(2) Reinisch, R. F., Gloria, H. R., “A Survey of the Photodegradation of Organic Polvmers ExDosed to Ultraviolet Radiation”, Sol. Energ;, 12 (l), f 5 (1968).
(3) Pansius. P. J.. Watson, J. H.. Scott. J. R., “Operational Experience Since 1967 With the Navy’s Water Wall Refuse Incinerator Steam Plant”, Am. Inst. Che Eng. Symp. Ser., #22, V68, 1972. (4) McElroy, W. F., “Polyurethane Plastics”, US. Pat. 3,300,417 Assigned to Mobay Chemical Co., 1967. (5) Mahoney, L. R., Weiner, S. A., Ferris, F. C., “Hydrolysis of Polyurethane Foam Waste”, Enuiron. Sci. Technol., 8 (2), 135 (1974). (6) Pizzini, L. C., Patton, J. T., “Process for Recovery of Polyether Polyols From Polyurethane Reaction Products”, U.S. Pat. 3,441,616,Assigned to Wyandotte Chemical Corp., 1969.
(7) Broeck, T. R. T., Peabody, P. W., “Methods for Reclaiming
Cured Cellular Polyurethanes”, U.S. Pat. 2,937,151, Assigned to the Goodyear Tire and Rubber Co., 1960. (8) McElroy, W. R., “Methods of Dissolving Polyurethanes”, U S . Pat. 3,117,940,Assigned to Mobay Chemical Co., 1964. (9) Kinoshita, O., “Process for Decomposition of a Polyurethane Resin”, U.S. Pat. 3,632,530,Assigned to Yokohama Rubber Co., Ltd., Tokyo, 1972. (10) “Recycled Urethane is Cheaper Than New”, Design News, 12 (3),24 (1973). (11) “Recycling of Scrap Foam”, The Donald S. Gilmore Laboratories, Upjohn Co., Rep. No. 9, 1974. Received for review August 5,1974. Accepted October 23,1975.
Moisture Anomaly in Analysis of Peroxyacetyl Nitrate (PAN) Michael W. Holdren” and Reinhold A. Rasmussen Atmospheric Resources Section, Chemical Engineering, College of Engineering, Washington State University, Pullman, Wash. 99 163
Preliminary results in our laboratory using gas chromatography with an electron capture detector (GC-ECD) to measure peroxyacetyl nitrate have shown particular anomalies when calibrating and measuring low ppb levels of PAN. At constant concentrations (10 or 100 ppb) of PAN but with changing humidities (0-loo%), a definite instrument response change was observed. Maximum response was obtained a t 100% relative humidity. Humidities below 30% resulted in much lower response values. The possibility of erroneous measurements with the electron-capture analysis of PAN in ambient air can occur unless the proper experimental precautions are observed. During the past few years, numerous laboratories have measured peroxyacetyl nitrate (PAN) in ambient air (1-7). T h e concentrations of PAN are determined routinely by gas chromatography with electron-capture detection (GCECD). This technique provides a very sensitive and selective method for the atmospheric analysis of PAN. The range of PAN concentrations reported in urban and suburban air has been 1-200 ppb (by volume). Preliminary results in our laboratory on the GC-ECD analysis of PAN have demonstrated particular anomalies that may be of concern to scientists and engineers studying air quality. When the instruments were calibrated for PAN under varying humidity conditions, a definite response’ anomaly was observed a t the lower humidity levels. This effect is most pronounced a t the low-ppb range of PAN and a t levels less than 30% relative humidity (R.H.). The possibility of erroneous measurements with the electron-capture analysis of PAN in ambient air due to this humidity effect is discussed in this report.
Experimental In the investigation of this phenomenon, three different types of electron-capture detectors were used: a direct-current mode 3H detector in an Aerograph Hy-Fi Model 600 gas chromatograph, a pulsed-current mode 3H detector in a portable A.I.D. Model 511-06 gas chromatograph, a constant-current mode 63Ni detector in a Hewlett-Packard Model 5713A gas chromatograph. T o verify that the humidity anomaly was independent of the type of chromatographic column, a variety of stationary
phases and supports were tested. These column materials included: 5% Carbowax 400 on Chromosorb W AW-DMCS (80- to 100-mesh), 10% Carbowax 400 on Anakrom ABS (70- to 80-mesh), 10% Carbowax 600 on Gas Chrom Z (60to 80-mesh), Durapak Low K’ Carbowax 400 on Porasil F (100- to 120-mesh), and 4% Ucon 50-HB-2000 on Chromosorb W AW-DMCS (60- to 80-mesh). The gas chromatographic columns were fabricated from both Teflon and glass tubing in lengths varying from 12 in. to 6 ft. In most cases, j/8-in.-o.d. tubing was used. Synthesis of peroxyacetyl nitrate was accomplished by photolysis of ethyl nitrite in oxygen (7). One microliter of %%-purity ethyl nitrite obtained from Mallinckrodt Chemical Works was syringe-injected into a 20-1. Tedlar bag previously flushed and filled with oxygen. Both ethyl nitrite and the syringe used to dispense it were kept under refrigeration to minimize loss due to vaporization. After it was mixed, the ethyl nitrite-oxygen in the bag was photolyzed for 6-8 h with 24 Sylvania (F15T8-BL) blacklights. T h e concentrations of PAN produced were approximately 2 ppm, as determined by the colorimetric method reported by Stephens (8). This method of analysis agrees very well with the infrared method, which is based on the PAN absorbance a t 7.76, 8.60, and 12.61 wm. The colorimetric procedure involves the hydrolysis of PAN with base to produce molar yields of acetate ion, nitrite ion, and the molecular oxygen: 0
II
CH,-C-O-O---h’O,
+ 20H-
e
0
II
CH,CO-
+ NO,-
iO2
+ H,O
The nitrite ion then is analyzed in the standard way with Saltzman’s reagent (9). Standard dilutions of PAN were made in 2-1. glass flasks and 2-1. stainless steel vessels. Concentrations of PAN from 10-100 ppb were obtained and analyzed by the GC-ECD system. The apparatus used for adding moisture to the containers prior to adding various amounts of PAN is shown in Figure 1. By varying the water level in the impinger, humidities 10-50% were obtained. The humidity was meaVolume IO, Number 2, February 1976
185
1 HYGRO-
METER
Flgure 1. Apparatus for adding moisture to the dilution vessels prior to adding PAN
sured by an Electric Hygrometer Indicator, Model 15-
3030E. Results and Discussion The observation that water affected the PAN response of a GC-ECD system first became evident when specific concentrations of PAN (10 and 100 ppb) prepared with dry tank air were compared with the same concentrations prepared with laboratory air of 30% R.H. The shmples in both cases were made in 2-1. glass dilution vessels. With dry tank air, the response of PAN was lower by a t least an order of magnitude. Qualitatively this phenomenon occurred regardless of the column used for the PAN analysis (Table I). Further investigation using dry Nz, He, and Ar/CH4 as dilution gases gave results similar to those observed for tank air. Figure 2 illustrates the effect of changing the moisture content of a PAN standard (100 ppb) prepared in tank air. Relative humidities of 0, 10, 30, and 100% were used in this experiment. The chromatograms clearly illustrate a decrease in PAN response when the relative humidity is below 30%. The effect of humidity was examined subsequently a t different concentrations of PAN (10, 100, 1000 ppb). A plot of the response of PAN measured vs. the percent humidity was constructed as shown in Figure 3. For each concentration examined, the ratio of the peak height a t 100%humidit y (maximum response) was calculated. As can be seen, the changes in humidity had no effect on the 1-ppm standard.
However, a t the lower concentrations of 10 and 100 ppb PAN, simulating ambient air concentrations, the effect of water on instrument response a t 30% R.H. and lower was quite apparent. Three possible causes of this water anomaly were investigated. These were the possibility of sample-injection or sample-container interaction, the possibility of sample-column interaction, and the possibility of water interacting with the electron-capture detector, changing its response t o PAN. Several experiments were conducted to determine if there were any differences between syringe injections and valve-loop injections of PAN. Concentrations of 10 ppb PAN were made in both glass and stainless steel dilution vessels a t 100% humidity. These samples were transferred to the column by syringe and by means of valved sample loops. The procedure was repeated a t lower humidities. No difference was observed between the two methods. In all cases the instrument response to PAN was much lower a t humidities below 30%. The possibility of the PAN sample reacting with the container was tested by withdrawing a sample (10 ppb PAN) prepared in dry air and then humidifying it to 100%.The response after humidification was identical to the response obtained for the same concentration prepared initially a t 100%R.H. T o determine if column-sample interaction with PAN could be better defined, the columns were modified deliberately. This was accomplished by purging with high concentrations of PAN, treatment with dimethyl dichlorosilane, acid treatment, and continuous automated sampling of PAN in air. All of the treatments had no measurable effect on the PAN-humidity anomaly. In addition, other compounds were investigated under conditions similar t o those used with PAN. These included ethyl nitrate, methyl nitrate, carbon tetrachloride, and Freon-11 a t low ppb levels. All four of thebe compounds showed constant response values regardless of humidity changes. The possibility of water interacting with the electroncapture detector then was investigated. Preliminary work has been completed studying the effect of continuously supplying humidified carrier gas to the electron-capture detector cell. A stainless steel tee of minimum dead volume was connected between the end of the column and the de-
Table l . PAN Analysis (All concentrations" 50 p p b PAN)
Carrier Column type 5% Carbowax 400 on Chromosorb W AWDMCS (80-100
a
186
Column Detector temp, "C temp, " C 25
25
mesh) 10%Carbowax 400 on 25 25 Anakrom ABS (7080 mesh) 10% Carbowax 600 on 25 25 Gas Chrom Z (6080 mesh) D u r a p a k Low K' Carbo25 25 wax 400 on Porasil F (100-120 mesh) 4% Ucon 50-HB-2000 25 25 on Chromosorb W AW-DMCS (60-80 mesh) 10% Carbowax 400 on 25 25 Anakrom ABS (7080 mesh)a Analysis column on loan from another laboratory. Environmental Science & Technology
m in
Response a t 100% R. H.
25
100
25-30
30
100
0-5
30
100
0-5
30
100
0-5
in. 0.d.
30
100
5-10
'IR in. 0.d.
30
100
25-30
flow ml/
Column dimen. 'I8 in. 0.d. Teflon
24 in. X
20 in. x Teflon 3 ft. x 20 in. x 6 ft. x
in. 0.d. in. 0.d.
in. 0.d:
O/O
O/O
Response at-O% R. H.
Teflon 12 in. x
Teflon
in IOOppb 10% R.H.
100 p p b 3096 R ti
11
8ot*F
100 p p b 100% R H.
60
,TN
Y
z v)
#I
I O p p b PAN
#2
IOOppb PAN
# 3 1 0 0 0 p p b PAN
40
7 a
P v) W
20
0 TIME-
Figure 2. Chromatograms of PAN at 100 ppb with the humidity varying from 0 % to 100% Column used was 10% Carbowax 400 on Anakrom ABS, 20 in. long, ’/8 in. 0.d. Oven, 25 OC; carrier flow, 30 ml/min; ”Ni detector
tector. In this way, a continuous stream of humidified carrier gas could be added to the column effluent just prior t o the detector. The humidity a t the detector exist was measured at 30% R.H.Azain, samples of PAN a t various humidities (0-100%) were injected into the gas chromatograph. The same water anomaly as described earlier resulted. From the experiments we conclude t h a t the most probable cause of this water anomaly is some type of columnsample interaction. Further studies of this phenomenon are under way. Researchers analyzing for PAN by GC-ECD should be aware of the effect of humidity upon detector response when calibrating their instruments in the low-ppb range. The diluent air should be air of atmospheric humidity in order to give realistic results. Furthermore, in carrying out these measurements, the air sampled must be assessed as t o its initial humidity content. Studies were conducted recently in our bag irradiation chamber for peroxyacetyl nitrate, and ECD response values were increased five- to tenfold when the humidity was increased 10-50% R.H. Unless
0
20
40 Yo RELATIVE
60
80
100
HUMIDITY
Flgure 3. Illustration of the effect of humidity at different concentrations of PAN Column used was 10% Carbowax 400 on Anakrom ABS, 20 in. long, 0.d. Oven, 25 ‘C; carrier flow, 30 ml/min; 63Nidetector
1/8 in.
the proper experimental precautions are observed, significant errors in the quantitative analysis of atmospheric PAN by GC-ECD can be expected.
Literature Cited (1) Stephens, E. R., Price, M. A., J . Chem. Educ., 50,351 (1973). ( 2 ) Penkett, S. A., Sandalls, F. J., Lovelock, J. E., Atmos. Envi-
ron., 9,139 (1975). (3) Tingley, D. T., Hill, A. C., Utah Acad. Proc., 44,387 (1967). (4) Bufalini, J. J., Lonneman, W. A., Enuiron. Lett. 4,95 (1973). (5) Spicer, C., personal communication. (6) Mayrsohn, H., Brooks, C . , paper presented at the Western Regional Meeting of the American Chemical Society, November 18, 1965. (7) Stephens, E. R., in “Advances in Environmental Sciences and Technology”, J. N. Pitts, R. L. Metcalf, Eds., Vol. 1,Wiley, New York, N.Y., 1969. (8) Stephens, E. R., Price, M. A., paper presented at the 8th Conference on Methods in Air Pollution and Industrial Hygiene Studies, Oakland, Calif., February 1967. (9) Saltzman, B. E., Anal. Chem., 26, 1949 (1964). Received for review May 28, 1975. AcceDted November 6. 1975. Work supported by the- Coo.rdinating Rksearch Council Project No. CAPA-I 1-71,
Determination of Free Carbon Collected on High-Volume Glass Fiber Filter Ved P. Kukreja and John L. Bove’ The Cooper Union for the Advancement of Science and Art, 51 Astor Place, New York, N.Y. 10003
A convenient and precise method is reported for determining free carbon in a high-volume glass fiber filter. A low analytical blank was found, allowing the determination of small quantities of free carbon.
X-ray photoelectron spectroscopy (ESCA) has been applied to study the correlations between the diurnal variations of sulfates and free carbon ( l ) and , it was suggested t h a t perhaps some of the steps in the mechanism for the production of sulfate involve the interaction of sulfur diox-
ide with finely divided airborne carbon particles. If, indeed, carbon (soot) does play an important role in the production of airborne sulfates, the entire question of the control of the SO&042- would need reevaluation. I t became of interest in this laboratory to develop an analytical technique that could be used t o determine the amount of free carbon present in a 24-h high-volume sample. Since the technique would be used in conjunction with both short- and long-term carbon sulfate studies and would include a large number of samples, the free carbon determination technique should be both relatively simple, inexpensive and, yet, possess good reproducible qualities. Volume 10, Number 2 , February 1976
187
