but then the flow-reversing valve, the detector and all connecting lines would have to be heated sufficiently to keep the hydrocarbon effluent vaporized ; also the peak areas should be corrected b y applping response factors for the various hydrocarbons. For adapting the technique t o apparatus not equipped for carbon dioxide conversion, a n alternative flow scheme would be t o connect the Molecular Sieve column and a heated flow-reversing valve upstream from the GLC column. With this arrangement, the sample would pass through the sieve column first and the direction of travel through the GLC column would be the same for both normal and nonnormal paraffins. We have not yet tried the method for determining n-paraffins above (311. The Molecular Sieve 5A is known t o be a n effective retainer for high boiling normals; according t o Whitham (12) i t can be used as a subtractor for n-
paraffins up to Cdo. However, the present method requires not only absorption of the normals but their complete desorption as well. Process studies on desorption from the 511 sieve ( 2 ) indicate that n-paraffins are readily desorbed at their critical temperatures. The desorption temperature employed here, 400’ C., happens to be the critical temperature of n-Cla. It is, therefore, likely that the method described could be extended at least up to this carbon number, provided that the absorption temperature is adjusted upward to prevent interference b y highboiling nonnormals. Desorption of the normals is, of course, favored by the back-flushing technique, since they are eluted through only a fraction of the sieve bed. LITERATURE CITED
(1) Am. SOC.Testing Materials, “ASTM
Standards on Petroleum Products and Lubricants,” ASTM Designation D 1319-58T.
( 2 ) Ballard, IY.P., Dickens, S. P., Smith, B. F., U. S. Patent 2,818,455 (Dec. 31, 19571. (3) Baker, R. M., Belchetz, L., J. SOC. Chern. Ind. 64, 131 (1945). (4) Brenner, N., Coates, V. J., Nature 181, 1401 (1958). (5) Eggertsen, F. T., U. S. Patent 2,987,471 (June 6. 1961). (6) Eggertsen, ‘F. T., Groennings, S., Holst, J. J., ANAL.CHEM.32,904 (1960). (7) Guild, L., Bingham, S., Aul, F., p. 137 ot “Preprints of Papers Read at the
Second Symposium on Gas Chromatography, May 1958, Th:, Royal Tropical Institute, Amsterdam, D. H. Desty, Ed., Butterworths, London, 1958. (8) Larson, L. P., Becker, H. C., ABAL. CHEM.32, 1215 (1960). (9) Nelson, K. H., Grimes. M. D..’ Heinrich; B. J., Zbid., 29,1026 (1957). (10) O’Connor, J. G., Norris, M. S., ’
Ibid.. 32. 701 11960). (11) Schwartz, ‘R. -D’., Brasseaux, D. J., Ibid., 29, 1022 (1957). (12) Whitham, B. T., h‘ature 182, 392 (1958). . . RECEIVEDfor review March 2, 1961. .4ccepted May 31, 1961. Division of Petroleum Chemistry, 139th Meeting, ACS, St. Louis, hIo., March 1961. I
-
-
.
~
Determination of Volatile Hydrocarbons in Aqueous Emulsions and Latexes by Gas Chromatography F. M. NELSEN,
F. T. EGGERTSEN, and J. J. HOLST
Shell Developmenf Co., Emeryville, Calif.
b Volatile hydrocarbons in a polymerwater system or latex can be determined gas chromatographically in a few minutes. Samples, weighed in discordable glass capillary tubes, are flushed into the vaporizer with the carrier gas. After separation on a short gas chromatography column, the volatile components are oxidized to carbon dioxide and water over hot copper oxide. Water is removed with calcium sulfate, and the carbon dioxide is measured by a thermal conductivity detector. The system is designed to minimize difficulties in charging latex samples and to eliminate water interference. The method furnishes very reliable results, and as little as 0.05% of volatiles can be determined.
I
polymers by emulsion polymerization, the product is a latex, containing, in addition to water and polymer, small amounts of unreacted monomers and possibly other volatile organic compounds. Determination of volatile materials in the latex is often desired not only for control in the process, but also as a specification for the final product. For instance, small N MAKING
1150
ANALYTICAL CHEMISTRY
amounts of free styrene in styrenebutadiene latex give rise to objectionable odor, and its determination down to a few hundredths of 1% is required. An accepted method for this analysis is based on bromometric determination of styrene, previously separated by azeotropic distillation with methanol (6). However, this method requires about 1 hour, and the blank, which is equivalent to 0.05% styrene, limits the accuracy when small amounts are being determined. It seemed likely that gas chromatography would be more expeditious and possibly more reliable for small concentrations. Gas chromatography has already been applied successfully to the determination of volatile components in adhesives (S), lubricating oils (6), and waxes (I). However, none of these methods is well suited for latexes. I n the present method, designed specifically for latexes, the separations are made with only one gas chromatography column; no intermediate trapping step or forecolumn is required as in the methods cited above. Interference from the large amount of water present in a latex is avoided by oxidizing the eluted volatile organic compounds and detecting them as carbon dioxide
( 2 , 4), the water being removed by Drierite (calcium sulfate). The injection of latex samples presents certain problems. Sampling from a hypodermic syringe is unsatisfactory because the plunger tends to bind, often resulting in breakage of the glass barrel; also the needle tends to plug, and cleaning is difficult. T o circumvent these difficulties, a device was designed for introducing samples from disposable glass capillary tubes. Weighed amounts can be readily introduced, eliminating the need for an internal standard. Suitability of the scheme is demonstrated below for the determination of residual styrene in a styrene-butadiene latex, but other latexes can be analyzed similarly. APPARATUS AND PROCEDURE
The apparatus (Figure 1) consists of the sample injector and vaporizer, a short separating gas chromatography (GC) column, the oxidation-dehydration train, and a thermal conductivity detector. The detector is the hot wire type (Gow-Mac Instrument Co. Model 9285) operated at 50’ C. with a bridge current of 200 ma. The carrier gas is helium.
The separating column, 5/)/10 x 12 inches, is packed with C-22 insulating brick, 30- to 60-mesh1 containing 20 grams of silicone oil [General Electric Co. SF-96 (1000)l per 100 grams of support, and its temperature is controlled with a water bath. The oxidizer consists of an 8-inch length of '/&ch stainless steel tubing containing 14- to 48-mesh copper oxide maintained a t 675' C. The combustion unit has been described (2). Sample injector and vaporizer are shown in Figure 2. The glass capillary sampling tube, which is disposable, is approximately 1-nim, i.d.. by 65 mm. long and fire-polished a t both ends. For better retention of low viscosity samples, ,the mid-portion of the tube is constricted to about half its original diameter. This is done by laying the tube on a firrbrirk and partly collapsing it with a torch. The vaporizer section is packed with glass wool, and heated electrically. The column is operated at 75" C. and the vaporizer a t 140" C., and thc helium flow is 60 f 0.5 ml. per minute. The sample is taken by dipping the end of a tared caDillarv tube into the latex. Viscous samples are diluted beforehand with water to near water consistency, so that the residue in the tube aftrr charging does not exceed 0.2 mg. The styrene-butadiene latexes for the present tests were sufficiently fluid to be used without dilution, the residue generally not exceeding the precision of weighing, 0.1 mg. The amount of sample in the tube is adjusted to 10 to 15 mg. by removing some from the capillary if necessary. 'The tube is tilted so that the sample drains into the constriction, excess liquid is wiped off, and the sample weight is obtained. The spherical glass joint on the injector is removed and the vent valve opened. An empty capillary tube, placed in the injector during the purging of the column with helium, is replaced b y the charged tube. The spherical glass joint is reconnected quickly, and after 2 to 3 seconds of helium flushing the valve is closed, whereby the sample is swept out of the tube into the vaporizer and the column to obtain the chromatogram. The glass wool in the vaporizer is renewed after two or three analyses, because an accumulation of residue tends to retain styrene, which may be partly eluted in the next analysis. The copper oxide is regenerated with air (2) once each day for latex samples. Peak areas are converted to absolute amounts of hydrocarbon by means of calibration factors. These factors are obtained by chromatographing samples of a stripped styrene-butadiene latex containing known amounts of added styrene, or of solutions of hexane in n-octane. In the latter case, the GC column was operated at 30" C. In one series of tests (Table 11) the factor used for styrene was computed from the hexane factor by adjusting for the difference in carbon content. This was done by multiplying the hexane Factor by the ratio of per cent carbon
TYCON TUBING
Table I. Comparison of Gas Chromatographic and Distillation-Bromination Methods [Sample. Styrene-butadiene latexes (20 to 25 weight To solids)]
S A M P L E LYJECTOR
-
1
5 Sample
CC COLUMN IN U ATER BATH
Figure 1. apparatus
C u O COMBUST. TUBE
Schematic
diagram
of
in styrene to per cent carbon in hexane. The precision of the calibration was tested with 0.4 to 4.8 weight % solutions of hexane in n-octane. Fourteen measurements were made for 30 to 10oO pg. of hexane over a 2-week period and on 7 working days. The standard deviation for peak area per milligram was 1.7%, the extreme results differing by only 5%. RESULTS
The accuracy of the method for styrene was first tested by comparing results with those obtained by the distillation-bromination method (6),given in Table I. For these tests the latex samples were prepared b y steam-stripping for different lengths of time, and had varying amounts of free styrene. Sample 1 with 0.52 weight % of added styrene was employed as a calibration standard for calculating the other results by gas chromatography. The results, shown in Table I, are in good agreement. Therefore, i t appears that es-
S . J . 1 2 ' 5 CLASS +LASS
SAMPLE CAPILLARY
S . J . 1 2 1 5 ST. S T E E L
,
PIPECAP
ILICOVE R U B B E R DISK
I,
ST S T E E L T L B E LASS U O O L
1
RASS BLOCK U l T H U E L l S OR T H O 5 0 U A T T x Ill, CARTRIDGEHEATERS .
& - - 4 c
Figure 2. izer
'.
S U A C E LOCK UNlOS COLLalN
Sample injector and vapor-
1 2 3 4 5
Styrene Found, Wt. 7 0 Bromination GC method" method 0 . 0 5 to 0.07b 0.05 0.53 1.68 5.35 5.31
0.50 1.51 4.85 5.43 Calibration standard used for GC method was sample 1 (O.o5Q/o)plus 0.52%
added styrene = 0.57%. b Range of values from 10 determinations.
Table 11. Recovery of Added Styrene by Gas Chromatography [Sample. Styrene-butadiene latex (22.6
A
wt. Tosolids)] Styrene, Wt. yo Added Present" Foundb None 0.13 0.12
B
0.59
0.72
C
1.27
1.40
D
5.42
5.55
Sample
0.14 0.68 0.74 0.69 0.71 0.64 0.70 1.36 1.39 1.35 5.30 5.41 5.33
a Amounts added plus amount found in original sample A, 0.13%, which is assumed correct. b Peak areas evaluated using a response factor obtained by calibration with hexane.
sentially complete elimination of free styrene from the polymer was achieved in the vaporizer. Application of the method to styrene was tested in another series of experiments in which the peak areas were evaluated by the absolute method based on calibration with hexane. These data, shown in Table 11, indicate good recovery of added styrene and satisfactory precision. Typical chromatograms for the determination of styrene are presented in Figure 3, together with the tracing for a water blank. The Chromatograms had a double "air" peak, not shown in Figure 3. This is due to the momentary stoppage of carrier gas flow during charging of the sample with the special injector. The flow upset peak occurs just ahead of the normal air peak. The size of the peak for 0.13% styrene and the low water blank, indicate that the minimum detectable amount of styrene is of the order of a few hundredths of 1%. VOL. 33, NO. 9, AUGUST 1961
1151
CONCLUSIONS
The method described is a n effective and rapid means for determining volatile hydrocarbons in water mixtures. In styrene analysis, the agreement obtained with the distillation-bromination method is good evidence that the techniques employed in the gas-chromatographic method are satisfactory and the vaporization of styrene from the polymer and its combustion are essentially quantitative. The capillary tube sdmpling device is believed to be an effective means of charging aqueous emulsions which are difficult t o handle with a hypodermic syringe. This application of the combustion technique illustrates one of its advantages, that of eliminating water interference. consequently, the column and conditions can be designed entirely for optimum and rapid separation of the hydrocarbons. Other advantages of the technique are that detection as carbon dioxide increases sensitivity, provides uniform thermal conductivity response, and allows room temperature operation of the detector.
I
0.1 hlV.
SAMPLE A 7.1
MC.
0.(3% STYREKE
The method is demonstrated here only with styrene in styrene-butadiene latex, but it has also been applied in this laboratory for volatile components in polyisoprene latexes. If one wishes to extend the method for the determination of several volatile compounds, longer columns may be employed. LITERATURE CITED
(1) Durrett, L. R., ANAL. CHEM. 31, 1825 (1959). (2) Eggertsen, F. T., Groennings, S., Horst, J. J., Zbid., 32, 904 (1960). (3) Haslam, J., Jeffs, A. R., Analyst 83, 455 (1958). (4) Hunter,' I. R., Ortegren, V. H., Pence, J. W., ANAL.CHEM.32, 682 (1960). (5) Porter, R. S., Johnson, J. F., Zbid., 31, 866 (1959). (6) U. S. Reconstruction Finance Corp., Office of Synthetic RubberllResearch
cm WATER, 10 MG.
I
0
I 5
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io
AII>LTES
Figure 3. Typical chromatograms of free styrene in latex Column temperature, 75' C.
and Development Division, Specifications for Government Synthetic Rubbers," rev. ed., Sect. E2, Oct. 1, 1962.
RECEIVEDfor review March 2, 1961. Accepted May 2, 1961. Division of Petroleum Chemistry, 139th Meeting, ACS, St. Louis, hto., March 1961.
I
Low I emperature Gas Chromatography ROGER S. PORTER and JULIAN F. JOHNSON California Research Corp., Richmond, Calif.
b Gas chromatography has been studied at -78' C., solid COZ temperature. Separations were performed over glass beads and crushed brick and with these supports coated with n-heptane, n-octane, and acetone. Column characteristics were studied a t n-heptane concentrations on glass beads from 0.02 to 2.0 weight and from 0.5 to 28.0 weight on crushed brick. Components from Hz io isopentane were eluted in studies which evaluated.the naiure of separations, the imporiance of sample size, and possible analytical applications. With this simple equipment, for example, the major components in ambient air may be analyzed a t -78" C. on a column of 28 weight % n-heptane on crushed brick.
70 70
T
evaluates the nature and analytical advantages of low temperature gas chromatography. Although gas-liquid is the most common type of vapor chromatography, this method has been virtually unreported at solid C o n temperatures, -78' C., and below. Exploration of this region is inviting because of the low molecular weight compounds that may be used as partitioning agents. Low temperatures also take advantage of differences HIS WORK
1152
ANALYTICAL CHEMISTRY
in heats of solution for the separation of close boiling components (3, 11). Gas and liquid diffusion phenomena, which reduce column efficiency, should be less a t low temperature (3). Finally, a number of practical analytical problems, such as air pollution, appear potentially amenable to low temperature gas chromatography. These mild analytical conditions can be important for systems which contain reactive species such as olefins and oxides of nitrogen. The chromatograph used was a custom-built thermal conductivity detector unit. The unique features were column temperature and partitioning agents. Separations were performed a t -78" C. over n-heptane, n-octane, and acetone, as well as on the support materials, crushed brick and glass beads. Studies were made at n-heptane concentrations from 0.5 to 28.0 weight yo on crushed brick and from 0.02 to 2.0 weight % on glass beads. Tests revealed several marked effects which lead to useful applications and to an understanding of the partitioning process. METHOD
The conventional design gas chromatograph was built especially for these tests. Samples were commonly injected with a gas Elample loop, nominal
volume 0.25 cc., connected to the chromatograph through a commercial O-ring injection valve. The columns consisted of copper refrigeration tubing, '/r-inch o.d., which were packed with either 42- to 60-mesh size JohnsManville C-22 insulating brick or glass beads, of which 85% were retained on No. 230 U. S. sieve but passed No. 140. These soda-lime-silica beads, average nominal diameter 0.10 mm., were obtained from the Minnesota Mining and Manufacturing Co. The brick support columns were 20, 50, and 100 feet in length. Glass bead columns were all 10 feet long. The columns were coiled and maintained during tests in a n 9 quart, metal Labline Dewar contaiting Y solid COz-acetone slurry. Phillips 99 mole % normal heptane was used as a partitioning liquid. Constants for pure normal heptane are: melting point, -90.5" C., boiling point, +98.4" C. Normal octane, 99 mole %, was also used: pure freezing point, -56.5' C. Acetone, Baker's analyzed reagent grade, was also tested as a partitioning liquid: pure melting point, -95" C., boiling point, $56.5" C. Column packings were prepared b y adding partitioning liquid to dry brick or to glass beads in the desired weight ratio. The mixing was performed in a jar which was then tightly capped and vigorously agitated at room temperature for a prolonged period. The packing was then added to the column with little
