Nucleic Acid Concentration (A260)

About Nucleic Acid Concentration (A260)

This tool turns spectrophotometer absorbance readings into a nucleic acid concentration and checks purity. Enter A260, optionally A280 and A230, the dilution factor and the sample type. The concentration comes from A260, and the two ratios flag protein or chemical contamination in a DNA or RNA prep.

How to use it

1. Enter the A260 reading, plus A280 and A230 if your instrument reported them.
2. Enter the Dilution factor, using 1 if the sample was measured undiluted.
3. Choose the Sample type: dsDNA (x50), ssDNA (x33), RNA (x40) or ssOligo (x33).
4. Read the concentration in ng/uL and ug/mL, and compare the A260/A280 and A260/A230 ratios with the ideal badges.

A 1:50 dilution of a dsDNA prep

A260 1.0, A280 0.55, A230 0.45, dilution 50, dsDNA

2500 ng/uL (2500 ug/mL), A260/A280 1.82, A260/A230 2.22

When to use it

• Quantifying a plasmid miniprep before sequencing or transfection.
• Checking an RNA extraction for protein carryover before reverse transcription.
• Deciding whether a column cleanup is needed based on a low A260/A230 ratio.
• Converting an oligo's absorbance to a working concentration.

Questions about Nucleic Acid Concentration (A260)

Where do the multipliers come from?

One absorbance unit at 260 nm over a 1 cm path corresponds to about 50 ug/mL of double-stranded DNA, 40 of RNA and 33 of single-stranded DNA or oligos. Concentration is A260 times that factor times the dilution.

What ratios count as pure?

The tool flags about 1.8 for A260/A280 in DNA and 2.0 in RNA. A260/A230 is normally expected between 2.0 and 2.2. Low values point to protein or phenol on the 280 side and salts, EDTA or carbohydrate on the 230 side.

Why leave A280 or A230 blank?

Both are optional. If a value is empty or zero, its ratio is shown as a dash and the concentration still calculates.

Should I still enter a dilution factor for a microvolume reading?

Use 1 if the instrument already normalizes to a 10 mm path and you measured neat. Only use a factor above 1 for a sample you diluted yourself before reading.

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