Explain why it is considered a \"best practice\" to keep the total absorbance be

Question

Explain why it is considered a "best practice" to keep the total absorbance below 1 when conducting quantitative work. What were the market forces that have allowed array spectrophotometers to dominate the UV-vis spectrometer market? During the course of this chapter, we discussed the following best practices. Describe the objective of each of these best practices. (a) Keep absorbance values below 1 when conducting quantitative analysis. (b) Keep analyte concentrations below 0.01 M when conducting quantitative analysis. (c) Take absorption readings at the lambda_max value when conducting quantitative measurements. Why is the regulation of the radiant source less critical in a dual-beam spectrophotometer than it is in a single-beam spectrophotometer? Refer back to Determine the total spin multiplicity of the ground and excited states for panels A & B. state if the transition is spin allowed or spin forbidden. In the fluorescence spectrum of a given molecule, an emission peak at 490 nm is from S_1(v_0) to S_0(v_0). In the absorption spectrum, the peak is near 395 nm (a) Calculate the difference in energy between the S_1and S_0 states associated with emission. Determine this energy in joules. (b) Calculate the thermal energy imparted to the molecules as a result of the absorption to emission process A molecule phosphoresces with a single peak wavelength of 700 nm. The single fluorescence peak is at 590 nm. The absorption peak is at 490 nm. Based on this information, roughly sketch the Jablonski diagram, labeling transitions and calculating differences in each energy state in nm and cm^-1. For this question, consider anthracene and tetracene. (a) Which molecule would you expect to have a larger quantum yield ? (b) Which molecule would you expect to have a shorter peak wavelength for fluorescence? You have been given a report on luminescence measurements for an important molecule in your biochemistry lab. The report describes the fluorescence of the molecule with a peak at 675 nm. absorption peak at 455nm. and phosphorescence peak at 560 nm. What is wrong with this information? The absorption spectrum for the molecule fluorescein is shown here in part (A) along with the fluorescence spectrum when excited at 488 nm. How would the fluorescence spectrum change if this

Explanation / Answer

Problem 1

Let's remember the formula that relates absorbance (A) to transmitance (%T):

A = log10 (100/%T)

Let's substitute A = 1 to see how much the %T is:

101 = 100/%T

%T = 10%

Which means a 90% of light is absorbed when the absorbance is 1. And when the absorbance is 2, 99% of the light is absorbed. We should considered a total/maximum absorbance of 1 for minimal sources of error. If the absorbance of a sample is greater than 1, we should consider diluting it first so its absorbance falls between 0 and 1.

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