Page 25 - Instrumental Analysis - Pharm D Clinical- 07-PA403

UV-visible Spectrophotometry

3- Cells (Cuvettes)

• They are rectangular in shape. The most commonly used cell has a
pathlength of 10 mm (1 cm), but longer or shorter pathlengths can be used.
Two faces of the cell are transparent and the other two are opaque.

• Made of quartz for measurement in the UV region. Glass cells are common
for visible range only. Also, plastic is common for visible range if the solvent
does not damage the plastic.

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3- Detector

• A device that transfers optical energy (light) to electrical energy.
• There are two types of detectors:

I- Phototube
II- Photomultiplier tube
• A phototube consists of a semi-cylindrical photocathode and a wire
anode sealed inside an evacuated transparent glass or quartz
envelope. The concave surface of the cathode supports a layer of
photo-emissive material, such as an alkali metal or metal oxide that
emits electrons when irradiated with light. These electrons are
attracted to the positively-charged anode, creating an electric current.

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