Environ. Sci. Technol. 1990, 2 4 , 1196-1203
An Intercomparison of Sampling Techniques for Nicotine in Indoor Environments Fern M. Caka, Delbert J. Eatough," Edwin A. Lewis, and Hongmao Tang Chemistry Department, Brigham Young University, Provo, Utah 84602
S. Katherlne Hammond Department of Family and Community Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01655
Brian P. Leaderer John B. Pierce Foundation and Yale University School of Medicine, New Haven, Connecticut 065 19
Petros Koutrakls, John D. Spengler, Adam Fasano, and Jack McCarthy School of Public Health, Harvard University, Boston, Massachusetts 021 15
Mlchael W. Ogden R. J. Reynolds Tobacco Company, Winston-Salem, North Carolina 27 102
Joellen Lewtas US. Environmental Protection Agency, Research Triangle Park, North Carolina 277 1 1
A study using several types of sampling systems was conducted in the chamber facility at the Pierce Laboratory to compare the determination of nicotine in environmental tobacco smoke generated by volunteer smokers. The sampling systems used included filter packs, annular denuders, sorbent beds, and passive samplers. Total nicotine determined by the various sampling systems was generally in good agreement. Agreement among samplers was also generally good for gas-phase nicotine. The most notable exception was the determination of nicotine with a stainless steel passive sampler where the results were low due to adsorption of nicotine by the sampler. Agreement, but with poor precision, was seen for the determination of particulate-phase nicotine with a Tenax microtube sorbent sampling system and two different annular denuder systems. However, loss of particulate nicotine to the gas phase occurred during sampling with the filter pack system, and determination of particulate-phase nicotine by these systems was in error. Because greater than 95% of the nicotine was in the gas phase, this loss of particulate nicotine did not significantly affect the determination of gas-phase nicotine with a filter pack sampling system. Introduction
There is an increased emphasis on the accurate determination of exposure to environmental tobacco smoke (ETS) due to the prevalence of ETS in indoor environments and due to the suspected adverse health effects associated with ETS exposure for the nonsmoker (1,2). In the past, nicotine has been extensively used as a marker and tracer to assess ETS exposure. The determination of nicotine in indoor environments with ETS present has been reported in studies that either measure the airborne concentration of nicotine (3-13) or monitor nicotine and cotinine in the urine of exposed populations (14-20). The results of a workshop to compare the techniques available for the determination of nicotine and cotinine in body fluids have been reported (21). However, no intercomparison studies on the determination of airborne nicotine have been reported. In the indoor environment, nicotine is primarily found in the gas phase (3,22-25). It is now clear that early data based on collection of nicotine on a filter significantly 1196
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underestimated the concentration of nicotine present in the environments studied. Several recent studies have attempted to monitor only gas-phase nicotine or to use a sampling procedure that collects both gas- and particulate-phase nicotine. It is possible that the different methods of sampling may result in substantial differences in the concentration of nicotine reported in indoor environments. The sampling method itself could, for example, influence the apparent gas-phase-particulate-phase distribution for nicotine. Hence, a need exists to directly compare the sampling and analysis methods used to determine nicotine in indoor environments. In the past, the major sampling techniques that have been used for the determination of nicotine in ETS have been the following: 1. Filter pack sampling systems where particles are removed on a filter, and gas-phase nicotine collected on acid-saturated filters (6, 8-10, 24). 2. Passive samplers for the specific collection of gasphase nicotine after diffusion to the sampling surface (7, 26, 27, 34). 3. Diffusion denuder sampling systems where gas-phase nicotine is first collected on an acidic surface by diffusion denuding followed by collection of particulate-phase nicotine by a filter pack designed to collect particles and any nicotine lost from particles during sampling (3,22-24,28). 4. Sorbent bed sampling systems that collect gas-phase nicotine (4, 11, 12, 23, 29). An intercomparison study of nicotine determination was conducted to evaluate the precision and equivalency of examples of each of the sampling techniques presently being used. Results from the study for the determination of airborne gaseous and particulate-phase nicotine are given here. Experimental Section
Four laboratories participated in the study using the sampling techniques and analysis procedures described below. Sampling Procedures. Brigham Young University. The group from BYU used four sampling techniques: 1. The annular diffusion denuder (BYU AD) has been described (26). This sampling system determines gas- and particulate-phase nicotine by collection of gas-phase nic-
0013-936X/90/0924-1196$02.50/0
0 1990 American Chemical Society
otine in an acid-coated annular diffusion denuder, followed by collection of particulate nicotine. The inlet to the sampler is a Teflon cyclone with a cut of 2.5 pm to remove coarse particles. The inlet is followed by two annular denuder sections (30) to collect gaseous nicotine. The surfaces of the denuders are prepared by coating with an aqueous 5% (w/w) benzenesulfonic acid (BSA) solution. The collection efficiency for gas-phase nicotine is determined by comparing the amount collected on the two denuder sections. Two BSA-coated glass fiber filters follow the denuder sections. The filters collect particulate nicotine and any gas-phase nicotine that evolves from the collected particles plus gas-phase nicotine not collected by the denuder. Thus, the results obtained with the annular denuder give gas-phase, particulate-phase, and total nicotine concentrations. Flow through the system was controlled a t 20 standard L/min (sLpm; at 25 "C and 1 atm) by Tylan mass flow controllers. 2. The filter pack (BYU FP) sampling system consists of a 47-mm Teflon filter followed by two BSA-coated glass fiber filters. Particulate nicotine is collected on the Teflon filter, and the BSA-coated filters collect gas-phase nicotine as well as any nicotine lost from particles collected on the first filter. Data generated from the filter pack include particulate-phase (assumed to be the nicotine collected on the Teflon filter), gas-phase, and total nicotine. Flow through the sampler for the study was controlled at 5 sLpm by a Tylan mass flow controller. 3. The passive sampling device (BYU PAS) collected gas-phase nicotine on a BSA-coated glass fiber filter. The design of the passive sampler used was originally described by Lewis et al. (31)and is marketed by Scientific Instrumentation Specialists (Moscow, ID). A description of the sampler and its flow calibration has been published (26). The effective collection rate for the sampler is 50 mL/min. 4. The Tenax semi-real-time sampler (BYU TEN) has been described by Tang et al. (32). It consists of two glass microtubes in sequence. For the intercomparison study, the first tube contained 3 mg of silanized glass wool to collect particulate nicotine. The second tube contained a 20-mg bed of Tenax sorbent, 35/60 mesh, to collect gas-phase nicotine. Up to 24 sets of tubes can be put into the multiport sampling box. The sampling time for each port can be varied from 1 to 60 min. During the intercomparison study, data were obtained by sampling over 10- or 20-min intervals. Flow rate through the system was controlled at 0.10 sLpm by a Tylan mass flow controller. The Tylan mass flow controllers were calibrated for the intercomparison study by use of dry gas meters, mass flowmeters, and bubble flowmeters. Harvard University. The group from Harvard used two sampling systems: 1. The miniannular denuder (HAR AD) is a personal annular denuder including a Teflon-coated glass impactor, which serves as a size-selective inlet, and a Teflon filter pack to collect particulate nicotine (33). The Harvard denuder system contains a single diffusion annular denuder section coated with an aqueous 4% (w/w) citric acid (CA) solution. Data previously reported (33)indicate that the expected efficiency of the denuder section for nicotine collection is 98.6%. The filter pack following the denuder section contains a 37-mm Teflon filter followed by a CAcoated glass fiber filter. Flow rate through the system was controlled by a modified Kurz Model 250 mass flow controller a t 2 L/min. 2. The Millipore cassette (HAR FP) consists of a Teflon filter followed by a CA-coated glass fiber filter. Particulate-phase nicotine is collected on the Teflon filter; gas-
phase nicotine and any nicotine lost from the particles are collected on the acid-coated filter. Flow through the system was controlled by a modified Kurz Model 250 mass flow controller at 2 L/min. Flow was calibrated for the denuder and cassette sampling systems by using rotameters. R. J. Reynolds. The group from Reynolds used two sampling systems: 1. The normally used configuration for the XAD-IV sampler (REY XAD) has been described (12, 29). It consists of a 7 cm X 0.6 cm glass tube containing two sections of 20/40 mesh XAD-IV sorbent (80 mg primary, 40 mg backup) separated by a glass wool spacer (no. 22630-11-04, SKC Inc., Eighty Four, PA). Flow through the sorbent bed is controlled a t 1 L/min by an SKC (Model 224-PCXR7) personal sampling pump. The data from the two XAD-IV sorbent sections allow determination of the efficiency of the XAD sorbent bed for the collection of gas-phase nicotine. The Reynolds sampling procedure normally entails connecting the outlet end of the XAD-IV sorbent tube directly to the sampling pump with rubber tubing. To provide a check on the amount of nicotine passing the two sorbent beds, in the experiments reported here, the XAD-IV sorbent tubes were followed by a 25-mm BSAcoated glass fiber filter prepared and subsequently analyzed by BYU. A threaded Delrin filter holder was connected in-line between the tube and the pump. The filter holder used a rubber O-ring to seal the BSA-coated 25-mm glass filter in place. The XAD-IV sorbent tube was connected directly to the inlet of the filter holder with a l/.Jn. Swagelok-'/,-in. NPT Teflon union using a 1/4-in.Teflon 2-piece ferrule. Since the ferrule is slightly larger than the outside diameter of the sorbent tube, leaks will occur a t this junction if the Swagelok nut is not tightened with a wrench. Also, leaks will occur within the Delrin filter holder if the two halves are either under- or overtightened or if the O-ring is placed on the downstream side of the filter. With the exception of experiment 1,samples for this intercomparison study were not collected by RJR scientists. Flow calibration of the sampling pumps for this system was done with a rotameter. 2. The passive sampling device (REY PAS) consists of a stainless steel diffusion sampler (34) available from Scientific Instrumentation Specialists containing a 600-mg bed of XAD-IV sorbent. The sampling rate used for nicotine in this device was 62.5 mL/min. University of Massachusetts Medical School/Yale University. The group from the University of Massachusetts and Yale University used two sampling systems: 1. The active sampler (UM/Y FP) has been described (6, 8). A polystyrene air sampling cassette (Millipore) contains a 37-mm Teflon coated glass fiber filter (Pallflex) followed by a Teflon-coated glass fiber filter coated with an aqueous 4% (w/w) NaHS04solution. Particulate-phase nicotine is collected on the first filter and gaseous nicotine is collected on the acid-coated filter. Flow through the systems was controlled by Gilian personal sampling pumps a t 3 L/min. Flow rate for the UM/Y samplers was calibrated by using rotameters. 2. The passive sampling device (UM/Y PAS) and its flow calibration (24 mL/min) have been described (7,27). The collection surface is a NaHS0,-coated, Teflon-coated glass fiber filter held in a modified 37-mm-diameter polystyrene air sampling cassette (Millipore) protected with a PTFE filter (S&S) used as a windscreen. Sampling. Six experiments were conducted during the week of December 14-18, 1987, in the chamber facility Environ. Scl. Technol., Vol. 24, No. 8, 1990
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Table I. Experimental Conditions in Each of the Six Experiments.
expt 1 2 3 4 5 6
expected total nicotine concn nmol/m3 pg/m3 800 200 200 200 800 800
sampling time, h
av RSP,” wug/m3
6 3 2 6 3 1
930 196 184 190 930 990
125 30 30 30 125 125
Sampling Systems: 3 6 from floor. 1 9 average distance from back wall
A I CI
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BI
HI
GI
D
C
A
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Tenax Sampler Cart
RSP. resDirable sumended Darticles. ~
described by Leaderer (35, 36) and Hammond (6). Environmental tobacco smoke was generated in the chamber by four smokers at a rate of one cigarette smoked every 10 min. The commercial cigarette used has an FTC tar rating of 17 mg and a nicotine rating of 1mg. Steady state was achieved by controlling the air circulation and ventilation rates (36). In order to simulate typical indoor environments, nicotine concentrations were varied in the experiments by changing the fraction of air exchanged. The sampling time at two different nicotine concentrations was varied in the six experiments conducted. Details of the experiments are given in Table I with the location of the various samplers relative to the smokers shown in Figure 1. The lower expected concentration of nicotine used in this study (200 nmol/m3 or 30 pg/m3) represents the higher concentrations found in indoor environments where smoking is present, including homes (3, 18),work environments (5,6,37),and restaurants (4, 7). The higher concentration of nicotine used (800 nmol/m3 or 125 pg/m3) has been reported in indoor environments (3, 9) but in practice is seldom seen (38). The amount of nicotine collected in the high- and low-concentration experiments was altered by varying the sampling time. Sampling was started 1 h after the start of smoking to allow time to establish steady state in the chamber. During the experiments each sampler was run in triplicate with the exception of BYU TEN. Only one Tenax sampler was used in all the experiments, with a sample being obtained every 10 or 20 min. Appropriate blank samples were obtained by each participant during the experiments. The results reported by each investigator have been corrected by using the data from these blank samples. Analyses. Analyses were done on the samples in the four organizations’ respective laboratories. A summary of analytical techniques is given below. Brigham Young University. BYU analyzed all collected samples by gas chromatography. Nicotine collected on the BSA-coated annular denuder surface was removed by extraction of the annular surfaces with 5 mL of water. Filters from all BYU samplers were extracted with 5 mL of water for 30 min in an ultrasonic bath. The resulting solutions were made basic with 0.25 M NaOH. A 2-mL sample of the basic solution was extracted with 4 mL of dichloromethane. Recovery of nicotine in the dichloromethane extraction is 80 f 4% (39). Results obtained in the GC analysis (FID detector) of the dichloromethane solutions were corrected for this extraction efficiency. The technique for analyzing the Tenax samples (GC-NPD detector) has been described by Tang et al. (32). The nicotine collected on Tenax or on the silanized glass wool was thermally desorbed and collected on a capillary column submerged in liquid nitrogen. Upon completion of desorption, the cold trap was removed and the column was ramped through a temperature program. The nicotine 1198
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Nephelometer
n
Flgure 1. Schematic showing the location of the table where the smokers were located and the location of the various sampling systems in the chamber Key: A, BYU AD; B, BYU FP; C, BYU PAS; D, HAR AD; E, HAR FP; F, REY PAS; G,REY XAD; H, UMIY FP; I, UMIY PAS.
concentrations were corrected for the experimentally determined 88 f 3% collection efficiency of the Tenax trap (40). Harvard University. Collected nicotine was recovered from the denuder surfaces by an aqueous extraction technique. The inlet, impaction plate, and filter pack were removed and one end of the denuder was capped. By use of a micropipet, 500 pL of ethanol was added dropwise to the denuder to wet the inside surfaces. After the denuder surface had been coated with ethanol, 1 mL of extraction solvent was added. The solvent was prepared by dissolving 0.17 g of NaHSO, in 100 mL of water. The other end was then capped and the denuder was rotated, coating all internal surfaces. The extract was then transferred to a 5-mL Wheaton vial. A second and third extraction were then made following the same procedure and the extracts were combined; however, the ethanol was added only prior to the first extraction. The Teflon and citric acid coated filters were extracted by the same procedure. The denuder or filter extracts were transferred to a 50-mL Erlenmeyer flask. Ten milliliters of 10 M NaOH was then added. The solution was mixed for 5 min with a magnetic stirrer and Teflon-coated stirring bar. Ammoniated heptane (5 mL) was then added and the mixture stirred for an additional 10 min. The ammoniated heptane was prepared by bubbling anhydrous NH3 through reagent/GC grade heptane for 2-3 min. The flask was removed from the mixer and the organic and aqueous layers were allowed to separate. An aliquot of the organic layer was decanted into a Wheaton vial. The extract was then analyzed for nicotine content by using gas chromatography with an NPD detector. The nicotine extracts were stored at 5 “C. If the extracts were stored more than 24 h, the ammoniation process was repeated. Recovery of nicotine in the analytical procedure was 100% for the denuder and 95% for the filter. R. J. Reynolds. RJR determined nicotine by using capillary column gas chromatography as described by
Ogden (29,41).Nicotine was extracted from the XAD-IV with ethyl acetate modified to contain 0.01% (v/v) triethylamine. Nicotine recovery by this procedure is 100.1 f 2.2% (41). The resulting extract solutions were analyzed directly by GC using nitrogen-selective detection with quinoline as an internal standard. Primary and backup sections of the XAD-IV sorbent were analyzed separately to enable assessment of any breakthrough. Although ETS contains trace amounts of quinoline ( N 1% of the nicotine concentration), the use of quinoline as an internal standard in this method is appropriate in most circumstances. In field-sampling situations, the volume of air sampled in conjunction with typical nicotine concentrations results in 0.1-2.0 pg of nicotine collected on the XAD-IV resin (29). For samples in this range, the mass of quinoline also collected on the resin is below the limit of detection and poses no interference with the 5 pg of quinoline added as internal standard. However, in these experiments, the nicotine mass collected on XAD-IV ranged as high as 40 pg, thus imposing a low bias as great as 8% (0.4 pg of ETS quinoline collected; 5 pg of quinoline added). The results presented in Table I1 have been corrected for any bias attributable to quinoline. If this method is used routinely for large quantities of collected nicotine ( > l o pg), the standard method should be modified. Recommended modifications are either an increased amount of quinoline or use of N-ethylnornicotine as internal standard (41). University of Massachusetts Medical School/Yale University. The NaHS04-treated filters from both the UM/Y F P and UM/Y PAS samplers were placed in centrifuge tubes containing 2 mL of water and 60 pL of ethanol and mixed for 1min. A 2-mL aliquot of 10 M sodium hydroxide was added and the resultant solution mixed for 1min. Nicotine was concentrated into 500 pL of ammoniated heptane by liquid/liquid extraction. Nicotine recovery by this method was 95 f 5% (6). An aliquot of the heptane solution was injected into a Hewlett-Packard 5890 gas chromatograph with nitrogen-selective detection for quantification of nicotine. Details of the analytical procedure have been published (6). Spiked Samples. To compare analytical techniques for the various laboratories involved, spiked NaHS04-coated filters were prepared with a known amount of nicotine. Each group was given a set of coded spiked filters. The Reynolds laboratory did not analyze the spiked filters because the acid-coated filters were not compatible with their analytical scheme. The filters, provided by the U.S. Environmental Protection Agency, National Environmental Research Center, Research Triangle Park, NC, were prepared by addition of 100 pL of a standard 1 mg/mL or 20 pg/mL nicotine solution in ammoniated heptane to a Teflon-coated glass fiber filter. The filter had been coated with NaHSO, following the procedure outlined by Hammond et al. (6). Samples were prepared containing 2.0 and 100 pg of nicotine to provide each laboratory with three filters at each concentration. A set of three blank filters was also given each laboratory. In addition, as part of their standard protocol, spiked filters were prepared daily by this same procedure by the University of Massachusetts for independent analysis by that group. Results Results from the intercomparison study are given in Table I1 and are shown as bar graphs in Figures 2-4. The bar graphs give the average and standard deviation of an observation for the replicate samples for each sampling system except for the BYU TEN sampler. For this sampler, the average concentration of nicotine over the time
0BYU AD m ~ y PAS u
1000 r9
E
750
0
500
250 0
2
1
3
4
5
6
Experiment
Flgure 2. Gas-phase nicotine concentrations obtained with the various samplers.
0BYU AD K Y B Y U FP I HAR FP eZa BYU TEN m HAR AD
T
40! 3n
1
2
3
4
5
6
Experiment
Figure 3. Particulate-phase nicotine concentrations obtained with the various samplers. I
T
1
2
3
4
5
6
Experiment
Figure 4. Total nicotine concentrations obtained with the various samplers.
period corresponding to operation of the other samplers was calculated from the sequential time data points. An estimated uncertainty was assigned to this average based on previously reported results (32, 40). Results from analysis of the spiked samples are given in Table 111.
Discussion Collection Efficiencies of the Sampling Systems. The collection efficiency of the samplers was evaluated for three of the systems by determining the amount of nicotine present in two sequential, identical collection units. These included the XAD-IV sorbent bed in the REY XAD sampler, the BSA-coated denuder sections in the BYU AD sampler, and the two BSA-coated filters in the BYU AD sampler. If XIand X 2 are the amounts of nicotine found Environ. Sci. Technol., Vol. 24, No. 8, 1990
1199
Table 111. Results of Spike Sample Analysis EPA-Prepared Samples"
BYU high
108 103 99.3 2.16 1.59 1.37 0.11 0.00 0.00
low blank
nicotine, pg Harvard
UMMC 156 127 122 1.64 1.46 0.77 0.02 0.02 0.01
108 103 92.2 1.35 1.59 1.20
