V O L U M E 2 6 , NO. 5, M A Y 1 9 5 4 color, and its occurrence in high concentration presents a probleni in colorimetry. The addition of buffers above p H 4 to methyl Cellosolve in equal volumes favors the formation of the monovalent, dithizonate ion. At pH’s of the buffer lower than 4 t,he inorganic salts precipitate out of solution. Precipitation takes plare over a period of hours a t pH 3.8 but becomes very rapid when the p H is lowered further. Critical adjustment of the p H of the buffer is therefore mandatory. The final pH of the niisture, while a meaningful, practical measurement, is not a true measure of hydrogen ion concentration in such mixtures of polar and nonpolar solvents as here employed. The formation of zinc dithizonate is sensitive to and readily affected by the zinc ion and dithizonate ion concentration, pH, the character and concentration of the buffer, as well as the character and concentration of the complex formers. Interferences are controlled, keeping in mind the ions and their concentrations likely to be encountered in serum or plasma. S o n e of tlie ions, especially cobalt and nickel, are likely to esceed the concentrations of other ions listed here as not interfering with the analysis of zinc in sera. The changes in absorption of dithizone in methyl Cellosolve when water or buffer are added from that seen in carbon tetrachloride are worthy of note. ;\s is apparent from Table I, the rhange from green to blue-green must be attributed t,o the hyporhromic effect on the peak a t about 600 mp relative to the one a t about 460 mp rather than the bathochromic or hypsochromic shifts in the two masima which are relatively small in terms of wave lengths. That such changes in absorption do occur is in line with the previously reported marked effects which solvents nay have on the spectral characteristics of dyes. .I 1 to 1 proportion of methyl Cellosolve and aqueous solution was found a suitable percentage in which dithizone and the inorganic ions could reniaiu stable in solution. The two components were mised prior to the addition of dithizone. The dye
917 was dissolved in methyl Cellosolve and added to the esothermic misture after it had been cooled, since dithizone was osidized by it. The buffer containing potassium cyanide and sodium thiosu1f:rte was added to complex copper. Sodium citrate neutralized to p H 4 was required to comples iron and manganese. Samples should be read within 15 minutes of the addition of the dithizone, as the color fades thereafter, though only slo\vly. This feature presents no practical difficulty, since dithizone is generally not added until immediately prior to measurement. The reproducibility obtained wit,h this technique approache3 the limits imposed by the instrumentation. Both reproducibility and recovery measurements compared favorably with the extraction technique as shown in Table 117. The addition of zinc to a protein-containing solution with subsequent attempts at recovery confirmed previous observations that the handling of the biological sample superimposes variability of measurements on the colorimetry ( 1 ). ACKNOW LEDGMEST
It is a pleasure to acknowledge the escellent technical aasistance of Thomas L. Coombs. This work was supported by a bjgrant-in-aid from the Hood Foundation, Boston, ~ I R s s .and , the Research Corp., S e w York, 9. Y. LITERATURE CITED
Hoch. E’. L., and T’allee, €3. L . . -1.B i d . Chenr., 181, 295 (1919). Pandell, E. E., ”Colorimetric Determination of Traces of 1\Ietals,” Xew I-ork. Interscience Publishers, 1950. ( 3 ) Yallee. R . L.. .%s.ir.. CHEM.,25, 985 (195.3). (4) Yallee. 13. I,,, and Gibson. J . G , , 11, < J , Ri’ol. Chcrri,, 176, 4.35 (1918J.
RECEIVED f o r review Sovember 16, 1953. hrrepted February 3, 1954, Presented a t tlie Conference on Analytiral Cheiriistr>- and .lpplicd R p e c t r o r copy, Pittsburgh, Pa., March 1953.
Determination of Aldehydes in the Presence of Ketones And Procedure for Acetals H. SIEGEL and
F. T. WEISS
Shell D e v e / o p m e n t Co., Emeryville, Calif.
A
GENERAL method for the quantitative determination of aldehydes in the presence of ketones and other organic materials is a very useful tool in the analysis of many types of experimental and commercial products. For this purpose several methods employing osidation with silver oside or ammoniacal silver have been published recently. However, each of these methods suffers from some important defect in general laboratory operations. The use of ammoniacal silver (Tollen’s reagent). a3 described by Siggia and Segal (a), does not permit the quantitative determination of aldehydes which can undergo the Cannizzaro reaction. In addition, Tollen’a reagent is generally consi(lered to be potentially hazardous because of the occasional formation of a silver compound in this reagent, Ivliich ran esplode with violence not, only in the dried state but also in aqueous solution (3j. The procedure of 3Iitchell and Smith ( d ) , involving the use of silver oxide and employing acidimetric determination, gives low recovery with formaldehyde and suffers from interference if acids or esters are present. The use of a column packed n i t h silver oxide for the determination of aldehydes, as employed tiy Bailey and Knos (21, does not overcome the interference resulting from the hydrolysis of esters. I n the authors’ esperience, the argentimetric method published a number of year3 ago
by Ponndorf ( 6 ) , after suitable modification, has provided a safe, rapid, and reliable met,hod for the determination of aldehydes. The Ponndorf method involves the reaction of aldehyde with silver oside, formed in situ by addition of sodium hydroside t o the aqueous or alcoholic reaction misture containing dilute silver nitrate. S o side reactions-such as the Cannizzaro reaction or aldol condensation-are expected, since the reaction misture is kept dilute with respect to the sample and is made strongljbasic only in the last stages of osidation. The unreduced silver ion is determined in the filtered reaction misture, after acidification to redissolve silver oside. .I number of modifications have been introduced in Ponndorf’s method to make it more rapid and convenient, including final titration with thiocyanate reagent according to T-olhard. -4further application of the method ha3 been for the determination of acetals, after acid hydrolysis. Other methods for the determination of acetals have heen described hy Siggn ( 7 ) and Smith and Mitchell ( 9 ) . APPARATUS AND 3IATERIALS
A shaking machine, of suitable construction to accommodate
tffo or
more lOO-ml, or 250-ml. volumetric flasks.
ANALYTICAL CHEMISTRY
918
A water bath, maintained a t 60' f 2" C. Ethyl alcohol, absolute. If appreciable carbonyl compounds or other reactive impurities are present, purify the solvent by distilling over excees solid silver oxide. PROCEDURE
Pipet 25.0 nil. of 0 1 S silver nitrate solution into a 100-nil. volumetric flask. Add a quantity of sample containing approximately 0.5 millimole of aldehyde. If the sample is volatile, or the carbonyl content is high, weigh the required amount in a glass ampoule. If the sample is not volatile from water or alcohol, the sample containing 5 millimoles of aldehyde may be dis6 0 h d in 100 ml. of water or alcohol and a 10-ml. aliquot of the Eolution may be taken for analysis. Add 5 ml. of 0.5LV sodium hydroxide solution and shake the mixture on a shaking machine for 15 minutes. ,4t the end of this time, add 2 ml. of 0.5,V sodium hydroxide solution and continue the shaking for 10 minutes. Add 10 nil. of 6 S sodium hydroxide solution and repeat the shaking for the same period of time. Acidify the reaction mixture with 5 ml. of 1 8 s sulfuric acid solution. After allouing the mixture to cool to room temperature, dilute t o the mark with distilled water. Filter the mixture through a dry S o . 41 Whatman filter paper into a 400-ml. beaker. Pipet 50.0 ml. of the filtrate into a 500-ml. glass-stoppered Erlenmeyer flask and add 4 ml. of ferric alum indicator. Titrate with 0.05-V thiocyanate solution until the end point is approached, as indicated by a more ~ l o ~ 1 -fading 1 ~ . red color. Stopper the flask, shake rigorously for
Table 111. Determination of Aldehyde in Presence of Various Substances by Argentimetric Method Substance Tested
Substance Added, % W
Methyl alcohol E t h y l alcohol Isopropyl alcohol
99.7 99.7 99.7
Ethylene glycol Triethylene glycol hIannitol Formic acid Acetic acid Propionic acid Lactic acid n-Caprylic acid Ethyl acetate Diallyl phthalate Benzyl benzoate Diallyl maleate Methyl benzoate Methylal n-Propyls1 Dimethyl acetal Diethyl acetal Di-n-butyl acetal Propylene oxide a b
Table 1. Determination of Aldehj-des Aldehyde Tested Torinaldehyde Acetaldehyde Propionaldehyde n-Butyraldehyde .4crolein Benzaldehyde Valeraldehyde a
b c
Aldehyde Found, V0 Wt. Hydroxylamine Argentimetri6 niethod method 27.4b 27.0 27.0 05.5b 94.2 94.2 94.2 94.4b 94.2 94.2 93.6 93.5c 95.2 94.9 95,lb 99.9 99.4 99.3c 99.2 97.7 87.9C 86.2 88.0
C
d
Ketone rldded, 9 Wt.
Methyl ethyl ketone
.4cetalde'h'yde Propionaldehyde
90.9 60.1 100
49.7 87.0 65.5 9.3
98.5 98.5 98.5 95.8 99 8 99.1 101.8 101.5
104 R 104 4 99 9 98.4 P8 9 100.1
.4ldehyde, cjb R-t. Added Found
9 1 39.9
9.2.9.2 39 8 , 40 2
0.0 0.3 13.0 34.5 91.7 0.0
