Ultraviolet–visible spectroscopy (UV-Vis) is a very common technique used for determination of the concentration of substances in a solution. In this way, it enables researchers to work out the reactions rate, equations of reactions rate, and reactions mechanisms.
Although all atoms and molecules will undergo electronic excitation after absorption of light, but most of them usually require very high energy radiation in the ultraviolet range of electromagnetic spectrum with wavelengths not longer than 200 nm. However, the UV region ranges from 200 to 400 nm and the visible region ranges from 400 to 800 nm. In order to absorb light in the region from 200 – 800 nm (UV-Vis spectroscopy), the molecule has to contain either V bonds or atoms with non-bonding orbitals, e.g. π orbitals and electronic transition thereof. Most absorption spectroscopy of organic compounds is based on this electronic transition, i.e. from π electrons to the π* excited state. It is also possible to introduce the π-electron systems (in a form of conjugated system) to a desired solution in order to act as chromophores agents for detection of much wider range of substances. As a consequence, the absorption peaks for any desired substances may fall in the region of the spectrum 200 ~ 800 nm (UV-Vis spectroscopy).
For analyzing given samples by this technique, the samples have to be dispersed into cuvette and placed in the path between a UV-Vis light and a detector. According to a law, known as Beer-Lambert’s law, with a constant light path length and known absorption coefficient, the concentration of an analyte can be determined from the light absorbed by the same analyte.
UV-Vis spectroscopy is used in analytical chemistry for the quantitative determination of different analytes such as transition metal ions, conjugated organic compounds, and biological macromolecules. In the UV-Vis spectroscopy, for example analyzing metal ions concentrations, a respective solution may be better to first be colored or modulated its primary colors by adding some chemicals (particular anions and ligands). This color modulation changes the analyte color (wavelength) so that it falls within UV-Vis detection range. For instance, the color of copper sulfate dilute solution is a very light blue, so its detection by UV-Vis may be problematic. Adding a chemical like ammonia changes the wavelength of maximum absorption to fall within UV/Vis range, therefore, the UV/Vis spectroscopy can easily analyze the cupric ions (as analyte).
One of the important applications of UV-Vis spectrometer is detection of poisonous ions of lead and mercury in environments. Using indicators like DTZ causes the dilute solution containing lead and mercury ions to be clearly painted, and therefore, will be readily detected by UV-Vis. Then, by plotting calibration curve and using UV-Vis, the concentrations are quantitatively calculated. However, if the concentrations are below the threshold detection, the solution may be pre-concentrated before analyzing. The other applications of UV/Vis spectrophotometry are as follows:
- Measuring absorption, transmission or reflection from solid and/ or liquid samples.
- Chemical analysis of solid/liquid samples.
- Chromatic analysis of colors and textiles
- Fluorescence measurement
- Kinetic studies of enzymes in biological science, biochemistry, and pharmaceutical laboratories.
Miniature spectrophotometer offered by the manufacturer is able to work within UV-Vis and NIR range of electromagnetic spectrum (190 to 850 nm). This spectrophotometer can be used in all absorption, transmission, reflection and radiation modes as it has been equipped with optical fiber probes. Using CCD with 2048 and 3648 pixels, multi-purposed, user friendly software, low cost and accessories according to the customer requirements, are some features of this device. Details of technical specifications are presented in the following Table.
UV-Vis spectroscopy is a fast, facile and very reliable method for determination of the concentration of an analyte in a solution. Its application does not limit to the certain domains, rather it cover all fields in natural science including nanotechnology. The point is that an analyte to be analyzed must be prepared as a solution.
- In case of using the spectrometer in reflective mode, connect one head of reflective probe to the light source and the other head to the spectrometer. Make the probe end fixed at a 4 mm vertical distance away from the surface of interest.
- Before running experiment, the dark current, a current establishes when the light source is off, must be calculated. To do so, just click on icon titled Dark in the user interface. Then, the full brightness current, a current establishes when the light source radiates its maximum energy, must be calculated.
- For more details on how to use the device, refer to the device catalog and user guide.
- The apparatus must be installed on the hard surface, in a dry and clean environment.
- The apparatus must be kept away from the vibration-making instrument, such as centrifuge and mixer.
- For air to be properly ventilated around the spectrometer, leave a distance of at least 50 mm between the apparatus and the facing walls.
- Use a proper electrical cable to connect the apparatus to a compatible AC adaptor, and then to connect the AC adaptor to the grounded wall plug outlet.
- After turning on the light source, wait for a while until the apparatus warms up and reaches thermal and electronic stability (it usually takes 4 minutes).
- Temperature changes must lie in a range between 10 and 40 °C.
- Avoid installing the apparatus in a place exposed to electromagnetic radiations or inside electromagnetic fields.
- Cover the tip of the fiber optic connectors with a specific plastic cap to avoid contamination.
- Regular inspections must be done every six months. Ensuring the apparatus cleanliness, correct connection of cables, and regular cleaning of the cuvette are necessary for valid analysis of liquids.
Certificate of Nanotechnology
Standard Date : 2017/11/21
Expire Date : 2020/11/21
Standard Date : 2017/11/21
Expire Date : 2020/11/21