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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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What is the specific absorbance of aspirin?
The specific absorbance of a substance like aspirin refers to its unique ability to absorb light at a specific wavelength. To find the specific absorbance of aspirin, you would need to measure its absorbance at a specific wavelength using a spectrophotometer.
How to calculate lambda max?
To calculate lambda max (λ max), generally used in spectrophotometry, you can use the formula: λ max = 1 / εmax, where εmax is the molar absorptivity (extinction coefficient) of the compound at its maximum absorbance wavelength. The λ max represents the wavelength at which the compound absorbs light most strongly.
What is the formula on how to find starch in water?
To find the concentration of starch in water, you can use a spectrophotometric method by measuring the absorbance of the solution at a specific wavelength. Prepare a standard curve using known concentrations of starch solutions to correlate absorbance with concentration. Then, measure the absorbance of your sample and use the standard curve to determine the starch concentration.
Why you are use monochromator in uv spectroscopy?
A monochromator in UV spectroscopy is used to isolate a specific wavelength (or range of wavelengths) of light from the UV region of the spectrum. This helps in achieving better wavelength selectivity and accuracy in UV spectroscopic measurements by allowing only the desired wavelengths to pass through to the sample.
Is Beer-Lamberts law for absorption spectroscopy?
Yes, Beer-Lambert's law is commonly used in absorption spectroscopy to relate the concentration of a sample to its absorbance. It states that the absorbance of a substance is directly proportional to its concentration and the path length of the light passing through the sample.
Why do you use the wavelength with the maximum absorbance in spectroscop?
The wavelength with the maximum absorbance corresponds to the peak absorption of the compound being analyzed, providing the most accurate and precise measurement. By measuring absorbance at the maximum wavelength, we can ensure the highest sensitivity and specificity in detecting and quantifying the compound of interest.
What is the specific absorbance of aspirin?
The specific absorbance of a substance like aspirin refers to its unique ability to absorb light at a specific wavelength. To find the specific absorbance of aspirin, you would need to measure its absorbance at a specific wavelength using a spectrophotometer.
Which equipment is most useful when measuring wavelength?
A spectrophotometer is typically the most useful equipment for measuring wavelength. It can measure the absorbance or transmittance of a substance at different wavelengths, allowing for the determination of the wavelength of maximum absorbance or transmittance.
Why you use wavelength of 680nm to find absorbance of glucose?
Glucose absorbs light at a specific wavelength of 680nm due to its chemical structure. By measuring the absorbance of glucose at 680nm, we can quantitatively determine the concentration of glucose in a sample through the Beer-Lambert Law, which relates absorbance to concentration.
How to calculate lambda max?
To calculate lambda max (λ max), generally used in spectrophotometry, you can use the formula: λ max = 1 / εmax, where εmax is the molar absorptivity (extinction coefficient) of the compound at its maximum absorbance wavelength. The λ max represents the wavelength at which the compound absorbs light most strongly.
Why do we use a wavelength of 540 nm for KMNO4?
A wavelength of 540 nm is used for potassium permanganate (KMnO4) because it corresponds to the absorption maximum of the permanganate ion (MnO4-) in solution. At this specific wavelength, the absorbance is directly proportional to the concentration of permanganate ions, making it ideal for quantifying the amount of KMnO4 present in a sample.
What is the formula on how to find starch in water?
To find the concentration of starch in water, you can use a spectrophotometric method by measuring the absorbance of the solution at a specific wavelength. Prepare a standard curve using known concentrations of starch solutions to correlate absorbance with concentration. Then, measure the absorbance of your sample and use the standard curve to determine the starch concentration.
Why you are use monochromator in uv spectroscopy?
A monochromator in UV spectroscopy is used to isolate a specific wavelength (or range of wavelengths) of light from the UV region of the spectrum. This helps in achieving better wavelength selectivity and accuracy in UV spectroscopic measurements by allowing only the desired wavelengths to pass through to the sample.
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.
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.
What is λmax?
A more powerful version of Wi-Fi that can provide wireless internet access over wider geographic location such as a city.
Is Beer-Lamberts law for absorption spectroscopy?
Yes, Beer-Lambert's law is commonly used in absorption spectroscopy to relate the concentration of a sample to its absorbance. It states that the absorbance of a substance is directly proportional to its concentration and the path length of the light passing through the sample.
