composition products of H N 0 3 interfere with the extraction; this interference is manifested by an appreciable extraction of 64Cu together with Ig8Au. T h e procedure given above removes H N 0 3 completely. Extraction and Washing. T h e solutions resulting f'runi t h e dissolution of the irradiated samples were extracted with M in CH@13,b u t 3.4 X lo-,' M in the Ni(DDC):! (1.7 X case of Fe203),as described in the experimental part. T h e organic phase was washed with 20 mL washing solution (1M HC1, 0.1 M HC104, 0.5 g CuC12.2H20) for 2 min. Counting. T h e washed organic phase was counted in a well-type Ge(Li) detector. Radiochemical Purity. T h e high-resolution ?-spectra showed only "'Au. Decontamination factors were evaluated for some activities and found t o be > l o 3 for Cu, >IO4 for Sb, a n d > l o 5 for Na, Sc, Cr, M n , Fe, Ca, S n , La, Sm, arid Ga. These decontamination factors are high enough for almost all practical applications. If in special cases it would be necessary to improve them, this could be achieved by using a n extraction cycle. Chemical Yield. In order to confirm t h a t the whole procedure works quantitatively, independenr experiments with inactive matrices spiked with 198Au3+(100 p g ) were carried out. T h e results are given in Table 111. Precision and Accuracy. T h e results of t h e neutron activation analysis of some materials which contain Au in the p p b range are given in Table IV, together with literature values. T h e relative standard deviation is 1% for the S n matrix, 6% for t h e F e 2 0 3 matrix, and 10% for t h e rocks (except DTS-1). In the case of the rocks, it is suspected t h a t part of t h e scattering is due t o sample inhomogeneity. Because of the large range of values found in the iiterature for the Au content of the analyzed standard rocks, it is difficult t o make a meaningful statement about the accuracy. T h e same reservation has t o be made for standards of biological material like kale or orchard leaves. Relative standard deviations of most values given in the literature amount t o 3 0 7 ~ .Analysis of 1 2 aliquots (250 mg each) of
Buwen~skale by the present method gave a relative stdndard deviation of 39%; in view of these results, the chemical yield of the separation was checked carefully by spectrophotometry a n d found to be quantitative, in agreement with tracer experiments on inactive samples of other biological material (Table 111). We therefore conclude t h a t Bowen's kale is extremely inhomogeneous as to its Au content and do not give our experimental valuea in Value IV.
LITERATURE CITED F. E . tieamisn, "The Analyricai Cnernisrry of the Noble Metals", 1st ed., Pergamon Press, Oxford, 1966. F. E. Bearnish and J. C. Vari Loon. '*Recent Advances in the Analytical Chemistry of ?ne Noble Metals", Pergamon Press, Oxford. 1972. N. R. Das and S. N. Bhattacharyya, Talanta, 23, 535 (1976). F. Kukula, M. Krivanek. and M. Kyrs, J . Radioanal. Chem., 3, 43 (1969). F. Kukuia, Cnem. Zvesti, 23. 521 (1969). A . Wyttenbach and S. Bajo, Ana!. Chem.. 47, 2 (1975). H. Chermette, J. F. Colonat. and J. Tousset, Anal. Chim. Acta, 80, 335 (1975). H. Chernrerte, J F. Colonat. anu J. Tousset, Ana/. Chim Acta, 66, 331 (1977). H. Chermetta, J. F. Colonat, and J. Tousset, Anal. C h m Acta, 88, 339 (1977). D. A. Baardsley, G. B. Griscoe, J. Ruzicka. and M. Williams, Taianra, 12, 829 (1965). A . Wyrtenbach ana S. Bajo, Anal. Cnern., 47, 1613 (1975). S. Bajo and A. Wyttenbach, Anal. Chem., 48, 902 (1976). W.Fischer and W. Harre, Angew. Chem., 66, 165 (1954). G. 0. Brink, P. Kafalas, R. 4 . Sharp, E. L. Weiss, aria J. W. Irvine. Jr.. J . A m . Chem. SOC.,79, 1303(1957). S J. Lyie and A. D Shendrikar, Ana,. C h m Acta. 32, 575 (1965). F. J. Fianagan. Geochim. Cosmoschim. Acra, 37, 1169 (1973). V . Caramella-Crespi. U. Pisani, M. T. Ganzerli-Valenrini, S. Melone, and V . Maxia, J , Radioanal. Chem., 23, 23 (1974). K. Nornura, A. Mikani. T. Kaio, and Y. Oka, Anal. Chim. Acta, 51, 399 (1970). J. H. Crocket, R , R. Keays, ana S. Hsieh, J . Radioanal. Chem., 1, 487 ( 1 068).
R . A. Nadkarni and G. H. Morrison, Anal. Cheni., 46, 2 3 2 (1974). F. J. Flanagan, Geochim. Cosmochm Acta. 33, 81 (1969). T. E. &een, S. L. Law, and W. J. Campbell, Anal. C b m . . 42, 1749 (1970). W.D. Ehmann, P. A. Baedeker, and D. M. McKnown, Geochim. COSmochim. Acta. 34, 493 (1970). H. T. Millard, Jr., and A. J. Barrel. in A. 0. Brunfeit and E. Steinnes, Ed., "Activa:ion Analysis in Geochemistry and Cosrnochamistry", Pub. Universitetsforlaget, Oslo-Bergen-Tromso. Proc. NATO Adv. Study Inst., Kjeller. Norway. 7-12 Sept. 1970, p 353.
KEC'EI\-E:L) for review May
2, 1977. Accepted July 27, 1577.
Determination of Phosgene in Air by Gas Chromatography and Infrared Spectrophotometry G. G. Esposito,' Daniel Lillian,' G. E. Podolak, and R. M. Tuggle U.S. A r m y Environmental Hygiene Agency, Aberdeen ?roving Ground, Maryland 2 10 70
Gas chromatographic (GC) and infrared ( I R ) analytical methods for the determination of phosgene in air are described. Instrument operating parameters are presented along with data obtained on synthetic mixtures and field samples. GC analyses were conducted on a gas chromatograph equipped with an electron capture detector and a phosphoric acid modled silica gel column. I R measurements were made on a portable infrared gas analyzer equipped with a 28-m path cell. Known dilute concentrations of phosgene In dry nitrogen were generated from permeation tubes. The methods have been field tested and offer wide application in process stream monitoring, and the areas of industrial hygiene and air pollution control. Present
1774
address, USERDA, W a s h i n g t o n , D.C. 20545.
ANALYTICAL CHEMISTRY, VOL. 49, NO. 12, OCTOBER 1977
Phosgene is commercially important in dye manufacture and in the production of polycarbonate and polyurethane resins, carbamates, organic carbonates and chloroformates, and pesticides. Its occurrence in air is often unpredictable, since many organochlorine compounds thermally and photochemically decompose t o produce significant concentrations of phosgene. Because of its wide use and toxicity, considerable effort has been directed t o the development of arialytical methods for the determination of phosgene in air. Most of the early analytical methods (1-4) were colorimetric procedures. Of these, the most specific and sensitive reagent used was 4-(4'-nitrobenzyl)pyridine plus N-benzylaniline. This reagent has been modified (5) using diethylphthalate as an absorbing medium which permits t h e determination of phosgene concentrations as low as 0.1 ppm in air. Gas chromatography employing an electron capture dewcwr
Dry Nitrogen
30.00+0 . 0 5 O C Figure 1. Schematic of permeation tube system
has been used to separate, identify, and measure various ievels of phosgene in air. Priestley et al., (6) employed a gas chromatograph system consisting of an aluminum column packed with 30% didecyl phthalate on 100/120 mesh GC 22 Super Support; Jeltes, Burghardt, and Breman (7) reported a similar method for the simultaneou:, determination of low concentrations of both phosgene and dichloroacetylene. Dahlberg and Kihiman (8) recommenced a stainless steel GC column packed with 2070 DC-200 on Chromosorb W. Sensitivities down to 1 ppb were achieved with all three GC methods; however, because of the reactivity of phosgene the GC’s required frequent column conditioning and recalibration. Recently, Singh, Lillian, and Appleby ( 9 ) used pulsed flow coulometry for the determination of sub-ppb concentrations of phosgene. They demonstrated t h a t it is possible t o compensate for column losses by extrapolating to zero retention time in the column, thereby eliminating the necessity for routine calibration. This method requires B special gas chromatograph equipped with two electron capture detectors connected in series. A chromatograph of this type is not commercially available a t the present time. Two innovations, long path sample cells and fixed wavelength peak measurement, have greatly increased the capability of infrared spectrophotometry to measure trace concentrations of many gaseous pollutants. Long beam paths are folded into sample cells of relatively short physical dimensions by means of multiple-reflection mirror systems. Typically, a 20-m path is accommodated by a cell only m long. Measurement a t a fixed wavelength allows the use of a very broad bandpass (40 cm-’ bandwidth vs. 2 cm-l bandwidth for a typical scanning spectrometer) covering most, if not all, of the absorption band of interest. In effect, the spectropho. tometer measures the “integrated” absorption band rather t h a n recording the spectral profile. T h e result of long path, fixed wavelength measurement is a greatly enhanced sensi. tivity and signal-to-noise ratio relative t o conventional scanning spectrophotometers. A previous study ( I O ) (using a long path cell, sample pressurization to 10 atm, and a scanning Spectrophotometer) suggested that air concentrations of phosgene as low as 0.08 p p m may be measurable by infrared spectrophotometry Phosgene is reactive, and its survival during passage through
a compressor in a pressurization t o 10 a t m is questionable. However, the enormous bandwidth advantage of a fixed wavelength spectrophotometer should more than compensate for the low (1 atm) sample pressure disadvantage. This investigation was initiated to determine the applicability of GC and IR to the field measurement of phosgene in air in the range of 1 ppb to 1 pprn and to demonstrate their general use for industrial hygiene, air pollution control, and process control monitoring.
EXPERIMEN’TAL Gas Chromatography. The GC used in this investigation was a Model 510 AID (Analytical Instrument Development, Inc., West Chester, Pa.) portable GC equipped with a pulsed electron capture detector containing 200 mCi of tritium. This instrument, in addition to being operable from 110 volts ac, is also equipped with a rechargeable nickel-cadmium battery and is capable of up t o 8-h operation before the batteries must be recharged. The carrier gas flow rates and oven temperatures were varied according to the type and length of columns used. The columns described in Table I were evaluated using syringe and gas sampling valve injections of phosgene from the permeation tube system shown in Figure 1. This system was also used to calibrate instruments in the field. The stainless steel gas sampling valve was fitted with a 2-mL Teflon loop. Most of the sampling was conducted with glass syringes containing either Teflon or glass plungers. Variable results were obtained with different syringes that had not been conditioned. The conditioning procedure was relatively simple. A new syringe was flushed five times with 2 ppm of phosgene standard at which time the syringe was filled with 2 ppm of the phosgene calibration mixture and allowed to condition for 10 min. An additional 10-min treatment was sometimes required with syringes containing Teflon plungers. From the outset of the gas chromlatographic study, it was decided t o develop a system as completely inert as possible t o avoid reaction and adsorption of phosg’enewithin the GC system. To accomplish this, Teflon materials, which are known for their inertness, were evaluated. Some of the column packings studied are graphitized carbon, porous polym(srs,silica gel, and various liquid phases on Teflon solid supports. In addition, potential interferents were tested to determine their effect on the phosgene analysis. The first phase of this study was directed at column evaluation and optimization of chromatographic operating conditions. ANALYTICAL CHEMISTRY, VOL. 49, NO. 12, OCTOBER 1977
1775
Table I.
Chromatographic Columns
Column
Liquid phase
Solid support
1 2 3
none none 30% didecyl phthalate 30% didecyl phthalate 2 5 % polyphenyl ether 10% didPcyl phthalate 10% polyphenyl ether none
none none 80-100 mesh Gas-Chrom P 80-100 mesh Gas-Chrom P 80-100 mesh Gas-Chrom P 40-60 mesh Chromosorb T 40-60 mesh Chromosorb T none
4 5
6 7 8 a
Available from Waters Associates, Inc., Milford, Mass.
Adsorbent
Tubing
Dimensions
Teflon Teflon Glass
6 ft 6 ft 6 ft
X X X
in. in. ‘ I 8 in.
none
Teflon
6 ft x
in.
none
Teflon
10 ft x ’ I 8in.
none
Teflon
1 0 ft
X
in.
none
Teflon
1 0 ft x
in.
Chromosil 310b
Teflon
10 f t
Porapack Qa Carbopack Ab none
X
lib
in.
Available from SuDelco. Inc.. Bellefonte. Pa.
Columns were tested for their inertness t o phosgene and their ability to efficiently resolve phosgene from potential interferents. The second part of this investigationwas concerned with the study of detection limits, linearity of detector response, and quantitative aspects of the GC method. I n f r a r e d Spectrophotometry. A MIRAN I1 infrared gas analyzer (Wilks Scientific Corporation, South Norwalk, Conn.) was used in this study. The basis for infrared phosgene detection is a strong absorption band (C-C1 stretch) a t 11.8pm (850 cm-’). This band was chosen over the 5.5 pm (1830 cm-’) carbonyl absorption band, because of its slightly greater intensity and its relative freedom from interferences. The blank region at 11.2 pm (890 cm I) was used as the reference wavelength. Known, dilute concentrations of phosgene in dry nitrogen generated by the permeation tube system (Figure 1)were supplied to the MIRAN I1 on a continuous flow basis. Baseline measurements were made before and after each day’s run after purging the sample cell with dry filtered air. All measurements were made with the MIRAN I1 set for a slow (8-s time constant) response and the sample cell set for a 20.25-m path. The scale expansion was generally set for a 0.01-absorbance unit full scale deflection (1OOX). Extremely low phosgene concentrations were measured at a 200X scale expansion. Initial experiments were directed at determining the phosgene detection limit of the MIRAN I1 and assessing the day-to-day variability of phosgene measurements. In the second phase of this investigation, potential interferences were examined. Finally the instrument was tested under field conditions.
C
al 0,
0
-
I L -
2
c
U
.-al
C -
1 -
RESULTS AND DISCUSSION Gas Chromatography. Several-2 mL injections of a 2-ppm concentration of phosgene were analyzed on t h e columns described in Table I. With columns 1 and 2, t h e phosgene was completely reacted or irreversibly adsorbed. Attempts t o passivate the column with large injections of phosgene did not improve t h e results; consequently, further use of these two columns was terminated. Columns 3 , 4 , and 5 are similar to the ones used for phosgene by others (6-8). Initial injections of phosgene on these columns produced extremely low results. Approximately 20 injections were required to “condition” the columns t o the point where reasonable reproducibility was obtained with phosgene peak height measurements. Even after the columns had been thoroughly conditioned, when low concentrations of phosgene (less t h a n 50 ppb) were sampled, periodic conditioning with injections of higher concentrations of phosgene was necessary. Columns 6 and 7 contained the same two liquid phases used in columns 3 and 5; however, 40-60 mesh Teflon was substituted for diatomaceous earth supports. T h e use of Teflon in place of diatomaceous earth caused less of t h e phosgene t o be adsorbed; therefore, t h e columns required less conditioning. On the other hand, the overall efficiency and resolving power of t h e columns were diminished because of t h e characteristic nonuniformity of Teflon support materials. 1776
A N A L Y T I C A L CHEMISTRY, VOL. 49, NO. 12, OCTOBER 1977
5
0
Time, Minutes Figure 2. Chromatogram of 50 ppb of phosgene in nitrogen
Column 8 (Chromosil310) provided the best recoveries and resolution of phosgene a t all the concentration levels studied. This column consists of a specially treated silica gel packed in l/s-inch Teflon tubing. T h e column is inert t o phosgene and permits the determination of phosgene down t o 0.1 ppb. T h e chromatogram presented in Figure 2 was obtained on a 50-ppb phosgene standard. T h e Chromosil310 column was operated with a carrier gas (5% methane in argon) flow rate of 15 mL/min a n d a column temperature of 30 OC. T h e Chromosil310 column was evaluated for interferences from water a n d ammonia by inserting an ammonia tube in the permeation tube system (Figure l), allowing the mixture of phosgene and ammonia (7 ppm) to pass over a pool of water at point B; samples were taken at point C. Figure 3 shows t h e chromatograms from 50 p p b of phosgene standard in nitrogen, and phosgene with ammonia and water. Ammonia and water have no noticeable effect on t h e height of the phosgene peak. Similar experiments were conducted with C02,HC1, Freon 11,Freon 12, and Freon 113. These materials were separated from phosgene on the Chromosil310 column, and they had no significant adverse effect on the determi-
Table 11. Phosgene Measured, ppmb
Sample No.
Sample mat r ixa
GCIC
...
zero air scrubber zero air scrubber scrubber scrubber scrubber zero air zero air scrubber scrubber scrubber
le 2 3f 4f 5 6 7
8 9 10 11 12
0.33 0.23( 1 ) 0.22(2) 0 . 2 2 (3) 0.062(9) 0.057 0.043( 11) 0.019 0.016
GC2 0.49 0.29
0.24( 1) 0.21(3)
...
0.065 0.060
0.013
0.044( 6) 0.019 0.019 0.010
0.006
0.004
IR
... 0.38 0.29( 1) 0.27( 1 )
0.20(4) 0.066( 3 ) 0.048 0.03 9( 6 ) 0.021
... ...
...
No. of measurementsd 1 1 3 6
2 2 1
2 1 1 1 1
Numbers in parentheses Scrubber matrix is air at 95% relative humidity after passage through an 18% caustic spray. are estimated standard deviations in the last figure quoted as determined from replicate runs. Gas $chromatographicanalyses were performed simultaneously on two different instruments b y two operators. Each measurement was determined from the average of at least three injections in the case of the gas chromatographs, or the average absorption during 15-min continuous monitoring in the case of the infrared spectrophotometer. e Actual concentration was 0.494 ppm as determined from permeation and flow rates. Actual concentration was 0.24 ppm as determined by the colorimetric method o f Noweir and Pfitzer ( 5 ) . a
-
A Phosgene and Nitrogen
e Phosgene, Nitro en Ammonia and V?at
