SPECTROPHOTOMETER

Typical Number in Hospital: 5

Cost Bands: 4,5

References: 9

This is a general term for a class of instruments of which photometers and colorimeters are examples. Spectrophotometry is based on the property of some substances of clinical interest to absorb or emit radiation at characteristic wavelengths. In laboratory applications, the wavelengths involved are ultraviolet (200-400 nm) or infrared (700-800 nm), but the majority are in the visible range (400-700 nm). The spectrophotometer usually has four main components: a light source, a wavelength selector (a filter, prism, or diffraction grating), a sample chamber (cuvette), and a detector and readout device.

The light source may be a hydrogen or deuterium discharge lamp for ultraviolet, or a tungsten filament lamp for other wavelengths. The filter selects a specific range of wavelengths for transmission to the cuvette or detector and may be a special glass or interference filter with layers of dielectric with high and low refractive indices or it may use a prism or diffraction grating as a monochromator from which individual wavelengths with very narrow bandwidths can be selected by rotating the angle between the light source and the detector. The cuvette is usually a special glass or plastic chamber. The detector (photometer) may be a photomultiplier tube or semiconductor device.

flame photometers also exist in which the sample is ionized in a gas flame to emit light or to absorb it by using the flame in place of the cuvette. flame photometers determine the concentrations of pure metals. The absorption type of flame photometer is sometimes called an atomic absorption spectrophotometer.

In a colorimeter the particular chemical is identified after mixing with a specific reagent to produce a material with a characteristic colour or wavelength for easier identification in the spectrophotometer. Since only a single colour is to be detected these normally use filters rather than monochromators.

Spectrophotometers are found in the clinical chemistry department for the chemical analysis of samples taken from blood, urine, the tissues, and other body fluids.