Microgram analysis; further studies of determination of glucose and its application to the determination of sucrose.

Commonly, microanalysis of plant sugars is conducted on a mg. scale (1); on the microgram level, a general method appears to be lacking. Some calorimetric methods suitable for determination of microgram quantities of sugars are available, but for a combination of high sensitivity and good accuracy these are not very satisfactory. Anthrone, for example, has been used recently to determine sucrose in amounts as low as 2 y (2), but there is no indication by the author as to the degree of accuracy possible. A summary of the various color reactions for different sugars by Umbreit (3) indicates a lower limit in all cases of 10 Y with an accuracy of f4 per cent. Our aim has been to make possible the analysis of sugars in amounts .as low as 1 y, with a maximum variation for single determinations of f2 per cent. Since non-reducing sugars are easily hydrolyzed to reducing ones, the problem is largely one of determining reducing sugar. This has already been solved by Heck, Brown, and Kirk (4) titrimetrically by the use of ferricyanide and ceric sulfate, a method inherently more accurate than calorimetric procedures. In the original work, however, a number of small factors were overlooked which nevertheless strongly limited the accuracy of determinations, especially at the lower limits of the method. Our present report deals, therefore, with these accessory points of technique and further describes the adaptation of the method to sucrose analysis. In an accompanying publication methods of extraction and separation of sugars from plant tissues with weights of the order of 1 mg. are discussed.