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A spectrophotometer is a photometer that detects the composition of substances. It does this by passing light through a substance and comparing before and after wavelength characteristics. Typically, a single beam spectrophotometer projects one beam of visible, near-ultraviolet (UV) or near-infrared (IR) light through liquids, solids, and gases, to analyze beam absorption and intensity changes. A double beam device compares the test beam with a second reference beam, and is often viewed as an easier, more stable improvement on the technology. The single beam variety, however, offers certain advantages; these include a simpler, more compact design, a larger dynamic range, and greater versatility.
Often resembling a desktop printer, the device is employed across industries and sciences. In typical spectrophotometers, light emits from a source such as tungsten filament, light-emitting diode, or xenon arc, depending on the required spectral traits. The beam hits a grating, where it reflects and disperses in another direction. This passes through an aperture and then the substance in question.
An electronic light detector captures the diffracted beam. The light energy is converted to electrical energy, and the resulting voltage fluctuations are analyzed on a computer. Computer software then translates the spectral wavelength characteristics. With a single beam spectrophotometer, the resulting spectral characteristics are compared to the initial beam, with changes and discrepancies detected. This allows the equipment to evaluate the composition of the substance.
Usually, a single beam spectrophotometer is sufficient for conducting analyses of the UV-visible light range. Formulas can be applied to selectable, single-wavelength absorptions to help calculate and infer compositions. Using a fixed or continuous light source, these devices may rely on simple solid state diode emitters and detectors to apply beams consistently for repeatable processes.
Fewer components mean single-beam devices are less costly to purchase or operate. They are less complex, so they may introduce fewer operational inconsistencies. Software assists in analysis and plotting resulting graphs; equipment is capable of rapid absorbency calculations and baseline correction of data.
Modern devices can determine substances from thousands of reference spectra stored in memory. Compact equipment can more easily be transported for field use and on-site applications, such as monitoring CO2 concentrations in greenhouses. Available in a variety of shapes and sizes, single beam spectrophotometer equipment requires less precision than double-beam types, and is not as sensitive to component flaws and internal dust buildup. Nor does it go through extra lengths of recombining double beams for detection.
With fewer moving parts to wear or get out of alignment, the single beam spectrophotometer is designed for increased stability and reliability. Technical innovations and techniques narrow the advantage of double beam models over this type. Additional developments in electronics and lamp technologies introduce more consistent single beam readings. Regular calibrations and proper equipment maintenance can ensure that single beam detection of a substance's spectral curve fingerprint can be reliably obtained.
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