A Spectrophotometer is a specialized kind of instrument that is designed to not only separate but also measure the variation of a physical phenomenon within a particular range. Some of the measurements here in question can be in the form of a mass spectrometer, an NMR spectrometer, or to an extent in the form of an optical Spectrophotometer. These three which are the optical spectrometer, the mass spectrometer, and the NMR spectrometer are some of the noticeable types of spectrometer found in most research labs in various continents.
The optical spectrometer is the most popularly used spectrometer for research out of the rest. A lot of times it is easy to denote the particular type of spectrometer even without the qualifier. So, without wasting additional time our main focus in this article is on the diverse spectrometer and how best they perform. To gain more understanding, you must keep reading as it sure promises to be educational as well as enlightening. But first of all, how does an optical Spectrophotometer work or function?
The Optical Spectrophotometer: How it works
The optical Spectrophotometer carries out two distinctive purposes:
- To measure from a sample the emission (which can either be electroluminescence, fluorescence) of electromagnetic radiation
- To measure from a sample the interaction (which can either be in the form of reflection, absorption, or scattering) of electromagnetic radiation.
The optical Spectrophotometer is focused more on the optical region of the electromagnetic spectrum. Some of the regions of the spectrum are visible and infrared wavelength, and also the ultraviolet. For the sole purpose of gaining additional insight, the emission of light or rather the interaction should be determined as a function of wavelength. The wavelength selection happens to be a common attribute of optical Spectrophotometer. What is predominantly used are optical filters. This is meant to keep aside the wavelength terrain or rather range of value in situations where accurate wavelength selection is of lesser value. To best determine the generation of spectra or connote a precise wavelength selection, an entirely different wavelength especially one which separates light into its constituent is needed. The dispersive element in modern spectrometers is a diffraction grating whereby both destructive, as well as constructive interference, is used to differentiate the polychromatic light although spatially, is dependent on the grating.
One of the key components of a monochromator is diffraction gratings. This particular kind of device is used to choose a specific wavelength of light from a polychromatic light source. The diffraction grating is twisted to change the wavelength in a monochromator. In spectrophotometers, you would get to find the excitation monochromators to reach a white light source sample. There are two approaches by a sample, that would enable one to detect the light emitted. The first approach is an emission monochromator. This is somewhat similar in its approach to the previously mentioned one. The only difference here is that the monochromator is responsible for choosing the wavelength of light to get to the detector. The next approach which happens to be the second is to detect at once the spectrum of dispersed light. However, this is only possible when an array detector which can be a spectrograph comes to play. In spectrofluorometers and Raman spectrometers, there is one emission of either the spectrograph or that of the monochromator.
Having been able to identify the key component of the Spectrophotometer, their role, and not to mention the different types of spectrometer can now be looked at more critically. It would interest you to know that the spectrofluorometers, spectrophotometers, and Raman spectrometers happen to be the most common optical spectrometers. So, let us have a run-through each.
A spectrofluorometer or fluorescence as it is also known as is the property of molecules as well as atoms used to measure the fluorescence emission of a particular wavelength. It would interest you to know that different manufacturers call them differently, given that the spectrofluorometer, fluorescence, or even in most cases photoluminescence are all interchangeable. All three might mean something entirely different from the other. For instance, a spectrofluorometer looks more into being a benchtop instrument that bears similarity in size to that of a spectrophotometer. A well-known example is an FS5 spectrofluorometer. On the other hand, a photoluminescence spectrometer or the term fluorescence is used for spectrometers that are not only larger, but also have a performance that is quite superior with diverse functionality. A good example is that of an FLS1000 photoluminescence spectrometer.
Excitation and emission spectra happen to be the two popularly known spectral measurement undertaken in spectrofluorometers. When trying to measure an excitation spectrum, you have to consider the following:
- There is a particular wavelength the emission monochromator would be in
- In the wavelength region, the excitation monochromator would be scanned
- The detector would be in charge of monitoring the change in fluorescence intensity.
When it comes to emission spectra, there are a couple of things to bear in mind. Now, let's look at some of the things to note when it comes to emission spectra. They:
- When there is strong absorption of the sample, the wavelength of the excitation monochromator is set
- In the wavelength region, the emission monochromator is swept across.
- The fluorescence features of the sample will then be revealed once the fluorescence detects a change.
A spectrophotometer or a UV-Vis Spectrometer as it is also known to be called deals with measuring light with the use of a variety of instruments. However, this is dependent on the area of industry or that of science. The term "photo" is used to specify that there is a quantitative measurement of light intensity in the spectrometer. The term spectrophotometer especially when being considered in an academic research perspective, such as in biology and chemistry laboratories, basically refers to the measure or rather an absorption of light on a spectrometer.
The absorption spectrum of a sample happens to be a well-known measurement carried out in a spectrophotometer. A transient absorption spectrometer is a more advanced type of spectrophotometer. This advanced type can measure the absorption spectrum evolution with time. Also, it is vital in the sense that it looks at short-lived photoexcited states of temporary species.
A Raman spectrometer is a chemical analysis that from a sample can measure a Raman scattering of light. A Raman spectrometer and a spectrofluorometer are similar in their designs. Although they both have a minor key difference that separates them. The excitation monochromator and the white light source which is detected in spectrofluorometers are substituted with a laser. Twofold happens to be the reason for such substitution. The first is a result of the light not being absorbed by the sample since Raman is a scattering effect. What is not required for matching the absorption here is a broadband tunable light source. Secondly, is what is of lesser strength than fluorescence is the Raman effect. This means that to maximize the signal, what is essential here is the sources that have higher photon flux.
Plus, it would interest you to know that Raman spectrometers can be applied to multiple fields, such as solid-state physics, or even biochemistry.
Configuring a Spectrometer to Improve Performance
A spectrometer is a device that detects and analyses wavelengths of electromagnetic radiation. It separates and measures components of physical phenomenon into spectra; For example, white light is separated into spectra of colors with individual bands. Spectrometers are mostly used in fields of science like chemistry, physics, astrology, etc. There are different types of spectrometers, depending on the physical phenomenon of each spectrometer.
- Mass spectrometer deals with measuring the mass-to-charge ratio of ions, elements, and molecules.
- NMR spectrometer analyses the nuclei in a magnetic field.
- Optical spectrometer analyses light in an electromagnetic spectrum.
Spectrometers have eight (8) components-light sources; the entrance slit, where light comes in from the source; mirrors; diffraction grating, this splits the physical characteristic into a spectrum; holder; the detector that measures the intensity and wavelength of the radiation; interface; and the software. The type and size of each of these components determine how the spectrometer will function.
Here is a guide to configuring a spectrometer to get the best results from it.
- Configure the wavelength. The range of the wavelength is the main parameter of the grating in the spectrometer. For higher resolution but less range, choose a B-type grating or one that has 600lines per mm. For a broadband wavelength, 300lines/mm is suitable.
- Configure the detector. The type of detector must be suitable for the set wavelength. There are three (3) groups of detectors in the range; these groups are based on the general requirements.
The second group- Based on speed and signal to noise
The third group- Based on general-purpose and wavelengths
- Configure slit size and optical resolution. Slit size and optical resolution determine how much light (or other electromagnetic radiation) enters the spectrometer. If you want to achieve a high optical resolution, higher lines per mm are the appropriate choice. The C-, E-, and F types of grating will accomplish this result
- Configure speed and timing. Speed and timing are how fast the instrument receives a trigger to produce results.
Having gone through the most commonly encountered optical spectrometers as well explaining the type of measurements they can produce, we hope this article has given you an in-depth knowledge or a basic introduction on the touched areas. For clarity purposes or improved information regarding spectrometers or fluorescence spectroscopy, why not explore our range of transient absorption spectrometers and that of the fluorescence.
MRC-laboratory equipment provides a wide range of spectrophotometers. Contact us for more details