Types of lc detectors and recorders

A detector is a device used in high performance liquid chromatography (HPLC) to detect components of the mixture being eluted off the chromatography column.
• The detector senses the presence of the individual components as they leave (elute) the column.
• The detectors converts a change in effluents into an electric signal that is recorded by data system

1. TYPES OF LC DETECTORS AND RECORDERS

2. A detector is a device used in high performance liquid chromatography (HPLC) to detect components of the mixture being eluted off the chromatography column. • The detector senses the presence of the individual components as they leave (elute) the column. • The detectors converts a change in effluents into an electric signal that is recorded by data system. INTRODUCTION

3. High sensitivity. Good stability and reproducibility. A linear response to solute. Should be inexpensive. Capable of providing information on the identity of the solute. A short response time independent of flow-rate. High reliability and ease of operation. IDEAL PROPERTIES OF A DETECTOR

4. Selective detectors (solute property) : These detectors respond to a particular physical or chemical property of the solute, being ideally independent of the mobile phase. They are as follows: Absorbance detectors Fluorescence detectors Electrochemical detectors Mass spectrometric detectors Detectors used in HPLC

5. Universal detectors (bulk property): Measure the difference in some physical property of the solute in the mobile phase. They are generally universal in application but tend to have poor sensitivity and limited range . They are as follow: Refractive index detectors Evaporating light scattering detectors

6. UV/VIS - Fixed Wavelength - Variable Wavelength - Diode array (PDA) Refractive index -Deflection Detector -Refractive Detector (Fresnel refractometer ) Fluorescence Detector Electrochemical Detector Conductivity Detector Evaporative light scattering (ELSD) Mass detector (LC-MS) CLASSIFICATION OF HPLC DETECTORS

7. Measures the ability of solutes to absorb light at a particular wavelength(s) in the ultraviolet (UV) (200-400nm) or visible (400-800nm) wavelength range. When light of a certain wavelength is directed at a flow cell, the substance inside the flow cell absorbs the light. As a result, the intensity of the light that leaves the flow cell is less than that of the light that enters it. An absorbance detector measures the extent to which the light intensity decreases (i.e., the absorbance). ULTRAVIOLET/VISIBLE SPECTROSCOPIC DETECTORS

8. Fixed Wavelength Detector: absorbance of only one given wavelength is monitored by the system at all times (usually 254 nm) Simplest and cheapest of the UV/VIS detectors. Limited in flexibility. Limited in types of compounds that can be monitored. Variable Wavelength Detector: a single wavelength is monitored at any given time, but any wavelength in a wide spectral range can be selected Wavelengths vary from 190-900 nm. More expensive, requires more advanced optics More versatile, used for a wider range of compounds Three Common types of UV/Vis Absorbance Detectors

9. It is an advanced type of UV detector and operates by simultaneously monitoring absorbance of solutes at several different wavelengths. Tungsten and deuterium lamp is used as light source. When the polychromatic light passed through the cell it is divided by diffraction grating and dispersed light guided to PDA The array may contain many hundreds of diodes and the output from each diode is regularly sampled by a computer and stored Photo Diode Array Detector

10. Fluorescence is a phenomenon whereby substance emit light when they themselves are irradiated with light. It is a near-ideal detector for those solutes that exhibit molecular fluorescence. Their sensitivity depends on the fluorescence properties of the components in the elute. FLUORESCENCE DETECTOR

11. Refractive index detector measures the molecule’s ability to deflect light in a flowing mobile phase in a flow cell relative to a static mobile phase contained in a reference cell . The amount of deflection is proportional to the concentration of the solute in the mobile phase. REFRACTIVE INDEX DETECTOR

12. It is based on the measurement of the current resulting from an oxidation/reduction reaction of the analyte at a suitable electrode. The level of current is directly proportional to the analyte concentration. Three electrodes are employed which are: Working electrode Auxiliary electrode Reference electrode ELECTROCHEMICAL DETECTORS

13. Evaporative light scattering detectors are general-purpose detectors that can detect any non-volatile substance by spraying the column eluate to remove the mobile phase by evaporation. Then irradiating the solute with light and detecting the scattered light. It is a universal detector and does not require a compound to have a chromophore for detection. EVAPORATIVE LIGHT SCATTERING DETECTOR (ELSD)

14. There are three steps involved in detection: Nebulization Mobile phase evaporation Detection WORKING The flow from the column is nebulized with a stream of inert gas The mobile phase, which must be volatile, is evaporated, leaving tiny particles of the analytes The particles are passed through a laser beam and they scatter the laser light.

15. MASS SPECTROMETER AS AN HPLC DETECTOR The principle of mass spectrometry (MS) is to generate ions from either organic or inorganic compounds. The molecules are ionized and broken up into many fragments, each kind of ions has a particular mass to charge ratio and detected them qualitatively and quantitatively by their respective (m/z) and abundance.

16. Recorders are used to record the response obtained from the detector after amplification. They record the baseline and all the peaks obtained, with respect to time. Retention time for all the peaks can be calculated. Integrators are improved version of recorder with data processing capabilities. They can record the individual peaks with retention time, height and width of peak area. Recorders and Integrators

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