Experiment Station Record, Volume 92, January-June, 1945 Page: 10
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10 EXPERIMENT STATION RECORD Vol. 92
man (about 27 mg. daily) corresponds approximately to the daily requirement of
50 mg. of ascorbic acid.
The rapid determination of ascorbic acid bVy the adaptation of Stotz's method
to plant materials, L. P. PEPKOWITZ. (R. I. Expt. Sta.). (four. Biol. Chem.,
151 (1943), No. 2, pp. 405-412).-Stotz's method (E. S. R., 88, p. 153) for ascorbic
acid in blood and urine is adapted for application to extracts of plant tissues prepared
by homogenizing representative 30-50-gm. samples in 200 cc. of 1.0 percent
metaphosphoric acid in a Waring blendor. The method depends upon the fact that
unreduced 2,6-dichlorophenolindophenol can be selectively and quantitatively extracted
from the reaction mixture with xylene and the fact that the xylene solution
of the dye follows Beer's law, permitting quantitative determination in a photoelectric
colorimeter with a filter transmitting at 500 mgl. Two procedures are presented
to correct for extraneous xylene-soluble pigments contained in certain plant
extracts. Because of its simplicity, the method is rapid, permitting 60-70 determinations
to be made in a day. The method was found applicable to all plant materials
tried, whether fresh, frozen, or dried, and to be particularly useful for highly colored
or turbid extracts. Protocols of recovery experiments with a number of foods
indicate a recovery of 99 percent. Other data show, in general, satisfactory agreement
with the method of Bessey (E. S. R., 82, p. 14).
The determination of ascorbic acid in whole blood and its constituents by
means of methylene blue; macro- and micromethods, A. M. BUTLER, M. CUSHMAN,
and E. A. MACLACHLAN (four. Biol. Chem., 150 (1943), No. 2, pp. 453-461).
-Macro- and microprocedures are described for the determination of ascorbic acid
in oxalated whole blood, in the plasma, and in the buffy layer of white cell platelets
separated from: the red cells by centrifugation. The photochemical method employed
involves the reduction of methylene blue by ascorbic acid in the presence of strong
light at the optimum pH of 4.5 maintained by acetate buffer in the dye solution. To
prevent the rapid reversal of this reaction, with the conversion of the leucomethylene
blue back to the colored form, the pH of the medium is changed by'rapid addition of
HC1 immediately preceding discontinuance of the illumination. This stabilization
permits a photocolorimetric determination without change in color. "Because
methylene blue under the condition of the procedures developed is a more sensitive
and specific oxidation-reduction indicator for ascorbic acid than are the commonly
used indophenol indicators, its use provides micromethods that are more satisfactory
than those heretofore available." Satisfactory analyses can be obtained with 0.2 cc. of
capillary whole blood.
A new method for the bioassay of antiscorbutic substances: Assays of dehydroascorbic
acid, 2-ketogulonic acid, iron ascorbate, and the effectiveness of
oral and parenteral administration of ascorbic acid, B. S. GOULD and H. SHWACHMAN
(Jour. Biol. Chem., 151 (1943), No. 2, pp. 439-453, illus. 4).-The method is
based upon the observations of Shwachman and Gould (E. S. R., 88, p. 569) that
an increase in serum "alkaline" phosphatase occurs in scorbutic guinea pigs after
administration of a critical dose of ascorbic acid, and involves depletion of guinea
pigs on a scorbutic diet to phosphatase levels of 3-5 units or lower, following which
individual animals in respective groups are fed daily the sample equivalent (as determined
by titration) of 0.2, 0.225, and 0.25 mg. of ascorbic acid. On the fifth day
after the first dose the animals are bled and the serum phosphatase determined. In
interpreting the results, it is considered that groups in which 50 percent or more of
the animals show a decrease in serum phosphatase, while none shows a significant
increase, have been receiving less than 0.225 mg. ascorbic acid daily; with most of
the animals in a group showing an increase and some no extensive change, the group
has been receiving the critical dose, 0.225 mg. If all show marked increases, the
critical level may have been exceeded. Increases of about 10 percent should be dis
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U.S. Department of Agriculture. Agricultural Research Administration. Office of Experiment Stations. Experiment Station Record, Volume 92, January-June, 1945, book, 1947; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc5064/m1/23/: accessed July 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.