A260/A280 Ratio
Definition
Absorbance ratio at 260 nm and 280 nm used to assess nucleic acid purity. Values of 1.7-1.9 indicate pure DNA; lower values suggest protein or solvent contamination.
- Wavelengths compared
- 260 nm and 280 nm
- Pure DNA range
- 1.7 to 1.9
- Low ratio suggests
- Protein or solvent contamination
- Method
- UV spectrophotometry
Common questions
Does the A260/A280 ratio tell you how much DNA is present?+
Not reliably. It is a purity check, not a quantity measurement, and it cannot distinguish human DNA from other nucleic acids. Fluorometric or qPCR methods are used separately when an accurate, human-specific quantity is needed.
Why still run this check if fluorometry is more accurate?+
It is fast and gives an early warning of protein or reagent carryover from extraction that could interfere with downstream PCR, which a fluorometric quantity reading alone would not necessarily flag.
Related terms
- Cq (Cycle Threshold)
- The PCR cycle at which fluorescence crosses a defined threshold; inversely proportional to starting template concentration and used to calculate DNA quantity...
- Degradation Index (DI)
- The ratio of large-amplicon to small-amplicon Cq values in Quantifiler Trio or equivalent kits; a DI above ~3 indicates significant fragmentation of...
- InnoQuant HY
- Human-specific qPCR quantitation kit with internal PCR control, providing autosomal and Y quantitation plus degradation index; widely used in Japanese and East...
- PicoGreen
- SYBR Green I-related fluorescent dye that intercalates specifically into double-stranded DNA, used for sensitive fluorometric quantitation in plate-reader or Qubit formats.
- Plexor HY
- Promega qPCR quantitation kit using isoguanosine/isocytidine quenching chemistry, providing autosomal and Y-chromosome quantitation with degradation index.
- QuantiBlot
- Human-specific slot-blot quantitation kit (Applied Biosystems) using a probe directed at the D17Z1 alpha-satellite repeat on chromosome 17.
- Quantifiler Trio
- Applied Biosystems qPCR kit reporting autosomal total DNA (small + large amplicon targets) and a Y-chromosome target, with a computed Degradation Index...