and BMA also gave a linear plot. Because all gave linear curves any one could have been used as an internal standard for the other. The peak produced by AMA overlapped the EIAMA peak. Therefore, BMA was substituted for AMA. Benzyl- and benzalmalonic acids gave no peaks unless their concentrations were very high and a column temperature of 220' C. was used. Under these conditions a broad tailing peak was produced. Hydrocinnamic and cinnamic acids, the decarboxylation products of these acids, behaved in exactly the same manner. Thus, it is probable that the malonic acids were decarboxylated in the normal manner, but the reaction products could not be properly eluted on the column used. Recently, Hill and Hill (6) have shown that a short column with a packing similar to that used in this investigation can be used successfully t o chromatograph aromatic carboxylic acids. Therefore, it is likely that the aromatic carboxylic acids could have been analyzed in the usual way had a shorter column been used. It was conceivable that, because a chemical reaction was occurring in the injector, the volume of the sample injected might affect the peak height ratio. Care would then have to be exercised in measuring the volume injected. Table I1 shows the results of a study of the B;\Ih-AX4 peak height ratio as a function of injection volume. I n the
Table IV. Relationship between Temperature and Peak Height Ratio
(Injector 190" C.) Peak Coliimn height ratio" temperature, "C. IMA to AMA 110 1.04 1.04 116 1.03 126 145 1.19 a IhIA 4.3970, AXIA 9.557'0.
great. It can be concluded that, from run to run, only moderate temperature control is necessary. A calibration curve obtained a t one temperature could be used at another temperature providing the latter is not too different from the calibration temperature. These results have provided a n approach to analysis of malonic acids in biological materials. This aspect of the problem is under current investigation. LITERATURE CITED
range of 2-8 pl., the volume had no effect on the peak height ratio. Table I11 presents data obtained in a study of the reproducibility of peak height ratios of three pairs of malonic acids. The relative standard deviation was about 5% or less. The BhIA-AN.4 and BblA-EIAMA samples had the same ratio of malonic acids but their total concentration varied. The results showed total malonic acid concentration had no effect on the peak height ratio. T o determine how closely column temperature had to be controlled to get reproducible results, a study was made of the effect of temperature on the peak height ratio obtained from an IM.4XlIA sample. The results are given in Table 117. Small temperature changes have no effect on the peak height ratio. A greater change, 35" C., did change the ratio. In light of the reproducibility of the method, even this change is not
(1) Ackman, R. G., Burgher, R. D., ANAL.
CHEM.35, 647 (1963). (2) Adams, R.,ctJohnson, J. R., Wilcox, C. F., Jr., Laboratory Experiments in Organic Chemistry," 5th ed., p. 448, The Macmillaii Co., New York, 1963. (3) Barness, L. A., Young, D. G., Xocho, It., Science 140, 76 (1963). (4) Byars, B., Jordan, G., J . Gas Chromatog. 2, 304 (1964). (5) Cox, E. V., White, A. hl., Lancet ii, 853 (1962). (6) Hill, J. T., Bill, I. I)., ANAL. CHEM. 36, 2504 (1864). ( 7 ) Welilry, I., Merenstein, G. B., Maybee, I). A., Paper presented at the LIid-America Symposiiim on Spectroscopy, June 1964, Chicago, Ill. RECEIVEDfor review June 21, 1965. Accepted August 19, 1965. Investigation supported in part by Public Health Service Research Grant GM12399-01, from the National Institute of General Medical Sciences and part by National Science Foundation Grant GE 3181. Mid-America Symposium on Spectroscopy, Society for Applied Spectroscopy, Chicago, Ill., June 1965.
Gas Chromatographic Determination of Perma nent Gases in Helium at Reduced Sample Pressures J. E. ATTRILL, C. M. BOYD, and A.
S. MEYER, JR.
Analytical Chemistry Division, Oak Ridge National laboratory, Oak Ridge, Tenn.
b Commercially available components were used to adapt a process chromatograph for the injection of samples taken at the pressure of the sample source. The sample loop on the linear sampling valve is connected to a vacuum system through a three-way solenoid valve which, when actuated, connects the evacuated loop to the sample source. The actuation and return of the sampling valve i s delayed to permit the loop to fill to source pressure and to prevent the injection of carrier gas back into the sample source. Sample consumption is reduced and analytical data are recorded in terms of partial pressures of components within the system sampled. Percentage concentrations of Hr, 0 2 , Nt, CH4, CO, and C 0 2 were determined in helium at 100 mm. of Hg.
C
COKTAMINANTS Of helium reactor blanket gas (Hz, 02, Nz, CH4, CO, and COz) were monitored during a study of their reactions at low pressures and high temperatures with various structural metals. Specimens of the metals were suspended from quartz springs in a test chamber where they were heated in a prepared atmosphere of helium plus the contaminants. To reduce the effect of convection currents which interfered with weight monitoring, these experiments were done at an absolute pressure 5 100 mm. of mercury. Operation of the test chamber at reduced pressures complicated sampling but offered the advantage that for any particular partial pressure of a contaminant, its relative concentration was increased as a result of the reduced partial pressure of diluent helium. OMhION
Several methods (3-5) have been used to inject a single gas sample from a partial vacuum onto a chromatographic column. During this investigation, Casey, Edgecombe, and Jardine (1) described an automatic chromatograph for analyzing samples from a reducedpressure system. However, no means of adapting commercial process instruments to reduced-pressure systems has been reported. EXPERIMENTAL
a. Hz, 10 volume yo,and 1 volume % each of 01, Nz, CH4, CO, and COz in helium; b. 10 volume yo of each of the components of mixture a except O2in helium. Chromatographic Conditions. A Beckman Model 320C process gas Standard Gas Mixtures.
VOL. 37, NO. 12, NOVEMBER 1965
1543
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ACTUATING
PRESSURE
---7
POSITION OF VALVES DURING SAMPLING
ACTUATING PRESSURE
r- II -
- - ~ I
BUFFER VOLUMES
I
DETECTOR SIEVE MOLECULARCOLUMN
D Q O ~ TO PREVENT SUCTION
OF AIR TO DETECTOR DURING SAMPLING
TUREE-WAY SOLENOID VALVE
NO
VALVE
I
I
/
I
HEAT EXCHANGER
CARRIER HELIUM
I
1
Figure 1 . Diagram of chromatograph adapted for single-point sampling at reduced pressure
chromatograph with dual tungsten filaments was used. One column was 3.0 feet long X 3/16-inch 0.d. coiled stainless steel tubing packed with Burrell high activity silica gel, 80- to 100-mesh; the other was 6.0 feet long X ,3/16-inch 0.d. coiled stainless steel tubing packed with Linde 5A Molecular Sieve, 40- to 60-mesh. The carrier gas was helium at a flow rate of 50 cc. per minute. Operating temperature was 50' C.; bridge current was 350 ma. The process chromatograph assembly was originally designed to inject samples bled from a system under positive pressure. It includes a linear sampling valve, a dual-column valve, a programmer with a 15-minute repetitive cycle, and a stream-selector switch. The attenuated signals from the detector are presented in either spectrum or bar-graph form on a 2-mv. recorder. Columns were installed in the conventional dual-column configuration (Figure 1) so that the molecular sieve column was bypassed during the period when the COz was being eluted from the silica gel column. To selectively reduce the retention time of CO, the sieve column was partially poisoned according to the following procedure. The column was partly saturated with water either by packing it with moist sieve or by injecting several milliliters of water, added as steam, to a helium stream flowing through the packed column. The column was then activated for 1 to 3 hours at 200' C. and at a helium flow of about 50 cc. per minute until a test chromatogram showed that the CHp and CO peaks were just adequately resolved. This poisoning procedure 1544
ANALYTICAL CHEMISTRY
minimizes the analysis cycle without materially degrading the resolution of the more rapidly eluted components. Sampling Apparatus and Techniques. Figure 1 is a diagram of the chromatograph adapted for reduced pressure measurements. The sample loop is filled and evacuated through a three-way solenoid valve (Skinner Precision Industries, Inc., catalog No. X5H15150) which is actuated by the closing of the sampling cam switch of the programmer unit. Dried samples are drawn at pressures controlled by
1
SA s M~P~L I -N ,G - ~ ~
I I
II
vacuum regulators (Matheson Co., Inc., No. 49) from a small volume manifold assembled from three-way diaphragm valves (G. W. Dah1 Co.. tvoe hI1BT). These are used to select Gt'her sample gas, a standard gas mixture, or a null sample of carrier helium for leak checking and for evaluating base line stability during a blank analysis. These components function as follows. During the major period of an analysis cycle, the sampling cam switch is open and the sample loop is evacuated through the three-way solenoid valve. When this switch closes, the three-way solenoid valve is actuated immediately, but injection of the sample is delayed for 1 minute by a 60-second thermal time-delay relay (Amperite Company, Inc., No. 115K060) connected in series with the solenoid valve that controls the actuating pressure to the linear sampling valve. Thus, when a sampling signal is generated by the control unit, the sample loop is isolated from the vacuum pump and is connected to the sample source, and the heater of the time-delay relay is energized. During the 60-second delay period, the sample loop is filled to equilibrium pressure with gas from the sample source. One minute after the sampling signal is received, the sampling solenoid is energized to actuate the sampling valve, which injects the contents of the loop into the carrier stream. When the sampling cam opens to terminate the samplinq signal, the reverse cycle is followed-i.e., the three-way solenoid valve is immediately de-energized to the evacuate position, while the sampling valve remains actuated during the recovery period of the time-delay relay. Thus, injection of pressurized helium carrier from the sample loop back into the sample 3ource is prevented. Figure 2 is a schematic diagram of the simple circuit used to introduce the required delays in sample injection. Throwing the switch converts the system to the conventional sampling mode by continuously energizing the three-
-
(ATMOSPHERIC S A M P L I N G CED-PRESSURE
\; I
I
CAM SAMPLING SWITCH
11
t 15- Volt AC
CONTROL SECTION
eJ
Figure 2.
1 I
THREE-WAY SOLENOID
/ I
NEUTRAL
>
" t
j
L-
I
I
,
I
T I
I
I :
I
1
ANALYZER SECTION
Diagram of delay circuit
SAMPLING SOLENOID
Table 1.
Operational Sequence Sampling
Function Sampling cam Time-delay relay Delay period Total actuated Recovery period Sampling solenoid
of
Time after start of cycle, min. On Off 0
2
0 1 2 1
1 3 3 3
ABSOLUTE
PRESSURE GAGES AND REGULATORS
15
stream solenoid Stream trigger cam
TO VACUUM
>3
PUMP
