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Because DNA and RNA absorb ultraviolet light, with an absorption peak at 260nm wavelength, spectrophotometers are commonly used to determine the concentration of DNA or RNA in a solution. Inside a spectrophotometer, a sample is exposed to ultraviolet light at 260 nm, and a photo-detector measures the light that passes through the sample. The more light absorbed by the sample, the higher the nucleic acid concentration in the sample.

Using the Beer Lambert Law it is possible to relate the amount of light absorbed to the concentration of the absorbing molecule. At a wavelength of 260 nm, the average extinction coefficient for double-stranded DNA is 0.020 (μg/ml)-1 cm-1, for single-stranded DNA and RNA it is 0.027 (μg/ml)-1 cm-1 and for short single-stranded oligonucleotides it is dependent on the length and base composition. Thus, an optical density (or \\\”OD\\\”) of 1 corresponds to a concentration of 50 μg/ml for double-stranded DNA. This method of calculation is valid for up to an OD of at least 2.[1] A more accurate extinction coefficient may be needed for oligonucleotides; these can be predicted using the nearest-neighbor mode

AmpliQuant offers two different instruments for the quantification of DNA, RNA, and protein via the 260nm and 280nm absorbance methods. For small sample numbers, the AQ-07 is designed for single sample detection. To process more samples at one time, the AQ-08 will measure 8 samples using the 8-channel sample vessel.