The document describes how to calculate the concentration of an RNA stock solution given absorbance measurements of a diluted sample. It explains that an absorbance of 1.0 at 260nm corresponds to 40 μg/mL of RNA. It then shows the calculations to determine that a diluted sample with an absorbance of 0.142 corresponds to 5.7 μg/mL, and that multiplying this by the dilution factor of 1000/40 gives a stock concentration of 142.5 μg/mL.

1. MEASURING RNA
CONCENTRATION
DR. S. SIVASANKARA NARAYANI., M.SC., M.PHIL.,PH.D.,MRSB (UK)
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2. THE FOLLOWING RELATIONSHIP IS USED FOR
QUANTIFYING RNA
A260 unit of RNA = 40 µg/mL
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3. Forty microliters of a stock solution of RNA is diluted with water to give a final volume of 1000 µL.
The diluted sample has an absorbance at 260 nm of 0.142. What is the concentration of the RNA stock
solution in µg/mL?
1 OD = 40 µg/mL
0.142 OD = x µg/mL ?
x µg/mL = 0.142 OD X 40 µg/mL
= 5.7 µg/mL
Therefore, the concentration of the diluted sample is 5.7 µg/mL
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Ratios are set up that read ‘x µg RNA/mL is to 0.142 OD as 40 µg RNA/mL is to 1.0 OD.
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4. To determine the concentration of the RNA stock solution, this value must be multiplied by
the dilution factor:
5.7 µg/mL X 1000µl/40µl = 142.5 µgRNA/mL
= 142.5 µgRNA/mL
Therefore, the stock solution has a concentration of 142.5 µg RNA/mL
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5. REFERENCE
• Calculations for molecular biology and Biotechnology – A Guide
to mathematics in the laboratory, Second Edition – Frank. H.
Stephenson
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6. 29-09-2021
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