Measurement of aliphatic amines in ambient air and rainwater

Chemosphere, Voi.24, No.lO, Printed in Great Britain

pp 1533-1540,

1992

0045-6535/92 $5.00 + 0.00 Pergamon Press Ltd.

MEASUREMENT OF ALIPHATIC AMINES IN AMBIENT M R AND RAINWATER

Lena Gr6nberg', Per I_~vkvist and Jan/~d~e JOnsson Department of Analytical Chemistry, University of Lund, P O Box 124, S-221 00 Lund, Sweden

ABSTRACT Amine concentrations in ambient air and rainwater were measured at several sites in southern Sweden. Air samples were obtained by sampling in dilute H2SO 4 and measured by gas membrane enrichment in a liquid flow system followed by gas chromatography. The major amines in both air and rain were trimethylamine and methylamine, but dimethylamine, diethylamine and triethylamine were also detected and individually quantified. The total amine concentration was 0.16 - 2.8 nmol/m 3 in air and 30 - 540 nM in rain.

INTRODUCTION Environmental concentrations of aliphatic amines are poorly known. A few measurements of methylamines and ethylamine have been made in marine air, showing concentrations of individual amines ranging from less than one to several hundred pmol/m 3 [1-3]. The amines were found both in the gas phase and as aerosols. These authors also found methylamines and ethylamine in nM concentrations in rainwater. Some data have also been published concerning atmospheric concentrations near emission sources, indicating levels in the low ppb range (nmol/m 3 range) [4-7]. A number of short-chain amines were identified in air samples from cattle feedlots and near livestock buildings [4,6,8]. In these environments trimethylamine appears to be the most common amine, followed by methylamine. Trimethylamine, dimethyl- and diethylamine were found in the air near a rendering plant [5]. In addition to the above mentioned sources, short-chain aliphatic amines are emitted from industrial activities [9-11], car exhausts [12], waste incineration [10] and sewage treatment [10,11]. Presumably, a natural background level of aliphatic amines also exists, originating from animal wastes, microbiological activities etc.

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Modelling studies suggest that amines react with NO x and OH radicals in air to form compounds such as nitrosamines, nitramines, amides and aldehydes [10,13]. As short-chain aliphatic amines are highly water-soluble they are also removed from the atmosphere by rain [2]. Dry deposition of aerosol particles may also be important [3]. Amines may be an important form of reduced organic nitrogen in the atmosphere. The quantitative significance for the global nitrogen cycle is presently unclear, mainly due to the limited information available on concentrations and on the relevant atmospheric chemistry [2,3]. Recently, we described a method for the determination of very low levels of amines in air, using impinger sampling in dilute sulphuric acid followed by gas membrane enrichment in a liquid flow system directly coupled to a gas chromatograph [14]. Enrichment in a flow system has several advantages: manual sample handling is minimized, losses and contamination are avoided and the technique is easily automated. A further advantage is that enrichment time and sensitivity are interrelated, so that a lower detection limit can be obtained at the expense of a longer analysis time. Enrichment factors of approximately 25 times could be obtained for C1 to C6 n-alkyl amines. An interface connecting the flow system to a packed column gas chromatograph was described [15]. Gas chromatographic methods for the trace analysis of amines, using packed columns and nitrogenselective detection were previously developed [16-20]. In this work we apply the recently developed technique [14] to the determination of short-chain aliphatic amines in air and rain samples taken at various sites in southern Sweden.

EXPERIMENTAL Equipment Details of construction and operation are given in refs. 14 and 15 and will only briefly be summarized here. The flow system was assembled from commercially available valves, pneumatic actuators, tubing, fittings, etc, as detailed in the cited works. A peristaltic pump was used to provide the flow and the system was controlled by a personal computer via a custom-made pneumatic interface. The PTFE membrane (Fluoropore FG, Millipore, Bedford, MA, USA) was held between two blocks of PTFE with spiral channels (0.25 mm deep, 1.5 mm wide and 150 mm long) facing each other. The PTFE blocks were backed up with aluminium blocks to ensure rigidity.

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OH 4-

RNH

3

Ac/d/c ~rr~le

L

:~ R N H 2

4-

H -4"

RNH a ~

RNH 2

c,~orr~

to~r'oz~7

OH

Figure 1. Enrichment principle

The enrichment principle is described in fig 1. The acidic sample is deprotonated by mixing with 2.5 M NaOH. In the membrane separator the amines diffuse from the donor solution through the gaseous phase contained in the PTFE membrane. The amines are then trapped in the stagnant acidic acceptor phase (0.05 M H2SO4 with 0.01 M (NH4)2SO4). After the entire sample has passed the membrane unit the plug of enriched amines is swept through the loop of the injection valve after first being deprotonated again with 2.5 M NaOH. A portion of the sample plug, centred on the peak maximum of the plug profile, is transferred to the GC injector. A simple interface between the flow system and the gas chromatographic injector was constructed [15], using a modified low-pressure valve connected to the gas chromatographic injector with a piece of PEEK tubing (polyetheretherketone, Upchurch Scientific, Oak Harbor, WA, USA). The gas chromatograph (Model 3700; Varian, Walnut Creek, CA, USA) was equipped with a nitrogen selective detector (TSD; Varian) and a glass column, 2 m x 2 mm I.D., packed with Chromosorb 103, 80 - 100 mesh (Manville, Denver, Colorado, USA). The injector temperature was 25ff'C and the detector temperature 300°C.

Sampling Air samples were collected by bubbling unfiltered air at a flow rate of ca 2 L/min through a midget impinger filled with 10 ml of 0.05 M HzSO4. For practical reasons, the inlet was prolonged by a teflon tube (0.8 m, 5 mm i.d.) at some of the sample sites. To compensate for evaporation, water was added when needed. The pump was a portable air sampling pump (Model P4000, DuPont, Wilmington, DL, USA) and the sampled volume was measured by a gas volume meter (Dehm & Zinkeisen, Frankfurt, Germany), connected after the pump. The sampling was carried out at 1 to 5 m above ground level, depending on practical circumstances. Typically a volume of 5 to 10 m 3 was collected in periods during several days. The sample volumes were corrected for temperature when

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applicable. The efficiency of impinger sampling of amines can be assumed to be close to 100%, according to earlier studies [21]. Rainwater was collected in a wide glass container (collection area 310 cm 2) during active precipitation. 30 mL rainwater was immediately mixed with 600 pL 2.5 M HESO4. All glass used for sampling and storage of air samples were washed, first with acid and then with ammonia (1% in water) and finally rinsed with deionized water.

Chemicals Stock solutions (0.3 - 0.5 M) of the amines were prepared in 2.5 M H2SO 4 from the liquid amines, water solutions or the hydrochloride salts. Methylamine hydrochloride, ethylamine (70% in water), dimethylamine hydrochloride and trimethylamine hydrochloride were obtained from Janssen Chimica (Beerse, Belgium), propylamine, butylamine, pentylamine, ammonium sulphate and sulphuric acid from Merck (Darmstadt, Germany), hexylamine from Aldrich Chemic (Steinheim, Germany), diethylamine from BDH (Poole, Great Britain), triethylamine from Fluka (Buchs, Switzerland) and sodium hydroxide from EKA (Bohus, Sweden). The water was purified with a Milli-Q/RO-4 unit (Millipore).

RESULTS AND DISCUSSION The concentration of amines in ambient air samples, obtained at several locations in southern Sweden, are presented in table I. The locations represent both urban and rural sites. Amines were detected in all samples and the total concentrations ranged from 0.16 to 2.8 nmol/m 3 range. These values are somewhat higher than levels observed in marine air [2,3], but about three orders of magnitude lower than measurements carded out close to emission sources [4-9]. Methylamine and trimethylamine were generally found at the highest concentrations. Diethylamine and dimethylamine were also found in appreciable concentrations and traces of triethylamine were found in some samples. Ethylamine was not detected, but the practical detection limit for this compound is somewhat higher

(ca. 20 pmol m 3) due to partial coelution with trimethylamine, which

is a dominant amine in most samples. The possible presence of ethylamine below this level is not assumed to introduce any significant bias for trimethylamine.

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Table I.Amines in ambient air (Me = -CH3, Et = -C2H5)

Site

Date (1991)

Temperature and wind directionr

Concentration / pmol m "3 e MeNH 2

Me2NH

Me3N

Et2NH

Et3Nh

Total

Lund a

Jan 24-31

0

var

480_+110

120_+40

500_+200

410±100

tr

1500

Lunda

Feb 7-13

-2

E g

150±40

50_+20

250_+80

17_+7

tr

470

Lund a

Feb 13-14

-5

W-NW

1200+_260

230_+80

1500_+500

60_+25

nd

3000

Lund a

Mar 1-13

3

var

550±130

60_+20

200_+70

14_+5

tr

820

Lund a

June 11-13

13

SW

680_+150

90±30

440_+160

30±9

tr

1240

Lund a

July 1-5

19

E

330±70

26±12

250±80

80+_20

tr

700

Lurid a

July 9-13

20

W

390_+90

40_+20

310_+100

60_+20

nd

800

Lurid a

July 17-24

15

W-SW g

230_+50

23_+9

200_+70

190±50

tr

640

S6dra Sandbyb

May 28-31

15

NW

1100_+200

310_+100

1200_+500

60_+20

tr

2700

Vallbyb

July 25-29

19

NW-NE

480±140

80__.30

1600±700

72_+17

tr

2200

Maim0 c

Aug 13-15

16

W

200_+50

50_+20

390_+140

27_+9

nd

700

Maim0 d

Aug 16-18

16

W-NW g

100__.30

27_+14

240_+80

16_+7

nd

380

Gothenburg d

Aug 24-26

15

var

160_+40

30_+20

60_+30

40_+20

nd

290

Gothenburga

Sept 27-29

8

var g

60±20

23__.19

46__.30

30__.20

nd

160

a Outside the Chemical Center, ca. 1 km from agricultural areas. b Rural c Coastal d Residential area e The results are presented with 95% confidence intervals, derived from the calibration regression lines [22]. f Mean temperature (°C) and predominant wind direction during the sampling period, var = varying. g Appreciable precipitation occurred during the sampling period. h nd=not detected (< ca. 2 pmol m3), tr=traces ( ca: 2 - 10 pmol m3).

T h e origin o f t h e a m i n e s c a n n o t b e definitively e s t a b l i s h e d f r o m t h e limited d a t a available. T h e h i g h e s t total a m i n e c o n c e n t r a t i o n s w e r e f o u n d in s a m p l e s f r o m rural areas, w h i c h could indicate a n agricultural origin o f t h e a m i n e s , especially t r i m e t h y l a m i n e . This is s u p p o r t e d by t h e relatively low values in b o t h t h e M a l m 6 s a m p l e s , t a k e n close to t h e s e a with i n s h o r e w i n d a n d t h e G o t h e n b u r g samples, taken

ca.

13 k m f r o m t h e s e a a n d far f r o m active agriculture areas. D u r i n g p e r i o d s o f

c o n s i d e r a b l e p r e c i p i t a t i o n t h e total c o n c e n t r a t i o n s o f a m i n e s s e e m to b e l o w e r t h a n during similar dry p e r i o d s , a l t h o u g h it is difficult to d r a w any definite conclusions.

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2

3

I

I

1

2

4

5

I

4

3 t/rain

t

I

5

6

Figure 2. Chromatogram of an air sample (Vallby, July 28-31 1991). Peak identities: 1. Ammonia, 2. Methylamine, 3. Dimethylamine, 4. Trimethylamine, 5. Diethylamine.

It is likely that a part of the amines in air are p r e s e n t in aerosol form [3]. U n d e r certain circumstances, amines b o t h in gaseous and aerosol form are collected with impinger sampling [23,24]. Also, amines occurring b o t h as free amines and as a m m o n i u m ions are collected. Consequently, the m e a s u r e d values are assumed to closely r e p r e s e n t the total concentration of amines in the air sampled. Table II. Amines in rainwater

Site

Date (1991)

Temperature and wind direction

Concentration /nM e MeNH2

Me2NH

MeaN

Et2NH

Total

Lunda

July 16

20

W

280±60

32±12

220±110

8±4

540

Luridb

Aug 16

17

SW

150±30

< 10

< 100

< 5

150

Luridb

Aug 19

13

NW

30__-20

< 10

< 30

< 5

30

Vallbyc

Aug 17

14

SW

90±20

10±7

110-.60

5---4

220

Gothenburg

Sept 29

8

E

40±20

< 10

< 100

< 3

40

MeUbystrandd

Aug 29

16

< 10

30±20

< 100

< 3

30

a North b Centre c Rural d Coastal e see note e in Table I.

NW

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Rainwater is of interest in this context, because of the scavenging effect of rain on the concentration of atmospheric species. The concentration of amines in rainwater should roughly correlate with the concentration in air [2]. In Table II, some amine concentrations measured in rainwater are presented. A pattern similar to the air samples is observed in most of these samples, except for the last rainwater sample, where the dominating amine is dimethylamine. Unfortunately, no air samples were taken at this location.

CONCLUSION The concentration of various amines in ambient air and rainwater can be measured with the technique presented. The values found for individual amines in air range from below 20 pmol/m 3 up to 1.6 nmol/m 3. In rainwater the concentrations range from below 5 to 280 nM.

ACKNOWLEDGEMENT This work was supported by the Swedish Environmental Protection Agency.

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2.

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(Received

in USA 14 November

1991; accepted

30 March

1992)