Principles and Applications of Fluorescence Spectroscopy
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Contents:
Atomic fluorescence spectroscopy AFS is a method that was invented by Winefordner and Vickers in as a means to analyze the chemical concentration of a sample.
Fluorescence lifetime spectroscopy and imaging
The idea is to excite a sample vapor with the appropriate UV radiation, and by measuring the emitting radiation, the amount of the specific element being measured could be quantified. Cold vapor atomic fluorescence spectroscopy CVAFS uses the same technique as AFS, but the preparation of the sample is adapted specifically to quantify the presence of heavy metals that are volatile, such as mercury, and allows for these elements to be measured at room temperature. The theory behind CVAFS is that as the sample absorbs photons from the radiation source, it will enter an excited state.
As the atom falls back into the ground state from its excited vibrational state s , it will emit a photon, which can then be measured to determine the concentration. For CVAFS, the sample must be digested, usually with an acid to break down the compound being tested so that all metal atoms in the sample are accessible to be vaporized. The sample is put into a bubbler, usually with an agent that will convert the element to its gaseous species.
An inert gas carrier such as argon is then passed through the bubbler to carry the metal vapors to the fluorescence cell. It is important that the gas carrier is inert, so that the signal will only be absorbed and emitted by the sample in question and not the carrier gas. Once the sample is loaded into the cell, a collimated almost parallel UV light source passes through the sample so that it will fluoresce.
A monochromator is often used, either between the light source and the sample, or between the sample and the detector. These two different setups are referred to as excitation or emission spectrum, respectively. In an excitation spectrum, the light source is kept at a constant wavelength via the monochromator, and multiple wavelengths of emitted light are gathered, whereas in the emission spectrum, only the specified wavelength of light emitted from the sample is measured, but the sample is exposed to multiple wavelengths of light from the excitatory source.
The fluorescence will be detected by a photomultiplier tube, which is extremely light sensitive, and a photodiode is used to convert the light into voltage or current, which can then in turn be interpreted into the amount of the chemical present. Mercury poisoning can damage the nervous system, kidneys, and also fetal development in pregnant women, so it is important to evaluate the levels of mercury present in our environment. Some of the more common sources of mercury are in the air from industrial manufacturing, mining, and burning coal , the soil deposits, waste , water byproduct of bacteria, waste , and in food especially seafood.
In , J. Kopp et al. While atomic absorption can also measure mercury concentrations, it is not as sensitive or selective as cold vapour atomic fluorescence spectroscopy CVAFS. As is common with all forms of atomic fluorescence spectroscopy AFS and atomic absorption spectrometry AES , the sample must be digested, usually with an acid, to break down the compounds so that all the mercury present can be measured.
Principles and Applications of Fluorescence Spectroscopy
Once the mercury is in its elemental form, the argon enters the bubbler through a gold trap, and carries the mercury vapors out of the bubbler to the first gold trap, after first passing through a soda lime mixture of Ch OH 2 , NaOH, and KOH trap where any remaining acid or water vapors are caught. A standard solution of mercury should be made, and from this dilutions will be used to make at least five different standard solutions. Depending on the detection limit and what is being analyzed, the concentrations in the standard solutions will vary.
Note that what other chemicals the standard solutions contain will depend upon how the sample is digested. The calibration factors for the other four standards are calculated in the same fashion: 2. Also, making sure the glassware and equipment is clean from any sources of contamination. Furthermore, sample vials that are used to store mercury-containing samples should be made out of borosilicate glass or fluoropolymer, because mercury can leach or absorb other materials, which could cause an inaccurate concentration reading.
Mercury pollution has become a global problem and seriously endangers human health.
Inorganic mercury can be easily released into the environment through a variety of anthropogenic sources, such as the coal mining, solid waste incineration, fossil fuel combustion, and chemical manufacturing. It can also be released through the nonanthropogenic sources in the form of forest fires, volcanic emissions, and oceanic emission. Mercury can be easily transported into the atmosphere as the form of the mercury vapor. The atmospheric deposition of mercury ions leads to the accumulation on plants, in topsoil, in water, and in underwater sediments.
Some prokaryotes living in the sediments can convert the inorganic mercury into methylmercury, which can enter food chain and finally is ingested by human. One example is that many people died due to exposure to methylmercury through seafood consumption in Minamata, Japan. Exposure in the organic mercury causes a serious of neurological problems, such as prenatal brain damage, cognitive and motion disorders, vision and hearing loss, and even death.
Moreover, inorganic mercury also targets the renal epithelial cells of the kidney, which results in tubular necrosis and proteinuria. The crisis of mercury in the environment and biological system compel people to carry out related work to confront the challenge. To design and implement new mercury detection tools will ultimately aid these endeavors. Therefore, in this paper, we will mainly introduce fluorescence molecular sensor, which is becoming more and more important in mercury detection due to its easy use, low cost and high efficiency. Fluorescence molecular sensor, one type of fluorescence molecular probe, can be fast, reversible response in the recognition process.
There are four factors, selectivity, sensitivity, in-situ detection, and real time, that are generally used to evaluate the performance of the sensor.
Fluorescence spectroscopy is an important investigational tool in many areas of analytical science, due to its extremely high sensitivity and. Principles and Applications of. Fluorescence Spectroscopy. Jihad René Albani. Laboratoire de Biophysique Moléculaire. Université des.
In this paper, four fundamental principles for design fluorescence molecular sensors are introduced. Photoinduced electron transfer is the most popular principle in the design of fluorescence molecular sensors. In the PET sensors, photoinduced electron transfer makes the transfer of recognition information to fluorescence signal between receptor and fluorophore come true.
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The receptor could provide the electron to the vacated electoral orbital of the excited fluorophore. The excited electron in the fluorophore could not come back the original orbital, resulting in the quenching of fluorescence emission. The coordination of receptor and guest decreased the electron donor ability of receptor reduced or even disrupted the PET process, then leading to the enhancement of intensity of fluorescence emission.
Therefore, the sensors had weak or no fluorescence emission before the coordination. However, the intensity of fluorescence emission would increase rapidly after the coordination of receptor and gust. Intramolecular charge transfer ICT is also named photoinduced charge transfer. The characteristic structure of ICT sensors includes only the fluorophore and recognition group, but no spacer. The recognition group directly binds to the fluorophore. Further information about the course can be found on the Course web at the link below.
Pre- and post-filter effects can arise owing to absorption of light prior to reaching the fluorophore and the reduction of emitted radiation. A standard solution of mercury should be made, and from this dilutions will be used to make at least five different standard solutions. The use of microcuvettes containing less material can also be useful. Stock Image. In these diagrams, energy transitions are indicated by vertical lines. The rate constants for phosphorescence are much longer and phosphorescence thus happens with a long delay and persists even when the exciting energy is no longer applied. A key element of the book is the inclusion of practical laboratory experiments that illustrate the fundamental points and applications of the technique.
Information on the Course web will later be moved to this site. All members of a group are responsible for the group's work. In any assessment, every student shall honestly disclose any help received and sources used.
Emerging applications of fluorescence spectroscopy in medical microbiology field
In an oral assessment, every student shall be able to present and answer questions about the entire assignment and solution. About course Course information Course development and history. Show course information based on the chosen semester and course offering: Choose semester Autumn No offering selected Select the semester and course offering above to get information from the correct course syllabus and course offering. Course information. Based on knowledge on these techniques and their physical principles, describe and motivate what the factors are that limit their performance, and how the obtained measurements data are evaluated Follow, report on, and discuss relevant parts of the latest development in the field of fluorescence spectroscopy.
Course Disposition No information inserted. B Valeur, Molecular fluorescence. Principles and applications, Wiley-VCH.
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