Table 1.
Fluorine Synthetic Sample Results
(1-gram sample) Fluorine, P.P M. Calcd. FOUL o-Fluorotoluene 63 65 33 30 15 13 5 6.5 Trifluoroacetic acid 25 22 10 8 Sodium fluoride 5 4 2 4
‘
Table II.
Boron Synthetic Sample Results
(1-gram sample) P.P.M. Boron Added (as boron triacetate) 0.50 0.50 0.50 1.00 1 .oo 2.0 2.0
Table 111.
P.P.M. Boron Found 0.35 0.40 0.60 0.85 0.90 1.7 1.9
Sulfur Synthetic Sample Results
(1-gram sample)
P.P.M. Sulfur Added (aa sulfanilamide) 25.0 25.0 25.0 12.5 12.5 12.5
P.P.M. Sulfur Found 23.0
2i.5
24.0 10.0 10.0 11 .o
cussed previously (9, 8). Table I illustrates results obtained by the analysis of samples of known fluorine concentration. The known samples were prepared by combustion of the required quantity of compound in p-xylene. Boron Determination. Burkhalter and Peacock (4) have presented a detailed discussion of this boron-polyhydric alcohol cornplev formation. However, this reaction can be made quantitative by the procedure indicated here. The calibration curve (Figure 1) is not linear and must be checked with each series of samples to be analyzed. The known calibration samples do not have to be burned or prepared in the bomb. Table I1 indicates results obtained from the complete analysis of samples of known boron concentration, prepared by adding boron triacetate to acetic acid. The boron procedure outlined here is designed for the 0.2- to 5-p.p.m. concentration range. The scope of the method may be increased by adjusting the blank and sample solutions to a deeper blue color prior to addition of the mannitol or by using large volumes. The color change is nearly instantaneous and the resulting yellow solution is stable for a t least 30 minutes. To ensure a positive absorbance reading, the color of the blank solution must be as intense as, or deeper than, the color of the sample. Sulfur Determination. Turbidimetric measurement are generally conceded to be lacking in reproducibility for the reasons cited by Toennies and Bakay (12). However, in trace ion analysis, a certain degree of inaccuracy is generally tolerable. As illustrated in Table 111, the results ob-
tained were felt to be exceptionally good. Synthetic samples were prepared by addition of sulfanilamide to cyclohexane and completely analyzed. The calibration curve obtained was essentially a straight line. I t was necessary to measure the sample absorbances before and after addition of barium chloride as discoloration of the combustion absorbant (water) was not constant and contributed slightly to the absorbance a t 400 mp. The success of this method largely depends on the care and technique of the analyst. The analyst must be thoroughly trained in the techniques involved in this method and suitable practice must be obtained by analysis of known samples. LITERATURE CITED
(1) Agazai, E. J., Fredericks, E. M., Brooks, F. R., ANAL. CHEM. 30, 1566 (1958). (2) Arthur, P., Annino, R., Donahoo, W. P., Ibid., 20,1852(1957). (3) Belcher, R.,Leonard, M. A., West, T. S., J. Chem. SOC.1959, 3577. (4) Burkhalter, T. S., Peacock, D. W., ANAL.CHEM.28,1186 (1956). (5) Granatelli, L., Ibid., 27, 266 (1955). (6) Hinsvark, D. N.,O’Hara, F. J., Ibid., 29, 1318 (1957). (7)Hudy, J. A., Mair, R. D., Ibid., 27, 802 (1955). (8)Leonard, N. A,, West, T. S., J. Chem. Soc. 1960,4477. (9) Parr Instrument Co., Moline, I11 Parr Peroxide Bomb Apparatus ana Methods No. 121,1950. (10) Schoniger, W., Mikrochim. Acta Heft 1,123 (1955). (11) Schoniger, W., Ibid., Heft 1-6, 869 (1956). (12) Toennies, G., Bakay, B., ANAL. CHEM.25, 160 (1953). RECEIVEDfor review April 24, 1961. Accepted August 28, 1961. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, February 1961.
Determination of Oxygen in Organometallic and Inorganic Compounds by a Modified Unterzaucher Method MITCHELL KAPRON and MANUEL BRANDT Research laborafories, Ethyl Corp., Detroit, Mich.
b Direct determination of oxygen in organometallic and inorganic compounds may be accomplished by a modified Unterzaucher method in which the sample is reacted with cuprous chloride in the presence of excess carbon. The method gives quantitative recovery of oxygen in cases where the conventional Unterzaucher method fails. It is applicable to in1762
ANALYTICAL CHEMISTRY
organic oxygenated compounds and organometallic compounds in which the metal is bonded to oxygen.
0
can be determined directly by the Unterzaucher method (6) in oxygenated organic compounds and in organometallic compounds in which the metal is bonded to carbon and the oxygen is in the organic moiety (Table XYQEN
I), However, the method is unsatisfactory for analyzing compounds whose metallic oxides are not readily reducedi.e., aluminum, calcium, and magnesium compounds. Huber (3) determined oxygen in alkali and alkaline earth salts of organic acids by treating the sample with silver chloride and heating in B hydrogen atmosphere. Sheft and Katz
3
Figure 1.
Quartz reaction tube
Carbon-platinum packing in detail
( 4 ) extended their fluorination method for inorganic oxides to include organic compounds. However, special reagents, equipment, and considerable time are required. This paper describes a modification of the Unterzaucher method which makes it applicable to organometallic and many inorganic compounds. Formation of metal oxides is eliminated by reacting the sample with lead chloride or cuprous chloride in the presence of excess carbon. The oxygen content of inorganic compounds of barium, calcium, copper, lead, magnesium, manganese, molybdenum, and nickel are determined. EXPERIMENTAL
Apparatus. The apparatus is similar to that described by Unterzaucher (6). The quartz tube and the sample are heated by a Brinkman-Heraeus microcombustion assembly. The sample heater has a maximum operating temperature of 1200" C. Indentations in the quartz tube (Figure I) hold the carbon packing in place and prevent it from shifting when the gas flow is reversed. Platinum partitions minimize channeling of the carbon packing. Reagents. DEOXYGENATED CARBON. Spheron 9 carbon, Godfrey L. Cabot, Inc., Boston, Mass. Treat carbon with hot hydrochloric acid, wash with water, reduce with hydrogen, and heat a t 1100" t o 1150" C. for 2 hours in a stream of argon or nitrogen. CUPROUS .4ND LEADCHLORIDES.Dry reagent grade chloride powder a t 130" C. to a constant weight. The samples studied were generally of reagent grade quality. In other cases, materials of the highest available purity were used. Procedure. The procedure is substantially that described by Aluise et al. ( l ) , except that a weighted amount of cuprous chloride is placed in the boat before adding the sample; the sample in turn is covered with a weighed amount of deoxygenated carbon. An escess of cuprous chloride and carbon are required. Loss of volatile sample during the pre-analysis flush is prevented by cooling the sample area of the tube with dry ice. A convenient holder for the dry ice is made by shaping a copper sheet in the form of the letter W and fitting it over the tube. The holder is removed before the pyrolysis cycle.
The blank of the deoxygenated carbon and the cuprous chloride is determined using 20 to 30 mg. of each. Burger (2) suggested eliminating interference by hydrogen formed in the pyrolysis of organic compounds by treating the iodine pentoxide with hydrogen for 7 hours a t 118" C. While
Table I.
pounds analyzed successfully in the presence of twice the theoretical amount of carbon are listed in Table 11. For many compounds, pyrolysis in the presence of arbon alone does not liberate all of the oxygen. Analysis of the barium and calcium carbonatea showed that only two of the three oxygen stoma were determined. X-ray diffraction showed the presence of the metal oxide in the sample residue. Analysis of manganese dioxide, manganese sulfate, and manganese acetate likewise showed that one oxygen atom waa not determined; x-ray diffraction identified manganese monoxide aa a fiml product. I n the case of Ni(NO8)r. 6H20, 11 of the 12 oxygen atoms were determined and one atom remained as nickelous oxide.
Determination of Oxygen in Organometallic Compounds
Oxygen, Wt. % Calcd. Found
Compound (Di-tert-butylcyclopentadienyl)manganese
tricarbonyl
Benzene iron tricarbonyl
20.7
[2,3-Bis(ethoxycarbon 1)-2~,5-norbornadien-7-yl] (n-cyclopentadienylynickel(11)
15.0 15.4 20.8 20.7
17.8
18.2 18.4
hydrogen was not confirmed as an interference here, the blanks were reduced by heating the iodine pentoxide under hydrogen for approximately 2 hours a t 190" to 200" C. and for an additional 3 hours a t 118" to 120" C.
15.1
Table 111.
Calcd., Wt.
%
Compound
20.1
MnSOl. HPO MnO,
