Determination of Total Sulfur in Petroleum Products Combustion and Disodium Ethylenediamine Tetraacetate Titrimetric Method 0. N. HINSVARK and FRANCIS J. O'HARA
The Girdler Co., Louisville, Ky.
b An improved method, applicable to control procedures, permits determination of all types of sulfur in petroleum samples ranging from low boiling naphthas to high boiling coker gas oils. In general, the sample i s aspirated into an oxyhydrogen flame of a Beckman atomizer-burner and burned. Products of combustion are swept by air into a hydrogen peroxide scrubber, where oxides of sulfur are converted to sulfate, The sulfate formed in the scrubber i s measured b y adding an excess of barium acetate and determining the excess barium b y EDTA titration. Samples covering concentrations from 100 to several thousand parts per million of sulfur have been successfully analyzed without interference from halides or nitrogen. A statistical analysis of naphtha and Diesel fuel control samples shows excellent repeatability, with a maximum standard deviation of *8 pap.m. in concentration ranges of 100 to 200 p.p.m. of sulfur.
number of samples, seriously limit the conventional lamp ( 1 ) and oxygen bomb (8) methods of combustion. New techniques involving induction furnaces (8, 9) are extremely rapid, but are not sensitive to low concentrations of sulfur. Nethods using catalytic combustion furnaces (6) require too much time for completion. The combustion method (5) offered the most promise; however, it was difficult to maintain a flame when more viscous samples were burned. By modifying the Granatelli procedure so that the combustion is carried out in an open quartz tube, samples can be burned a t the rate of 1 to 3 grams per minute, depending up011the viscosity of the material. A nuniher of procedures are avail-
able for determining sulfate in the absorbent; the choice depends on the number of samples, sulfate concentration, and accuracy desired. Nephelometric techniques (11) are highly sensitive and selertive; however, they are too slow and subject to too many external influences. Gravimetric procedures, lvhile selective, are slow and require relatively large sulfate concentrations. I n general, titrimetric procedures are quickest and most versatile for final measurement. The direct titration of sulfuric acid by sodium hydroxide (3) is used extensively in ASTM lamp methods, but is subject to too many interferences in the proposed combustion method. Conductometric titrations (6) appear feasible,
E-
xmNsIvE catalytic reforming of naphthas to form high octane gasoline has made large quantities of hydrogen available to the refiner. Utilization of this by-product hydrogen in the hyclrodesulfurization of widely differing types of feed stocks has emphasized the need for a reliable analytical method for measuring variable sulfur concentrations in a wide variety of petroleum samples. I n about 45 minutes, the proposed technique furnishes a reliable value for sulfur a t concentrations as low as 100 p.p.m. in samples ranging from naphtha to residuum. The sample is aspirated into an oxyhydrogen flame and burned; the combustion products are swept into a hydrogen peroxide scrubber, where oxides of sulfur are converted to sulfate. Ultimate determination of the sulfate is made volumetrically by using disodium ethylenediamine tetraacetate (EDTA) to titrate excess barium ion. The wide variation in sample type and sulfur concentration, and the large 13 18
ANALYTICAL CHEMISTRY
Figure 1.
Combustion-absorption system for liquid petroleum samples
Oxygen pressure regulator Hydrogen pressure regulator Oxygen gage, 0-30 pounds D. Hydrogen gage, 0-16 pounds E. Hoke valve, l / &inch F. Hoke valve, I/, inch G. Electric furnace, Shaar and Co., Type 123-2, 12.5-inch i.d., 9-inch length, 115 volts, 15 amperes, 1.51 kw.-hr. H . Quartz tube and 35/20 ball joint, Ace Glass, code 7657 (see Figure 2) I . Borosilicate glass J. Atomizer-burner, oxygen-hydrogen, Beckman Instruments, Inc., code
A. B. C.
B-4020
K. Sample holder (Figure 3)
L.
Variac, 115 volts, 50/60 cycles, I phase, output 0-135 volts, 7.5 amperes
M . 2-liter beaker A'. Absorber, Harshaw Scientific, code H-54260-4 0. Condenser, 300 ml., Harshaw Scientific, code H-16210 Y . Spray trap, Harshaw Scientific, code H-54260-6 Q. Spray trap R. Rotameter, tube 8, tantalum ball S. Screw clamp T . Circulating ump, Model 2 5 , Samue S. Gleber, 8hicago, Ill. U I-liter beaker
but additional equipment is necessary. The use of tetr:tl\ydroyuinone (THQ) and barium chloride is too insensitive ( I d ) . An adaptation of a titrimetric procedure for the determination of barium (10) has proved satisfactory: By adding escess standard barium acetate to the scrubbing solution containing the sulfate and back-titrating the excess barium ion with standard disodium ethylenediamine tetraacetate (EDTA), reliable values for sulfur are obtained. APPARATUS
Combustion-absorption 111 (,
system (Fig-
1).
Quartz combwtion tube (Figure 2). Liquid sample holder (Figure 3). Vacuum pump, 1000-liter-per-hour capacity. Water demineralizer, Crystal Rewarch Laboratories, Inc., Model GL-5. Hypodermic syringe, 25-ml., with 18gage needle.
ml. reagent grade 307, hydrogen peroxide per 500 nil. of demineralized water. STANDARDIZATION
OF
EDTA
I n aqueous solution under controlled p H conditions, EDTA reacts stoichiometrically n ith polyvalent metal ions to form solulile, slightly ionized metal chelates. IVith respect t o the alkaline earth ions, the preferential order of chelation at pH 10 is: calcium, magnesium, strontium, and barium. Barium forms the least stable chelate FI ith E P T A , according to the equation. BaC+
+ EDTA
+
Ba (EUTA)
(1)
I n aqueous solution a t pH IO Friochrome Black T (EBT) albo forms slightly ionized soluble complexes with the alkaline earth ions. It is a soluble blue dye between p H 6.3 and 11.5 C APILL A R Y HOLE
CHEMICALS AND REAGENTS
Barium chloride solution (0.0100M), 2.4431 grams of reagcnt grade barium chloride dihydrate (standardized gravimetrically) per 1000 d.of demineralized water.
Place 5.00 ml. of magnesium chloride solution, 10.0 ml. of pH 10 buffer solution, and 10 drops of Criochrome Black T solution in :t 500-nil. Erlenmeyer flask. Adju>t the resulting solution to 50 ml. nith demineralized water and titrate n i t h E D T A solution to a blue end point, nliich is heqt recognized by comparison n ith a 5O-ml. volume of p H 10 buffer solution containing 10 drops of Eriochrome Black T solution under R tungsten light source. Use 5.00 ml. of magnesium chloride solution in determination of the ratio: rnl. of EDTA to nil. of MgC1,. I n all subsequent titrations involving the addition of barium chloride, hold the volume of magnesium chloride solution at 2.00 ml. With these volumes, approximately the same amount of EDTA is used in all titrations and consequently the percentage error in measuring VI is approximately the same as in obtaining V fto he used in the folloning calculation. I n a second 500-ml. Erlenmeyer flask, place 10.00 ml. of standard barium chloride solution, 2.00 ml. of magnesium chloride solution, 10 drops of Eriochrome Black T indicator, and 10 ml of p H 10 buffer solution. Adjust the resulting solution to about 50 ml. and titrate with E D T A solution t o the snme end point as in the first titration. From the two titrations the molarity of the EDTA solution is calculated according to the equation.
Figure 3. Liquid sample holder
Figure 2.
Quartz combustion tube
Magnesium chloride solution (0.026M), 2.64 grams of reagent grade magnesium chloride hexahydrate per 500 ml. of demineralized xater. EDTA solution (0 0149M), 5.00 grams of disodium ethvlencdiamine tetraacetate per 1000 ml. of demineralized water. Eriochrome Black T solution, 0.02 gram of Eastman Practical Eriochrome Black T and 2.0 grams of Eastman White Label hydroxylamine hydrochloride per 50 ml. of demineralized water. Barium acetste solution (0 O l O M ) , 2 74 grams of reagent grade barium acetate monohydrate per 1000 ml. of demineralized water. Buffer solution (pH 4), 45.7 ml. of reagent grade acetic acid and 27.7 prams of reagent grade sodinm acetate trihydrate per 1000 ml. of demineralized water. Buffer solution (pH lo), 67.5 grams of reagent grade ammonium chloride and 570 ml. of 29% reagent grade ammonium hydroxide. Hydrogen peroxide solution 670, 100
Molarity of EDTA
(4, whereas the magnesium and calcium dye complexes are red. The Eriochrome Black T complex of magnesium is lcss stable than the EDTA complexes of magnesium and barium but more stable than the Eriochrome Black T complex of barium. Singer reported to hlanns (10) that the formation constants of these complexes are: magnesium-Eriochrome Black T (107.0), magnesium EDTA (108.69), barium E D T A (107.76) and barium-Eriochrome Black T (lo2 or less), According to Manns and coworkers (10) the reaction
+ Ba (EBI') 102 Ba(EDTA) + Rlg (LET) 107.0
?iIg (EDTA) 108.69
-+
(2)
107.76
proceeds to the right, because the product of the formation constants on the right is greater than the product of the constants on the left. pH 10 + EDTA -+ Ba (FI)T.4) Mg (EBT) + EDTA rcd Mg (EDTA) + EBT blue
Ba++
(3a)
-f
(3b)
The E D T A solution is standardized according to the following procedure.
where hl,,
=
VBn
=
V,
=
TTn
=
=
AfBn
x
VBa
vz - VI
molarity of standard barium chloride solution volume, ml., of barium chloride solution ml. of E D T A solution required to titrate ml. of magnesium chloride solution added t o form Mg (EBT) color total volume EDTA, in ml. required to titrate standard barium chloride-magnesium chloride solution to ERT end point PROCEDURE
Assembly of Combustion Apparatus. T h e combustion apparatus is assembled as shown in Figure 1, with the atomizer burner positioned about 0.25 inch below the quartz tube ring. Furnace G is used t o prevent adsorption of sulfur on the cold malls of the combustion tube immediately after the sample is introduced. Because of their rapid burning and the consequent higher temperature attained by the combustion tube, the furnace is not needed when low boiling materials such as naphtha are burned. Combustion of Petroleum Samples. T h e input t o furnace G is regulated through Variac L. About 30 minutes is allowed for t h e furnace t o reach VOL. 29, NO. 9 , SEPTEMBER 1957
1319
temperature (500' C.). The following steps are completed during this warm-up period. 1. Reservoirs M and U are charged to half capacity with tap water. 2. Absorber S is charged with 25 ml. of 6% hydrogen peroxide solution. 3. K i t h Hoke valve E completely open, the oxygen cylinder is turned on and the pressure a t gage C is adjusted to 15 pounds per square inch gage by regulator A . The Hoke valve is then turned off. 4. With Hoke valve F turned off, the hydrogen cyhnder is turned on and the pressure at gage D is adjusted to about 3 pounds per square inch gage by regulator B. 5. The petroleum sample is introduced into sample holder K by the hypodermic syringe. When completely filled with the sample, the holder is weighed by suspending it from the balance arm by a wire cradle (highly volatile samples should be neighed immediately prior to burning). After furnace warm-up the combustion procedure is completed according to the following steps. 6. To reservoir Lr are added about 2 liters of crushed ice; the inlet tube to pump T is primed with tap water, and the pump is turned on. A steady stream of water should flow from the exhaust tube of condenser 0. 7 . Reservoir Af is supported in place ,,urrounding absorber N to encompass as much of the absorber as practical. The reservoir is then filled to the brim with crushed ice. 8. Oxygen is supplied to burner J by fully opening valve E. Burner atomization is tested by immersing the capillary in demineralized water. A steady and continuous spray should emit from the burner tip. The water is removed; and nith a match flame held just below the burner tip, valve F is opened and the hydrogen-oxygen mixture ignited. By manipulation of valve F, the oxyhydrogen flame is adjusted to a height of about 1 inch. The burner tip is then centered beneath quartz tube H . 9. Clamp S is tightly closed on the vacuum line and the vacuum pump is turned on. The clamp is then gradually opened until the float in rotameter R registers 90. This value corresponds to a flow rate of approximately 800 liters per hour of air and burner gases. 10. The burner capillary is immersed as far as possible into the liquid sample through the small hole in the very top of the (filled and weighed) sample holder, K . The holder is then held in place by a clamp attached to the buret stand. 11. After sufficient sample has been burned, K is removed from burner J and the vacuum pump is turned off. Hoke valve F is closed to extinguish the flame and the burner is moved to one side of quartz tube H . The burner capillary is immersed in demineralized water to remove by aspiration any incrustation which may have accumulated at the burner tip during combustion. Hoke valve E is then turned off. 1320
ANALYTICAL CHEMISTRY
12. Spray traps P and Q are removed from the assembly and rinsed with three separate, small portions of demineralized water. The rinsings are delivered into a 500-ml. Erlenmeyer flask. Condenser 0 is then rinsed down and the rinsings are collected in absorber Itr. The absorber is removed from the assembly, and its contents, along with three separate demineralized water rinsings, are added t o the Erlenmeyer flask. 13. Sample holder K is reweighed and the weight of burned sample is calculated. (Highly volatile samples are reweighed immediately after step 11.) 14. A combustion blank is obtained by burning only hydrogen for the time required to burn the average samplei.e., all manipulations are performed with the exception of actually burning a petroleum sample. This blank correction is applied to the calculation. I n this work the blank is negligible in sample concentrations as low as 100 p,p.m. of sulfur. Titrimetric Analysis of Absorbent. This procedure is carried out directly on the absorbent and rinsings obtained from step 12 of the combustion procedure. Two drops of methyl orange indicator are added to the solution and the solution is titrated with standard barium acetate from a 50-ml. buret until the indicator color changes from red to orange. ilfter the end point is reached, 2 ml. of barium acetate are delivered into the solution. The total volume of barium acetate added to the solution is read from the buret and recorded. Then 5 ml. of pH 4 buffer solution are added. The buffered solution is placed on a hot plate and allo1ved t o boil for about 10 minutes to remove carbon dioxide and to destroy the indicator color. ilfter boiling, the solution is cooled and to it are added 2.0 ml. of magnesium chloride solution, 10 ml. of pH 10 buffer solution, and 10 drops of Eriochrome Black T indicator solution. The excess barium acetate is then titrated with standard EDTA solution to a definite blue end point. The end point is best recognized under a tungsten light source by comparison to a pH 10 buffer solution-equsl in volume to the total volume of the sample solutioncontaining 10 drops of Eriochrome Black T indicator solution. A blank analysis is performed in exactly the same manner by burning only hydrogen and oxygen for the average burning time of the samples. Calculation of Total Sulfur. The total sulfur content of a burned petroleum sample is calculated according t o the following equation: P.p.m. (wt.) sulfur = ViMj - (Vd.12
where VI
=
Vt
=
- V.'aMz)X s
32,000
ml. of barium acetate added to absorbent total ml. of EDTA re-
quired to titrate absorbent Va = ml. of EDTA required t o titrate added magnesium, obtained under standardization MI = molaritv of barium acetate solutron M z = molarity of EDTA solution S = grams of petroleum sample burned A blank value is calculated according
to this same equation and is algebraically subtracted from the sample value. EXPERIMENTAL RESULTS AND DISCUSSION
Several experiments were designed to show the applicability of this method to the determination of total sulfur in petroleum stocks. The experiments described below demonstrate the versatility of the technique and prove the validity of the answers obtained in the determination. To evaluate the effect of drawing unpurified air through the combustion tube into the scrubber, a series of runs was made in which only hydrogen was burned in the system. When the scrubbing solution was analyzed, the result corresponded to a blank. Table I compares blank to standardization values-Le., the amount of EDTA necessary to titrate 1 ml. of barium acetate solution.
Table I. Comparison of Blank and Standardization Values
111. EDTA/RIl. Ba Deviation, Standard B l z M1. 0 i8
0 80
0 82 0 78 0 el 0 74
0 75 0 73
+o
02 +O OS 0 00 +o 03 +O 01 -0 02
These blank values mere obtained on successive days, the result of an average of two separate analyses. On the basis of the constancy of these values, it may be possible to eliminate the blank; however, to help assure control of the procedure, blanks are run daily. A titrimetric procedure, using standard sodium hydroxide, was employed in the development of the method. A very small blank mas obtained when hydrogen was burned alone; but when a higher temperature was obtained, as in the combustion of a petroleum sample, a very high titration blank was observed. This would indicate that, in
Table II.
Effect of Burning Rate on Apparent Sulfur by Sodium HydroxideTitration
Burning Rate, N, Solveut G./hIin. P.P.hI. Jso-octane 2.26 100 1.63 100 1.10 100 0.55 100 1.10 0 Ijieael fuel 1 .86 40 1.59 40 1.2tj 40 0.81 40 Xaphtha 1.60 80 1.60 77 1.60 3 1 .60 101 1.60 61 Xone
a=
Pressure of 0 2 to Burner 15
12 9 6 9
15 12 9 6
12 12 12 12
12 12
Apparent Sulfur, P.P .M . KaOH F m 69 0 73 0 91 0 108 0 92 0 188 110 196 110 203 110 205 110 127 46 179 92 126 50 162 90 108 21 0
0
A Sulfur SaOH-EDTA 69 73 91 108 92
78 86
93 95 81 87
87 0
ISOOCTANE (0% S U L F U R ) 0 FUEL NAPHTHA@
addition to sulfuric acid, another acid is being formed in the scrubber, presumably nitric acid. To check this effect, a solution of 100 p.p.m. of nitrogen, as 8-quinolinol in spectrographic purity iso-octane, was prepared. This solution was burned in the usual manner and the scrubbing solutions were analyzed by titrating with sodium hydroxide and compared to an EDTA titration. Table I1 illustrates the results for apparent sulfur in this solution and in petroleum samples which had been analyzed previously for nitrogen. T h e oxygen pressure to the burner was varied; consequently, the rate of aspiration of the sample into the combustion tube varied. Figure 4 shows the proportionality of log apparent sulfur to burning rate of sample. These data confirm Granatelli's statement ( 5 ) that the convenient acidimetric titration used in lamp sul-
Effect of Excess Barium on Measured Sulfur
Values by S Added hlg++ as NazSOa, solution, Mg. ml. 0.5 1.00
0.5 1.0 2.0 3.0
2.00 2.00 2.00 2.00
EDTA Titrat& Ba++ hleassolutian, ured ml. mg. S 50.00 1.29 5.00 0.58 10.00 0.73 20.00 0.96 10.00 0.54 50.00 1.22 50.00 2.26 50.00 3.33
76 72
e: D I E S E L *a
Table 111.
furs is inipractical when a combustion technique such as that described here is employed. Apparently the amount of nitrogen in the fuel does not affect the values obtained; only the rate of burning determines the measured quantity of sulfur in excess of the actual concentration present. A qualitative test performed on the gases passing into the scrubber showed the presence of oxides of nitrogen mhen pure isooctane was being burned. This would explain the inability to obtain a low blank by a sodium hydroxide titration. I n evaluating the titrimetric procedure employing EDTA it was found that a large excess of barium, over that necessary to precipitate the sulfate, resulted in apparent sulfur values much too high (Table 111). This was observed by using solutions containing known amounts of sulfate as sodium sulfate.
These data curroborate Xlann's statement that the amount of barium in excess is closely related to the amount of magnesium required. Apparently, an equilihrium is in effect which affects the end point of the XIg (ERT) indicator. This difficulty is minimized by using a barium acetate solution and adding it to the color change of methyl orange. By this procedure, it is possible to maintain close control over the amount of excess barium. I n addition, 2 ml. of magnesium solution are added to assure an adequate supply of magnesium ion. The combination of these techniques results in the sulfur values given in Table IV.
Table IV. Analyses of Petroleum Samples of Known Sulfur Content
Sample Type Elemental S in iso-octane" 1-Penthanethiol and 3,4-dithiahexane in iso-octanea 3-Thiohexane and thiacyclohexane in 150octanea Thiocyclohexane and thiophene in iso-octane" Thiophene in Diesel fuel Thiophene in heptane
Sulfur Content, P.P.M. Added Found 945
954
1050
1072
1020
1008
950
949 74 68 2910 1438 744 444 293 153
59 60
2968 1484 742 445 297 148
~~
a Samples distributed for total sulfur in cooperative program with Committee on Analytical Research, Refinery Division, American Petroleum Institute.
The values in Table IV illustrate the accuracy and versatility expected when this technique is used. Excellent results are obtained in almost all cases, although the percentage error increases as the concentration is lessened. At concentrations considerably less than 100 p.p.m. of sulfur, the deviation beVOL. 29, NO. 9, SEPTEMBER 1957
* 1321
tween added and found is from 10 to 25%. Higher sulfur values result in a much lower percentage error. Up to this point the data were gathered by research grade chemists. To demonstrate applicability of this technique to control procedures, the data in Table V are presented. These samples \\-ere submitted on a daily basis, disguised as routine samples. The choice of sample depended on the expected concentration level as well as the type of fuel predominantly present in the day’s sample schedule. These data illustrate the excellent repeatability obtainable in a control laboratory by this method. No explanation is offered of the higher standard deviation of sample 11; however, the higher value for sample I is probably attributable to the higher volatility of the naphtha samples.
Table V. Repeatability of Disguised Samples Submitted to Control Laboratory for Routine Analyses
Sulfur Found in Different Samples, P.P. I f . _ _ _ . ~ _ _ _ Ia 1 1 6 IIIb IV* 105 189 204 189 204 212 196 203 200
148 12G 136 183 133 125 124 117 130
168 1Gl 185 1C,G 167 163 166 1Gl 1G5
143 1-10 144 13G
1:37 130 140 138 135
Average 199 129 164 139 Standard deviation, p.p.m. (7) 3t7 f 8 f 2 &3 Naphtha sample. Diesel fuel samples.
SUMMARY
Excellent results are obtained for sulfur in excess of 100 p.p.m. by using a Beckman atomizer-burner to aspirate and burn combustible petroleum samples in a n open combustion tube, drawing the products of combustion through a hydrogen peroxide scrubber, and determining sulfate in the scrubbing solution by a n EDTA titrimetric procedure. The method is rapid, furnishes selective results, and is adaptable to
a control program. The data gathered in this laboratory indicate that this method can be used on a wide variety of sample types covering a wide boiling range and containing high concentrations of unsaturates and aromatirs. If the precautions noted are followed, a wide variation of sulfur concentrations are analyzable and all samples are burned completely with no smoking
and without the necessity of dilution. The work done indicaates that all types of sulfur can be determined; the time of combustion of a 5- t o 7-gram sample is 3 to 10 minutes, depending on volatility and viscosity of the sample. LITERATURE CITED
(1) Am. Soc. Testing %Taterials, Phila-
delphia, Pa., “Standards on Petroleum Products and Lubricants,” p. 15,1952.
( 2 ) Ibid., p. 77. ( 3 ) Ihzd., part 5, pp. lG7-73, 1954. ( 4 ) Bersworth Cheniica! Co., Framingham, Mass., “The Versenes,” Tech. Bi111. 2, (1951). (5) Granatelli, L., ANAL.CHEW27, 2669 (1955). (6) Hidy, J. A , , Rlair, R. D., Ibid., 27, 802-5 (1955). ( 7 ) Hoel, Paul G., “Introduction to
Mathematical Statistics,” Wiley, New York, 1948. (8) Laboratory Equipment Corp., St. Joseph, Mich., private communication, 1954. ( 9 ) Lindberg Engineering Co., Chicago 12, Ill., private communication, 1955. (10) Manns, T. J., Resahovsky. h l . U., Certa, A. J., ANAL. CHEM. 24, 908 (1952). (11) Toennies, J., Bakay, B., Ibid., 25, 160 (1953). (12) Walter, R. N., Ibid., 22, 1332 (1950).
RECEIVED for review June 11, 1956. Accepted April 27, 1957. Group Sewion on Analytical Research, Division of Refining, American Petroleum Institute, Montreal, Canada, May 14, 1956.
Direct Determination of Oxygen in Organic Compounds IRVING SHEFT and JOSEPH J. KATZ Chemistry Division, Argonne National laboratory, lemonf, 111.
> Oxygen can b e obtained quantitatively from numerous organic compounds by heating with BrFnSbFe a t 500’ C. It is essential that the reaction vessel b e shaken vigorously to assure completion of the reaction. Oxygen has been quantitatively recovered from alcohols, aliphatic and aromatic acids, ethers, ketones, phenols, phosphate esters, sulfones, and organic nitrogen-containing compounds in which the oxygen is not bound directly to the nitrogen. This method of direct oxygen determination can be applied to solid, liquid, or gaseous samples.
A
many methods for the direct determination of oxygen in organic compounds have been described, generally oxygen is obtained by difference. The earlier literature on direct oxygen determination has received a LTHOUGH
1322
ANALYTICAL CHEMISTRY
critical review by Elving and Ligett ( 3 ) . More recently several new methods have been described. One method is based on the conversion of the oxygen in the organic compound to an insoluble carbonate by means of strontium oxide (6). Another is a n isotope dilution procedure in which the dilution of oxygen18 in enriched oxygen gac that is used t o oxidize the sample is measured ( 4 ) . The development of simple fluorination procedures for the quantitative release of molecular oxygen from a wide variety of inorganic materials suggests the use of these procediires for the analysis of oxygen in organic compounds. Bromine trifluoride has 1)wn used in the direct determination of oxygen in oxides and oxygen-containing compounds which are fluorinated a t or near room temperature ( 5 ) . Recent work indicates the feasibility of using addition compounds of bromine trifluoride for the determination of oxygen
in inorganic compounds ~ h c hdo not react completely with tmmine trifluoride ( 8 ) . Most inorganic oxides are completely fluorinated and molecular oxygen is r c ~ v e r e dquantitatively by heating a t 500” C. with RrFzSbFe or potassium fluohromite (potassium bromotetrafluoridc). This paper estends the successful use of BrFQSbFB t o the direct determination of oxygm in organic compounds. Because molecular oxygen is obtained and measured tensimetrically, the method is particularly useful for oxygen isotopp studies of orqanic compounds nhere thr dilution due to the combustion methodc of analysis is a disadvantage. CHEMISTRY A N D PROPERTIES OF FLUORINATION REAGENTS
Bromine trifluoride is a n ionizing solvent with a high electrical conduc-
