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Question

The molar extinction coefficient of proline ninhydrin complex at 520 nm is 0.34 $\mu$M$^{-1}$Cm$^{-1}$. A solution of the proline ninhydrin complex has an absorbance of 0.68 in a one centimeter cuvette. The concentration ($\mu$M) of proline is

The correct answer is
2

Calculating Proline Concentration Using Beer-Lambert Law

This question requires calculating the concentration of a proline ninhydrin complex using the Beer-Lambert Law.

Beer-Lambert Law Principle

The Beer-Lambert Law relates the absorbance of a solution to the concentration of the analyte and the path length the light travels through the solution. The formula is:

$A = \epsilon lc$

Where:

  • A is the absorbance (unitless)
  • \(\epsilon\) is the molar extinction coefficient (in $\mu$M$^{-1}$Cm$^{-1}$)
  • l is the path length of the cuvette (in cm)
  • C is the concentration of the analyte (in $\mu$M)

Given Information

  • Absorbance, A = 0.68
  • Molar extinction coefficient, \(\epsilon\) = 0.34 $\mu$M$^{-1}$Cm$^{-1}$
  • Path length, l = 1 cm

Calculation Steps

  1. Rearrange the Beer-Lambert Law formula to solve for concentration (C):

    $C = \frac{A}{\epsilon l}$

  2. Substitute the given values into the rearranged formula:

    $C = \frac{0.68}{0.34 \, \mu \text{M}^{-1}\text{Cm}^{-1} \times 1 \, \text{cm}}$

  3. Calculate the concentration:

    $C = \frac{0.68}{0.34} \, \mu \text{M}$

    $C = 2 \, \mu \text{M}$

Result

The concentration of the proline is 2 $\mu$M. This corresponds to Option 4.

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