Components of UV/Visible Spectrophotometer

Components of UV/Vis Spectrophotometer

Learning Outcomes

Wavelength Selector

INTRODUCTION

• For most spectrosopic analysis, radiation that consists of a limited and narrow band of wavelength is required.

• A narrow band enhances both sensitivity and selectrivity of the instrument.

• The effective bandwith is a measure of the quality of the wavelength selector.

• The ideal wavelength selector has a high throughput of radiation and a narrow effective bandwidth.

RADIATION FILTERS

MONOCHROMATORS

• FUNCTION

• HOW IT WORKS?

Grating

Prism

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SOURCE

RADIATION SOURCE

Source of Electromagnetic Radiation

• A source of electromagnetic radiation must be intense and stable in the desired electromagnetic spectrum region .
• Sources of electromagnetic radiation are classified as either continuum or line sources.

Continuum Source in the UV/Vis Region

How the lamps work?

Hydrogen & Deuterium Lamps

Tungsten/ Halogen Lamp

1. Deuterium (or hydrogen) is stimulated by electrical energy.
2. Excited molecules is produced.
3. Excited species is dissociated to 2 deuterium (or hydrogen) atoms plus UV photons.

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DETECTORS

INTRODUCTION

• Detectors is used to convert a signal consisting of photons into an easily measured electrical signal.

• Ideally the detector’s signal, S, should be a linear function of the electromagnetic radiation’s power, P,

S = kP + D where k is the detector’s sensitivity, and D is the detector’s dark current, or the background electric current when all radiation from the source is blocked from the detector.

• Widely used detectors in UV/Vis spectrophotometer are phototubes and photomultiplier tubes (PMT)

PHOTOTUBE

What is photoelectrons?

(4)

(1)

(2)

What is photocurrent?

(3)

PHOTOMULTIPLIER TUBE

(3)

D 7

(5)

D8

D6

D4

D2

D8

D6

(1)

D4

D5

D2

D3

D 7

D5

D1

(4)

(2)

D1

D3

Conclusions

Advantage of PMT

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