1449’
V O L U M E 2 5 , NO. 10, O C T O B E R 1 9 5 3 LITERATURE CITED
(1) American Society for Testing Materials, Philadelphia, Pa., “ASTh4 Methods of Chemical ilnalysis of Metals,” p. 134,
1950. Berger, K. C., and Truog, E., IXD.ENG.CHEM.,ANAL.ED.,11, 540 (1939). (3) Brewster, D. A , , AXAL.CHEM.,23, 1809 (1951). (4) Ellis, G. H., Zook, E. G., and Baudisch, O., I b i d . , 21, 1345 (1949). (5) Foster, A I . D., IND.ENG.CHEM.,ANAL.ED., 1,27 (1929). (6) Friend, J. N., and Twiss, D. F., “Textbook of Inorganic Chemistry,” Vol. VII, Part I, p. 338, London, Charles Griffin and Co., 1924. (7) Hatcher, J. T.,and Wilcox, L. V.,~ ~ N ACHEM., L . 22, 567 (1950). (8) Hillebrand, W. F., and Lundell, G. E. F., “Applied Inorganic Analysis,” p. 611, New York, John Wiley & Sons, 1929. (9) Ibid., p. 617. (10) Ibid., p. 619. (2)
(11) Naftel, J. A., ISD.EXG.CHEM.,~ ~ X A ED., L . 11, 407 (1939). (12) Pigott, E. C., “Chemical Analysis of Ferrous Alloys and Fourldry Materials,” p. 7 5 , London, Chapman and Hall, 1942. (13) Ibid., p. 76. (14) Scott, W. W., “Standard Methods of Chemical Analysis,” 1-01. I, p. 185, New York, D. Van Kostrand Co., 1939. (15) Scott, W. W., and Webb, S. K., IND. ENQ.CHEM.,- ~ X . \ L ,El)., 4, 180 (1932). (16) Tschischem-ski, K.,I n d . E n g . C h u . , 18, 607 (1926). (17) U. S. Steel Co., “Sampling and Analysis of Carbon and -4lloy Steels,” p. 283, New York, Reinhold Publishing Corp., 1938. (18) Ibid., p. 284. (19) Weinberg, S.,Proctor, K. L., and Niliier, O., ISD.Esc,. CHEM., ANAL. ED., 17,419 (1945). (20) Wilcox, L. V., Ibid., 4,38 (1932). (21) Winsor, W. W., I b i d . , 20, 176 (1948). RECEIVED for review September 20, 1952. Accepted December ”2, 1952. Presented before the Pittsburgh Conference on .4nalytical Chemistry a n d -4pplied Spectroscopy, Pittsburgh, Pa.. March 2, 19.53.
Direct Determination of Oxygen in Organic Compounds Report of the Subcommittee on Analysis of Oxygenated Compounds, Committee on Analytical Research, Division of ReJining, American Petroleum Institute W. H. JONES, Chairman Esso Laboratories, Esso Standard Oil Co., Baton Rouge, La. Cooperative work of a number of laboratories has shown that in general the total oxygen content of organic materials in the low range of 0.01 to 1.0% can be determined with reasonable accuracy by four different modifications of the Unterzaucher method. In the original Unterzaucher method the effect of pyrolytic hydrogen on the iodine pentoxide is a source of considerable error in the lowoxygen range. I n each of the four modifications, the effect of the pyrolytic hydrogen has been obviated in a different manner. Comparable precision and accuracy were obtained by methods utilizing titrimetric, gravimetric, and manometric techniques.
B
Y THE end of World War I1 the technology of petroleum re-
fining had become relatively complev and broad in scope, owing to the introduction of many new and varied processes and products. With the advent of petrochemical manufacture and with increased problems in product stability during storage and use, the role of oxygen in the petroleum industry had become of considerable importance. I n November 1946 the Committee on Analytical Research, Division of Refining. -4merican Petroleum Institute, established a subcommittee t o investigate analytical methods pertaining to oxygen in petroleum and related materials. The original subcommittee was composed of rcpresentativea from four different petroleum laboratories, and eventually qome 14 laboratories representing petroleum and othey fieldq participatediri this cooperaative work. The main objective :it the outset \vas t o develop and prove a method for total oxygen contcnt, particularly as applied to relatively low oxygen concentrations found combined in petroleum products. For such analysis, most petroleum laboratories had usually calculated osygen content b y difference between 100% and the sum of all the other elements. The limitation of this difference method is obvious, particularly when the sample is composed of several constituents and also when the oxygen content is low. Many analytical methods had been reported in the literature for the determination of oxygen by direct methods, but these are either generally considered very poor or so difficult as to be an a r t
with a particular operator. An escellent review of this literature was published by Elving and Ligett in 1944 (IO). At the time of the organization of the subcommittee, a f e u petroleum laboratories had already begun work on a direct procedure based on the thermal decomposition of the organic compound over carbon, oxidation of the resulting carbon monoxide with iodine pentoside, and titration of the liberated iodine as first proposed b y Schutze (16, 1 7 ) and further improved by Uotereaucher (18). Some consideration was also given to utilizing the conventional oxygen-type determinat,ions for carboxylic acid (3),ester (Q), alcoholic hydroxyl (15), and carbonyl ( 5 ) groups. These type determinations would give not only a value for total oxygen b u t also a breakdown which in many cases mould he Iielfpul. The limitat,ions in cases of very low oxygen contents were again recognized. I n 1918 the first cooperative work was initiated for comparing these three different methods for total osygen. TKOsynthetic samples containing I and 5% osygen, rcepectively, were prepared from mixtures of pure n-caproic acid, ethJ-1 n-caprylate. isoamyl alcohol, and methyl n-amyl ketone in iso-octane. Five different petroleum laboratories participated in this cooperative program arid the results are summarized in Table I . The conclusions reached in this preliminary phase of the work of the subcommittee iwre as follows: Oxygen by difference, ut,ilizing combustion only, gives a good average value with a relatively large sbandard deviation. The chemical methods appeared r e r y satisfactory for the
ANALYTICAL CHEMISTRY
1450
for blank studies and particularly to study the effect of hvdroeen content of the sam" pie on the blank values. The two peSynthetic Mixture 1 Synthetic Mixture 2 troleum stocks were selected as typical Difference Chemical Direct Difference Chemical Direct samples requiring accurate oxygen de(com(functional (Unter(corn(functional (Untergroup) zaucher) group) zaucher) bustion) bustion) termination. Synthetic value 4.96 ,1 .oo The data from this cooperative work are Av. value 5.14 5.16 5.24 1.00 1 .oo 1.21 Av. minus syngiven in Table 11. In general, the results thetic +0.18 f0.20 +0.28 0.00 0.00 +0.21 Gtandard deviation +O . 2 4 *O.l5 f0.22 &0.24 f0.032 f0.12 were erratic and almost every laboratory No, of analyses used 17 49 12 16 39 12 reported considerable difficulty in atNo. of analyses re1 1 0 1 10 0 tempting to adapt this procedure. Bejected No. of laboratories 5 4 3 5 4 3 cause of the wide variations. the blank study involving the pyrolysis of the hydrocarbons of relatively high and low hysimple synthetic samples, but it is conceded that in general pracdrogen contents waa inconclusive. However, several laboratories tice these methods are subject to interferences and limited to reported the results of experiments which indicated that the reacreactive functional groups. tion of hydrogen with the iodine pentoxide led to high blank valThe direct method appeared promising but required further ues. It was concluded that the Unterzaucher method was not development. yet adaptable with satisfactory accuracy to samples of relatively It was considered that the efforts of this group should be dilow oxygen content. rected toward further developing and testing the direct pyrolysis Shortly after this second program was concluded, a roundor Unterzaucher method. This seemed particularly desirable, table discussion (2) of the Unterzaucher procedure was held a t the because the need for determining very low oxygen contents, in AMERICANCHEMICAL SOCIETYmeeting in Chicago in 1950. the range of 0.1 to 1.0%, was more urgent than ever. The second Here, considerable discussion was directed toward the possible phase of the work by the subcommittee was started in 1950. By reasons for difficulties in obtaining consistently low blank values. this time the experience of Aluise et al. ( I ) , Dinerstein and Klipp Factors such as impurities in the iodine pentoxide and carbon, (8), Maylott and Lewis (IS), Deinum and Schouten (7), and othtraces of hydrogen and oxygen in the nitrogen, adsorption of carers had become available. bon monoxide on the carbon. and reaction of the carbon with the I n the second exchange program, two pure hydrocarbons, quartz tube were considered. It was generally concluded that naphthalene and cetane, a topped crude oil, and a clarified used although many investigators had reported satisfactory results on lubricating oil were analyzed by seven laboratories for oxygen by samples of relatively high oxygen concentrations, the Unterthe direct Unterzaucher method. Each laboratory used the zaucher method was not readily adaptable in the low oxygen procedure or modification currently in use in that laboratory. range. The two pure hydrocarbons, cetane and naphthalene, were chosen Table I.
Statistical Evaluation of Cooperative Analyses by Various Methods Total Oxygen, Weight %
I
Table 11. Laboratory
Topped crude oil
Analysis of Cooperative Samples by Conventional Unterzaucher Procedure
Total Oxygen, Weight % Clarified used oil Naphthalene
Cetane
1.53 2.42 2.20 1.72
1.39 1.39 1.40 1.38
0.37 0.41 0.37 0.40
0.69 0.56 0.53 0.59
Av. 1 . 9 7
1.39
0.39
0.59
1.13 1.08 1.11 1.10
0.84 0.83 0.82 0.83
0.14 0.15 0.15 0.15
0.20 0.16 0.14 0.16
Av. 1.11
0.83
0.15
0.16
1.87 2.18 1.74
1.45 1.38 1.32
0.34
1.6 1.2 1.1 1.3 1.3
Laboratory
Topped crude oil 1.37 1.30 1.26
0.84 0.85 0.75
0.00 0.08 0.04 0.15 0.00 0.01
Av. 1 . 3 1
0.81
0.05 0.07 0.06
..
.. 1.21 1.26 0.90 0.78 0.76 0.98
Av.
Av. 1 . 9 3
1.38
0.34
1.3
1.06 1.15
0.76 0.77 0.82 0.78
0.08
0.03 0.09
1.37 1.37 1.15 1.23 1.24
0.06
Av. 1 . 2 8
1.00 1.19 1.26 1.22
0.72 0.76 0.72
0.26 0.20
0.19 0.23
Av. 1 . 1 7
0.73
0.23
0.21
0.72 0.4.5 0.41
...
..
Av. 1 . 1 0
0.08 0.10 0.09
-4v. 0 . :3
b
C
0.14
0.0
0.0
0.E 0.13 0 19 0.24 0.2;
0.21
Employing 100- to 306mg. samplea. Fully conditioned carbon and 1201. Partly conditioned carbon and fully conditioned 1:Os. d Employing 13- to 25-mg. samples. e Employing 48- to 123-mg. samples. I 1 2 0 s at 80-82' C. u LOa at 110' C. .z
Av. 0 . 6 6 3
Total Oxygen, Weight % Clarified used oil Naphthalene
Cetane 0.14 0.08 0.06
0.15 0.07 0.10 0.09 0.09 0.09 0.10
0.35 0.27 0.33 0.29 0.31 0.94 0.66 0.35 0.40 0.34 0.32 0.28 0.47
V O L U M E 25, NO. 10, O C T O B E R 1 9 5 3
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Table 111. Analysis of Cooperative Samples by Modified Unterzaucher Procedures
Laboratory 1
Total Oxygen, Weight 75 Topped Clarified ?rude oil used oil Vaphthalene (sample 3) (sample 1) (sample 2)
Method hlodification .4
0 913 0.917 0,936
0,615 0.607 0,600
1 0 . 01 10.01
