1. K. Hasegawa, Shokuhin Bunseki (Food Analysis, in Japanese), Baifukan, Tokyo, 1993, Ch. 5, p. 72.
2. Resources Council, Science and Technology Agency, Japan, Standard Tables of Food Composition in Japan, 4th Revised Edition, Ministry of Finance, Japan, Tokyo, 1995, Ch. 1, p. 35.
3. M. Okamura and N. Arakawa, in The Vitamin Society of Japan, Bitamin Bunseki Ho (Method of Vitamin Analysis, in Japanese), Kagaku Dojin, Kyoto, 1994, Ch. 16, p. 135.
4. A. Rizzolo and S. Polesello, J. Chromatogr., 624 (1992) 103.
5. L.L. Lloyd, F.P. Warner, J.F. Kennedy and C.A. White, J. Chromatogr., 437 (1988).