organic mobile phase. They require the working electrode, reference electrode and therefore the auxiliary electrode.
4. Light Scattering HPLC Detectors
Light scattering detectors are of two types which include low angle laser light scattering detector and therefore the multiple angle laser light scattering detector. They are supported measuring the scattered light and are useful for detection of huge relative molecular mass molecules present within the eluent, which is examined by being skilled an appropriate sensor cell counting on molecular sizes. Other sorts of HPLC detectors are the evaporative light scattering detectors, IR detector, transport detectors, aerosol-based detectors, chiral detectors and therefore the pulsed amperometric detectors.
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