A detector is a device used in high performance liquid chromatography (HPLC) to detect components as they elute from the chromatography column. Detectors sense individual components, convert changes in effluents to electrical signals, and must have high sensitivity, stability, reproducibility, and response times independent of flow rate. Common detectors include absorbance, fluorescence, electrochemical, and mass spectrometric detectors which respond selectively to solute properties, and refractive index and evaporative light scattering detectors which have universal application but poorer sensitivity.

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.

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.

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

5.  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)

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).

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

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

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.

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.

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

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.

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.  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.

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