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THE CRITERIA OF PURITY USED IN THE STUDY OF LARGE MOLECULES OF BIOLOGICAL ORIGIN
Author(s) -
PIRIE N. W.
Publication year - 1940
Publication title -
biological reviews
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.993
H-Index - 165
eISSN - 1469-185X
pISSN - 1464-7931
DOI - 10.1111/j.1469-185x.1940.tb00945.x
Subject(s) - solubility , crystallinity , chemistry , precipitation , molecule , chromatography , organic chemistry , crystallography , physics , meteorology
Summary The limits, in weight and chemical stability, of the group of substances referred to as large molecules are discussed and the range is arbitrarily taken as from particles unresolvable by the microscope to those with molecular weight 5000. A unit of molecular weight is proposed and its advantages are discussed in cases where the nature of the bonds holding a particle together is uncertain. Four distinct meanings that can be carried by the word pure are described, and examples are given of each type of purity. The types of observation generally made and presented as evidence that a substance is pure are considered under seven headings. Chemical analysis and crystallinity are the least reliable, and specific serological tests can only show the absence of contaminants whose presence is suspected. The measurement of end‐points, whether by serum precipitation or infection, is subject to several errors and can at best only indicate whether or not the major constituent of a preparation may be serologically active or infective. Electrophoresis, ultracentrifugation and studies based on the principles of the Phase Rule, i.e. solubility and partition measurements, give the most reliable evidence of purity at present available. Several reasons are given for thinking that even these methods may be fallible.