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Negative absorbance values typically indicate that the measured sample has lower light absorption than the baseline or reference. This can occur due to factors such as instrument noise, incorrect baseline correction, or interference from other substances. In some cases, it may suggest the presence of scattering or fluorescence rather than true absorbance. Negative absorbance values should be interpreted cautiously and may require further investigation to clarify the underlying cause.
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What are the units of absorbance?
Absorbance is a dimensionless quantity and has no units. It is calculated using the formula A = log10(I0/I), where A is absorbance, I0 is the intensity of the incident light, and I is the intensity of the transmitted light. Since it is a logarithmic ratio of two intensities, absorbance is expressed simply as a number, typically ranging from 0 to 3 for most applications.
How can you calculate absorbance of unknown from linear equation?
To calculate the absorbance of an unknown sample using a linear equation, you first need to establish a calibration curve by plotting the absorbance values of known standards against their concentrations. The resulting linear equation, typically in the form (y = mx + b), relates absorbance (y) to concentration (x), where (m) is the slope and (b) is the y-intercept. By measuring the absorbance of the unknown sample and substituting this value into the linear equation, you can solve for the concentration of the unknown sample. This allows you to determine the absorbance based on its concentration derived from the calibration curve.
What is maximum absorbance of methyle orange at 242 nm?
The maximum absorbance of methyl orange typically occurs at around 464 nm, not 242 nm. At 242 nm, the absorbance may be lower or not significant, as this wavelength is outside the main absorption range for methyl orange. For accurate absorbance values, it is important to refer to specific absorption spectra or experimental data for methyl orange.
Is it possible to calculate the chromacity coordinates using absorbance values?
Yes, it is possible to calculate the chromaticity coordinates using absorbance values. The best way to calculate the chromaticity coordinates using absorbance values is by using the formula x = x/x+y+z.
Why should a graph of absorbance versus concentration go through the origin?
A graph of absorbance versus concentration should pass through the origin because, according to Beer-Lambert Law, absorbance is directly proportional to concentration. When the concentration of a solution is zero, there are no absorbing species present, resulting in zero absorbance. This linear relationship indicates that as concentration increases, absorbance increases proportionally, reinforcing that the graph should start at the origin (0,0). Any deviation from this could indicate issues such as instrument calibration errors or scattering effects.
What is difference between specific absorbance and absorbance interms of spectroscopy?
specific absorbance- it is absorbance in a solution containing one gm of substance in 100 ml solvent in 1cm shell. so it is having a difference with absorbance which is negative logarithm of incident light to the transmitted light. divya.chakraborty@gmail.com
What is the specific absorbance of hypericin?
Hypericin salts are red in organic solvents and show a typical absorbance at 590 nm, which is useful to quantify hypericin in the drug extracts
Is wavelength or absorbance the dependent variable?
"absorbance"Since in the experiment, you probably choose the wavelength, then measure the absorbance (absorption?, the absorbance is the dependent variable.
What is the purpose of the blank?
Blank Sample in Spectrophotometry is used to measure the absorbance of light without sample. It is subtracted from the total absorbance for measurement of Absorbance from a sample's absorbance.
Why acetone show absorbance at 280nm?
Acetone exhibits absorbance at 280nm due to the presence of its carbonyl group (C=O), which is associated with a peak in the ultraviolet-visible spectrum at that wavelength. The absorbance at 280nm is a characteristic feature of the electronic transitions within the molecular structure of acetone.
Is absorbance considered a discrete or continuous variable?
Absorbance is considered a continuous variable.
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.
What is the different between primary absorbance and secondary absorbance in fluorescence?
in primary light absorbed by outer molecule while in secondary re-absorbance occurs
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 baseline in uv?
In UV spectroscopy, the baseline refers to the horizontal line at zero absorbance on the absorbance axis. It represents the reference point for measuring the absorbance of the sample. The baseline should be stable and noise-free to ensure accurate measurement of the absorbance of the sample.
What is the abbreviation for Absorbance?
A
Why spectophotometer gives negative value?
A spectrometer can provide absorbance information in a number of ways.. For example transmissivity can be given as a percentage value. The absorbance is often represented on a log scale. It may be calculated by: A = -log10(I/I0) Since incident light intensity must be greater than detected light intensity, Absorbance technically can't be negative. However, a spectrometer must be zeroed before each use to provide a baseline. If a material which is contaminated or otherwise inappropriate is used to zero the spectrometer, it may give a bad baseline, and thus a sample may appear to give negative absorbance. The 'blank' which was used to zero the spectrometer would have had higher absorptivity than the sample. Another instance in which you may get negative absorption could be fluorescence. If your material is excited by light, it can emit light at a different frequency. Detecting at this frequency may produce negative absorption. Similarly, 'upconversion' by certain porphyrins may also cause emission at certain wavelengths.
