Quick Review Cards for Medical Laboratory Science

Photometric Methods Clinical Chemistry Review 73

METHOD PRINCIPLE COMPONENT PARTS OTHER

Spectrophotometry

Atomic absorption
spectrophotometry

Fluorometry

Chemical rxn produces colored

substance that absorbs light of a

specific wavelength. Amount of

light absorbed is directly propor-

tional to concentration of analyte.

Measures light absorbed by

ground-state atoms.

Atoms absorb light of specific

wavelength & emit light of

longer wavelength (lower

energy).

Light source (tungsten lamp for

visible range, deuterium lamp for

UV), monochromator (diffraction

grating), cuvette, photodetector,

readout device

Hollow cathode lamp, atomizer,

flame, mixing chamber, chopper,

monochromator, detector, readout

device

Light source (mercury or xenon arc

lamp), primary monochromator,

sample holder (quartz cuvettes),

secondary monochromator,

detector, readout device

One of most common methods.

Used for many routine chem-

istry assays. A = 2-log % T.

Hollow cathode lamp with

cathode made of analyte pro-

duces wavelength specific for

analyte. Sensitive. Used to

measure trace metals.

Detector at 90ºto light source

so that only light emitted by

sample is measured. More sen-

sitive than colorimetry. Used to

measure drugs, hormones.

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