Method 714 Determination of water soluble carbohydrate by autoanalysis

See the discussion in Chapter 4 'Nitrate and water soluble carbohydrate'.

Note: the extract obtained for determining nitrate in plants, which is also in saturated benzoic acid, may be used for the water soluble carbohydrate determination if diluted x2.

Reagents.

• Anthrone reagent - dissolve 0.5 g anthrone in 500 ml sulphuric acid, 76% v/v. Prepare fresh daily and keep at 0-5°C.

• Benzoic acid, saturated solution.

• Sulphuric acid, 76% v/v - Caution: wear PPE. Carefully add 760 ml sulphuric acid (approximately 96% m/m H2SO4) to 330 ml water in a 2-l beaker standing in a sink containing cold water. Stir slowly with a glass rod to mix and allow to cool. The solution will 'shrink' to approximately 1 l. Pour into a 1-l volumetric flask, make up to the mark, firmly stopper and carefully invert to mix.

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