Extinction Coefficient from Time series data

In summary, the absorbance of Br2 formation using UV Vis spectroscopy is linearly related to the concentration of BrO3, Br and the expected concentration of Br2. However, if you are using the same cuvette, wavelength and instrument you do not need extinction coefficient. You can use linear regression to determine the extinction coefficient.
  • #1
lee403
16
1
I have some time series data of the absorbance of Br2 formation using UV Vis spectroscopy and I need to figure out the extinction coefficient/ absorptivity.
The overall reaction is
BrO3-+5Br- +6H+-->3Br2+3H2O
which is expcted to go to completion
I know that the equation relating absorbance to concentration is
A=εcl
and I have times series A measurements and can calculate the initial concentrations of BrO3, Br -and the expected concentration of Br2 from the solutions I made. I just need to find ε.

I first attempted to plot the absorbance v. time and find the slope where it was most linear but I don't know how valid this approach is.
 
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  • #2
lee403 said:
I first attempted to plot the absorbance v. time and find the slope where it was most linear but I don't know how valid this approach is.

It is about as good as it can be.

I would record an additional point after waiting for some time to make sure the amount of Br2 produced is just stoichiometric. That would give a good calibration point.

Besides, if all you are after is a time series (for kinetic measurements), all you are interested in is the rate of changes - are you sure you need absolute values for that?
 
  • #3
Maybe I'm thinking about this wrong. I need to know the extinction coefficient for Br2 because in another reaction I measure its loss over time. So I dd an initial run for the formation of Br2 in order to determine its extinction coefficient. Then in a second run I added a compound that reacts with it and measured the absorbance again. I am interested in the rate of loss so does that mean the extinction coefficient from the initial run is not an exact value?
 
  • #4
If you are using the same cuvette, wavelength and the same instrument you don't need extinction coefficient but a calibration curve. Linear regression on the data is typically a way to go.

What I don't get about your setup is why you use time series instead of just making a series of samples of different concentrations?
 

What is extinction coefficient from time series data?

The extinction coefficient from time series data is a measure of how much light is absorbed by a substance over time. It is typically used to quantify the concentration of a particular substance in a sample.

Why is extinction coefficient important?

The extinction coefficient is important because it allows scientists to accurately measure the concentration of a substance in a sample by measuring its absorbance of light. This can be used in a variety of fields, such as environmental science, chemistry, and biology.

How is extinction coefficient calculated from time series data?

The extinction coefficient is calculated by dividing the absorbance of a substance by its concentration and the path length of the sample. This value is then multiplied by the inverse of the molar absorptivity, which is a constant that is specific to the substance being measured.

What factors can affect the accuracy of extinction coefficient measurements?

Several factors can affect the accuracy of extinction coefficient measurements, including the purity of the sample, the wavelength of light used, and the path length of the sample. It is important to control for these factors in order to obtain accurate and reliable results.

How can extinction coefficient be used in practical applications?

The extinction coefficient can be used in a variety of practical applications, such as monitoring pollution levels in water or air, determining the concentration of a drug in a patient's blood, and studying the growth of microorganisms in a culture. It is a valuable tool for scientists in many fields and can provide important insights into the behavior of substances over time.

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