# You have a protein solution with unknown concentration. Its extinction coefficient at 280 nm is...

## Question:

You have a protein solution with unknown concentration. Its extinction coefficient at 280 nm is 23,000 M{eq}^{-1} {/eq}cm{eq}^{-1} {/eq}. You measure the absorption at 280 nm in a 1 cm path-length cuvette and get 0.3. What is the protein concentration? Explain your answer.

## Beer-Lambert's Law:

Beer-Lambert's law relates the absorbance of a solution with its concentration. It says that the absorbance is directly proportional to the molar concentration of the solution and thus, the graph between A and c is a straight-line and hence can be used to find the concentration of an unknown solution. Mathematical expression for the relation is:

{eq}A=\epsilon bc {/eq}

where b is the path length that light travels = length of the cuvette

c = molar concentration of the solution

{eq}\epsilon {/eq} is the molar absorptivity

A is the absorbance of the solution

Although the law is valid only for very dilute solutions

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Chapter 4 / Lesson 9Understand the Beer-Lambert Law equation and Beer's law units. Explore how Beer's Law is used in spectrophotometry and solve problems involving Beer's Law example.

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