Elements of a Spectrometer

A spectrometer uses wavelengths to measure light intensities. Light from a source passes through a subject to be diffracted into a spectrum. The diffracted light is identified by a sensor and then interpreted, usually as data on a graph. Although a spectrometer can operate over a wide range of wavelengths, if it uses the visible spectrum it is called a spectrophotometer.

Light Source

• The light source varies, depending on the type of the spectrometer and the spectral region it is using. Light emitting diodes are often used for the visible spectrum of wavelengths. A tungsten filament or deuterium arc lamp may be used for ultraviolet spectrometers. The light radiation source may also either be single beamed or double beamed. A single-beam spectrometer passes all of the light through the subject. A double-beam source splits the light into two beams before it reaches the subject. One passes through it, and the other one is used for reference.

Subject

• The subject through which the light of a spectrometer passes through depends on its application. It is often used in solution chemistry in determining the presence, concentration and charge of various atoms. For example, light passing through a solution with transition metals can excite the metal ions into another electron state and produce specific colors indicative to their presence. Light passing though organic compounds can help determine if they are water soluble, or soluble in ethanol.

Detector

• The detector is found at the end of the light path. The detector absorbs photons of light and generates an electrical signal; the strength of the signal is a measure of the amount of photons absorbed and, therefore, an indication of the wavelength. The type of detector varies with the spectral region of the spectrometer. A spectrophotometer, for example, uses a charge coupled device. A charged coupled device is a type of image sensor that is programed for the visible range of wavelengths.

Interpreter

• The interpreter receives the data from the detector and then presents in it a viewable format. Generally, the information is displayed on computer screens in the forms of graphs. Wavelength measurements are typically on the x axis of the graph, and transmittance or absorbance on the y axis, although the software used will be specified to the type of spectrometer collecting the data.