Introduction
A phenol-chloroform extraction is a liquid-liquid extraction. A liquid-liquid extraction is a
method that separates mixtures of molecules based on the differential solubilities of the
individual molecules in two different immiscible liquids (28). Liquid-liquid extractions are
widely used to isolate RNA, DNA, or proteins1.
Brief History
Volkin & Carter reported the first use of guanidinium chloride in the isolation of RNA in 1951
(30). In 1953, Grassmann & Defner described the efficacy of phenol at extracting proteins
from aqueous solution (16). Utilizing this find, Kirby demonstrated the use of phenol to
separate nucleic acids from proteins in 1956 (18). Cox and others renewed interest in the use
of guanidinium chloride in the isolation of RNA from ribonucleoproteins in the 1960s
(11,12,13). From then on, guanidinium extractions were the method of choice for RNA
purification, replacing phenol extraction. The use of guanidinium thiocyanate instead of
guanidinium chloride was first briefly mentioned by Ullrich et al. in 1977 (29), and later
successfully employed by Chirgwin et al. in 1979 (8). Chirgwin et al. used guanidinium
thiocyanate to isolate undegraded RNA from ribonuclease-rich tissues like pancreas. A
combination of guanidinium thiocyanate and hot phenol for RNA isolation was reported by
Feramisco et al. in 1981 (14). In 1987, Chomczynski & Sacchi combined guanidinium
thiocyanate with phenol-chloroform extraction under acidic conditions (9). Since its
inception, the Chomczynski & Sacchi method has been the method of choice to isolate RNA
from cultured cells and most animal tissues (10).
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