Anal. Chem. 1982, 5 4 , 1947-1951 (16) (17) (18) (19) (20) (21) 122) i23j (24) (25)
Oberhoitzer, J. E.; Rogers, L. B. Anal. Chem. 1969, 4 1 , 1590. Rix, H. These d'Etat e6 !Sciences, IMAN, Universit6 de Nice. Rix, H. J . Chromatogr. '1981, 204, 163. Goedert, M.; Gulochon, (2. Anal. Chem. 1973, 45. 1188. Kleseibach, R. Anal. Chem. 1963, 35, 1342. Vidai-Madjar, C.; Guiochnn, G. J . Chromatogr. 1977, 142, 61. Petltclerc. T.: Guiochon. G. J. Chromatour. Sci. 1976. 14. 531. Yamaoka, K.; Nakagawa, T. Anal. C h e 6 . 1975, 4 7 , 2050. Guiochon, G. J. Chromntogr. 1964, 1 4 , 378. Conder, J. R.; Purneii, J. H. Trans. faraday Soc. 1966, 6 4 , 3100.
1947
(26) Keuiemans, A. I . M. "Gas Chromatography"; Reinhold: New York, 1957. (27) Conder, J. R. Chromatographia 1974, 7 , 387. (28) Ladurelli, A. These d'Etat es Sciences, Universit6 de Paris VI, Paris, 1978.
RECEIVED for review October 19, 1981. Resubmitted March 31, 1982. Accepted June 25, 1982.
Determination of Trace Levels of Nitrosamines in Air by Gas Chrornatography/Low-Resolution Mass Spectrometry Richard S. Marano," Wllliam S. Updegrove, and Ronald C. Machen Ford Motor Company, Analytical Sciences Department, Engineering & Research Sra ff, Dearborn, Michigan 48 12 1
The selective determlnatlon of volatile nltrosamlnes In alr was demonstrated wlth gas chromatography/low-resolutlon mass spectrometry (GC/MS). Hn accepted sampllng method uslng ThermoSorWN cartridges was used. These cartridges were preeiuted to remove interferlng compounds prior to standard nitrosamine elution and selective Ion monrltorlng (SIM) MS detection. Enhanced sensltlvlty was achleved by use of a commercla! concentrator whlch permltted the lntroductlon of 40 pL of eluant onto fused silica capillary and packed columns. Estimated from recovery studies, detectlon iimlts were In the 0.1-0.2 pg/m3 range for seven volatile nitrosamines. The method was applied to the analysls off alr in tire storage areas. N-MitrosodimethyWamlne In the 0.1-0.3 pg/m3 range and N-nltroeomorphoilne (NMOR) In the 0.3-12 pg/m3 range were determined by both QC/MS and the QC/thermal energy analyzer (7'EA). Cartridges not preeiuted tended to yield lower TEA values by a factor of 2-3. A suppressive TEA Interference is suggested.,
The occurrence and determination of N-nitrosamines has received a great deal of attention in recent years (1). These suspected carcinogens have been found in a number of ambient environments and consumer products (2-4). The necessity of determining these compounds at low levels, in complex matrices has resulted in a number of analytical schemes (5-8). Usually, the final analysis has been done with a chemiluminescence based detector (TEA, Thermo Electron Corp., Waltlham, MA) combined with gas or liquid chromatography. This method of detection has proven to be both sensitive and selective. However, interferences have been noted (9-11). Gas chromatographylmass spectrometry (GC/MS) has been the main method of confirmation (12-14). In many instances, it has been necessary to use high-resolution MS to achieve unambiguous confirmation of TEA results (13-15). This paper describes a GC/low-resolution MS method for the selective determination of volatile nitrosamines a t low concentrations in air.
EXPERIMENTAL SECTION Materials,, Methanol (MleOH) and dichloromethane (DCM) were distilled in glass (Burdick and Jackson Inc., Muskegon, MI). Tenax GC (60/80 mesh, Applied Science, State College, PA) was cleaned by heating to 300 "C under a 100 cm3/min flow of carrier grade helium for 4 h. Standards were supplied by the Analytical
Services Laboratory of Thermo Electron Corp. The four-component standard contained N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-nitrosodi-n-butylamine (NDBA) and N-nitrosomorpholine (NMOR) each at 25 yg/mL in ethanol. The seven-component standard included Nnitrosodi-n-propylamine (NDPA), N-nitrosopiperidine (NPIP), and N-nitrosopyrrolidine (NPYR) in addition to the four above each at 10 yg/mL in ethanol. Caution: Nitrosamines should be handled with extreme care. Safe procedures have been described elsewhere ( I ) . Apparatus and Operating Conditions. Two Unacon Series 780 (Envirochem Inc., Kemblesville, PA) trapping-concentrators were used. The design and operation of this instrument have been described elsewhere (116). Trap 1 and trap 2 were glass 81/8 in. long X 1/4 in. 0.d. with internal volumes of 2.5 cm3 and 0.1 cm3, respectively. Each was packed with selective adsorbents as supplied by Envirochem Inc. This dual trapping system has been shown to be an efficient means of concentration and solvent removal in a number of similar complex analyses (16). This is the first known application of such a system to nitrosamine determination. The concentration cycle parameters for each Unacon were identical and are given below in Samples and Analysis. One concentrator was connected to a Unacon 780B GC containing a 50 m X 0.2 mm i.d. Carbowax 20M fused silica capillary column (Hewlett-Packwd, Part No. 19091-60150). The column was initially held a t 50 "C for 2 min and then programmed at 4 "C/min at 230 "C. Tho helium carrier was flow controlled at a linear velocity of 30 cm/s. After the helium exited the GC oven, the column was heat traced (230 "C) directly into the ion source of a VG Micromass 16F mass spectrometer (VG LTD. Sussex, England). The MS was scanned from 25 to 300 amu once every second, under standard electron impact conditions (70 eV). Data were collected and analyzed with a Finnigan (INCOS) 4000 data system (method A). The other Unacon was interfaced to a Hewlett-Packard 5992B GC-MS-calculatorsystem equipped with a single 9885 floppy disk system. A 2 m X 2 mm 1i.d. glass column packed with Ultrabond 20M (80/100 mesh, Ultra Scientific Inc., Hope, RI) was used. It was held initially at 70 "C for 1min and then programmed at 10 "C/min to 230 "C. The Unacon transfer line and 5992 injection port were maintained at 230 "C. The helium carrier flow was 20 cm3/min. The GC/MS iinterface was a standard Hewlett-Packard supplied jet separator. Data were acquired and analyzed with Hewlett-Packard floppy disk software (Part No. 05992-10017) (method B). This software was used each day to tune the MS automatically as well as to optimize the optics for maximum throughput sensitivity in the region of 100 amu. When obtaining complete spectra, the quadrapole MS was scanned from 25 to 200 amu at 380 amu/s. Most of the actual nitrosamine quantitation was done by using selected ion monitoring (SIM). Three ions of interest were monitored under instrument software control. The
0003-2700/~l2/0354-1947$01.25/0 0 1982 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 54, NO. 12, OCTOBER 1982 SILANIZED GLASS WOOL
Table I. SIM Survey ofN-Nitrasamines
/ I \ A
\
/
ion (m/e) Group I
B
TENAX GC
NDMA NDEA NDBA and NMOR
Rgw 1. Pyrex g b blm (180 mm X 6.4 mm 0.d. X 4 mm 1.d.) used
for sample Introduction.
~
~
14 102 116
250 250 500
130 114 100
400 200 400
Group 2
total dwell time for all ions was 1 s using a window of f0.2 amu. Samples and Analysis. Replicate air samples were collected a t various tirefree locations (office, general storage, and outdoor ambient areas) and at tire-handling locations (among storage racks and near propane powered forklift transportation aisles) during the same time period. DuPont Model P-4OOOA constant flow sampling pumps (E. I. du Pont de Nemours & Co., Wilmington, DE) were used to draw air through ThermoSorb/N cartridges (Thermo Electron Corp., Waltham, MA) at a rate of 2 L/min for approximately 150 min. A DuPont calibrator was used to set flow rates and ensure that the pumps were compensating for the pressure drop across the cartridges. The cartridges have been shown to be an artifact free method of sampling for n i t r m i n e a (5). Cartridges were capped and stored at room temperature for 1 week prior to solvent desorption. Spiked cartridges were prepared hy adding 4 or 12 pL of the fourcomponent standard while sampling air from areas containing heavy hydraulic machinery. Prior testing had shown these areas to he free of nitrosamines. These spiked cartridgessimulated two sets of cartridges which had adsorbed the four nitrosamines at nominal levels of 100 and 300 ng. Recoveries were determined by comparing the eluants from these cartridges with solutions made hy injecting the appropriate amount of standard into vials containing 1.5 mL of 75/25% (v/v) DCM/MeOH. Each cartridge was preeluted and desorbed in the following manner. A 5.0-mL syringe with a 20-gauge needle was attached to "air in" side of the &ridge hy means of a pierced plastic cap. The syringe barrel was fded with 4 mL of DCM. In this manner, the restriction of the 20 gauge needle provided a slow gravity preelution flow of approximately 0.8 mL/min in the direction of the air sampled. After gravity flow had ceased, as much DCM as possible was air expelled from the cartridge hy means of the syringe plunger. The syringe assembly was then removed from the cartridge and the "air out" side was attached by means of a Teflon adapter to a buret containing 75/25 DCM/MeOH. From thispoint, the nitrosamines were backflusbed in a manner similar to the established method (17). A total of 1.5 mL was slowly collected in graduated vials over a period of 5 min. All eluants and nitrosamine standards were stored in the dark at -20 "C. Comparative nitrosamine determinations were done hy T E A a t the Analytical Services Laboratory of Thermo Electron Corp. Replicate ThermoSorb/N cartridges from the same sampling sites were divided into two groups. One group was eluted with DCM wash in the manner descrihed above. The eluants were analyzed by both GC/MS and TEA. The other group was eluted by Thermo Electron in essentially the same manner hut without DCM wash (18). In most instances, these eluants could only be analvzed bv TEA because of high backmound interferences in the GC/MS analysis. GC/MS analysis was performed in the following manner. Portions of the cartridee eluants were introduced onto a Tenax mntnjning Pyrex glass hx BP lollown (seeFigure 1): (1) the tube was removed from the Unacon and cooled w room temperature, (2) 20 PI. uf the 75/25 DCM/MeOH solution was placed on center region of glass wool. (9) the tube was purged with carrier grade helium at SO cm3 min from B to A for 2.5 min, (4) steps 2 and 3 were repented. The tube was then placed (Bend first) in the Unacon tube oven, which was initially at 100 O C . The microprocessor controlled 'liquid tube" trapping cycle was initiated immediately. The operation of the Unacon during a resulting n i t r m i n e concentration sequence is summarized as follows (see Figure 2). At the start of the first 3-min period. the solenoid valve closed resulting in a 45 cm3/min helium flow through the tube oven to the FID and vent. Greater than 96% of the sulvent is vented tn the atmosphere &q shown hy FID response I in Figwe 2. At the start of the second 3.5-min period. valve no. 1 rotated (valve oven at 230 "C) bringing trap no. 1 into line with the tube
dwell, ms
NDPA NPIP NPYR
Table 11. Recoveries ofNitrasamines from TnennoSorbIN Cartridges
5% recoverya NDMA NDEA NDBA NMOR
100 ng spike
300 ng spike
65 705 8 59t 13 92? 5
1 5 1 14 I1 I I 55? I 8 1 + 13
* Recovery based on the average offour determinations. I,
Recovery based on one determination.
oven. The tube oven was then heated to 280 OC, which transferred the notrmaminea tn trap no. 1 (both traps were initially at 65 "C) as shown by FID response 11. This transfer was compleled over the next 5 min while allowing the tube oven to cool. At the start of the third period, valve no. 1 rotated to its original position bringing trap no. 2 in line with trap no. 1. Simultaneously, trap no. 1 w a s ballistically heated (20 'C/s) to 300 "C. This hackflushed the contents of trap no. 1 as a narrow *plug" onto trap no. 2. This is shown by FID respnnse 111. After this step was completed, the entire contents of trap no. 2 were transferred to the GC column (therefore, this step is not shown in Figure 2). This involved the switching of valve no. 2 to bring trap no. 2 in line with the GC column and simultaneous hallistic heating of trap no. 2 to 300 "C. The entire Unacon trapping cycle took 15 min to the point of trap no.2 heat. At this point, GC p10gramminR and MS data acquisition were initiated. Quantitation of the nitrosamines was done by comparing single ion chromatogram peak heights for samples with those of standards in the same concentration range.
RESULTS AND DISCUSSION The effectiveness of the Unacon 780 two-trap system is demonstrated in Figure 3. By use of capillary method A, 111 mass spectra of good intensity were obtained for NDMA, NDEA, NDBA, and NMOR each at the 2 ng/pI. level. Other peaks shown resulted from residual solvent and trap concentrated solvent contaminants. The routine survey and determination of nitrosamines in ThermoSorh/N cartridge eluants were done hy using packed column method B combined with SIM. It was possible to do one analysis every 30 min with this method. Retention times were determined for each of the seven nitrosamines under MS scanning conditions. (See Figure 4.) The mass spectrum of each nitrosamine agreed with those previously reported (19). The seven nitrosamines were divided into twu groups for SIM. The ions and dwell times used for each member of a group are given in Table I. A detailed recovery study was done on the nitrosamines in group no. 1 since reports have shown these mast likely to occur in environments containing elastomer materials (20-22). The results of this study are given in Table 11. Preliminary experiments have demonstrated similar results for NDPA, NPIP, and NF'YR at the same spiking concentrations. Repeat analyses on the same eluants were reproducible within 6%. Both the 1Mand 300 ng standard solutions gave instrumental
ANALYTICAL CHEMISTRY, VOL. 54, NO. 12, OCTOBER 1982
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I
I
I
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2
3
4
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,LA I
I
I
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Figure 4. Total ion current chromatogram resulting from 15 pL of seven-component standard (10 ng/pL each in ethanol) (method B). m/e 102
0
2
4
6
8
1
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1
2
1
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m/e 116
T I M E (MIN.)
Figure 2. Simplified Unacon flow diagram and FID response during concentration sequence (see text). (J-RESIDUAL
J
m/e 74 --
SOLVENT
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i d I
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7
TIME (min.1
DBNA
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U I I
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1640
Flgure 3. Total ion current chromatogram resultlng from 4 pL of fourcomponent standard (2ng/pL each in 75/25 DCM/MeOH) through Unacon onto CW 20M fused silica capillary (method A). responses within 10% over a 3-day period. Figure 5 shows specific ion chromatograms resulting from the analysis of a 300-ng standard and a 300-ng spiked cartridge. After sampling 100 L of outdoor ambient air, the cartridge was eluted with only 7 5 / 2 5 DCM/MeOH. These experiments demonstrate the low background resulting from the cartridge and concentrator. A significant source of interference resulted from compoundai which were trapped on the cartridges during sampling and then coelulted with nitrosamines. The DCM preelution was found to be extremely effective in reducing or eliminating these background interferences presumably caused by nonpolar compounds also trapped on the cartridges. However, some interferences were still encountered in the determination of NDMA recoveries. Figure 6 shows specific ion chromatograms resulting from the analysis of spiked and unspiked cartridges sampled, preeluted and eluted in an identical manner. Less significant levels of interference for NDMA were encountered in the actual tire location air sam-
2
3 TIME (min
2000
1
Figure 5. SIM analysis of (A) 300 ng four-component standard and (B) 300 ng spiked cartridge after sampling 100 L of clear air (no DCM preelution). ples. Figure 7 demonstrates the effectiveness of the DCM preelution in reducing background interferences due to other compounds trapped on the cartridges during sampling. Note that NMOR can still be observed in both cases, however, due to its relatively high concentration on these cartridges from this particular sampling site. Recently, a similar preelution technique was used in the determination of nitrosamines in diesel crankcase emissions (23). The results for the analyses of the tire location air samples are given in Table 111. The estimated detection limits (in ng/cartridge) for the GC/MS technique are 35 ng of NDMA, 20 ng of NDEA, 27 ng of NMOR, and 40 ng of NDBA. The corresponding values quoted by ThermoElectron Corp. for TEA are 5 ng of NDMA, 8 ng for NDEA, NDPA, NPIP, NPYR, and NMOR, and 10 ng for NDBA. It should be stressed that the TEA method does not involve the use of a Unacon concentrator. Therefore, the GC/MS method detection limits are brought nearer to the sensitivity of TEA by the fact that the Unacon permits 10 times larger sample in-
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ANALYTICAL CHEMISTRY, VOL. 54, NO. 12, OCTOBER 1982
Table 111. Nitrosamine Levels in Storage Areas Containing New Tires NDMA sampling ThermoSorb/N analysis site cartridge method ng/ cartridge d m 3 1 1 GC/MS NDa
