High-performance size-exclusion chromatography (HPSEC) is being used increasingly for the determination of molecular weight and size distributions of polysaccharides. This information is of fundamental importance both for the characterisation of these materials and for developing a better understanding of the structural origins of their physical and functional properties.
An accurate measure of the molecular size distribution of carrageenans can only be obtained under conditions in which aggregation of the sulphated galactan chains does not occur. This has been achieved in conventional gel permeation chromatography (GPC) by operating both column and eluent at high temperature (ca. 60Β°C) and by using either lithium' or sodium2 salts as the electrolyte in the eluant. Universal calibrations, in which the distribution coefficient (J&J is expressed as a function of the molar volume (nTi, (q]), h as shown3 that Sepharose CL-4B is able to characterise carrageenans with molar volumes up to 8.32 . lo4 l/mol whilst Sepharose CL-2B separates carrageenans with molar volumes up to 1.85 . lo5 l/mol.
Similar conditions have been used in the measurement of molecular weight distributions of carrageenans by HPSEC using a column set that comprises of a TSK G 6000 PW and TX G 5000 PW (each column 60 cm x 7.5 mm I.D.), with 0.1 M lithium chloride as eluent at an operating temperature of 60"C4. The molecular weight of the carrageenan eluted from the column set was determined directly by on-line light-scattering photometry but an upper limit of molar volume resolvable by this column set was not reported.
This paper describes an HPSEC system for measuring the molecular weight and size distributions of carrageenans using a LiChrospher 1000 DIOL column under similar conditions to those used in conventional GPC2. The LiChrospher 1000 DIOL column is packed with a silica of pore size 1000 b; surface-modified with 1,2-dihydroxy-3-propoxypropyl groups 5. This type of column has been used for the separation of biopolymers, especially proteins6v7.