spectroscopy
- - June 26, 2017
Absorption of light correlates to the energy of a photon that is taken-up by electrons of the substance atom. The electromagnetic energy is transformed into internal energy of the absorbent substance. The absorbance of a substance quantifies how much of the incident light is absorbed by it (instead of being reflected or refracted). Precise measurements of the absorbance at many wavelengths allow the identification of a substance via absorption spectroscopy, where a sample is illuminated from one side, and the intensity of the light that exits from the sample in every direction is measured (see Fig. 1). A few examples of absorption are ultraviolet–visible (UV-Vis) spectroscopy or infrared (IR) spectroscopy.
- - June 26, 2017
The use of fluorescent probes in cell physiology has emerged as indispensable tool in the analysis of cell functioning over recent years. The physics underlying fluorescence is illustrated by the electronic-state diagram (so-called Jablonski diagram, see Fig. 1), showing the three-stage process to create the fluorescent signal (Excitation - Excited/State Lifetime - Fluorescence Emission) in a fluorophore/indicator and simplified described below.
Fig. 1– Jablonski diagram illustrating the processes of fluorescence by absorption of higher photon energy by a fluorophore and subsequent emission of lower photon energy, resulting in fluorescence during the fluorescence-lifetime.
Fluorescence is obtained when an excitation photon (hνEX) from an external source, such as a high-power LED, is absorbed by a fluorophore that elevates its energy (S1’). During the fluorescence-lifetime, the elevated energy (S1’) decays to a lower energy state S1. Then, fluorescence results in the emission of a photon...more
- - June 26, 2017
Absorption of light correlates to the energy of a photon that is taken-up by electrons of the substance atom. The electromagnetic energy is transformed into internal energy of the absorbent substance. The absorbance of a substance quantifies how much of the incident light is absorbed by it (instead of being reflected or refracted). Precise measurements of the absorbance at many wavelengths allow the identification of a substance via absorption spectroscopy, where a sample is illuminated from one side, and the intensity of the light that exits from the sample in every direction is measured (see Fig. 1). A few examples of absorption are ultraviolet–visible (UV-Vis) spectroscopy or infrared (IR) spectroscopy.
Fig 1. Concept of absorbance spectroscopy using white light and optical components to filter out light of a specific wavelength that interacts with molecules in the solution. Absorbance at this specific wavelength by the molecules in the solutions is detected as a decrease in light intensity...more
- - April 30, 2013
Cuvettes come in a variety of shapes and sizes, but one of the most important specifications of a cuvette is its Z-dimension. The Z-dimension of an instrument (cuvette holder or spectrometer) is the distance from the bottom of the cuvette chamber floor to the center of its light beam (see image). A cuvette’s Z-dimension must match the Z-dimension of the instrument with which it will be used. Each manufacturer designs its instruments with a specific Z-dimension. Common Z-dimensions include 8.5 and 15mm, and sometimes 20mm. When purchasing small volume cuvettes, the correct Z-dimension becomes critical. Matching the Z-dimension of the cuvette to the Z-dimension of the instrument ensures that the light beam passes through the center of small samples.The table below shows the standard Z-dimension of the spectrometer sample compartments for many manufacturers.
...moreMANUFACTURER
Z-DIMENSION Agilent® 15 mm Avantes® 15 mm Beckman® 8.5 mm Bio-Rad® 8.5 mm Cecil® 15 mm Eppendorf® 8.5
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