Anal. Chem. 1980, 5 2 ,
fabrication (18)and behavior (19) of this dual sensor have been described elsewhere.
ACKNOWLEDGMENT T h e authors thank L. W. Niedrach and 0. H. LeBlanc for helpful discussions and S. F. Bartram for X-ray determinations.
273-276
(9) (10) (11) (12) (13) (14)
LITERATURE CITED (1) 0. H. LeBianc, Jr., J. F. Brown, Jr., J. F. Klebe, L. W. Niedrach, G. M. J. Siusarczuk, and W. H. Stoddard, Jr., J. Appl. ptrysioi., 40, 644 (1976). (2) R. G. Bates, J . Nectroanai. Chem., 2, 93 (1961). (3) R. Jasinksi, J . Electrochem. SOC.,121, 1579 (1974). (4) D. J. G. Ives and G. J. Janz, "Reference Electrodes, Theory and Practice", Academic Press, New York, 1961, (5) I.Levin, Chem. Anal., 41, 89 (1952). (6) P., Wulff, W. Kordatzki, and W. Ehrneburg, Z . Electrochem., 41, 542 (1935). (7) Ga. A. Perley and J. B. Godshalk, US. Patent 2 416 949 (1947). (8) L. W. Neidrach, unpublished data.
(15) (16) (17) (18)
(19)
273
R. A . Macur, U S . Patent 3 726 777 (1973). W. T. Grubb and L. H. King, U.S. Patent 3 7 0 9 8 1 0 (1973). J. P. Coughlin. U . S . Bur. Mines Bull., 542, 35 (1954). L. W. Niedrach, Report 73CRD194, June 1973, General Electric Co., Corporate Research 8 Development, P.O. Box 43, Schenectady, N.Y. 12301. W. M. Latimer, "Oxidation Potentials", 2nd ed.,Prentice-Hall, New York. 1953, p 203. J. F. Brown, G. M. J. Scusarczuk, and 0.H. LeBlanc. U.S. Patent 3 743 588 (1973). L. W. Niedrach and W. T. Grubb, U S . Patent 3 7 0 5 0 8 8 (1970). 0. H. LeBlanc. L. W. Niedrach, J. F. Brown, and R. W. Lawton, Report 77CRD078, General Electric Co., Schenectady, N.Y. J. Neurnark, A. Bardeen, and J. P. Kampine, J. Neurosurg., 43, 172-179 (1975). R. A. Macur, 0. H. LeBlanc. and W. T Grubb, U S . Patent 3 9 5 0 8 8 9 (1975). R. L. Coon, N. C. J. Lai, and J. P. Kampine, J . Appl Physioi., 40, 625 (1976).
RECEIVEDfor review J u n e 21, 1979. Accepted November 5 , 1979.
Nitrosamine Air Sampling Sorbents Compared for Quantitative Collection and Artifact Formation D. P. Rounbehler, J. W. Reisch, J. R. Coombs, and D. H. Fine* New England Institute for Life Sciences, 125 Second Avenue, Waltham. Massachusetts 02154
Eight wet and dry sorbents were evaluated both for their abiliy to retaln added nitrosamine standards and for artifactual formation of nitrosamines in the presence of added precursor amines and air containing oxides of nitrogen. The dry solid sorbents included activated charcoal, activated alumina, silica gel, Florisil, Tenax, and Thermosorb cartridges. The wet sorbents conslsted of impinger traps containing 1 N KOH and pH 4.5 phosphate-citrate buffer/20 mM ascorbic acid. The air concentrations of nitrogen oxides, preloaded amines, airflow rates, and air sample volumes were chosen to simulate actual field sampling in industrial atmospheres where nitrosamines and their precursors could be present. ThermoSorb/N was found to be the only sorbent which was both free of artifact formation and capable of retalnlng 100% of the preloaded nltrosamines.
Several investigators have recently reported finding airborne nitrosamines in samples taken in urban and industrial atmospheres (1-8). Since many nitrosamines are known to be potent animal carcinogens (9), these findings of airborne nitrosamines are of concern. However, in sampling air for nitrosamines, it is important t o avoid false analytical results d u e either to in-situ artifactual nitrosamine formation from airborne precursors or t o t h e inability of the chosen sorbent t o quantitatively retain the nitrosamines. Others have examined the problems of artifactual nitrosamine formation due t o analysis and sample preparation (10-13). In this study, we examined several types of sorbents for their ability t o collect and quantitatively retain a variety of volatile nitrosamines under simulated air sampling conditions. We also examined each sorbent for artifactual formation of nitrosamines from trapped amines and air containing nitrogen oxides. 0003-2700/80/0352-0273$01.00/0
EXPERIMENTAL Reagents and Materials. Activated charcoal 40/60 mesh (Alltech Associates), activated alumina F-1 80/90 mesh (Analabs), Florisil60/80 mesh (magnesium silicate, Floridin Co.), Tenax-GC 35/60 mesh (a porous polymer of 2,6-diphenyl-p-phenylene oxide, Applied Science Laboratories), silica gel 60/80 mesh (Applied Science Laboratories), and ThermoSorb/N (a mixture of metal silicates which have been activated in a reducing atmosphere together with amine trapping agents and a co-eluting anti-oxidant, Thermo Electron Corporation) were all tested as received. All solvents were distilled in glass (Burdick and Jackson). Potassium hydroxide (ACS grade pellets), phosphate-citrate buffer solution, and ascorbic acid were purchased from Fisher Scientific. Morpholine, piperidine, pyrrolidine, and diisopropylamine were purchased from Eastman Chemical. Dimethylamine (40% solution) was purchased from Aldrich Chemical, and the nitrogen oxide gas mixtures were purchased from Scientific Gas Products. All reagents were used as received. Nitrosamine standards were supplied by the Analytical Services Laboratory of Thermo Electron Corporation. All GC column materials were purchased from Supelco. Analytical. The nitrosamine determinations were made using a Gas Chromatograph (GC) (Thermo Electron, model 661), interfaced to a TEA analyzer (Thermo Electron, model 502) as described by Fine et al. (14). The GC was fitted with a 0.32 cm i.d. X 500 cm stainless steel column packed with 5% Carbowax 20M on Chromosorb W 100/120 mesh and was operated isothermally a t 160 "C with argon as the carrier gas a t 15 mL/min (15). All analytical determinations were made by comparing chromatographic responses to that of known standards by interfacing the TEA to an integrating recorder (Hewlett-Packard, model 3380A). Apparatus. The apparatus for generating known mixtures of nitrogen oxides in air and for maintaining specific flow rates is depicted in Figure 1. A constant flow of gas (2 L/min) was maintained by pumping air through a gas mixing apparatus controlled by a rotameter and monitored by a mass flow meter (Hastings, model ALL 10K). Oxides of nitrogen gas were intro1980 American Chemical Society
274
ANALYTICAL CHEMISTRY, VOL. 52, NO. 2, FEBRUARY 1980 NO, SUPPLY
i
I
.IDlNG COVER
LAMP
ACKFLUSHING
v
AIR IMPiNGER
T A I ~ L E S SSTEEL TEST TRAP
Figure 1. Schematic of instrumentation and apparatus for examining various sorbents for both the retention of volatile nitrosamines and for in-situ formation of nitrosamines from added precursor amines and sample air containing nitrogen oxides
duced into this air stream through a rotameter and a control valve from a supply tank which contained 1000 ppm NO and 73 ppm NO2 in nitrogen. Adjustment in the NO/N02 ratio in the gas stream was accomplished by in-situ generation of ozone with an ultraviolet lamp equipped with a sliding cover. The concentrations of NO and NOz were monitored at the inlet of the sorbent being tested using a NO, Chemiluminescent Analyzer (Thermo Electron, model 14B). Loss of nitrosamines from the test sorbents was quantified by analyzing ThermoSorb/N cartridges (Figure 2) which had been placed immediately following the test sorbent. A temperaturecontrolled (*l “C) water bath was used to determine the effect of temperature on the ability of liquid impingers containing either 1 N KOH or the pH 4.5 phosphate-~itrate/20mM ascorbic acid buffer to retain preloaded nitrosamines. Procedures. Nitrosamine and amine test solutions were prepared by sequential volumetric dilution of the pure compounds. A nitrosamine test solution was made up to contain 100 pg/mL in dichloromethane (DCM) of each of the following: N-nitrosodimethylamine (NDMA); N-nitrosodiethylamine (NDEA); Nnitrosodipropylamine (NDPA); N-nitrosodibutylamine (NDBA); N-nitrosopiperidine (NPiP); N-nitrosopyrrolidine (NPYR), and N-nitrosomorpholine (NMOR). The amine test solution contained 5000 pg/mL in DCM of each of the following: dimethylamine (DMA), diisopropylamine (DIPA), piperidine (Pip),pyrrolidine (PYR), and morpholine (MOR). The sorbents were preloaded by injecting 10 pL of the appropriate solution into a 2 L/min air stream and then allowing 10 min (20 L of air) to ensure that the added compounds were swept into the sorbent. The solid sorbent cartridges were prepared by packing the sorbent into 1.5 cm i.d. x 2 cm medical grade polyethylene holders with 100-mesh stainless steel screens at the inlet and outlet. The cartridges had standard Luer fittings to facilitate solvent elution of the trapped material, Figure 2 illustrates the cartridge construction and the sample elution technique. After preloading the sorbent cartridges, an air stream of 2 L/min was forced through the sorbent bed. One hundred liters of air a t 20 “C with 30-5074 relative humidity containing 1 ppm NO and 1 ppm NO2 was used to test the sorbents with added amines for in-situ nitrosamine formation. Two hundred and forty liters of air, without added nitrogen oxides (less than 0.02 ppm NO and less than 0.03 ppm NOz), was used to test the ability of the sorbents to retain nitrosamines. A t the completion of each test, the test cartridges and the following ThermoSorb/N cartridges (see Figure 1)were back-flushed with sufficient acetone (usually 2 mL) to quantitatively elute all of the test nitrosamines. The eluate was then analyzed by GC-TEA for nitrosamine content. Replicate samples with and without added
Figure 2. Cross section of a ThermoSorb/N cartridge showing sample
elution technique. Sample air was drawn through the cartridge in the opposite direction to that of elution. All solid sorbent used in these tests were packed in similar cartridges and eluted in the same manner amines and nitrosamines and without having had air passed through them, were used as the controls. The following ThermoSorb/N cartridges were examined to determine if breakthrough of the test nitrosamines had occurred. The wet traps consisted of 250 mm X 38 mm i.d. glass vacuum traps (Sargent-Welch) containing 45 mL of either 1 N KOH or pH 4.5 phosphate-citrate buffer/20 mM ascorbic acid. Fifty pg each of the five amines were added and tested for in-situ nitrosamine formation in the same manner as the solid sorbents. For analysis, the liquid contents of the traps were extracted with 3 X 15 mL dichloromethane (DCM),dried over sodium sulfate, and then concentrated on a Kuderna-Danish evaporator at 52 “C to a volume of 1 mL using 0.5 mL of isooctane added as a “keeper”. The concentrate was then analyzed by GC-TEA. Aliquots of these sorbents, with and without added amines and nitrosamines and without having had air passed through them, were used as controls. The test conditions of air flow rate, air sample volumes, air levels of nitrogen oxides, and amount of added amine were chosen to approximate conditions that have been encountered in sampling industrial environments for nitrosamines (1-8). For example, using the methods of Rounbehler et al. ( 7 ) ,a detection limit of 0.025 pg/m3 for NDMA can be achieved by sampling 240 L of air at 2 L/min with 1 N KOH impinger traps. To test for in-situ nitrosamine formation, 100 L of air was chosen because standard personal air sampling pumps, which operate at a maximum flow rate of approximately 0.2 L/min, would typically sample about 100 L over an 8-h workday. The amount of amines added to the test sorbent (50 pg each) are not unusual in industrial situations; for example, dimethylamine levels of 2 mg/m3 (200 pg/lOO L) and morpholine levels of 300 pg/m3 (30 pg/lOO L) have been reported in air being sampled for nitrosamines (1,6). The nitrogen oxide levels chosen were typical of industrial environments (16). The temperature ranges used to test the impinger traps represent seasonal variations. RESULTS AND DISCUSSION Sorbent R e t e n t i o n of N i t r o s a m i n e s . All of the dry sorbents with t h e exception of Tenax, which has a low breakthrough volume for NDMA ( l a ,retained 100% of the
ANALYTICAL CHEMISTRY, VOL. 52, NO. 2, FEBRUARY 1980
275
1
70
--
\
I-
1, I
I
0
'\ \
\
\
5
10
15 20 TEMPERATURE ( C " 1
\ NDY I 25
\
I
30
35
I
Figure 3. Temperature effect on the ability of the liquid sorbents to retain added volatile nitrosamines. The graph shows the percentages of each nitrosamine remaining after drawing air at 2 L min-' for 3 h through the sorbents at three different temperatures: 0, 15, and 35 O C
added nitrosamines. Tenax was re-tested under the same conditions but with lower total air volumes. After 100 L of air 90% of the added NDMA was recovered but after 190 L , only 7 % remained. T h e wet impinger traps were examined for their ability to retain the added test nitrosamines while an air stream of 2 L/min was bubbled through the sorbents. This test was performed a t three different temperatures: 0, 15, and 35 "C. The procedure consisted of adding 100 pg of each of the previously mentioned 7 nitrosamines in 0.02 mL of ethanol to 45 mL of the sorbent and analyzing a 0.5-mL aliquot of the trap contents at zero time and for every 30 min thereafter up to 3 h. Each aliquot was extracted with 1 m L of DCM and then directly analyzed by GC-TEA. The results of the zero time analysis were equated to 100% for the various nitrosamines in the solution. Similar extraction and analysis of serial dilutions of these sorbents with the added nitrosamines, were used as the controls. A t the end of the test, the volume of the remaining sorbent was measured and the results were adjusted for liquid evaporation with a constant rate of liquid loss being assumed. Since both of the wet impinger traps were found to be similar in their ability to retain the added nitrosamines, only the data for the KOH traps is presented in Figures 3 and 4. Although both liquid sorbents have been used extensively (2-8), it is seen t h a t NDEA, NDPA, and NDBA are rapidly lost from these systems. Thus, previous sampling for airborne nitrosamines with such sorbents may have failed to collect NDBA and NDPA and underestimated NDEA. The ability of these wet sorbents to retain nitrosamines appears to be dependent upon both the specific N-nitroso compound and the sampling temperature with the least polar nitrosamines being the ones most readily lost from these sorbents.
TIME ( HOLRS)
Figure 4. Loss of added volatile nitrosamines from impinger traps containing 45 mL of either 1 N KOH or pH 4.5 phosphate-citrate/20 mM ascorbic acid buffer with 2 L/min air flow through the traps at 15 OC. Trap contents sampled every 30 miti
In-Situ Formation. Nitrosamines are produced by the reaction between secondary amines and a nitrosating agent such as nitrogen oxides (18). Air containing these precursors may or may not contain nitrosamines. However, concentration of a precursor on the sorbent during sampling could result in an artifactual in-situ formation of nitrosamines. For this reason various sorbents were tested for this effect. Table I is a summary of the data from these in-situ artifact formation tests which employed constant N O / N 0 2 levels (1ppm each) and 50 kg each of the 5 added amines. All of the dry sorbents tested were found to be prone to artifactual formation of nitrosamines except ThermoSorb/N. Activated charcoal and Tenax were the two sorbents found to be the most prone to artifact formation. Both of the liquid traps were free of artifact formation. In order to determine what effect various levels of airborne nitrogen oxides could have on such in-situ nitrosamine formation, activated charcoal and Tenax cartridges with added amines (50 pg each of the 5 test amines) were subjected to a 2 L/min air stream containing different nitrogen oxide levels. A total of 100 L of air containing nitrogen oxide levels of either 0.2,0.5, 1, 2, or 4 ppm were forced through these cartridges. The N O / N 0 2 ratio was maintained a t 1/1 by adjusting the ozone level in the air stream. The contents of these cartridges were eluted and analyzed as previously described. Figure 5 shows artifactual formation of nitrosamines on Tenax and activated charcoal as a function of nitrogen oxide levels. Overall, morpholine was the amine most prone to nitrosation. At 4 ppm NO, over 50% of the added morpholine was nitrosated to NMOR on Tenax and over 20% was nitrosated on charcoal. In-situ nitrosation on these two sorbents is apparently also strongly dependent on the airborne nitrogen oxide levels with formation occurring even at the 0.2 ppm NO,. Some of the sorbents included in this study have been used in the past to monitor nitrosamines in atmospheres where
276
ANALYTICAL CHEMISTRY, VOL. 52, NO. 2, FEBRUARY 1980
T a b l e I. R e s u l t s of In-Situ F o r m a t i o n a f t e r S a m p l i n g 100 L o f Air C o n t a i n i n g 1ppm NO S o r b e n t s S p i k e d with 50 p g E a c h of 5 A m i n e S t a n d a r d s
-
1ppm NO, a t 2 L/min t h r o u g h
pgn of n i t r o s a m i n e f o r m e d
NUMA
sorbent activated charcoal activated a l u m i n a Florisil silica gel T e n a x GC ThermoSorbiN in KOH pH 4.5 a s c o r b i c a c i d a E a c h d a t a point i s samine.
NDiPA
NPIP
NPYR
1.7 0.10 N D ~ ND
5.0
1.5
1.2 0.59 1.9
0.22 0.20 0.56
0.10 0.21
0.17
0.45
3.8
ND ND ND
ND ND ND
ND ND ND
5.9
the average o f t r i p l i c a t e d e t e r m i n a t i o n s .
NMOR
0.58 1.3 ND ND ND
7.9 8.9 8.1 9.0 15.5 ND ND ND
ND = N o n e d e t e c t e d ; d e t e c t i o n limit, 0.01 p g of nitro-
-
TENAX
also been used to collect airborne nitrosamines but were not included in this study because they have been reported to be prone to artifact formation of NDMA (5) and because they are difficult to maintain in the field. Activated alumina, silica gel, Florisil, and ThermoSorb/N cartridges have not been previously reported as sorbents for airborne nitrosamines. We conclude that artifactual formation of nitrosamines from trapped amines and atmospheric oxides of nitrogen can occur on many dry sorbents. The wet impinger traps appear to be free of artifact formation but they lack the ability to quantitatively retain a broad spectrum of volatile nitrosamines. The only sorbent system found to be free of both of these problems was the ThermoSorb/N cartridges. These cartridges are presently being field tested in parallel studies with 1 N KOH impingers in industrial atmospheres.
/
- GC
/
ACKNOWLEDGMENT
/
The authors thank G. S. Edwards for his many helpful discussions and editorial suggestions. We also thank all of our co-workers a t the New England Institute for Life Sciences for their help and support.
LITERATURE CITED
k z
0.1
I
2
3
4
LL
161
"
01
I
I
2 PPM NO, (50%
3
4
NO1
Figure 5. Artifactual formation of nitrosamine on Tenax-GC and activated charcoal as a function of nitrogen oxide levels. Fifty g of each of the test amines were preloaded on the sorbents prior to passing air containing nitrogen oxides through them. See text for details
appreciable levels of both precursor amines and nitrogen oxides were present. The sorbents that have been reported for this use include: activated charcoal ( I ) , p H 4.5 phosphate-citrate/ascorbic acid traps (41, Tenax (3,17),and 1 N KOH impinger traps ( 3 , 5 , 7 , 8 ) . Cryogenic traps ( 2 , 3 )have
(1) K . Bretschneider and J. Matz, Arch. Geschwulstforsch., 42, 36 (1973). (2) D. H. Fine, D. P. Rounbehler, N. M. Belcher, and S.S.Epstein, Science, 192, 1328 (1976). (3) D. H. Fine, D. P. Rounbehler, E. D. Pellizzari, J. E. Bunch, R. W. Berkeley, J. McGee, J. T. Bursey, E. Sawicki, K. Krost, and G. A. DeMarrais, Bull. Environ. Contam. Toxicol., 15, 639 (1976). (4) K. D. Brunnemann and D. Hoffmann, in "Environmental Aspects of N-nitroso Compounds", E. A. Walker, M. Castegnaro. L. Griciute, and R. E. Lyle, Eds., International Agency for Research on Cancer, Lyon, IARC Scientific Publication No. 19, 343 (1978). ( 5 ) R. L. Fisher, R. W. Riser, and B. A. Lazaski, Anal. Chem., 49, 1821 (1977). (6) T. A. Gough, K. Goodhead, and C. L. Walters, J . Agric. Food Chem., 27, 181 (1976). (7) D. P. Rounbehler, I.S.Krull, U. E. Goff, K . M. Mills, J. Morrison, G. S. Edwards, D. H. Fine, J. M. Fajen, G. A. Carson, and V. Reinhold, Food Cosmet. Toxicoi., 17, 487 (1979). (8) J. M. Fajen, G. A. Carson, D. P. Rounbehler, T. Y. Fan, R. Vita, M. Wolf, G. S. Edwards, D. H. Fine, U. Goff, V. Reinhold, and K. Biemann, Science 205, 1262-1264 (1979). (9) P. N. Magee, R. Montesano and R. Preussmann, in "Chemical Carcinogenesis", C. E. Searle, Ed., ACS Monogr. No. 13 (1976). (10) I. S. Krull, T. Y. Fan. and D. H. Fine, Anal. Chem., 50, 698 (1978). (1 1) R. M. Angelis, L. K. Keefer and P. P. Roller, in "Environmental Aspects of N-nitroso Compounds", E. A. Walker, M. Castegnaro, L. Gricluie, and R. E. Lyle, Eds., International Agency for Research on Cancer, Lyon, IARC Scientific Publication No. 19, 109 (1978). (12) D. J. Freed and A. M. Mujsce, Anal. Chem., 49, 1544 (1977). (13) T. Y. Fan and D. H. Fine, J . Agric. Food Chem., 26, 1471 (1978). (14) D. H. Fine and D. P. Rounbehler, J . Chromatogr., 109, 271 (1975). (15) D. H. Fine and D. P. Rounbehler, Anal. Chim. Acta. 78, 383 (1975). (16) "Control Techniques for Nitrogen Oxide Formation", The Committee on Challenges of Modern Society, NATO, Brussels, Belgium, October 1973. (17) E. D. Pellizzari, J. E. Bunch. J. T. Bursey, and R. E. Berkeley, Anal. Left., 9, 579 (1976). (18) B. C.Challis and S. A. Kyrtopoulos, J . Chem. SOC.,Perkin Trans. 2 , in press.
RECEIVED for review June 22, 1979. Accepted November 15, 1979.
