ANALYTICAL CHEMISTRY
420 Voskuyl, who collaborated with the authors on other phases of the research, contributed by his counsel t o the development of the equipment described in this paper.
LITERATURE CITED
(1) Dole and Slobod, J. Am. Chem. 5 m . 62, -271 (1940). RECEIVED February 4, 1948
Sensitization of Fuchsin-Sulfurous Acid Reagent for Formaldehyde by Addition of Ketones CARROLL L. HOFFPAUIK AND ROBERT T. O'CONNOR Smithern Repionul Research Laborutory, .Yew Orleans, La. UCHSIS-sulfurous acid reagent, for the qualitative or quanFtitative determination of small quantities of formaldehyde has been used for many years ( I , 2, 3 ) . Efforts t o increase its sensitivity have usually been directed toward holding the sulfurous acid content t o a minimum. Thus, Tobie (5) suggests reducing the sulfur dioxide content from 5 to 2 grams per liter, a n d points out ( 4 ) t h a t the presence of considerable ethanol intensifies the color. T h e present authors have observed t h a t the presence of acetone causes the development of a more intense color in the reaction of a given amount of formaldehyde a n d a given amount of fuchsin-sulfurous acid reagent.
100
90
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0 ?!
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I n order to follow this effect, t o known amounts of a standardized solution of formaldehyde in a 25-ml. volumetric flask were added 5 ml. of 12 X sulfuric acid, 10 ml. of fuchsin-sulfurous acid reagent ( 2 ) , and increasing amounts of acetone. T h e flasks were made t o volume with water, the reagents mixed, and the per cent transmittance \Tas determined b y means of a n Evelyn photoelectric colorimeter with a So. 565 filter. T h e blanks for setting the instrument cont'ained all reagents, but distilled water was used to replace the formaldehyde solution. Increasing amounts of acetone u p to 2 nil. iricrease the intensification of color, but further increases in amount of acetone produce no further intensification. As shown in Figure 1, in the presence of acetone 3.25 hours are required for maximum color development compared to 2 hours for niaximuni color development in the absence of acetone. The color developed is more stable in the presence of acetone. Spectrophotometric curves plotted in Figure 2 show t h a t though the maximum color is more intense in the presence of acetone, there is no shift in the wave length of maximum absorption nor any change in the iiature of the curve in the visible spectrum. T h e curve of per cent transmittance us. concentration in the presence of acetone differs only 100 R
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T O
U W U
n
80
so 400
500
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700
600
LENGTH
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MILLIMICRONS
Figure 2. Transmittance Curves of Formaldehyde-Schiff's Reagent A.
B.
Schiff's-formaldehyde color Schiff's-formaldehyde color in presrnce of acetone
in intensity of absorption fi,orii t t i a t previourly published in the a h w i c e of acetone ( 8 ) . Similar effects were noted for inethyl n-propyl ketone, diethyl ketone, diacetone alcohol (4-hydroxy-4-methyl-2-pentanone), and methyl ethyl ketone. The time of niaxiriium color development and intensity were essentially the same as in the presence of acetone. Ethylene glycol was found to intensify the color slightly. However, fructose, a ketose, had no effect on the time or intensity of the color developed by fuchsin-sulfurous acid reagent with formaldehyde. As none of these ketones produces any more intense color than acetone, t h e use of t,his common solvent is recommended where maximum .-ensitivity is required when t h e fuchsin-sulfurous acid reagent is u s d . ACKNOWLEDGhIENT
T h e authors gratefully acknowledge the assistance of Elsie T Field in obtaining the spectrophotometric data used in these studies.
2ot
I
per 25 ml.
C. 0.069 mg. CHiO and 10 ml. fuchsin-sulfurous acid per 25 ml.
D.
0.069 mg. CHzO and 10 ml. fuchsin-sulfurous acid and 2 ml. acetone per 25 m l .
LITERATURE CITED
(1) Feigl, F.,"Qualitative Analysis by Spot Tests," 3rd ed., New York, Elsevier Publishing Co., 1946. (2) Hoffpauir, C. L., Buckaloo, G. W., and Guthrie, J. D., IND. Esr,. CHEM.,ASAL.ED.,15,605 (1943). (3) Schiff, H., Ann., 140, 93 (1866). (4) Tobie, W. C.,Food Research, 6,15 (1941). (5) Tobie, W.C.,IND. ENG.CHEM.,AXAL.ED., 14,405 (1942). RECEIVED April 2, 1948.
