Elimination of Nitrite Interference in Iodometric Sugar Determinations JULIAN GORMAN Northern Regional Research Laboratory, Peoria, III.
TT IS frequently A
desired to determine reducing sugars by iodometric methods (ferricyanide or copper reduction followed by iodometry) in bacteriological culture media containing nitrites. However, erroneous sugar -values are obtained when such a medium is assayed by any of these methods, as for instance, the Somogyi procedure {&). The cause of the error lies in the fact that potassium iodide, in an acidified sodium nitrite solution, produces free iodine. It is obvious, therefore, that nitrites must be eliminated before one proceeds with the sugar determination. In the Groak (I) iodine microdetermination excess sodium nitrite is eliminated by addition of urea to the hot acid solution.
HüNCONHj + 2HONO
—>
C02
+
2N2
Table I.
10-ML Aliquot in 100-ML Volumetric Flask
+ 3H20
Treatment
=*
indicated above, to show removal of nitrite interference. Similar experiments were performed with maltose and sucrose solutions. as
Ten milliliters of 1.0% sodium nitrite solution and 10 ml. of 10.0% urea were mixed in a 100-ml. volumetric flask. Five milliliters of 1 N sulfuric acid were added. The flask was shaken occasionally and after 30 minutes 2 drops of phenolphathalein were added. The solution was neutralized with sodium hydroxide and made up to volume with distilled water. Assay of a 5-ml. aliquot resulted in a titration of 24.50 ml. of thiosulfate, equal to the blank titration. Thus in the absence of sugar, nitrite interference had been eliminated completely. was
0.005 .V
Thiosulfate Titration Titration Difference' Ml. Ml. None (control) 14.20 10.30 0.3% glucose Nitrite 47.10 Negative Nitrite 4- urea 4- H2SO1 14.20 10.30 None (control) 13.60 10.90 0.53% maltose Nitrite 45.00 Negative Nitrite 4- urea 4- H2SO4 10.90 13.60 None (control) 24.45 0.05 1.0% sucrose Nitrite 45.50 Negative Nitrite 4 urea 4- HsSO* 24.25 0.25 0 Titration resulting from presence of sugar minus reagent blank. Re24.50 ml. agent blank
Adaptation of this procedure for the elimination of nitrite interference prior to iodometric sugar determinations was therefore investigated.
The efficacy of this procedure
Elimination of Nitrite Interference in Iodometric Sugar Determinations
Results given in Table I show that interference by nitrite, in the presence of sugars, was completely eliminated. Sucrose was apparently hydrolyzed to a negligible extent by the mild treatment with sulfuric acid while maltose was not affected. Not only are nitrites commonly added as such to culture media, but they are sometimes formed by the action of microorganisms, as from the oxidation of ammonia or the reduction of nitrates. Regardless of the source of nitrite interference, this interference can be eliminated effectively as described above.
tested with different sugars.
Ten milliliters of a glucose solution were pipetted into each of three 100-ml. volumetric flasks. The solution in one flask was diluted to volume and assayed in the regular manner as a control. Ten milliliters of 1.0% sodium nitrite solution were added to each of the other two flasks. One of these was diluted to the mark and assayed to show the extent of nitrite interference. The remaining flask was treated with an excess of urea and sulfuric acid
LITERATURE
CITED
(1) Groak, B„ Biochem. Z.. 270, 291-6 (1934). (2) Somogyi, M., J. Biol. Chem., 160. 61-8 (1945).
Removal of Oxygen from Gas Streams LOUIS MEITES1 AND THELMA VIEITES1 Frick Chemical Laboratory, Princeton University, Princeton, N. J. most popular agents for removing oxygen from gases hot finely divided copper and a train of chromous sulfate solutions. Although either absorbs oxygen substantially completely, both have disadvantages that render their use
regeneration by addition of sulfuric acid (conveniently through a small separatory funnel whose stem projects through the stopper of the wash bottle) proceeds so rapidly that the solutions are again ready for use almost instantly. Unlike alkaline suspensions of hydrous chromic oxide, alkaline suspensions of hydrous vanadio oxide are highly effective in oxygen removal, being oxidized to vanadite, which itself strongly absorbs oxygen and is converted to vanadate. Therefore the absorptive capacity of a vanadous sulfate solution is much greater than that of an equiconcentrated chromous sulfate solution, and regeneration is necessary much less frequently.
are
inconvenient. Not only is a copper heater somewhat tedious to construct and place in operation, but much time is required to attain operating temperature: these are serious drawbacks when the apparatus is to be used only infrequently. Chromous sulfate solutions, generally prepared by the reaction of metallic zinc and acidified chromic sulfate, must be allowed to stand for many hours before they are ready for use. Further, because the hydrous chromic oxide formed on aging is dissolved and reduced only slowly on addition of acid, the maintenance of these solutions in operating condition is a source of constant annoyance. The authors have found that vanadous sulfate solutions present A solution initially 0.1 M in vanadyl none of these difficulties. sulfate and containing some free sulfuric acid is ready for use within a minute or two after amalgamated zinc is added, and i Present, address, Department of Chemistry H aven, Conn.
The authors have used a train of three wash bottles, the first two of which were initially charged with 100 grams of lightly amalgamated zinc and 100 ml. of 0.1 M vanadyl sulfate, and the third contains 100 ml. of water to ensure absence of vanadium This assembly has now been in from the emergent gas stream. operation for over 9 months, and has been regenerated only twice. Its performance in nearly continuous service has been
eminently'satisfactorv. Tank nitrogen passed through this train was used to remove dissolved air from 50 ml. of air-saturated 0.1 .V potassium chloride, 0.005 M sodium hydroxide, and 0.01 % gelatin contained in a polarographic H-cell (.?). and the oxygen diffusion current at
Yale University, New
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