1783
V O L U M E 2 7 , N O . 11, N O V E M B E R 1 9 5 5
pyrophosphoric acid and 96% as orthophosphoric acid. No change was noted on prolonged heating up to 150 hours at 100" C. At 176" C. the equilibrium mixture (Figure 6) contained 49% of the phosphorus-32 as orthophosphoric acid, 40% as pyrophosphoric acid, 10% as triphosphoric acid, 2% as tetraphosphoric acid, and 0.2y0 as a component believed to be pentaphosphoric acid. A combination of p$osphorus-32 labeling acd the separation and identification procedure described might well be used for the analysis of concentrated phosphoric acids, and even the so-called hexametaphosphate mixture might be separated into its components. ACKNOWLEDGMEhT
3
to
The authors are indebted to H . L. Hemphill for his work on the construction of the solution counter, to Victor Chemical Co. for samples of potassium triphosphate and sodium trimetaphosphate, to Ernest Leininger for a sample of sodium hypophosphate, and to Blockson Chemical Co. for a sample of sodium hexametaphosphate.
L
LITERATURE CITED -
0 C
5
I
IO
4
-
1 I I5 20 HOURS
- 1
2S
I 30
Figure 6. Composition of orthophosphoric acid as function of heating time at 176" C. I. 2. 3. 4.
Orthophosphate Pyrophosphate Triphosphate Tetraphosphate
of elution including various phosphates tested individually during identification of the labeled fraction is: orthophosphate, phosphite, hypophosphate, pyrophosphate, triphosphate, tetrametaphosphate, tetraphosphate, trimetaphosphate, fraction 5 , and the main component of a commercial sodium hexametaphosphate. The orthophosphoric acid solutions (used for the heating tests) that had been dried in an air stream and under vacuum a t room temperature were found to cbntain 0.3% of the phosphorus-32 activity as pyrophosphate. Heating of this dried acid a t 100' C. yielded after 24 hours 4% of the phosphorus-32 activity in the
(1) Baldwin, W.H., and Higgins, C. E., J . Am. Chew. S'oc., 74, 2431 (1952). (2) Bell, R. S . ,Ind. Eng. Chem.. 40, 1464 (1948). (3) Bell, R. K.,AKAL.CHEM.,19, 97 (1947). (4) Bell, R. K., Audrieth. L. F., and Hill, 0. F.,Ind. Eng. Chem., 44, 568 (1952). (5) Beukenkamp, J., Rienian, W.,and Lindenbaum, S., ANAL. C H E Y . , 26, 505 (1954). (6) Boyd, G. E., Myers, L. S., and Adamson, A . W., J . Am. Chem. Soc., 69, 2549 (1947). (7) Hautefeuille, P., and llargottet, J., Compt. T e n d . , 96, 1052 (1883). (8) Huttner, K., 2. anorg. Chem., 59, 216 (1908). (9) Leininger, E., and Chulski, T., J . Ani. Chem. Soc., 71, 2386 (1949). Anal. Chim. (10) Lindenbaum, S., Peters, T. \'., and Rieman, W., Acta, 11, 530 (1954). (11) Rieman, W., and Lindenbaum, S., ANAL.CHEM., 24, 1199 (1952). (12) Thilo, E., and Rata, R., 2. anorg. Chem., 260, 255 (1949). (13) Tompkins, E. R., Khym, J. X., and Cohn, W.E., J . Am. Chem. Soc., 69, 2769 (1947). RECEIVED for review April 1, 1955. Accepted July 23, 1355.
Baaed upon work performed under Contract No. W-7405-eng-26 for the Atomic Energy Commission a t Oak Ridge Kational Laboratory.
Determination of Formic Acid in Presence of Acetic Acid B. R. WARNER'
and
L. Z. RAPTIS
Philip Morris, I n c , Laboratories, Richmond,
Va.
A convenient and precise means for determining formic acid is described. The method is based on the azeotropic distillation of formic acid with chloroform. Quantitative separation of formic acid from other organic acids is easily accomplished by a method which involves no high temperatures or complicated reactions. Recovered formic acid is directly titrated with standard base. The method is not subject to the interferences of the usual oxidation methods.
F
OR the determination of formic acid in the presence of
acetic acid, a general procedure has been selective oxidation of the formic acid. Oxidizing agents are usually mercuric oxide ( 2 ) . mercuric salts (1, 3, 6), and lead tetraacetate (7). These methods can be in error if other oxidizable materials are present. The method described utilizes the fact that formic acid can be distilled as a n azeotrope with chloroform ( 4 ) ,whereas acetic and higher acids cannot (6). By this means the formic acid can be 1
Deceased.
separated and quantitatively determined by titration with base The advantages are that the formic acid is quantitatively separated, no high temperatures are involved, no complicated reactions occur, and the acid is recovered unchanged. APPARATUS AND MATERIALS
Materials. ACS grade formic acid, glacial acetic acid, chloroform, salicylic acid, and methanol were used. Stock solutions of formic acid and acetic acid were made up in chloroform and diluted as desired. Titrations were carried out with 5 x 10-8N methanolic sodium hydroxide solution, prepared by diluting a 1-V aqueous solution with methanol. Apparatus. The solutions were distilled in a column 100 cm. long, 20-mm. internal diameter, and packed with 4-mm. spherical glass beads. The column was surrounded by a 50-mm. glass tube, which in turn was surrounded by a 100-mm. column for insulation. Titrations. Titrations of the chloroform solutions were made after adding 10 ml. of methanol and 2 ml. of water t o 10 ml. of the solutions being analyzed. A Model G Beckman potentiometer with glass and calomel electrodes was used in the titrstion.
1784
ANALYTICAL CHEMISTRY -.
Table I. Analysis of Formic and Acetic Acid Solutions Formic Acid Added,
%
Mg.
Acetic Acid Added, .Mg.
Recovered Acid (as Formic), Rlg.
Formic Acid Recovered
2.10 1.70 1.30
7.50 7.00 12.50
2.05 1 ,63 1.28
97.6 97.0 98.5
EXPERIMENTAL
Stock solutions of formic acid in chloroform were prepared and aliquots were titrated. Fifty milliliter aliquots of these solutions were distilled after addition of 50 ml. of chloroform and 2;grams of salicylic acid. Slightly less than 50 ml. of distillate were collected and made up to volume in 50-ml. volumetric flasks. Aliquots were titrated and compared with the known formic acid content before distillation.
Table 11. Recovery of Formic Acid from Sodium Formate Solutions Sodium Formate as Formic Acid, hlg. 10.2 10.2 10.2 113.0a a
Formic AGid Recovered by Distillation, Mg. 9.8 9.6 9.9 107.5
the chloroform-formic acid azeotrope.) After acidification of the viater-free sample with salicylic acid, the procedure followed n-as as described for formic acid. RESULTS
Table I shows the recovery of formic acid in the presence of acetic acid. Distillation of chloroform solutions containing only formic acid indicated 95 t o 100% recovery. Distillation of chloroform sollltions of mixed formic and acetic acid showed that no acetic acid was present in the distillate. CONCLUSIONS
The isolation of formic acid by distillation with chloroform affords a convenient and precise means for determining formic acid. The method does not appear to be subject to the interferences to which the oxidation methods are subject. An aqueous solution of formic acid can be analyzed by evaporating the neutralized solution and distilling with chloroform after liberating the acid. ACKNOWLEDGMENT
%
Recovery 96 94 97 95
An acknowledgment is due to R. D. Carpenter for hid assistance in running the determinations of the sodium formate solutions.
Titrated with 0.1N standard sodium hydroxide.
Solutions containing known quantities of formic and acetic acids were mixed and distilled with chloroform in the presence of salicylic acid. T h e distillates were titrated against standard base. Aqueous sodium formate solutions were analyzed for formate content, which was done by neutralizing a n aqueous formic acid solution with sodium hydroxide (0.1.V) and removing the water by azeotropic distillation with chloroform. (Drying was required, because the water-chloroform azeotrope boils below
LITERATURE CITED
Ahlen, L., and Sarnuelson, O., AN.~L.CHEM., 25, 1263 (1963). Arthur, W. J., and Struther, G. R..Ibid., 21, 1209 (1949). Hopton, J. W., Anal. Chim. Acta, 8, 429 (1953). Horsley, I,. H., and others, Adzances in Chem. Ser., S o . 6, 20, No. 920 (1952). (5) Ibid., No. 928. (6) Marconi, AT., Chimica (MiZan). 6 , 315 (1951) (7) Perlin, A. S., ANAL.CHEM.,26, 1053 (1954). (1) (2) (3) (4)
RECEIVED for review February 9, 1955. ,Accepted July 19, 1955.
Determination of Total Carbon in Organic Materials by a Wet-Dry Com bustion Method W. P. PICKHARDT, A. N. OEMLER, and JOHN MITCHELL, JR. Polychemicalr Department, E. 1. du Pont de Nemourr & Co., Inc., Wilmington, An improved simple and rapid wet-dry combustion method has been developed for estimating small amounts of organic matter in water. Provisions have been made for analyses of aqueous samples containing high-boiling, steam-distillable, or volatile substances. There is no interference from halogens. Solids or liquids up to 100 ml. in volume containing organic matter equivalent to 1 to 150 mg. of carbon dioxide are taken for analysis. :is little as 0.5 mg. of carbon per 100 ml. of water can be determined with a precision and accuracy within 17' relative.
RE
LIABLE analytical methods are needed for determining organic matter in aqueous systems. This is reflected by the increasing literature pertaining to problems of sewage disposal, water pollution by industrial wastes, recovery of industrially important materials, and water treatment ( 4 ) . Relatively nonvolatile organic compounds have been analyzed successfully 4
Del.
by wet, combustion using chromic acid-aulfuric acid ( f , 8 ) and oxidizing agents such as dichromate (5, 7'), iodic acid, permanganate ( 5 ) ,and persulfate ( 3 ) . All of the laboratory procedures reported are limited in their applicability. Some are not suitable for all types of compounds, whereas others lack the sensitivity necessary for determining a f e n parts per million of carbon. Consequently, there is still a definite need for a simple and rapid general laboratory method of analysis for organic m a t k in aqueous systems. Oemler and Mitchell ( 6 ) developed a wet-dry combustion method Tvhich overcame the difficulties often encountered in the usual wet combustion procedures. Organic material was oxidized in the presence of aqueous chromic acid and concentrated sulfuric acid. High-boiling, steam-distillable compounds, which escaped from the reaction flask into the condenser, were washed back into the flask by concent'rrted sulfuric acid added dropwise at the top of the condenser. Halogen acids produced by the oxidation were removed in a gas-washing bottle containing 0.1N hydro-
