DISCUSSION
The data plotted in Figures 4 and 5 adequately demonstrate the practical utility of this analytical technique. These results constitute the first successful simultaneous determination of oxygen and nitrogen in an extended list of refractory metals with time requirements considerably less than those of other approaches which have been applied. Loading of the chamber with 8 electrodes, degassing, and loading of the samples require about 20 minutes. The extraction and analysis require only an additional 3 minutes per sample. Thus, the average time required per sample is about 6 minutes. Single samples niay be added to the outgassed electrode and chamber system through the side port. I f the chamber is flushed simultaneously with helium, subsequent outgassing is not required. I n this way, the total time required for determining both oxygen and nitrogen on a single sample is only about 4 minutes. The potentialities of extending the sensitivity of this technique several
orders of magnitude have been discussed (3). L-nder the operating conditions described in this paper>the blank for oxygen imposes the primary limitation on sensitivity. rl considerable reduction in the oxygen blank can be effected by using “low oxygen platinum” now available from the Baker Platinum Division of Engelhard Industries (12).
LITERATURE CITED
(1) Booth, E., Bryant, F. Analyst 82, 50 (1957).
S.,Parker, .A,,
(2) Elwell, W. T., in “Determination of Gases in Aletals,” Iran and Steel Inst. Spec. Rept. 68, 19-42, 1960. (3) Evens, F. AI., Fassel, 1.. -4.,ASAL. CHEM.35, 1444 (1963). (4) Everett, hl. R., rlnalyst83, 321 (1958). ( 5 ) Fassel, V . -4.) Evens, F. >I., Hill, C. C., AKAL.CHEM.36, 2115 (1964). (6) Fassel, 1.. A , , Goetzinger, J. R., Spectrochim. i l c t a , in press. ( 7 ) Fassel, V. A., Gordon, W. A,, A K A L . CHEM.30, 179 (1958). (8) Goward, G . W.,Pratt and Whitney Aircraft, Sorth Haven, Conn., private communication, 1963.
( 9 ) Ihida, AI., Japan Analyst 8, 786 ~ x, m j - l_ !. _ .
(10) Holt, B. D., Goodspeed, H. T., ANAL.CHEM.35, 1510 (1963). (11) lIcKinley, T. D., E. I. I>u Pont de Semours and Co.. LVilminrton. 1)el.. private communication, IXXI (12) McKinley, T. I)., Englehard Ind. Tech. Rd1. 2, Y o . 4, 140 (1962). (13) llallett, 11. W., Talanta 9, 133 (1962). (14) lIallett, Ll. W., Griffith, C. B., .Am. Soc. dletals 46, 375 (1954). ( 1 5 ) Sational Academy of Sciences, ”Report of the Panel on Analytical Problems In Refractory Jletals,” Rept. MAB-154-M( l ) , \-olume 11, pp. 17-22, 1959. (16) Parker, A , in “Determination of Gases in Metals,” I ~ o n Steel Inst. (London) Spec. Rept.(‘68, 64-74, (1960). (17) Still, J. E., in Determination of Gases in Metals,” Iron Steel Inst. (London) Spec. Rept. 68, 43-63 (1960).
RECEIVEDfor review August 10, 1964. Accepted October 23, 1964. X o r k performed in the Ames Laborator) of the U. S. .Atomic Energy Commission.
Determination of Subtoxic Concentrations of Phosgene in Air by Electron Capture Gas Chromatography L. J. PRIESTLEY, Jr., F. E. CRITCHFIELD, N. H. KETCHAM, and J. D. CAVENDER Research and Development Department, Chemicals Division, Union Carbide Corp., South Charleston, W. Vu.
b A gas chromatographic method for measuring subtoxic concentrations of phosgene in air is described. The method utilizes an electron capture detector which is extremely sensitive to phosgene. The combination of a gas chromatographic column and the electron capture detector provides a high degree of specificity for phosgene. Hydrogen chloride concentrations as high as 1% in air do not interfere. This method could possibly b e ured as the basis for developing a continuous monitoring system for detecting and measuring phosgene in the atmosphere.
T
use of phosgene as an industrial cheniical demands instrumentation continuously to monitor air for this contaminant. No completely satisfactory instrument has been reported to date. An analyzer utilizing a colorimetric reaction has been described ( 2 ) . This type of instrument is bulky, expensive, and coinplicated to maintain. This laboratory has developed a gas chromatographic method which can detect and measure phosgene in air in the range of’ 1 p.p.b. to 2 p.1i.m. and which the authors feel is a possible basis HE: INCREASING
70
0
ANALYTICAL CHEMISTRY
for the development of instrumentation for monitoring phosgene in the atmosphere. The method utilizes the electron capture detector (3) which is sensitive to most halogenated compounds. Under the conditions used in the laboratory, a determination can be made every 6 minutes. The method will detect and measure concentrations of phosgene on the order of 1000 times less than those of physiological interest. The threshold limit value for daily 8-hour exposure to phosgene has been set at 1 p.1i.m. by volume in air (4).The odor of phosgene can be detected by some people at a level of 0.5 p.p.m. or less, but this ability varies widely. EXPERIMENTAL
Apparatus. An herograph Model A-350-I3 gas chromatograph, equipped with a n electron capture detector, was used for this T\ork. The recorder was a 13rown -0.05 to +1.05 mv. equipped with a Disc integrator. The column consisted of two meters of 4.T-mIn. 1.d. aluminum tubing packed with 307, by \\eight Flexol plasticizer 10-10 (didecyl phthalate, Cnion Carbide Corp.) coated on 100- to 120-mesh
GC-22 Super Support (Coast Engineering Laboratory). The column was operated isothermally at 50’ C. The flow rate of nitrogen carrier gas was 50 cc. per minute. The potential applied to the detector was 90 volts. Procedure. Samples of known concentrations of phosgene in air were prepared in a dynamic triple dilution system (Figure I), placed in a fume hood. This system consists of a series of three glass mixing chambers in which the phosgene is progressively diluted with air. Measured flows of phosgene and air are injected into the first stage of the system where they are mixed as they flon. through baffle plates. A measured flon of this mixture is then allowed to enter the second stage and the surplup material is vented. I n the second stage of the system, the mixture is further diluted by a measured flow of air. If a further dilution is desired, the same procedure is followed with the third stage. Samples can be taken at the venting points of all three stages. .ill flows are measured by Fischer & Porter Co. precision bore flowrator tubes;. For calibration purposes, the compressed air used in the dilutions should be as dry as possible, and hypodermic syringes used to inject samples into the
I5 cm
45cm
-----------s
4
30
B%
4I
ui
20
f
PINCH CLAMP TiBES
8 B
IO
gas chromatograph should be thoroughly dried before use. This is necessary because phosgene reacts readily with water adsorbed on ,a surface. Samples were prepared in the range of 4 1i.p.b. to 2 1i.p.m. These samples were transferred to the analyzer with a hypodermic syringe. The sample size used for calibration purposes was 0.5 cc.; however, because of the limited dynamic range of the detector, concentrations of phosgene above 2 1i.p.m. would require the use of a smaller sample size. Peak area measurements were recorded by a Disc integrator. DISCUSSION
Results. h chromatogram is presented in Figure 2 showing the analysis of phosgene in air. Figure 3 shows a calibration curve for determining phosgene in air belo wthe 1p.p.m. level. .ill determinations made during this study were made on t h e basis of this calibration curve. Table I shows the repeatability in the same general range. Examination of the results indicates that the relative standard deviation of the method is approximately 2%. Concentrations of phosgene as low as 4 p.p.b. were measured. On the basis
of the signal obtained of this level, less than 1 1i.p.b. should be measurable. The response of the electron capture detector, with respect to the concentration of phosgene, is linear as long as the phosgene peak height is not in excess of half of the standing current, and the concentration is a t least, 0.25 p p m . Since a portion of the calibration curve is nonlinear, the curve should be used empirically. Standing current is defined as the electron flow in the ionization chamber with pure carrier gas flowing ( 1 ) . Slight variations in standing current may be observed from day to day. The various points on the calibration curve shown in Figure 2 were obtained over a period of 6 days. The highest standing current, observed was that which produced 3416 pv. on the recorder and the lowest produced 3080 pv. The variations in this range had little apparent effect on the sensitivity of the detector. Of course, large variations in standing current would be expected to affect the detector
Table
Sample No. 1
Mean 2 Mean 3 Mean 4 RETENnoN TIME, MINUTES
Figure 2. Gas chromatogram of prepared sample of 0.05-ppm phosgene in air
Mean 5
Detector voltage, 9 0 ; input impedance, IO’; output sensitivity, 1 X; attenuation, X 1 ; sample size, 2 cc.
Mean
I.
Repeatability Data for Phosgene in Air
Concn., p.p.m. 0 0 0 0
0095
0089 0094 0093 0.0288 0.0293 0.0284 0 0288 0 117 0 118 0 120 0 118 0 398 0 418 0 420 0 412 0 910 0 935 0 928 0 924
Dev. from mean +o 0002 -0 0004 + O 0001 0 0002 0.0000 +O ,0005 -0.0004 0 0003 -0 001 0 000 +o 002 0 -0 +O +O 0 -0
+o
Rel. std. dev.,
Yo
3 5
0
0.2
0.4 0.6 0.8 ppm., PHOSGENE
1.0
1.2
Figure 3. Calibration curve for the determination of phosgene in air
sensitivity, and calibration< would have to be corrected accordingly by running a standard sample. Possible interfering compounds likely to be present with phosgene were investigated. These compounds are HC1 and carbon tetrachloride. h l though HC1 has a retention time similar to that of phosgene on the column used, concentrations as high a$ 1% in air gave no interference. The electron capture detector is extremely sensitive to carbon tetrachloride; however, carbon tetrachloride does not elute until approximately 30 minutes after injection of the sample. Five samples can be injected before the carbon tetrachloride from the initial injection appears. At this point a second identical column can be switched into the system while the original column is being purged. The authors feel that this method can possibly be used as the basis for an automatic, continuous monitoring system for detecting and measuring phosgene in the atmosphere in both the toxic and subtoxic ranges. LITERATURE CITED
1.5
001
0 8
014 006 008 009 014 011
2 9
+O 004 0 010
0
13
(1) Clark, S. J., “Gas Chromatographic Analysis of Pesticide Residues Using
the Electron Affinity Detector,” publication furnished by the Jarrell-Ash Co., Wewtonville 60, Mass. (2) “Detects 0.01 p.p.m. of Phosgene,” Chem. Process., p. 138, (November 1956). (3) Lovelock, J. E., AKAL. CHEM.33, 162 (1961). (4) Stokinger, Herbert E., et al., A m . Ind. H y g . Assoc. J . 23, KO.5 , 419 (September-October 1962). RECEIVEDfor review March 11, 1963. Resubmitted September 3, 1964. Accepted November 16, 1964. Southeastern Regional ACS Meeting, October 1964. VOL. 37, NO. 1 , JANUARY 1965
71
