Fluorescent Spectrometer
Fluorescence spectrometry is a fast, simple and inexpensive method to determine the concentration of an analyte in solution based on its fluorescent properties. It can be used for relatively simple analyses, where the type of compound to be analyzed (‘analyte’) is known, to do a quantitative analysis to determine the concentration of the analytes. Fluorescence is used mainly for measuring compounds in solution.
In fluorescence spectroscopy, a beam with a wavelength varying between 180 and ∼800 nm passes through a solution in a cuvette. We then measure – from an angle - the light that is emitted by the sample. In fluorescence spectrometry both an excitation spectrum (the light that is absorbed by the sample) and/or an emission spectrum (the light emitted by the sample) can be measured. The concentration of the analyte is directly proportional with the intensity of the emission.
There are several parameters influencing the intensity and shape of the spectra. When recording an emission spectrum the intensity is dependent on the Excitation wavelength, Concentration of the analyte solvent, Path length of the cuvette, Self-absorption of the sample
Fluorescence Spectroscopy Configuration
In fluorescence spectroscopy, a light of a specific wavelength band is passed through a solution, which emits the light towards a filter and into a detector for measurement. The amount of light that is absorbed by the sample (excitation spectrum) and the amount of light that is emitted by the sample (emission spectrum) can be quantified. The concentration levels of the analyte compound within the solution can be determined as these levels are directly proportional to the emission spectrum.
Fluorescence Spectroscopy Filters
We briefly mentioned filters when outlining the configuration of a fluorescence spectroscopy device, and most of these devices are based on the filters within them. There are various types of filters that can be used within a fluorescence spectroscopy instrument, and here we’ll outline a few of them. An interference filter reflects a certain wavelength range and transmits another, with virtually no absorption. In a fluorescence spectroscopy instrument, these filters work as a wavelength selector, by reflecting the undesired wavelengths. These filters come in many forms, including bandpass filters. Bandpass filters work by allowing certain wavelengths to pass through and blocking any wavelength outside of that range. Bandpass filters are used within these fluorescence spectroscopy instruments to measure the excitation and emission spectrum. They are used to block out any other sources of excitation or emission that may affect the results. A beamsplitter is used to split incident light into multiple wavelengths, or by intensity. Within a fluorescence spectroscopy device, a dichroic beamsplitter is used to reflect and transmit light into the bandpass filters.
Questions & Answers
1. Which of the following components of the X-ray fluorescent spectrometer induces fluorescent radiation?
a) Excitation source
b) Energy analyser
c) X-ray spectrometer
d) Detection System
Answer: Excitation source
2. Why is a mono-energetic radiation source required in X-ray fluorescent spectrometer?
a) To provide good sensitivity
b) To provide high accuracy
c) To provide a proper range
d) To reduce unwanted background
Answer: To reduce unwanted background
3. Which of the following does not make the X-ray tube nearly monochromatic?
a) Transmission-anode X-ray tube
b) Secondary fluorescence target
c) Slit
d) Filters
Answer: Slit
4. Which of the following components make use of a thin metal foil to isolate a nearly mono-energetic excitation beam?
a) Transmission-anode X-ray tube
b) Secondary fluorescence target
c) Slit
d) Filters
Answer: Filters
5. Energy dispersive system uses which of the following detectors?
a) Optical detector
b) Semiconductor detector
c) Thermistor
d) Bolometer
Answer: Semiconductor detector
6. In Energy dispersive system, the energy level and the number of pulses is related to which of the following?
a) Amount of sample, element involved
b) Element involved, concentration of the element
c) Concentration of the element, element involved
d) Number of atoms, amount of sample
Answer: Element involved, concentration of the element
7. The analysis of X-ray beam by diffraction is similar to spectrum analysis carried out with a diffraction grating.
a) True
b) False
Answer: True
8. The crystal used as X-ray grating has _______ dimensional lattice arrays?
a) One
b) Two
c) Three
d) Four
Answer: Three
9. Which of the following can be done to avoid loss of intensities of X-rays due to absorption of long wavelength X-rays?
a) Apparatus must be contained in a chamber
b) Air in the chamber must be replaced by helium
c) Inert gas atmosphere must be provided
d) Proper slits must be used
Answer: Air in the chamber must be replaced by helium
10. In curved crystal arrangement, angular velocity of the crystal is twice that of the detector.
a) True
b) False
Answer: False
11. Which of the following is the disadvantage of silicon semiconductor detector?
a) Low stable
b) Can be operated only at low temperatures
c) Have low count-rate
d) Low resolution
Answer: Can be operated only at low temperatures
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