ANALYTICAL CHEMISTRY
540
but the ignited residue is slightly colored. On a second precipitation the color disappears. Ferric iron is only partially precipitated in neutral solutions. Beryllium, aluminum, nickel, calcium, barium, uranyl, and trivalent rare earths (cerite group) are not precipitated. Sulfate interferes with the determination of zirconium.
( 3 ) and after removal of silica, zirconium was determined by double precipitation with m-cresoxyacetic acid in 0.20 iV hydrochloric acid. The results are shown in Table 111. For comparison, values obtained with the cupferron method ( 4 ) are included. LITERATURE CITED
ANALYSIS O F ZIRCOR
The method was checked by determining zirconia in a zircon ore from Travancore, India, which was found on qualitative analysis to contain silica, titania, and ferric oxide as well as zirconium. Thorium, aluminum, and the rare earths were not present in detectable amounts. The ore was fused with borax
(1) Koelsch, C. F., J . Am. Chem. Soc., 53,304 (1931). (2) Kumins, C. A., ANAL.CHEM.,19, 376 (1947). (3) Lundell, G. E. F., and Knowles, H. B., J . Am. Chem. Soc., 42, 1439 (1920). (4) U. S. Bur. Mines, BULL. 212 (1923). RECEIVED
April 4, 1950.
Fluorometric Determination of Benzil SAMUEL SASS AND JEROME GOLDENSON Chemical Corps, Technical C o m m a n d , Army Chemical Center, Md.
iX AX investigation of miticides for use in clothing, a method Iimpregnated was required for the determination of small amounts of benzil in cloth. Attempts to find suitable colorimetric n
method for this new effective miticide ( 1 , 2, 7 ) were unsuccessful ( 4 ) . An adaptation of a gravimetric method (6) was found to be accurate for larger quantities of benzil in pure finish cloth ( 4 ) ,but impurities which are soluble in ethyl alcohol and insoluble in dilute hydrochloric acid interfered and the method was not suitable for trace amounts. Application of ultraviolet absorption measurements a t the strong absorption band of b e n d (260 mp) wap limited because of marked interferences in cloth containing ultraviolet-absorbing material such as certain sizing preservatives The condensation reaction ( 3 )of diketones such as benzil and nitrobends with alkylated aminophenols to form blue-red dyestuffs with yellow-red fluorescence was utilized in the method described here. In the procedure developed, benzil is determined photofluorometrically as a eondensation product with m-diethylaminophenol. It was also observed that very small amounts of alkylated aminophenols can be detected by condensation with an escess of benzil. APPARATUS
Klett photofluorometer, Model 2070, with matched tubes and filters 597 and 351. Beckman quartz spectrophotometer, Model CUV, range 220 to 1000 mp, with interchangeable hydrogen discharge lamp in housing! power supply unit, and a pair of fused silica absorption cells with borosilicate glass covers. REAGENTS
Benzil, technical grade material, purified by recrystallization from 95% ethyl alcohol. Analysis: C, 79.9%; H, 4.77% (calculated for benzil, CllH1002: C, 79.98%; H, 4.79%). Reagents for fluorometric method. m-Diethylaminophenol, recrystallized from 95% ethyl alcohol. Reference solution, 0.0004 gram of fluorescein in 1 liter of water. Reagents for gravimetric determination. 2,CDinitrophenylhydrazine solution made by saturating 2 N hydrochloric acid with 2,4dinitrophenyIhydrazine, 2 S hydrochloric acid, and 95% ethyl alcohol. DEVELOPMENT 0F FLUOROMETRIC METHOD
Investigations were conducted to determine whether the condensation reaction ( 3 )could be adapted as a quantitative method for the estimation of benzil. Exploratory work with several aminophenols indicated that a compound melting below 100" C. would give the best results. m-Diethylaminophenol (melting point 78" C.) was found to be a satisfactory reagent !Then condensed with benzil a t 100" C. for 90 minutes. Two to 4 moles of the aminophenol are required for each mole of benzil ( 3 ) . Re-
coveries of 98% and better were obtained on purified samples of benail by this method. Unsized, undyed cotton pure-finish herringbone twill cloth was impregnated with known quantities of b e n d . The miticide w a i then extracted with ethyl alcohol and determined by the fluorometric method. Recoveries of 97% or better were obtained. With b e n d which had not been impregnated in cloth recoveries of 98% or better were obtained.
Table I. Comparison of Fluorometric with Gravimetric and Ultraviolet Absorption Methods for Determination of Benzil i n Cloth Benzil, % Sample NO.
Fixative Chlorinated paraffin Chlorinated paraffin Chlorinated paraffin Chlorinated paraffin Chlorinated uaraffin None None None None
Fluorometric 5.17 5.20 2.16
Gravimetric 5.10 LO2
2.07
0.07
0.01 7.66 0.17 0.25
0.76
7:47 0.19
0.27 0.80
Cltraviolet absorption measurement 5.35
5.29 2.08 0.07 0.01 7.61 0.18 0.25
0.78
The results given in Table I were obtained by application of the follo~-ingfluorometric method t o samples of pilot plant impregnated cloth. As this cloth did not contain material that would interfere in the gravimetric or ultraviolet absorption methods, these methods were used for comparison purposes and are also described below. Cut the cloth sample into 1-cm. squares and mix to make more homogeneous. Place a 3.000- to 5.000-gram sample of cloth (enough to contain a t least 1 mg. of benzil) in the thimble of a Soxhlet extraction apparatus. Extract with 95% ethyl alcohol for 2 hours. If the extract is turbid, let it stand overnight and filter. Make up the extract to a known volume in a volumetric flask with 95% ethyl alcohol, so that a concentration of 0.01 to 0.04 mg. of benzil per ml. is obtained. Using a pipet or microburet, accurately measure 1 ml. of the solution into a test tube. To the same test tube add from a microburet 1ml. of a 95% ethyl alcohol solution containing 50 mg. per ml. of m-diethylaminophenol. Place the test tube over a hot water bath maintained a t 100' C. and heat for 90 minutes. (A 3-liter beaker covered by a Transite board a i t h holes large enough to support a test tube by the flare serves as an escellent bath when heated on a hot plate. The water level should be just below the bottom of the tube.) Wash the melt from the test tube into a 100-ml. volumetric flask and make up to volume with 95% ethyl alcohol. Make measurements on a Klett photofluorometer using filter? 597 and 351 with a reference solution of 0.0004 gram per liter of fluorescein. Prepare a curve relating fluorometer reading with
V O L U M E 23, NO. 3, M A R C H 1 9 5 1
541 Ultraviolet Absorption Method. Ethyl alcohol wm used a5 the solvent and absorption measurements were made with a Beckman quartz spectrophotometer. The maximum absorption for benzil in 95% ethyl alcohol occurs a t a wave length of about 260 mp (6). Absorption readings were made a t 260 mp and a slit width of 0.5 mm. The Beer-Lambert law holds only approximately for benzil in 95% ethyl alcohol a t this wave length. For this reason it was necessary to plot a curve of log Io/I versus concentration. The cloth samples were extracted Tith 95’% ethyl alcohol and readings were made on concentrations in the range of 0.003 to 0.015 gram per litrr.
Table 11. Fluorometric Determination of Benzil i n Cloth Containing Various Impregnating Agents Additive Impregnated in 2.5 G. Cloth Sample Agent Weight, g. Sizing Cnknown Sizing rnknown h-m-eonsl -~ -~ 0 05 Naeeonal 0 05 Span 80 0 05 Span 80 0 05 Chlorinated paraffin 0 125 Chlorinated paraffin 0 125 Polyvinyl alcohol 0 013 Polyvinyl alcohol 0 013 ~
~~
Benzil Added t o Sample,
Benzil Found,
1Ig.
xg. 0 024 0 024 0 023 0 024 0 025 0 024 0 025 0 024 0 021 0 016
0 025 0 025 0 025 0 025 0 025 0 025 0 02.5 0 025 0 025 0 025
DISCUSSION
hlarked changes in the fluorescence of solutions containing the fluorescent compound took place with large changes of pH. Solutions made alkaline with ammonium or potassium hydrovide showed a great decrease in fluorescence. However, under the conditions of the procedure outlined above, only a slight effect due to small amounts of acidity in the alcohol was noted. Neutralization of the alcohol eliminated this difficulty. In all applications of the fluorometric method described hcre, a straight-line curve of Klett photofluorometer readings against milligrams of benzil in concentrations up to 0.03 mg. per ml. was obtained.
benzil concentration, using known solutions treated as described above, and make the quantitative determination of the unknown by applying the reading obtained. For best results the calibration curve and unknown samples should be run on the same day, because the aminophenols tend to darken on standing. Run a suitable blank under the same conditions with unimpregnated cloth. Tests were run using various fixatives, laundering agents, and emulsifiers which might be used in cloth impregnation studies. Of these materials, chlorinated paraffin gave the least interference and polyvinyl alcohol gave the greatest. In most cases, compensation for interferences could be made by use of suitable blanks. Results, corrected hy use of blanks, of the fluorometric determination of b e n d in the presence of various agents are listed in Table 11. Gravimetric Method. Recoveries of 97 to 98yGwere obtained in the estimation of benzil by a method for the determination of water-insoluble carbonyl compounds by means of 2,4-dinitrophenylhydrazine (6). The method used was essentially the same as described by Iddles et al. u ith the addition of a 2-hour estraction of the cloth sample with 95% ethyl alcohol, followed by the precipitation of the benzil compound from an aliquot portion of the extract.
LITERATURE CITED
Cross, H. F., J . Econ. EntOVIOl., 41, 731-4 (1948). Cross, H. F., and S n y d e r , F. XI., Soap Sanit. Chemicals, 25,No. 2, 135-49 (1949).
Farbenfabriken, fornierly E riedlander, Bayer, and Co., German Patent 57,151 (1891). Goldenson, J., and Sass, S., Office of Technical Services, r.S. Dept. Commerce, Rept. PB 78709 (1947). Iddles, H. A., Lon,, A. W., Rosen, B. D., and Hart, R. T., Im. ENG.CHEM.,h ~ aED., ~ . 11, 102 (1939). International Critical Tables, Vol. V , p . 378, New York, McGraxHill Book Co., 1929. King, W.V., Ani. J . T r o p . M c d . , 28, 487-97 (1948). RECEIVED July 1 , 1950.
Colorimetric Method for Determination of Traces of Carbonyl Compounds GERALD R . LAPPIN, University of .Arizona, Tucson, .4riz., AND
LELAND C . CLARK, Fels Research Institute f o r t h e Study of H u m a n Derelopment, Antioch College, Yellow Springs, Ohio H E addition of a solution of sodium or potassium hydroxide Tto an alcoholic solution of a 2,4-dinitrophenylhydrazone produces a very intense wine-red color, presumably due to the formation of the resonating quinoidal ion I. A similar quinoidal ion
NO?
has been suggested for the colored solution formed when base is added to the phenylhydrazone of a nitroaromatic aldehyde (1). This color reaction has been made the basis of a very sensitive method for the estimation of ketosteroids in biological extracts ( 2 ) . Herein is reported the extension of the method to the quantitative determination of traces of aldehydes or ketones in water, organic solvents, or organic reaction products. The method is most useful in the range of carbonyl concentration from to
10-8 molar, wherein fern if any other methods give reliable results or are of general application. Absorption spectra were run on alkaline alcoholic solutions of a number of 2,4-dinitrophenylhydrazones. It was found that the position of the maximum as well as the value of E,,, was nrarly independent of the structure of the carbonyl compound (with exceptions noted below) and were independent of the concentration of base as long as a sufficient excess was present. The colors formed were relatively stable, although slow fading over a period of several days was noted. Beer’s law was obeyed in the condetermined for a centration range studied. The value of E,,, large number of compounds averaged 2.72 X lo4 a t 480 mp. Table I gives more exact values for a number of compounds. For actual analysis it was found unnecessary to isolate the phenylhydrazone. If it was prepared in solution, using an excess of 2,4-dinitrophenylhydrazine,the addition of base converted the excess reagent to a very light yellow substance, the absorption of which was corrected for by using a blank determination. PREPARATION OF R E 4 G E N T S
Carbonyl-Free Methanol. To 500 ml. of C.P. methanol were added about 5 grams of 2,4-dinitrophenylhydrazineand a few
