Transcript
Spectroscopy – Signal and Noise in Spectroscopic Instruments Spectroscopy is the study of interaction between molecules that involve a change in the energy of a matter due to the emr such as abortion, emission, fluorescent and reflection. Spectroscopic is a techniques that used to measure a signal of the analyze species with respect to time periods. A signal in spectroscopic, however; is a physical quantity that provide the analyst with information about the analysis species by analysis the height of the peaks in infrared spectroscopy, area under a peak in gas chromatography and an average of a signal over a period of time. Thus, single in the spectroscopic instruments can be affected by the presence of noise. Noise, on the other hand; is a variation in an analyte signal which causes an error in reading the desired signal by causing a variation in the height of the peaks. However, noise is unimportant data of the analyze species that occurs due to false respond of a detector, electronic such as power supply and thus random error. In order to distinguish between signal and noise when analysing the element of interest, one can look at the frequency of the analyte species. For example, the signals will have a low frequency whereas the noise has a high frequency. There are two types of signal that can be detected in spectroscopic instruments which are continues and discrete signal. Continues signal can be defined as a signal intensity that has a set of signal real value which various at infinite time. Discrete single, therefore; is defined as discontinues in a measured signal due to the source of sampling. The source of a signal can be determine as the sample absorb a light from a source of radiation, detected by a detector and hence analysed as a signal. In addition, when a molecules in the sample absorb energy from a radiation sources (emr), it will gain kinetic energy, thus the electrons in a molecules will prompt to higher energy level due to its vibration and rotational motion hence the specie of interest will be analyzed by a detector as a signal. Noise in spectroscopic can be characterized by three different types such as photon, detector and fluctuation noise. Fluctuating noise or best known as flicker noise is one of the important noise that caused by dust, light of the radiation source and a vibrational motion of a molecules in a sample. Flicker noise, however, can be considered as s sources of noise which causes a drift in the optical spectroscopic instrument. However, there are many sources of noise which can be classified as a chemical and instrumental noise. Chemical noise caused by a random interaction and motion of analytic molecules due to instantaneously change in temperature, pressure and variation in a sample. Whereas, instrumental noise is another source that causes an error in the detected signal due to inaccurate set up of optical spectroscopy apparatus such as thermal, flicker, shot and environmental noises. Noise; though, can be affected by a chemical flicker noise which can be reduced by using dual wavelength and double beam since signal to noise ratio of a flicker is increasing with increasing the slit width of a sample. Limit of detection of a noise is define as the concentration of the analysis species caused by measuring a blank The signal to noise ratio is used to measure how accurate the spectrometer detected the light.the sources of the noice are light, detectors. References: Stephen Van Dulken (author) Inventing the 19th century, New York University Press, Washington Square, 2001, page 20 Peter Urben (editor) Bertherick’s Hardbook of Reactive Chemical Hazards, 7th ed., Academic Press, 2006 Soloway, S., Wilen, S. H. Improved Ferric Chloride Test for Phenols, Analytical Chemistry, 1952, 24(6), page 979-983. The 92st edition of the CRC Handbook of Chemistry and Physics, 2011-2012 Neil, M.J. ( editor) The Merck Index, Merck & CO.,INK , 14th ed., Whitehouse stations, NJ, USA,2006, 11,15,20. http://terpconnect.umd.edu/~toh/spectrum/SignalsAndNoise.html http://books.google.ca/books?id=LewyHGWTnEkC&pg=PA114&lpg=PA114&dq=types+of+noise+and+signal+in+spectroscopic+instruments&source=bl&ots=QIYJBkCKe-&sig=sb8DKatE5U3-u0f2bsmTU4DP3vo&hl=en&sa=X&ei=VJlTUbfGCsbK0AGMroCQDQ&ved=0CC0Q6AEwAA#v=onepage&q=types%20of%20noise%20and%20signal%20in%20spectroscopic%20instruments&f=false http://en.wikipedia.org/wiki/Signal_(electrical_engineering) http://myanswerz.blogspot.ca/2011/12/difference-between-continuous-discrete.html http://en.wikipedia.org/wiki/Spectroscopy
