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The experiment aims to clarify the meaning of purity in the chemical sense ; apply the method of recrystallization in the purification of a solid sample; recognize melting point as a physical property that can serve as an index of purity; determine the melting point of a substance using a simple apparatus; and compare the melting point of a pure versus impure sample of a substance.
DNA concentration can be determined measuring the intensity of absorbance of the solution at the 600 nm with a spectrophotometer and comparing to a standard curve of known DNA concentrations. Measuring the intensity of absorbance of the DNA solution at wavelengths 260 nm and 280 nm is used as a measure of DNA purity. DNA purification from detergents, proteins, salts and reagents used during cell lysis step. 2  The most commonly used procedures are: 3  Ethanol precipitation usually by ice-cold ethanol or isopropanol. 4  Since DNA is insoluble in these alcohols, it will aggregate together, giving a pellet upon centrifugation.