Analysis of Mixtures of Hydrogen Peroxide and Formaldehyde SIR: In II not-so-recent paper, Sattefield et a1 (I) have given a procedure for the determination of formaldehyde in aqueous solutions of hydrogen peroxide using Schiff s reagent. The concentrations of peroxide were in the range of 4-35 and the concentrations of aldehyde were in the range of 2-28 weight %. Because of the equilibria which were established,
+ i2 CH2(0H)OOH CHz(0H)OOH + CH20 $ CH2(0H)OOCH2(0H) CH2O
Table I. Determination of Formaldehyde in the Presence of Hydrogen Peroxide Initial solution Moles x lo9 Moles X 106 HICO Hz0z
H202
Formaldehyde found, of true value
10.0 7.5 5.0 2.5
2.5 2.5 2.5 2.5
88.9 87.0 88.4 90.6
10.0 7.5 5.0 2.5
5.0 5.0 5.0 5.0
85.4 81.4 84.4 82.6
10.0 7.5 5.0 2.5
10.0 10.0 10.0 10.0
67.5 67.8 69.9 64.4
(2)
analysis in the presence of hydrogen peroxide gave low results since Schiff's reagent detected free aldehyde and monohydroxymethyl hydroperoxide but not dihydroxydimethyl peroxide. Consequently, prior to analysis of the aldehyde, the peroxide in the original sample was removed by reaction with hydriodic acid. After titration of the liberated iodine with thiosulfate, the resultant solution was diluted to about 1 to 3 pmoles of aldehyde per ml prior to adding 1 ml to Schiff's reagent. Although the method described above was satisfactory for the initial high concentrations of formaldehyde and hydrogen peroxide used, its usefulness for gas phase reactions where the aldehyde and peroxide could be condensed for subsequent analysis was not obvious. A study of particular interest is the photochemistry of planetary atmospheres where both H 2 0 z and H2CO may be present or formed. In experiments in our laboratory on gas phase reactions of hydrogen peroxide and carbon monoxide, the formation of total formaldehyde corresponding to that contained in 1 ml of a 1 t o 3 pmole per ml solution was possible. With commercial 90 weight H 2 0 2at ambient temperature as a source of peroxide vapor and a 100ml reaction vessel, the gas phase contained some 7 pmoles of hydrogen peroxide. It occurred to us that it should be possible to carry out analysis satisfactory for our purpose without removing hydrogen peroxide which, under our conditions of very small amounts, might have proved troublesome. Freshly mixed solutions of formaldehyde and hydrogen peroxide were allowed to stand 1 hour after which 2 ml were added t o 2 ml of Schiff's reagent and 0.48 ml of 75 weight % sulfuric acid solution according to the method of Blacet and Blaedel (2). After two more hours, the absorbance was measured in a spectrophotometer at 580 nm. The results are given in Table I. The formaldehyde found is based on a calibration using solutions of formaldehyde without hydrogen peroxide. From our results the following conclusions may be drawn: the results of Satterfield et al. ( I ) on the interference by hydrogen peroxide are confirmed ;Schiff's test is qualitatively satisfactory for small amounts of formaldehyde in the presence of small amounts of hydrogen peroxide, albeit considerably greater than formaldehyde; the method is semiquantitative if the general range of peroxide quantity is known; the method is
quantitative if the amount of peroxide is known and calibration is made accordingly. Gaseous systems of formaldehyde and hydrogen peroxide d o not react in the dark at ambient temperatures (3). Therefore, postreaction-residence time in the gas phase will not affect the analytical results. However, establishment of the equilibria represented by Equations 1 and 2 are time dependent. Consequently, both the reaction mixture and the calibration standards should have the same residence time in the aqueous system and, of course, equal standing time after the addition of Schiff's reagent. The periods we have adopted, 1 hour prior to and 2 hours subsequent to addition of Schiff's reagent, appear to be satisfactory. It may be noted that formaldehyde, which otherwise gives no response, may be determined by gas chromatography using hydrogen flame ionization after reduction with hydrogen over a hot nickel catalyst (4) to yield methanol (5). The sensitivity is about equal to that of Schiff's test. Thus chromatography may be more suited to on-line applications in gas phase systems involving frequent analysis where construction of the catalytic system would be warranted. The Schiff's test, however, would seem to be simpler for infrequent analysis.
(1) C. N. Satterfield,R . E. Wilson, R. M. LeClair, and R. C . Reid,
(3) D. E. Hoare, Proc. Roy. Soc., Ser. A , 291,73 (1966).
ANAL.CHEM., 26, 1792 (1954). (2) E. E. Blacet and W. J. Blaedel, J. Amer. Chem. Soc., 62, 3374 (1940).
284
R. A. GORSE D. H. VOLMAN Department of Chemistry University of California Davis, Calif. 95616
RECEIVED for review July 30, 1970. Accepted October 19, 1970. This work was supported by Grant GP 13974 from the National Science Foundation.
(4) K. Porter and D. H. Volman, ANAL.CHEM., 34,748 (1962). (5) L. M. Toth and H. S. Johnston, J . Amer. Chem. Soc., 91, 1276 (1969).
ANALYTICAL CHEMISTRY, VOL. 43, NO. 2, FEBRUARY 1971
