Question

What is the concentration of DNA in a solution if its absorbance at 260 nm is 0.412? (Remember the appropriate constant to use: 50 ng of DNA/microliter of solution).

What is the expected absorbance of a DNA solution with a concentration of 125 ng of DNA/microliter of solution?

Imagine you have substance Z that absorbs light at 600 nm (i,e., its goldilocks wavelength of absorbance is A600) and its constant at this wavelength of light is 25 ng of Z/microliter of solution. What is its concentration if the absorbance is 0.15

Answer 1

To find the concentration of DNA in a solution based on its absorbance at 260 nm, you can use the Beer-Lambert law, which relates absorbance (A) to concentration (C) and the molar absorptivity constant (ε). The formula can be expressed as:

\[
C = \frac{A}{k}
\]

Where:
- \(A\) is the absorbance,
- \(k\) is the absorptivity constant, which is given as 50 ng/µL for DNA.

### Step 1: Calculate concentration of DNA

Given:
- Absorbance (\(A\)) = 0.412,
- \(k\) (constant for DNA) = 50 ng/µL.

Using the formula:
\[
C = \frac{0.412}{50} = 0.00824 \text{ µg/µL}
\]

To convert to ng/µL (since 1 µg = 1000 ng):
\[
C = 0.00824 \text{ µg/µL} \times 1000 = 8.24 \text{ ng/µL}
\]

### Step 2: Calculate expected absorbance for 125 ng/µL

To find the expected absorbance for a concentration of 125 ng/µL, use the formula:
\[
A = C \times k
\]

Where:
- \(C\) = 125 ng/µL,
- \(k\) = 50 ng/µL.

Calculating the expected absorbance:
\[
A = 125 \text{ ng/µL} \times \frac{1}{50} = 2.5
\]

### Summary of results for DNA:
1. The concentration of DNA in the solution with an absorbance of 0.412 is **8.24 ng/µL**.
2. The expected absorbance of a DNA solution with a concentration of 125 ng/µL is **2.5**.

### Step 3: Calculate concentration of substance Z

For substance Z at 600 nm, using the same approach as above:

Given:
- Absorbance (\(A\)) = 0.15,
- Constant (\(k\)) for substance Z = 25 ng/µL.

Using the formula:
\[
C = \frac{A}{k}
\]
Where:
- \(A\) = 0.15,
- \(k\) = 25 ng/µL.

Calculating concentration:
\[
C = \frac{0.15}{25} = 0.006 \text{ µg/µL}
\]

Converting to ng/µL:
\[
C = 0.006 \text{ µg/µL} \times 1000 = 6 \text{ ng/µL}
\]

### Summary of results for substance Z:
- The concentration of substance Z with an absorbance of 0.15 is **6 ng/µL**.