To find out how many microliters (µl) of the sample you need to obtain exactly 30 micrograms (µg) of protein, you can use the following formula:
\[ \text{Concentration} = \frac{\text{Amount of substance}}{\text{Volume}} \]
Given:
- Concentration of protein = 1.9 mg/ml
- Desired amount of protein = 30 µg
First, convert the concentration from mg/ml to µg/µl:
\[ 1.9 , \text{mg/ml} = 1.9 , \text{µg/µl} \text{ (since 1 mg = 1000 µg and 1 ml = 1000 µl)} \]
Now, we set up the equation to find the volume (V) needed:
\[ 30 , \text{µg} = 1.9 , \text{µg/µl} \times V , \text{(µl)} \]
Now solve for \(V\):
\[ V = \frac{30 , \text{µg}}{1.9 , \text{µg/µl}} \approx 15.7895 , \text{µl} \]
Rounding to the nearest 0.1 µl:
\[ V \approx 15.8 , \text{µl} \]
Thus, you would need approximately 15.8 µl of the "low salt" sample to obtain exactly 30 micrograms of protein.