A solution containing 50 µg per ml of double strand DNA has an aborbancy (optical density) of 1.0 at a wave length of 260 nm.
50/1.0 = (DNA)/OD read
(DNA) = 50 x ODread
DNA quality measurement is based on the fact that OD at 260 nm is twice that at 280 nm if the solution contains pure DNA. If there is a contaminant, there is some additional OD which decreases the OD ratio between 260 and 280 nm.
Clean DNA has a OD-260/OD280 between 1.8 and 2.0
If the measured value is somewhat smaller, it indicates a contamination. Purify the DNA again.
eg:若OD260 /OD280 > 2. 0,表明DNA 中含RNA杂质。若OD260 /OD280< 1. 6,表明样品中含酚或蛋白质。
一般单链是33 ug，双链是50 ug
为了确定引物浓度,可以在260nm(OD260)测量光密度值。然后使用光吸收值和微摩消光系数的倒数(nmol/OD),通过Beers法则（公式1计算引物浓度。
1个OD值的合成DNA的重量约为33ug。
1 OD260= 33 ug/ml. 。