Determination of Primary, Secondary, and Tertiary Amines in Air by

Determination of Primary, Secondary, and Tertiary Amines in Air by Direct or .... or liquid injection-like syringe drive systems, liquid pumps, electr...
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Environ. Sci. Technol. 2008, 42, 5217–5222

Determination of Primary, Secondary, and Tertiary Amines in Air by Direct or Diffusion Sampling Followed by Determination with Liquid Chromatography and Tandem Mass Spectrometry M I C H A E L R A M P F L , * ,† S T E F A N M A I R , † FLORIAN MAYER,† KLAUS SEDLBAUER,† KLAUS BREUER,† AND REINHARD NIESSNER‡ Fraunhofer-Institute for Building Physics, Fraunhoferstrasse 10, D-83626 Valley, Germany and Technical University of Munich, Institute of Hydrochemistry, Marchioninistrasse 17, D-81377, Munich, Germany

Received July 16, 2007. Revised manuscript received November 30, 2007. Accepted December 3, 2007.

Two different methods for sampling of primary, secondary, and tertiary aliphatic and aromatic amines in air have been developed for improving amine analysis in air. The aim was to have a quick method for direct sampling of amines at defined times, for example, for material testing as well as for longterm measurements of amines by diffusive sampling during field studies without sampling instrumentation. The goal of the study was chemical analysis of amines, especially focusing on an analytical method suitable for tertiary amines besides primary and secondary amines. For both direct and diffusive sampling, samplers working with phosphoric acid impregnated glass wool for trapping of amines by formation of quaternary ammonium salts have been designed and tested. Direct sampling was applied for in-car emission measurement and for polyurethane exhalation monitoring by drawing air from 1 m3 test chambers through amine sampling devices. Diffusive sampling was applied for the same in-car measurement and for field measurement at a landfill leachate uptake with an obnoxious smell. Quantification of sampled analytes was achieved by LCMS/MS analysis.

Introduction Many different synthetic raw materials, auxiliary components, and substances are used for construction of building products, furnishings, paints, office equipment, and consumer products. In numerous cases, volatile organic compounds (VOC) used for processing or generated by chemical reactions in materials and on material surfaces during and after production can be emitted into ambient air and indoor air of buildings, motor vehicles, aircraft, and other environments (1, 2). There is a broad variety of VOC compounds found in material exhalation, including hydrocarbons, organic chlorine compounds, phenols, alcohols, glycols, al* Corresponding author phone: +49 8024 643269; fax: +49 8024 643366; e-mail: [email protected] † Fraunhofer-Institute for Building Physics. ‡ Technical University of Munich. 10.1021/es071755+ CCC: $40.75

Published on Web 06/13/2008

 2008 American Chemical Society

dehydes, ketones, amines, carboxylic acids, esters, phthalates, furans, lactones, terpenes, and so on (1–5). In this study, the focus of VOC analysis is directed to amines because, in contrast to well-established analytical methods for most of the VOC groups listed above, there is a lack of analytical methods especially for analysis of tertiary amines. Major amine sources in everyday life are polyurethane foam products, for example, used in pillows, mattresses, sponges, thermal insulations, furniture filling materials, automotive interior lining, and clothes (1, 6, 7), where amines are applied as catalysts during polyurethane foaming. Amines are also used as raw materials in the production of other chemicals, pharmaceuticals, pesticides, dyestuffs, and corrosion inhibitors (8). Because of their odor activity, and in many cases also their toxicity, there is an interest in determination methods for amines in air for a minimization of health risks and for an improvement of ambient, indoor, and workplace air quality (6, 8–14). Several analytical methods such as isotachophoreses (9), ion chromatography (10), electrophoreses (11), gas chromatography (12, 15–17), and high performance liquid chromatography (8, 13, 14, 18–20) are described in literature for the separation and determination of amines, for example, in food and beverage samples and in material and air samples. Most of the methods described use derivatization techniques for the analysis of amines, for example, working with dansylation, silylation, or naphthylisothiocyanate derivatives, besides many other derivatization agents. A derivatization technique working with toluylchloride as derivatization agent, described by Wellons and Carey in 1978 (18) and used for amine analysis of material emissions by Simon and Lemacon (8), was well-established for the analysis of primary and secondary amines in air with limits of detection at levels of less than 1 µg/m3. Up to now, derivatization techniques primarily are used for amine analysis, and even during the past few years new derivatization methods have been developed for liquid chromatography (LC) and gas chromatography (GC) analysis of amines (15, 16, 19, 20). However, derivatization techniques are often time-consuming. Furthermore, the biggest disadvantage of most published derivatization-methods is that derivatization techniques are suitable for the measurement of primary and secondary amines but not for the determination of tertiary amines because tertiary amines do not react with the derivatization agents. Therefore, a derivatizationfree method for direct sampling and analysis of primary, secondary, and tertiary amines was developed. Phosphoric acid impregnated glass wool was used for sampling by trapping amines as quaternary ammonium salts. Sample preparation was done by aqueous elution of the amines bonded to the glass wool. Analysis of the aqueous extract was done by LC-electrospray ionization mass spectrometry (ESI-MS) (21). In addition to direct sampling of amines, the aim of this work was the development of a method suitable for diffusive amine sampling, for example, for field studies and longterm measurements. Diffusive sampling is based on diffusion and permeation processes described by Fick′s first law of diffusion as expressed in eq 1 (22, 23), m)

AD(ce - co)t L


where m is the mass uptake of the diffusive sampler [g], ce is the external concentration being sampled [g/cm3], co is the concentration at the interface of the sorbent [g/cm3], A VOL. 42, NO. 14, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY



is the cross sectional area of the diffusion path [cm2], D is the coefficient of diffusion [cm2/sec], L is the length of the diffusion path [cm], and t is the sampling time [sec]. Diffusion coefficients are needed for calculation, but accurate measurements of diffusion coefficients are time-consuming. Moreover, only few values of diffusion coefficients are available from literature, but literature (22, 24, 25) provides equations for the prediction of diffusion coefficients, for example, as described by Gilliland, Hirschfelder, or Chen and Othmer. The only disadvantage, according to Nelson (24) and Lugg (25), are deviations greater than ( 5% between theoretical and experimental diffusion coefficients, when equations for approximation of the diffusion coefficients are used.

Experimental Section Chemicals. Amines used for standard preparation, formic acid used for HPLC, and phosphoric acid used for the preparation of amine samplers were obtained from SigmaAldrich (Taufkirchen, Germany). Indicators used for the preparation of badge-type samplers were obtained from VWR (Darmstadt, Germany). Water and acetonitrile of high purity (HPLC grade) used for HPLC were obtained from Roth (Karlsruhe, Germany); synthetic air 5.0, nitrogen 5.0, and argon 5.0 were obtained from Linde (Unterschleissheim, Germany). The gases were used for the operation of a test chamber and of the mass spectrometer. Preparation of Sampling Tubes for Direct Sampling of Amines. Glass tubes of 6.25 mm outer diameter in pipet form with tips of 20 mm length and 2.5 mm outer diameter, delivered by Assistent (Sondheim, Germany), are used for the preparation of amine sampling tubes. The sampling sorbent for amines is 0.05 g of phosphoric acid impregnated glass wool filled in each sampling tube. For the preparation of phosphoric acid impregnated glass wool, 5 g of untreated glass wool, obtained from Supelco (Taufkirchen, Germany), were treated with 200 mL of 0.2% phosphoric acid in acetonitrile in a 500 mL round-bottomed flask and, subsequently, the acetonitrile was distilled off in a rotary evaporator. Preparation of Axial Badge Type Samplers for Diffusive Sampling of Amines. Air monitoring cassettes with 37 mm inner diameter, obtained from Supelco (Taufkirchen, Germany), are used as body of badge-type samplers for diffusive sampling of amines. The adsorbent for amine sampling were glass fiber filters of the type MN GF-1, with a diameter of 37 mm (cross sectional area A ) 10.75 cm2), delivered by Macherey-Nagel (Düren, Germany), and impregnated with phosphoric acid. The length of the diffusion path (L) through the sampler to the adsorbent is 1 cm. Phosphoric acid impregnation of glass fiber filters is done with 300 µL of 5% phosphoric acid in methanol. After impregnation, the methanol is removed in a drying oven at 65 °C with air change to keep methanol concentrations below the explosion limit, controlled by a detector for the lower explosion limit supplied by Honeywell Analytics (KirchheimHeimstetten, Germany). Additives of small amounts of acid–base indicators such as bromocresol green, thymol blue, or methyl orange with color change in the acidic pH range can be used for the visualization of the sorbent saturation of the samplers. The color change of a diffusive sampler with methyl orange added is provided as Supporting Information (Figure SF-1). Preparation of Test Gas Mixtures. The number of possible dynamic set-ups for the generation of gas mixtures is quite large. A summary of methods working with gas stream dilution or liquid injection-like syringe drive systems, liquid pumps, electrolytic methods, pulse diluters, and so on is published by Nelson (24). During this work, preparation of amine test gas mixtures was carried out using a piezoceramic droplet ejector working on the principle of an ink-jet printer 5218



for the injection of amines into an air stream. Detailed information of the piezoceramic device, the experimental set up, and its applicability for the generation of test gas atmospheres within a broad concentration range have been given by Meininghaus (26). Separation, Identification, and Quantitation of Amines by LC-MS. Liquid Chromatography (LC). For the separation of amines, an 1100 Series HPLC System from Agilent (Waldbronn, Germany) was used, equipped with a vacuum degasser, binary pump, temperature controlled auto sampler, and column oven. Separation of amines was done on Discovery HSF5 HPLC columns with dimensions of 150 × 2.1 mm with 3 µm particle size (Supelco, Taufkirchen, Germany) at a temperature of 40 °C. Individual separations of amines have been carried out with varying solvent gradients at a flow rate of 400 µL/min using acetonitrile and water with 0.02% of formic acid added. An efficient solvent gradient for amine separation on 150 mm columns started with 5% acetonitrile for the first 5 min, raised from 5 to 25% during the next 8 min, then from 25 to 40% during the following 10 min, and from 40 to 50% during the next 17 min. Mass Spectrometry (MS). A Micromass Quattro Micro API tandem quadrupole mass spectrometer (MS) from Waters (Milford, USA) equipped with an electro spray ionization source (ESI) operated in the positive ionization mode was used for the identification and quantitation of amines. Argon at a pressure of 300 Pa was used as collision gas to obtain product ions from precursor ions by fragmentation. The temperature of the ion source was set at 120 °C; the temperature of the desolvation gas was set at 420 °C; the nitrogen desolvation gas flow was set at 750 l/h, and the nitrogen cone gas flow was set to 50 L/h. The m/z values of precursor and product ions, the cone voltage, collision energy, and capillary voltage were optimized for 65 amines. A table containing conditions used for MS/MS detection of amines, the limits of detection, and limits of quantitation of the LCMS method, as well as the diffusion coefficients (D) used for the calculation of amine concentrations sampled by diffusive samplers, are provided as Supporting Information ST-1. The software module “Mass Lynx 4.0” (Waters, Milford, USA) was used for control of the LC-MS system and data acquisition; the software module “Quan Lynx” (Waters, Milford, CT) was used for quantitation. Determination of the Limits of Detection (LOD) and Limits of Quantification (LOQ). The determination of the LOD and the LOQ, both performance indicators of an analytical method, was done by calculation according to DIN 32645 (27). Storage of Samples. To ensure storage stability of samples, amine sampling tubes loaded with amine standards were stored in a refregerator and were analyzed after 3, 6, 9, 12, 18, 30, and 60 days. For comparison, aqueous eluate-solutions of sampling tubes also were stored at room temperature and alternatively in a refregerator. Environmental Influence on the Sampling Performance of Badge-type Diffusive Samplers. According to guideline EN 13528–2 (23), titled “Ambient air quality - diffusive samplers for the determination of concentrations of gases and vapours”, the sampling performance of diffusive samplers for the sampling of amines was tested in a 1 m3 exposure chamber with controlled temperature, humidity, and airflow, delivered by Vötsch (Balingen, Germany). The sampling performance was tested at relative humidities of 20, 50, and 80% at temperatures of 10, 20, and 30 °C with three air volume changes per hour in the exposure chamber. Test gas mixtures continuously added into the chamber were prepared by piezo injection as described by Meininghaus (26). For validation of the diffusive samplers air samples of the chamber, atmospheres have been drawn by direct sampling for comparison.

Sampling. Sampling of test chamber air was done by drawing 50 L of air through sampling tubes, sampling of in-car air was either done by drawing 50 L of air through sampling tubes at a flow rate of 1 l/min or by using diffusive samplers. Air of a landfill leachate uptake was sampled by a diffusive sampler. Sample Preparation for LC-MS Analysis. Sampling tubes were eluted using 0.5 mL of high purity water collected in graduated flasks. The eluate was transferred into vials for LC-MS analysis. Diffusive badge-type samplers were opened; the glass fiber filters were removed using tweezers and were put into reaction tubes. One milliliter of high purity water was added. The reaction tubes were closed and were shaken at 400 rpm for 1 h. The eluate solutions were filtered through polypropylene (PP) membrane filters, pore size 0.45 µm (Aldrich, Taufkirchen, Germany) to remove glass fibers and were used for LC-MS analysis.

Results Storage Stability. It was assumed that sampling tubes for direct sampling of amines and diffusive samplers for the collection of amines, both working with phosphoric acid impregnated glass wool, will not behave differently during storage regarding different amines. Therefore, experiments for the evaluation of the storage stability have been carried out by substitution with amine loaded sampling tubes and aqueous eluate solutions of amine loaded sampling tubes for both direct and diffusive sampling. Sampling tubes have been stored in a refrigerator at 6 °C; eluate solutions were stored at 6 and 23 °C (room temperature). Measurements were performed after 3, 6, 12, 18, 24, 30, and 60 days. Storing stability is given for sampling tubes as well as for eluate solutions of amine-loaded sampling tubes stored at room temperature or in a refregerator. No significant differences in the measured amine concentrations were detected during storing experiments over a period of 60 days; results seem to be normal distributed, with a mean value of 98.1% and a standard deviation of (9.9%. The Gaussian distribution of the storage stability experiments is provided as Supporting Information SF-2. Environmental Influence on Diffusive Amine Sampling. According to DIN 13528–1 (23), the environmental influence on diffusive samplers for amines was checked by sampler exposure to amine atmospheres at different temperatures (10, 20, and 30 °C) and at different relative humidities (20, 50, and 80%); exposure time was one hour. Concentrations of analytes collected by diffusive sampling can be calculated after the measurement of the mass uptake (m) of analytes by application of Fick′s first law (eq 1). Diffusion coefficients of amines in air needed for calculation can be found in literature for some amines (24, 25). Diffusion coefficients (D) not listed in literature can be calculated by approximation, for example, as expressed by Gilliland. Amines used for testing were the primary amines butylamine (D ) 0.087 cm2/sec (24)) and cyclohexylamine (D ) 0,071 cm2/sec), the secondary amines diethylamine (D ) 0,099 cm2/sec (24)) and dibutylamine (D ) 0,058 cm2/sec), the tertiary amine triethylamine (D ) 0,075 cm2/sec (24)), and the primary, secondary, and tertiary aromatic amines aniline (D ) 0,074 cm2/sec (24)), N-ethylaniline (D ) 0,065 cm2/sec), and N,N-dimethylaniline (D ) 0,065 cm2/sec) at concentration levels ranging from 300 to 400 µg/m3 in the test gas atmospheres. Results of the experiments are shown in Figure 1; results of direct sampling are used for comparison, whereas result values of direct sampling are assigned to 100%. Figure 1 indicates, that no significant differences can be detected for amine sampling by diffusive sampling at different environmental conditions and between direct and diffusive sampling at concentration levels of test gas atmospheres

FIGURE 1. Environmental influence on diffusive amine sampling; butylamine, diethylamine, dibutylamine, triethylamine, cyclohexylamine, aniline, N-ethylaniline, and N,N-dimethylaniline have been offered over a time period of one hour at concentration levels from 300 to 400 µg/m3 to 5 diffusive samplers per experiment in a 1 m3 test chamber. The test chamber was operated at different temperatures (10, 20, and 30 °C) and relative humidities (20, 50, and 80%) to get information of the environmental influence on amine sampling behavior of diffusive samplers.

FIGURE 2. Relative amine concentrations found in material emissions sampled from 1 m3 test chambers by direct amine sampling. ranging from 300 to 400 µg/m3. These results are comparable to results of Lindahl, Levin, and Andersson (14), who also described the environmental influence as “small and disregardable” for their samplers working with 1-naphthyl isothiocyanate as reagent for amine sampling. Practical Test Examples. 1 m3 Chamber Experiments for Determination of Material Emissions. Experiments for determination of material emissions were carried out according to the recommendation VDA 276 (28) of the German Association of the Automotive Industry (VDA). Equilibrium of material samples was achieved under dynamic conditions with an air volume change of 0.4 per hour in a test chamber at a temperature of 65 °C and a relative humidity of 5% within a time period of two hours before measurement. For amine sampling, 50 L of test chamber air were drawn through sampling tubes after equilibrium. Results of amine analysis of two different polyurethane foam systems and of a composite material tested in 1 m3 test chambers under dynamic conditions are presented in Figure 2. Besides primary and secondary amines, tertiary amines such as 3-dimethylamino-1-propanol, N,N-dimethylbenzylamine, and triethylamine are major constituents in the VOL. 42, NO. 14, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY



FIGURE 3. Direct and diffusive amine sampling of interior air of a parked car in autumn 2006. The figure shows the periods of time of diffusive sampling, the points of direct sampling, and the temperature profile during experiments. On day 7, the car was heated at 40 °C under controlled conditions in a garage using lamps for heating and temperature sensors inside the car. material emissions analyzed. The test chamber experiment of the polyurethane foam sample 1 indicates the necessity for a method suitable for determination of tertiary amines because this sample contains mainly tertiary amines, with the exception of small amounts of diethanolamine and methylamine, together below 5% of the total amine amount sampled. Also, a second polyurethane foam sample and a composite material analyzed in 1 m3 test chambers show high amounts of tertiary amine exhalations (N,N-dimethylbenzylamine, triethylamine, trimethylamine, etc.), which cannot be detected with most previously reported analytical procedures using derivatization for amine analysis. Hence, the method is replacing the derivatization method with toluylchloride used before. Direct and Diffusive Sampling Inside a Parked Motor Vehicle at Different Times. Sampling was carried out in a car parked on the institute parking lot in October/November 2006. The temperatures were logged during the sampling period and are shown in Figure 3. Diffusive samplers have been stored inside the car for time periods of 0–3, 0–7, and 0–9 days. Direct sampling of interior air was done at the beginning of diffusive sampling and after 3 and 7 days, before diffusive samplers were taken out of the car for analysis. Times of direct sampling and time periods of diffusive sampling are marked and noted in Figure 3. Amine concentrations in samples of direct and diffusive sampling have been determined and are shown in Table 1. Quantitation results of both methods are within the same orders of magnitude. Differences between direct and diffusive sampling are based on the fact that direct sampling is a spot measurement at a defined time for some minutes not exceeding one hour. Diffusive sampling, in contrast, is an integrating measurement over a much longer period of time of at least some hours up to more then a week during the experiments. Diffusive samplers provide results on the averaged air concentration during their exposure time. Spot measurements by direct sampling are more influenced by temperature differences than long-term measurements (diffusive sampling), as shown in Table 1, because temperature changes influence the mobilization of VOC. A remarkable increase for nearly all amine concentrations can be perceived in the air sample collected by direct sampling after 6 h of heating at 40 °C at day 7, in comparison to the results of direct samplers collected at the beginning 5220



and after 3 days of the experiment. For example, the concentrations of 2-dimethylaminoethanol measured increased from 6.3 µg/m3 (day 1) and 3.4 µg/m3 (day 3) to 15.5 µg/m3 at day 7 after heating, although the temperature tendency has dropped during the experiment (except for the period of heating). A comparable increase in the concentration values can be seen for other amines such as aniline, dimethylbenzylamine, or triethylamine. This trend was not recognizable for diffusive sampling. For example, triethylamine concentrations dropped from 15.8 to 11.7 and 11.2 µg/m3 from 0 to 3, 0–7, and 0–9 days. The same trend was also detected for diffusive sampling of 2-dimethylaminoethanol (from 2.7 to 2.1 and 2.2 µg/m3) or N-methyl-2pyrrolidone (from 54 to 34 and 29 µg/m3). The concentration decrease goes along with the temperature drop during the experiments. As expected, short-term events hardly influenced long-term diffusive sampling results, but for direct sampling the sampling point of time is very important. Landfill Leachate Uptake. Results of amine sampling in a landfill leachate uptake with a diffusive sampler are shown in Figure 4. Sampling was carried out for 6 days. Sampling was stopped at day 6 because a color change of the methyl orange indicator from red to yellow indicated the saturation of the diffusive sampler. The sampler was eluted with water, and the sampler eluate was used for the LC-MS measurement of the sample. Five amines have been detected in the uptake air by diffusive sampling. The highest concentration of 42.9 µg/m3 has been found for trimethylamine, an amine with an annoying fishlike odor and a low odor threshold. Odor threshold values for trimethylamine vary in literature between 1.5 and 2.5 µg/m3 (29, 30). Besides other obnoxious odor impressions such as ammonia and rotting, a weak fish smell was detectable near the exhaust, caused by trimethylamine. For long-time amine sampling in this case, diffusive badgetype samplers are the method of choice. No sampling equipment (e.g., pump) was needed, handling of diffusive samplers is easy, and sampling can be carried out by nonexperts. Tertiary amines such as trimethylamine, triethylamine, N,N-dimethylbenzylamine, etc. can represent major emissions of many material (e.g., polyurethanes) and environmental samples but may not be detected with most previously reported analytical procedures using derivatization tech-

0.2 0.9 0.05 2.2 0.15 0.8 0.1 0.4 28.7 0.45 11.2 0.5

heating for 6 h at 40 °C

1.9 1.1 0.1 15.5 0.3 6.1 0.4 1.9 72.7 1.1 37.3 1.9 0.35 1.35 0.05 4.85 0.25 2.35 0.2 0.5 54.3 0.6 14.2 1.15 0.3 0.8 0.05 3.4 0.2 2.2 0.2 0.4 49.2 0.5 11.9 1.1 0.4 1.9 0.05 6.3 0.3 2.5 0.2 0.6 59.4 0.7 16.5 1.2 0.074a 0.064 0.071a 0.073 0.069 0.059 0.061 0.090a 0.072 0.073 0.075a 0.091

0.25 1.1 0.05 2.1 0.2 0.8 0.15 0.6 34.1 0.6 11.7 0.55

for 9 days [µg/m3] for 7 days [µg/m3] day 7 [µg/m3] for 3 days [µg/m3] mean [µg/m3] day 3 [µg/m3] day 1 [µg/m3]

diffusive sampling direct sampling diffusive sampling direct sampling

Supporting Information Available

0.3 1.2 0.05 2.75 0.2 1.1 0.25 0.1 53.6 0.8 15.8 0.6

niques. The lack of a suitable analytical method for tertiary amines was the main motivation for the development of the procedure described.

Data cited from ref 24.

This project was financially supported by Bayerische Forschungsstiftung.


aniline 2-butylaminoethanol cyclohexylamine 2-dimethylaminoethanol 3-dimethylaminopropanol N,N-dimethylbenzylamine N,N-dimethylcyclohexylamine isobutylamine N-methyl-2-pyrrolidone p-toluidine triethylamine trimethylamine


diffusion coefficient [cm2/sec]

TABLE 1. Results of Interior Air Samples of a Motor Vehicle Collected by Direct and Diffusive Sampling in Autumn 2006


FIGURE 4. LC-MS/MS analysis of a landfill leachate air sample collected by 6 day diffusive sampling. Separation was carried out on a Discovery HSF5 HPLC column (150 mm × 2.1 mm, 3 µm particle size) using a solvent gradient of acetonitrile and water with 0,02% formic acid. A total ion current (TIC) chromatogram monitoring 32 MS/MS Channels acquired in the multi reaction monitoring mode (MRM) with 5 peaks and the 5 MRM chromatograms of the amines detected in the air sample are pictured. Trimethylamine (42.9 µg/m3), diethylamine (2.8 µg/m3), isobutylamine (0.5 µg/m3), cyclohexylamine (2.3 µg/m3) and diisobutylamine (1.5 µg/m3) have been quantified.

Figure SF-1, diffusive samplers with methyl orange indication of sampler saturation, is provided as well as figure SF-2, showing the Gaussian distribution of amines measured after storage experiments. Furthermore, Table ST-1 is available, containing conditions for MS/MS detection of amines, limits of detection and quantitation of the method, and diffusion coefficients for the quantitation of amines collected by diffusive sampling. This information is available free of charge via the Internet at

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