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Alginate, a polysaccharide of brown algae, has been used in various industries, e.g. textile, dyeing, paper, food and pharmaceutical.1) Alginate is a linear co-polymer of D mannurate (M) and L-guluronate (G), and is known to be composed of homo-polymer blocks of M and G, and hetero-polymer block.1,2) The physical and chemical properties of alginates, e.g. viscosity, solubility, interaction with metals, and the prop erties of gels, are closely related to their M/G ratio and the relative amounts of homo and hetero-polymer blocks3-6) besides the average degrees of polymerization (average molecular weights). In 1962, the determination of the uronic acid composi tion in alginate was attempted" by the complete hydrolysis with sulfuric acid followed by chromatographic separation of uronates on an anion-exchange column and orcinol reac tion. This method was modified by Gacesa et a1.,8) Bouffar-Roupe and Heyraud,9) Anzai et al.,10) and Hey laud and Leonard.11) In 1974, Haug et al. 12) reported another method to determine the M / G ratio by quantifica tion of homo-polymer blocks (M-block and G-block) and hetero-polymer block (MG-block); partial hydrolysis with diluted hydrochloric acid (HCI) followed by fractional precipitation by changing pH. Moreover, the methods us ing 1H13-15) and13 C-nuclear 16-18) magnetic resonance (NMR) spectroscopy, circular dichromism,19) and infrared spec troscopy20) were reported. The standard method to meas ure the M/G ratio, however, has not yet been established. Recently, many reportsa4-6,20-29) have been published on the composition and the sequence of uronate residues in al ginates using 1H and 13C-NMR spectroscopy. In these reports, the NMR spectra of alginates were measured after partial hydrolysis of intact alginates because solutions of intact alginates are too viscous to obtain desirable resolu tion of signals. None of these reports, however, discussed the following problems on the determination of M/G ratio in alginates by 1H-NMR spectroscopy. (1) The accuracy of integrated values (area) of signals; the areas of signals in spectra are measured by the routine integral program of spectrometers, but the integral values are affected by the drift of the base line. It might sometimes be difficult to ad just the start and the end of integral curve horizontal. (2) The spectrum must be measured in D20, in which the huge signal of HDO reduces the S/N ratio of the signals of al ginate. The pulse techniques to reduce the huge signal, e.g. homogated decoupling (HMG), have been used, but the there was no report which mentioned about power of ir radiation pulse (irradiation attenuation). (3) No report can assure that the M/G ratio in the partially hydrolyzed al ginate coincide with that of intact alginate. In this paper, we report the relationships between guluronate contents (G%) in partially hydrolyzed al ginates and their weight average molecular weights (WAMW) to evaluate the reliability of 'H-NMR method. The 'H-NMR spectra were measured by a 270 MHz spec trometer, and the spectra were transferred to digital im ages and processed by an image analyzing software to measure the area of signals.

Relationships between Guluronate Contents in Alginates Determined by <sup>1</sup>H-NMR Spectroscopy and Their Average Molecular Weights