How to choose Spectrometer Configuration effectively according to our need💯
Quality analysis technology has elevated the role of sensor and spectroscopy in many industries including the likes of Food industry, pharmaceutical manufacturing industry and agricultural industry. Often the ideal technology must be selected from many suitable candidates based on limited data available. also while taking a spectral measurement, it’s very important and essential to tune your measurement with spectral configuration such as the resolution of spectra, Scan count, Light intensity, warm-up scans, frequency rate, etc..
how many scans should be used?
The number of scans used to measure a spectrum is easily adjusted by simply typing the desired number in the correct field of the FTIR software program being used to run the instrument. Scan count is nothing but how many times the scanning mirror will be moved back and forth in an Spectrometer device or how many times light source blinks toward the sample.
after 1 scan. Bottom: The noise level in an infrared spectrum between 2200 and 2000 cm-1
after 100 scans. The y-axis scales in the two spectra are identical. Note the reduction in noise
for 100 scans versus 1 scan.
signal-to-noise ratio in a spectrum is proportional to the square root of the number of scans added together.
Imagine that for scan no. 1 of a sample the signal in the interferogram has a value of 9.0 units and the noise a value of 0.25 units, as shown in Figure 1.
Now, the sign of signal is always considered to be positive, but the sign of noise is random and fluctuates between positive and negative. When scan no. 2 is measured, the signal still has a value of 9.0, but the noise now has a value of -0.15,When the two scans are averaged the noise levels are averaged as well, giving a final noise level of [(0.25) + (-0.15)]/2 = 0.05. The noise cancels itself because its sign fluctuates. The signal does not cancel because its sign is constant. As more scans are added together the noise cancels itself to a greater extent.
What resolution to keep??
Setting up the resolution of spectra to be collected depends on application, some application demands high resolution spectra and some application demands low resolution spectra. The resolution of a spectrometer is a measure of how well an instrument distinguishes peaks that are close together. If resolution is less spectra is considers as ‘High resolution’ and if resolution is more spectra is considered as ‘Low resolution’.
The spectrum of water vapor measured at 32 cm-1 resolution.
The effect of instrumental resolution on spectral appearance is dramatically illustrated in Figure 2. The top spectrum is of water vapor measured at
0.5 cm-1 resolution. Note the series of sharp, well-resolved peaks. The bottom spectrum is also of water vapor but was measured at 32 cm-1 resolution. Note that there is a big, fat blob instead of a series of well-resolved peaks. The bottom spectrum was not measured with sufficient resolution to distinguish all the peaks in the water vapor spectrum, so the individual peaks merge together to form the broad feature seen. The top spectrum was measured with sufficient resolution to distinguish the peaks present in the spectrum of water vapor. These two spectra are of the same material but have radically different appearances because of the difference in instrumental resolution used. Also, note that the number of peaks in the high-resolution spectrum is greater than in the low-resolution spectrum. Since the peaks in a sample’s spectrum are information, a spectrum with more peaks has more information in it than a spectrum with fewer peaks. Thus, in general, the higher the resolution the higher the information of a spectrum.
You might be confused now, high resolution spectra comes with high noise but with rich full of information in terms of peaks, where as low resolution spectra comes with less noise but it is lacking in terms of valuable information.
As i said earlier, depends on your application demand you have to tune your spectrometer configurations.
To understand more about spectrometer figure of merits, go through this blog post
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Hope you enjoyed the reading…. happy reading…😊😊😊
