Clinical Chemistry 1
Analytic Techniques and instrumentation - provide the foundation for all measurements made in a
modern clinical chemistry laboratory.
The majority of techniques fall into one of four basic disciplines within the field of analytic chemistry:




Spectrometry
Atomic Absorption
Luminescence
Electroanalytic methods
Spectrophotometry

The instruments that measure electromagnetic radiation have several concepts and
components in common.
Photometric instruments

Measure light intensity without consideration of wavelength.
Most instruments today use filters (photometers), prisms, or gratings (spectrometers) to select (isolate)
a narrow range of the incident wavelength. Radiant energy that passes through an object will be
partially reflected, absorbed, and transmitted.
Electromagnetic Radiation

is described as photons of energy traveling in waves. The relationship between wavelength and
energy E is described by Planck's formula:
E=hv
Three Types of Spectra



Atoms line spectra
Molecules band spectra
Solids continuous spectra
Beer Law



The relationship between absorption of light by a solution and the concentration of that
solution has been described by Beer and others.
States that the concentration of a substance is directly proportional to the amount of light
absorbed or inversely proportional to the logarithm of the transmitted light.
Percent transmittance (%T) and absorbance (A) are related photometric terms that are
explained in this section.
Spectrophotometer

used to measure the light transmitted by a solution to determine the concentration of the
light-absorbing substance in the solution.
Components of a Spectrophotometer
Light Source

The most common source of light for work in the visible and near-infrared regions is the
incandescent tungsten or tungsten-iodide lamp.
The lamps most commonly used for ultraviolet (UV) work are the


deuterium discharge lamp
mercury arc lamp.
Deuterium

provides continuous emission down to 165 nm
Low-pressure Mercury Lamps

Emit a sharp line spectrum, with both UV and visible lines.
Medium and high-pressure Mercury Lamps

Emit a continuum from UV to the mid-visible region.
The most important factors for a light source are;

Range, spectral distribution within the range, the source of radiant production, stability of the
radiant energy, and temperature