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UV/Vis Spectrophotometry
Technique:
UV/Vis Spectrophotometry is a set of analytical techniques using the properties of specific light wavelength absorbance to measure the concentration of particular substance in a target material. Most commonly used for liquids and gases, it can be used for solids.
Application:
This analysis is used for single point analysis of liquids or gases. This makes a very cost effective method for expensive chemicals but is labor intensive. Commonly used for quantization of transition metal ions and organic compounds. Specific analyses include Chemical Oxygen Demand (COD), Ortho-phosphate, Cyanide (CN) and Ammonia (NH4).
The Science Behind:
The most common method for UV/Vis uses a fixed wavelength, meaning that only one wavelength of light is used. To generate this light often a simple incandescent bulb is used. To use the light, several methods are available such as single beam, split beam or chopped beam. This light travels to a sensor, ether a photodiode or CCD.
After the sample is placed in a cell it is then placed inside the instrument, in the light path. A single, specific wavelength of light is shown through the sample, measured for variation in intensity and the variation recorded. The generated result needs to be compared to previously generated response graph called a calibration curve.
Other References:
Wikipedia Definition of Ultraviolet-Visible Spectroscopy
Excellent UV/Vis e-Tutorial
UV/Vis - Part of the electro- magnetic spectrum.
UV stands for ultra-violet or beyond violet a section of the light spectrum most humans are unable to see (10 nm to 380 nm).
Vis stands for visible, which is the section of the light spectrum most humans are able to see (380 nm to 750 nm).
Cell - Also known as a cuvette when used for liquids, a cell is a container for the sample being analyzed of a known material and a specific length for the light path.
Single Beam - is where the result generated is the intensity after passing through the sample.
Split Beam - is where the result generated is the difference between the original beam and the beam after passing through the sample.
Chopped Beam - is where the result generated is the difference between the original beam and the beam after passing through the sample but only a single photodiode is used alternating between the two beams.
Cell - Also known as a cuvette when used for liquids, a cell is a container for the sample being analyzed of a known material and a specific length for the light path.
Single Beam - is where the result generated is the intensity after passing through the sample.
Split Beam - is where the result generated is the difference between the original beam and the beam after passing through the sample.
Chopped Beam - is where the result generated is the difference between the original beam and the beam after passing through the sample but only a single photodiode is used alternating between the two beams.