LITERATURE CITED
(1) Bailey, M. E., Kirss, V., Spaunburgh, R. E., Ind. Eng. Chew. 48, 794 (1956). ( 2 ) Bunge, W., Bayer, W. (to Farbenfabriken Bayer, A.G.), Brit, Patent 742,501 (Dec. 30, 1955).
( 3 ) Dombrow, 13. A.. “Polvurethanes,” ’ p. 20, Reinhold, New Yoik, 1957. (4) Felton, H. R., 1967 International Gas Chrom. Sym,posium, 1:istrument Society I
,
of America, Pittsburgh, Pa., 1957. A. (to Farbenfabriken
( 5 ) Gemasaer,
Bayer, A.G.), Brit. Patent 886,818 (Jan. IO, 1959). (6) Griffin, G. R., Willwerth, L. J . , Ind. Eng. Chem., Prod. Res. Develop, 1, 265 (1962). (7) Keulemana, A. 1. hf., “ G Chroma~ ~ tographs’” 2nd ed*’ 34’ Reinhold’ Xew York. --,1959. - --( 8 ) Marrali, IC., ANAL. CHEM. 29, 552 ~~
(1957). (9) McElroy, W. R. (to Mobay Chemical U. 6. Patent 2,969,386 (Jan. 24, 1961).
eo.),
(IO) Patton, T.C., Paintlnd. 74, No. 9, 15
(1957).
W. J., Paint Bulletin PB-5, E. I. du Pont de Nemours & Co.,,Inp,, 1958. (12) Slggla, s., Hanna, J. G., ANAL. CHEM.20, 1054 (1948). (13) Stagg, H. E., Analyst 71, 557 (1946). RECEIVED for review March 21, 1963. Accepted July 10, 1963. Preaerited at 14th Annual PittAburgh Conference on Analytical Chemistry and Applied Sprctroscopy, Pittsburgh, Pa., March 5, 1963. (11) Remington,
Chromatographic Liquid Leak Detection ISHMAEL ORTEGA and J. D. CYRUS Sandia Corp., Sandia Base, Albuquerque, N. M. A method for the detection of volatile silicone fluid leaking from sealed containers has Iheen established. The separating properties of the gas chromatograph were employed saiisfactorily in the determination of leak rates of sealed contaiiiers. The results show that this technique can b e used in many cases in preference to the more common helium and Radiflo leak detectors.
T
ARB severrl leak-detection schemes which permit the determination of gas leak ratcs; the most notable being the helium and the Radiflo tests. However, in cases of liquid leakage, the helium leak test is not applicable because: If a sealed container is liquid filled, there is no space for helium; even if space is purposely left for helium, the liquid may m e k the helium from the leak and thus prevent its detection; there is not necessaril> a correIation between helium leak rate and liquid leak rate; and the liquid 1cak rate is of concern, not the helium leak rate. The Radiflo technique, which requires the use of a radioactive gm, also is unsatisfactory for determinin; liquid leak rates for the same reasons, plus one additional reason: The Kr85 difl’uses into any exterior organic encapsulating compound, thereby yielding erroneous results. The containers of interest to us were ldled with 0.65-centistoke silicone oil, DC 200. Although 1,he use of a gas chromatograph as a liquid-leak-detection device is uniquti, gas chromatograph techniques have been used previously to detect and determine silicone oil, and have utilized silicone polymer columns (1-3,6). HERE
ments. Columns packcd with Apiezon L grease and a high-molecular weight polymer of silicone oil, D C 200, were found by experiment to be very suitable for this work. The test apparatus schematic is shown in Figure 1. Procedure. ilfter cleaning the eontainer with trichloroethylene to remove any surface silicone oil, the container was dried by placing i t in a stream of nitrogen. The cleaned container was then placed in the chamber and the vacuum lines were attached as shown in the schematic (Figure 1). The container to be tested was placed in a vacuum to speed the vaporization of any liquid that may leak from the container, to reduce the amount of air in the chamber and thereby improve sensitivity and permit the use of the ideal gas law, and to increase the leak rate. The sample chamber was then flushed thoroughly by opening valves B, C, and D, and pulling air through with the vacuum pump. The sample chamber was then closed by closing valve B. The pressure was reduced in the sample chamber
to approximately 20 mm. Hg. The time a t which a pressure of 20 mm. of Hg was reached was recorded. The sample chamber was then isolated by closing valve C and the manometer valve A. The evacuation of the sampling tube was done by opening valve E. The evacuation was continued until just before the sample was extracted from the sampling chamber. The samplingtube pressure was reduced to a pressure of 1 mm. of Hg or less. After a predetermined time, valve D was closed, isolating the sampling tube from the vacuum pump. Then valve C, between the sample tube and the sample chamber, was opened for a short interval (approximately 10 seconds) and closed immediately. The time when this operation was completed was recorded. The gas now contained in the sampling tube mas flushed through the chromatograph, using helium gas as a carrier, by opening valves F and G. The plot obtained on the recorder represented the fractions into which the gas sample was separated. From this
MANOMET LR
CHROMATO-
RECORDER
EXPERIMENTAL
Apparatus. A Per kin-Elmer Vapor Fractometer, Model 154D, with recorder, integrator, and gas-sampline; valve was employed for these experi-
INTEGRATOR
Figure 1 .
Schematic of test apparatus VOL 35,
NO. 1 1 , OCTOBER
1963
1649
Table I.
Salllple a b c ll
Chamber temp. K.) 300 300 300 300
( 0
measuring the weight change which was then converted to cubic centimeters. Since pressures involved in this work are relatively low, the number of moles of silicone oil (n) which leaks into the chamber and becomes vaporized can be calculated from the ideal gas law (4).
Data from Leak-Test Experiments
Time, see. 38,800 47,500 1.200 1.200
Area of air peak
Area of silicone peak
102,400 113,000 6 3 . 740 87 , 540
... 146 503 32
Chamber vol., cc. 33 35 29 29
Absolute pressure, mm. Hg 22.9 45.7 22.9 33.4
n = -PV
RT
plot, the mole per cent of DC 200 in the sxmple was calculated. From the mole per cent of DC 200, the leak rate for t h r leaking container, in turn, was determined. Known amounts of silicone oil were injected into the sample chamber to himulate a leak in a contaker. Tlie recovery was complete enough to ensure that all the oil injected was detectcd. The accuracy of detection improved as the quantity of oil was increased, while the accuracy was decreased as lesser amounts of the oil were used. However, in no instance was the indicated amount of oil less than the actual amount injected. The sample chamber was baked out under vacuum and then checked with the chromatograph to ensure that all residual si!icone oil was removed before placing the nest contsiner into the chamber. To leak-test containers contairiing hilicone oil, DC 200, with a viscosity greater than 0.65 centistoke, a small tmount of 0.65-centistoke oil was mixed with the more viscous, less volatile oil before sealing the container. The only change in the test procedure was t h a t the container was held in a vacuum in the sample chamber for periods of about 12 hours, rather than periods of about 20 minutes. RESULTS AND DISCUSSION
The fractions collected for typical containers are illustrated in Figure 2. The trichloroethylene peak indicates that not all the trichloroethylene was removed from the outside of the container. However, this did not lead to erroneous results because the calculations involved mole fractions. I n fact, the trichloroethylene peak, along with the air peak, brackets the silicone-oil peak, thereby making the silicone-oil peak easily identifiable. Figure 2a shows the results obtained from a cont:Jiner which did not leak; Figure 2b 4 o m s the results of a leaky container which contained 3.0-centistoke silicone oil and a small added amount of 0.65crntistoke silicone oil; Figures 2c and 2d illustrate the results obtained from containers which were filled with 0.65centistoke oil, which leaked a t different rates. The data for these peaks, which will be used in later calculations, are given in Table I. The free volume of the sample chamber with the container inside was established by vacuumfilling the chamber with alcohol and 1650
ANALYTICAL CHEMISTRY
Table II.
where P , V , R, and T are the pressure, volume, gas constant, and temperature, respectively. To find the leak rate, e, in cc. per second, one multiplies the value for n by NiW/td, where N is the mole fraction of silicone oil in the sample chamber, t is the time the container was in the chamber under vacuum, d i:, the density of the oil at 77" F. and 1
Calculated Leak Rates
Sample
Cc. per second
a
0
b
5.0 X 5.0 X 2 . 6 x 10-9
C
d
512X 512X
8
AIR -7
6
4
,--TRICHLOROETHYLENE
L SILICONE OIL
2
L
b X
B
5:
w
m
i
256X
256X
$ 8
1x 6
4
IX
2
L 6
I
I
4
2
6
4
2
0
RETENTION T I M E IN MINUTES
Figure 2. tested
Reproduction of chromatograms of samples from typical containers
atmosphere, and .If ia the molecular weight of the oil. Thut;,
e cc. per second
=
MPVA-/RTtd
(2)
N may be found by dividing the peak area of silicone oil by the sum of the peak areas of the silicone oil and air (and trichloroethylene if present). Neglecting the area of the trichloroethylene peak introduces only a 2out 1% error in the final result. Constant factors in Equation 2 were collected as shown in Equation 3.
Gsing Equation 3 ttnd the data in Table I, the results shown in Table I1 were calcula’ted. The main limiting factor of sensitivity in this technique is the length of time the container remains inside the evacuated sample chamber. Using representative values of 45 mm. of Hg pressure for 20 minutes yields a leak-?ate accuracy of 10-9 cc. pcr second. Using 200 minutes
will increase the limit another order of magnitude, which is sufficiently sensitive to detect leaks as small as 1 cc. per 30 years. Obviously the surface of the container in question and the sample chamber must be free of residual DC 200. Any containers which are silicone oil or liquid filled may be leak tested by this technique, provided the liquid can be partially vaporized at temperatures below the working temperature of the column used, 175” C. For higher temperatures, different columns must be used. The results gathered in this work show that this technique is valid and yields more meaningful data for a liquid leak test than does the helium or Radiflo tests. This leak-detection method is applicable to all components, both electrical and mechanical, t h a t must be stored for extended periods of time, and which, after storage, must perform properly. These components may be filled with any volatile liquid or a n y gas. Thus, the chromatographic leak-detection
method is applicable for both gas and liquid leak-rate determinations. There are several acceleration-sensing and integration devices used in the aerospace and missile field that are leak checked using this method. ACKNOWLEDGMENT
The authors express their appreciation to B. T. Kenna for his assistnnce in preparing this paper. LITERATURE CITED
(1) Bannister, D. W., Phillips, C. S. G.,
Williams, R. J. P., ANAL.CHEM.26,
1451 (1954). (2) Cropper, F. R., Heywood, A,, Y a t i o e 172, 1101 (1953). (3) Zbid., 174, 1063 (1954). (4) Glasstone, S., “Textbook of Physical Chemistry,” p. 193, Van Sostrand,
Kew York, 1958. (5) McCormick, H., Analyst 78, 562 (1953). RECEIVEDfor review May 20, 1963. Accepted July 22, 1963. This work was performed under the auspices of the United States Atomic Energy Commission.
Gas Chroima tog ra phic Ana lysis of ChIo rophe n o I Mixtures R. H. KOLLOFF, L. J. BREUKLANDER, and L. B. BARKLEY’ Monsanto Chemical
Co., 800
North lindbergh Blvd., St. louis 66, Mo.
b The use of a phosphoric acid additive and a thermally stable substrate capable of forming :,trong hydrogen bonds a t elevated temperatures makes possible the determination of free chlorophenols on on3 GLC column without sample pretreatment. The ortho effect is successfully applied to obtain the necessary retention time reversals for resolution of phenol and eight chlorophenols. Double peak formation is observed for the first time in a nonaqueous systern.
T
numerous approaches to the analvris of mixtures of chlorophenols include infrared spectrometry ( 6 ) , nonaqueous spixtrophotometric titrations ( 7 ) , ion exchange chromatography ( I S ) , and gas liquid chromatography (1, 2, 5 , l 4 ) . Of these techniques the titrimetric method ( 7 ) is the least promising, being limited to relatively simple mixtures of knoan components in roughly equal amounts. Ion exchange (13),while giving good resolution of most of the chlorophenols, requires 3 HL
Present address, Pennsylvania Industrial Chemical Corp , Clairton, Pa.
to 4 hours for a qualitative determination of o-chlorophenol (OCP), 2,4dichlorophenol (2,4-D C Pj , 2, 6-dichlorophenol (2,6-DCP), and 2,4,6-trichlorophenol (2,4,6-TCP), with quantitative work requiring still more time. Phenol and p-chlorophenol (PCPj are not determined. Infrared spectrometry (6) is versatile and will give a complete analysis of comples mixtures of chlorophenols, but sensitivity and precision are limited, a large number of standard curves are required, and the calculations are laborious (graphical solution of simultaneous equations by succesbive approximation). Gas chromatography offers a simple, rapid, and sensitive method of analysia but t o date has suffered major drawbacks-e.g., a lack of suitable substrates with high temperature stability, poor resolution, and tailing of the chlorinated phenols on many polar substrates. Extensive gas chromatographic work on alkyl-substituted phenols has been done ( 2 , 3, 8, 9, 11, 12), but extension of the techniques to chlorophenols has been relatively unsuccessful. Fitzgerald (2) recommended sample pretreatment (methylation) and GLC
analysis of the chlorinated anisolcs, rather than direct determination of the chlorophenols, particularly when the 2,6- and 2,4-DCP isomers were to be separated. Harvey and Xorman ( 5 ) also used sample pretreatment (titration with diazomethane) and stated t h a t mixtures of chlorophenols could not be analyzed directly. Barry, Vasishth, and Shelton ( I ) did analyze chlorophenols directly, but for mixtures containing PCP, 2,4-DCP, and 2,6DCP, two different GLC columns (polar and nonpolar) and two separate analyses were required. I n addition, 2,6-DCP was not completely resolved from 2,4-DCP but rode on the 2,4-DCP tail. I n the method described below, 2,6DCP is clearly resolved from and is eluted before 2 , 4 D C P , despite its higher boiling point. Because of this position reversal, i t is possible for the first time to determine small amounts of 2,6-DCP in 2 , 4 D C P quickly and accurately (Figures 1, 2, and 3). Complete resolution of eight chlorophenols and phenol can be obtained directly on one column (Figures 1 and 2 ) , and no sample pretreatment or additional analyses are required. h phosphoric VOL. 35, NO. 1 1 , OCTOBER 1963
1651
