GPC/ICP-AES法によるカラギナン分子量測定方法

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Carrageenan is one of a few high-molecular weight substances in nature, which has a lot of sulfur atoms in its molecule. High performance liquid gel permeation chromatography (GPC) can fractionate the high-molecular weight region, and vacuum-ultraviolet inductively coupled plasma-atomic emission spectrometry (ICP-AES) can detect sulfur directly, when GPC/ICP-AES method is used. Unfortunately, it was not acceptable chromatogram on GPC/ICP-AES, which measured the sulfur intensity by ICP-AES, to calculate the average molecular weight of carrageenan, because of higher noise level of the GPC/ICP-AES chromatogram had been obtained. As the results of modifications for GPC conditions by using lambda-type refined carrageenan, we obtained well-fractionated chromatogram on GPC/RI, when the GPC conditions are followed: eluent; 50 mM sodium nitrate, sample content of injected solution; 0.1 mg/mL, elution speed; 0.5 mL/min, elution temperature; 50℃. However, we obtained well-fractionated chromatogram on GPC/RI of lambda-type carrageenan, there was another concern about kappa- and iota-type carrageenan. Kappa- and iota-type carrageenan form a three-fold right-handed double helical structure in aqueous solution. This formation of double helical structure depends on carrageenan concentration, temperature, spices and concentrations of co-cations in aqueous solution. So, it was considered to check if the conditions of ion strength in eluent and elution temperature of GPC was enough to avoid the formation of double helical structure of kappa- and iota-type carrageenan, or not. As the results of optimization of ICP-AES condition and data integration time of GPC/ICP-AES chromatogram, we obtained good chromatogram on GPC/ICP-AES, when the conditions are followed: diffracting order; 4^<th>, RF-power; 1.50 kW, nebulizer pressure; 200 kPa, PMT voltage; 900 V, data integration time; 4.0 sec. The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of lambda-type refined carrageenan we tested, were 446 kDa and 990 kDa respectively, measured by GPC/ICP-AES method in this condition. And the vales of Mn and Mw measured by GPC/ICP-AES method, were almost same as the vales of average molecular weights measured by GPC/RI method respectively. But, when the average molecular weight is calculated via GPC/ICP-AES chromatogram, which measured the sulfur intensity by ICP-AES, the content of sulfur in each molecule must be equal. If the content of sulfur in each molecule is not equal, the sulfur intensity measured by ICP-AES dose not represent the content of solute. Because the average molecular weight of lambda-type refined carrageenan measured by GPC/ICP-AES method was almost same as that measured by GPC/RI, it was considered that the content of sulfur in each molecule of tested carrageenan is almost equal. Regarding this result, it seemed useful to measure the average molecular weight of such carrageenans by GPC/ICP-AES method. The sulfur recoverys of high-molecular weight substances from injected lambda-type refined carrageenan were varied from 97 to 108 % measured by GPC/ICP-AES method. And there was good correlation between lambda-type carrageenan contents in injected solutions and sulfur amounts of high-molecular weight substances measured by GPC/ICP-AES method. This result suggested that it was possible to determine sulfur content of high-molecular weight substances by GPC/ICP-AES method. And it was considered that the GPC/ICP-AES method might determine carrageenan contents in food applications, when it was available which carrageenan was use in a certain food application and the sulfur content came from high-molecular weight substances in its carrageenan was available by GPC/ICP-AES method or total and ionic sulfate analysis.
日本食品化学学会の論文
2001-03-31

GPC/ICP-AES法によるカラギナン分子量測定方法

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