Chrominfo: HPLC detectors and types of HPLC detectors

The detector is the tool used to identify the analytes eluted from the column. It is transforming the effluents into the electrical signal and recorded by the system.

There are different detectors are used in the LC analysis as below.

• UV/VIS and PDA Detector:

The UV/VIS and PDA detectors use as an absorbance detector, UV/VIS measure the ability of analytes to absorb the light at a particular wavelength in the UV/VIS range and PDA is monitoring the absorbance of analytes at several different wavelengths. It detects every compound having absorbance more than the zero this is the advantage of the PDA and the analytes with no UV activity cannot be detected.

The types of UV/VIS detectors available are as follows.

1-Fixed Wavelength Detector

Absorbance monitor at only one wavelength and which do not permit 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

Single wavelength monitors at any given time, but any wavelength from UV range can be selected. This type of detector is more sensitive than the fixed wavelength detector, it vagaries from 190-900 nm and used for a wide range of compounds.

• Refractive Index Detector:

Refractive index is the universal detector in HPLC because of its detection capabilities, RI Detectors measure the refractive index of (analytes) column eluent passing through the flow cell it is based on the two principal one is deflection and another is a reflection type refractometer.

Some advantages of a refractive index detector are as follows.

1. It Senses low to the air bubble and dirt in the cell.

2. Covers the whole range of the refractive index.

3. Detect everything with RI different from the 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 to provide structural information about analytes and also use to calculate the low detection limit of molecular components. It combines the best sensitivity with the most identification ability.

• Fluorescence Detector:

The compound with fluorescence can be measured by fluorescence detectors. The fluorescence detectors have better sensitivity than the UV/VIS detectors because of its high sensitivity to the selective groups of compounds at definite lambda max. It requires a high intensity of the light to detect the analytes.

• Electrochemical Detector:

The electrochemical detector uses to measure the electrochemical properties of the analytes on the base of electrochemical oxidation. It is a simple, convenient and sensitive detector. There are three electrodes are working for the detection i.e working electrode, auxiliary electrode, and a reference electrode.

• Conductivity Detector:

This type of detector used in ion chromatography to determine the electronic resistance in proportion to the concentration of ions present in solutions.

• Light Scattering Detector:

The detection of light scattering does not require analytes to have chromophores. the method of light scattering will not work with volatile analytes. It uses full for the detection of high molecular weight analytes; it also works with the gradient method. The nebulization, mobile phase evaporation, and detection are the steps that are 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.

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Tuesday, April 24, 2018

HPLC detectors and types of HPLC detectors

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