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Why do you use the wavelength with the maximum absorbance in spectroscopy?
Wiki User
∙ 14y ago
Short answer:
Using the maximum wavelength gives us the best results. This is because at the peak absorbance, the absobance strength of light will be at the highest and rate of change in absorbance with wavelength will be the smallest. Measurements made at the peak absorbance will have the smallest error.
Long answer: It really depends on what is the largest source of error. Taking the readings at the peak maximum is best at low absorbance, because it gives the best signal-to-noise ratio, which improves the precision of measurement. If the dominant source of noise is photon noise, the precision of absorbance measurement is theoretically best when the absorbance is near 1.0. So if the peak absorbance is below 1.0, then using the peak wavelength is best, but if the peak absorbance is well above 1.0, you might be better off using another wavelength where the absorbance is closer to 1. Another issue is calibration curve non-linearity, which can result in curve-fitting errors. The non-linearity caused by polychromatic light is minimized if you take readings at either a peak maximum or a minimum, because the absorbance change with wavelength is the smallest at those wavelengths. On the other hand, using the maximum increases the calibration curve non-linearity caused by stray light. Very high absorbances cause two problems: the precision of measurement is poor because the transmitted intensity is so low, and the calibration curve linearity is poor due to stray light. The effect of stray light can be reduced by taking the readings at awavelength where the absorbance is lower or by using a non-linear calibration curve fitting technique. Finally, if spectral interferences are a problem, the best measurement wavelength may be the one that minimizes the relative contribution of spectral interferences (which may or may not be the peak maximum). In any case, don't forget: whatever wavelength you use, you have to use the exact same wavelength for all the standards and samples. See http://terpconnect.umd.edu/~toh/models/BeersLaw.html
Tom O'Haver
Professor Emeritus
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∙ 14y ago
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What is the specific absorbance of aspirin?
If you have a spectrofotometer ( the thing to mesure the absorbance) then play with the setting and use a maximum. this will lay close to your specific absorbance or take the pharmacopea or a MERCK index
How do you find the concentration of potato cells immersed in salt solutions?
You would have to use a spectrophotometer to measure the absorbance of your unknown solution. But first, you need to make several solutions with known concentrations. Measure the absorbance of the known concentrations and plot them on an X and Y axis where X equals concentration and Y equals absorbance. Do a best-fit line for your data. Measure the absorbance of your unknown solution. Find this value on your Y-axis and find out where this value intersects with your line of best fit. The X value at the intersection is your concentration of potato cells. By the way, make sure you use the same wavelength throughout the experiment.
What is laser raman spectroscopy?
Raman spectroscopy is the vibrational spectroscopy. The ancient days the scientist use sunlight as a source for getting spectrum.but the modern world, the scientist use high energy laser for characterisation.so, it is called laser raman spectroscopy.
What is blank in spectrophotometer?
A blank is used in order to cancel out or zero the absorbance of all the other components in the sample except the component whose absorbance is to be measured. For example, if you want to measure the absorbance of a solute in water, you will use only water as a blank and the spectrophotometer will subtract the absorbance of water from the spectrum when you measure the absorbance of your solute in water.
Use of kbr in ir spectroscopy?
KBr is used mostly in IR Spectroscopy techniques because it do not absorbs moisture at room temperature as compared to NaCl. More over it do not give its own peak.
What is the specific absorbance of aspirin?
If you have a spectrofotometer ( the thing to mesure the absorbance) then play with the setting and use a maximum. this will lay close to your specific absorbance or take the pharmacopea or a MERCK index
What is UV spectroscopy?
UV Visible spectroscopy measures the response of a sample to ultraviolet and visible range of electromagnetic radiations. Molecules and atoms have electronic transitions while most of the solids have interband transitions in the UV and Visible range. Most molecules have a pi to pi* transition, involving pi electrons. The most important kind of UV/Vis Spectr. is Dispersion based spectroscopy. It involves a disperive medium like prism or grating to separate the different wavelengths.
Why are peaks important in spectroscopy?
In the field of spectroscopy absorption a peak means the wavelength of radiation where a sample absorbs. Different molecules absorb radiation of different wavelengths. An absorption spectrum will show a number of absorption bands, each one corresponding to structural groups within the molecule. Each band is represented by peak if you plot absorbance vs wavelength. By knowing which structural groups correspond to which peaks, you can often identify a compound by it's spectrum. For many molecules, the spectrum has been characterized, and you can use the spectrum to determine the purity, concentration, or other properties of the molecule by looking at the position and intensity of the peaks in the absorption spectrum.
Why is absorbance not measured directly?
Simply because we cannot measure light absorbed. We are, however, able to measure light transmitted through the use of a spectrophotometer. The device works by shining light of a specific wavelength on a substance and measuring the amount of light that gets through. This "transmittance" has a negative logarithmic relationship to absorbance.
How do you find the concentration of potato cells immersed in salt solutions?
You would have to use a spectrophotometer to measure the absorbance of your unknown solution. But first, you need to make several solutions with known concentrations. Measure the absorbance of the known concentrations and plot them on an X and Y axis where X equals concentration and Y equals absorbance. Do a best-fit line for your data. Measure the absorbance of your unknown solution. Find this value on your Y-axis and find out where this value intersects with your line of best fit. The X value at the intersection is your concentration of potato cells. By the way, make sure you use the same wavelength throughout the experiment.
What is laser raman spectroscopy?
Raman spectroscopy is the vibrational spectroscopy. The ancient days the scientist use sunlight as a source for getting spectrum.but the modern world, the scientist use high energy laser for characterisation.so, it is called laser raman spectroscopy.
How do scientists use gamma rays to determine the composition of a planet?
They use spectroscopy.
What is the definition of spectroscopy?
The use of the spectroscope; investigations made with the spectroscope.
Function of the spectrophotometer?
The spectrophotometer is an instrument that measures the amount of light of a specified wavelength which passes through a medium. This instrument operates by passing a beam of light through a sample and measuring the intensity of light reaching a detector.
How do you use a sentence with wavelength?
It was a wavelength thing-we just meshed.
What are the methods that astronomers use to identiy the composition of distant stars?
Spectroscopy.
What is blank in spectrophotometer?
A blank is used in order to cancel out or zero the absorbance of all the other components in the sample except the component whose absorbance is to be measured. For example, if you want to measure the absorbance of a solute in water, you will use only water as a blank and the spectrophotometer will subtract the absorbance of water from the spectrum when you measure the absorbance of your solute in water.
