Download detectors used in uv-vis, ir and mass spectroscopy

DETECTORS USED IN UV-VIS, IR
AND MASS SPECTROSCOPY
Presented by
Dr. A. Suneetha
Dept. of Pharm. Analysis
Hindu College of Pharmacy
DEFINITION:
Detector is defined as the device that
identifies and records the signals produced
by the sample components.
An ideal detector has:
• Adequate sensitivity – range 10-18 to 10-15 g
analyte/sec
• Good stability and reproducibility
• Good linearity
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A temperature range from room
temperature to at least 4000C.
A short response time that is
independent of flow rate.
High reliability and ease of use.
Nondestructive of sample.
DETECTORS USED IN
UV-VIS SPECTROSCOPY
Detectors used in UV-Visible
Spectroscopy mainly includes:
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Barrier layer cell or photo voltaic cell
Photo tubes or photo emissive cells
Photo multiplier tubes and
Photo diode array detector
Photo voltaic cell:

Also known as barrier layer cell
 A: Iron base plate
 B: Bi-layer selenium
 C: Thin layer of silver
 D: Glass
 E: Plastic case
ADVANTAGES:
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Simple in design and does not require any
external power supply.
Cheapest and inexpensive of all UV detectors
DISADVANTAGES:
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Amplification of the detector is not possible.
Lesser response of the detector with light
other than blue and red light.
Photo emissive cells:

Also known as Photo tubes.
ADVANTAGES:
• Better sensitivity
than photovoltaic
cell.
• Amplification of the
signal is possible.
PHOTO MULTIPLIER TUBES:
ADVANTAGES:
► PMT are extremely
sensitive i.e., can detect
very weak signals even
200 times than that
could be done using
photovoltaic cell.
► Extremely fast in
response.
Photodiode array detector:
Advantages:
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The wavelength need
not be selected, but
the detector detects
the responses of all the
compounds.
Resolves the problem
of peak purity.
Excellent sensitivity.
DETECTORS USED IN
IR SPECTROSCOPY
Detectors used in IR-spectroscopy mainly
includes:
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Bolometers
Thermocouple
Thermisters
Golay cell
Photo conductivity cell
Semiconductor detectors
Pyroelectric detectors and
Fourier transform systems.
BOLOMETERS:
.
ADVANTAGE:
 Bolometers have
considerable fast
response time(4 milli
sec).
Thermocouple:
Disadvantage:
Response time is slow
compared to
bolometers(60 milli
sec).
Golay cell:
Merits:
• Used for wide wavelength range.
• Linearity in response is seen.
Demerits:
• More expensive and bulky.
Fourier transform system:
Merits:
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Increasing in
sensitivity and
accuracy can be
achieved.
The sample is not
subjected to thermal
effects.
DETECTORS USED IN
MASS SPECTROSCOPY
Detectors used in mass spectroscopy
mainly includes:

Faraday cup detector
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Electron multiplier detector and
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Photographic detector
Faraday cup detector:
Electron multiplier detector:
Photographic detection:
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Photographic detection is used effectively for high
resolution in double focusing spectrometers
References:
• Instrumental methods of chemical analysis-by Gurudeep,
R.Chatwal, Sham k. Anand.
• Text book of pharmaceutical analysis-by S.Ravi Shankar
• Instrumental Methods Of Chemical analysis-by B.K.Sharma
• wikipedia