Introduction
I came across various articles while reading about Spectroscopic Instruments. I revised the work of several scholarly articles about spectroscopy. My goal in this paper is to discuss signal-to-noise ratio and detection limit in terms of spectroscopic instruments. I will do this by comparing and contrasting various devices. I will state the names of the most effective devices. I will also give a summary of their applications.
To achieve my goal, I have organized my paper into five main sections and a conclusion. In the first section, I give an introduction to the topic. In the second section, I give a brief background of noise and signals in spectroscopic instruments. In the third section, I provide a summary of the signal-to-noise ratio. In the fourth section, I define Detection Limit. In the fifth section, I explain the process of noise reduction. I end my paper with a conclusion, outlining the best devices used for spectroscopic measurement.
Spectroscopy is the measurement of electromagnetic radiation. Atoms and molecules are capable of absorbing and emitting various forms of energy. Energy is measured according to its level of transmission. Energy levels can therefore be compared based on their mode of transmission (Crowe 17). Electromagnetic can be absorbed (Jacobs 19). Electromagnetic energy can be emitted from one level to another (Jacobs 20).
Spectroscopic instruments are tools that are used to study the emission and absorption of radiation (Dereniak 16). Light and radiation can be absorbed depending on their specific wavelengths. Spectroscopy is the study of compounds in relation to the radiant energy that is emitted or absorbed at different wavelengths.
Types of Signals and Noise
“There are three types of noise in the field of spectroscopy: flicker, photon and detector noise” (Froehlich 31). Photon noise is evident in photomultiplier detectors. It disrupts the signals that are read by the machine. Photon noise is proportional to the square root of light intensity (Froehlich 31). The Signal to Noise ratio, therefore, shares a direct proportionality with the breadth of the slit (Basset 47).
Detector noise is evident in machines that use solid-state photodiode detectors. As a result, Detector noise is not affected by light intensity. Its Signal Noise ratio shares a direct proportionality with the intensity of the light (Jacobs 24). “Detector Signal to Noise ratio is proportional to the square of the slit width” (Dereniak 47).
Flicker noise is caused by suspended particles that scatter the wavelength of light (Basset 127). The incorrect positioning of spectroscopes also causes Flicker noise. Flicker noise may be evident if a source of light is unstable during an experiment. “Flicker noise is directly proportional to the intensity of light” (Jacobs 14). The Flicker Signal to Noise ratio can be adjusted using wavelength modulation and double beams.
Signal to Noise Ratio
“The quality of a signal is determined by the Signal to Noise ratio. The Signal to Noise ratio is inversely proportional to the relative standard deviation of the signal amplitude” (Crowe 24). If the level of the signal is high, then the noise may also be loud. The interference from flicker and photon noise also depends on the level of the signal. In various circumstances, the level of noise can be determined by subtracting the model signal from the experimental signal (Dereniak 35).
It is difficult to differentiate noise from signals. However, it can be done by determining the frequencies of each component. Noise has no discernible pattern. A signal, on the other hand, usually follows a specific pattern. This knowledge can be used to filter interference. Algorithmic signal processing methods can also be used to reduce noise (Jacobs 32). Isolation transformers are used to reduce noise in spectroscopic instruments (Crowe 24).
Detection Limit and Sensitivity
The detection limit relates to the signal-to-noise ratio of a spectroscopic instrument with regard to the dispersive emission of spectra (Crowe 73). It also relates to “the fluorescent quantum yield of analyzed particles and their excitation wavelengths” (Jacobs 58). The detection limit depends on the Raman scattering cross-section of the particles being analyzed (Jacobs 27). Sensitivity refers to an instrument’s ability to measure variables. Sensitive instruments give more accurate measurements. Compounds that have a high capacity for polarization also have high Raman cross-sections (Dereniak 26). Compounds exhibiting more polarity display weaker Raman signatures (Crowe 15).
Detection limits are also determined by the matrix, which measures the particles (Crowe 17). Detection limits depend on the conditions evident in spectroscopic measurement (Basset 62). These conditions include integration time, wavelength, and laser power (Froehlich 89).
Lasers with short wavelengths exhibit intense Raman scattering (Froehlich 34). This is caused b the v4 relationship between the scattering intensity and the frequency of the laser.
Measuring scattered particles frequently can improve detection limits (Dereniak 56). This can be done by improving the CCD time of integration.
Detection limits can be improved by adding the scans of separate integrations (Basset 71).
Noise Reduction
In spectroscopic instruments, noise is often caused by the strength of magnetic fields the concentration of the samples, and the machine’s design (Crowe 36). All these factors affect the signal of the Nuclear Magnetic Resonance (Jacobs 12). Noise can be reduced by applying the Signal Averaging technique (Dereniak 26). This involves reducing the frequency of the signal.
A parameter-fitting model can be used to extract spectral parameters (Basset 107). This process is known as Harmonic Inversion (Froehlich 47). “this involves a linear combination of decaying exponentials that can be used to improve the Nuclear Magnetic Resonance Signal” (Basset 126).
Conclusion
The Raman scattering of spectra is usually weak. Spectroscopic methods cannot easily identify spectra that have been scattered. The light intensity of scattered beams is outweighed by the intensity of stray light (Jacobs 37). This can be corrected by cutting the spectral range. This has to be done where the stray light has the greatest effect (Dereniak 65). The effect of stray light can also be reduced using multiple dispersion stages (Crowe 56). Multiple spectrometers can be used to observe the Raman spectra without employing the use of notch filters. Charge-Coupled Devices can also be used to observe various forms of spectra. They are more effective than most devices. It is therefore important to invest in the best forms of spectroscopic technology.
Works Cited
Basset, Jonathan. Annual Book of ASTM Standards. Standard Practice for Data Presentation Relating to High Resolution Nuclear Magnetic Resonance. Philadelphia, PA. 1993. Print.
Crowe, G. Devon. Understanding Physics. Optical radiation Detectors. New York: Saxton, 1984. Print.
Dereniak, L. Eustace. Optical radiation Detectors. New York: Saxton, 1984. Print.
Froehlich, Pietro. Understanding the Sensitivity Specification of Spectrometers. Cambridge, MA: Harvard UP, 1989. Print.
Jacobs, F. Samuel. Handbook of Optics. New York: Saxton, 1978. Print.