Amines are important drivers in particle formation and
growth, which have implications for Earth's climate. In this work, we
developed an ion chromatographic (IC) method using sample cation-exchange
preconcentration for separating and quantifying the nine most abundant
atmospheric alkylamines (monomethylamine (MMAH
Particles in the atmosphere can modulate climate through their direct and
indirect effect on the radiative balance of Earth's atmosphere (Boucher et al., 2013; Lohmann and Feichter, 2005). This potential warming
or cooling effect of particles represents the greatest uncertainty in
Earth's radiative forcing (Myhre et al., 2013). Additionally,
particles with a diameter of 2.5
Recent work has shown that organic compounds may contribute considerably to particle nucleation (Ehn et al., 2014; Ortega et al., 2016; Tröstl et al., 2016; Willis et al., 2016). In particular, the need to measure and quantify gaseous atmospheric alkylamines has gained interest because of their exceptional ability to partake in atmospheric particle formation. Multiple laboratory investigations have shown the nucleation potential of methyl- and ethyl-substituted amines through gaseous acid–base chemistry reactions (Almeida et al., 2013; Angelino et al., 2001; Berndt et al., 2010, 2014; Bzdek et al., 2010, 2011; Erupe et al., 2011; Jen et al., 2016a, b; Lloyd et al., 2009; Murphy et al., 2007; Qiu et al., 2011; Silva et al., 2008; Smith et al., 2010; Wang et al., 2010a, b; Yu et al., 2012; Zhao et al., 2011; Zollner et al., 2012). Theoretical calculations and studies have also found that amines have a high disposition to form atmospheric nanoparticles (Barsanti et al., 2009; Kurtén et al., 2008; Loukonen et al., 2014, 2010; Nadykto et al., 2015; Ortega et al., 2012). From these works, alkylamines have been shown to form clusters via neutralization reactions at rates up to 3 orders of magnitude greater than ammonia (Almeida et al., 2013; Berndt et al., 2010; Bzdek et al., 2011; Kurtén et al., 2008; Loukonen et al., 2010; Nadykto et al., 2015) and readily exchange with ammonium in ammonium–bisulfate molecular clusters (Bzdek et al., 2010; Lloyd et al., 2009; Qiu et al., 2011). These studies suggest that alkylamines can compete with ammonia to form particles even though they have been quantified at mixing ratios that are 3 or more orders of magnitude lower in the atmosphere (Chang et al., 2003; Ge et al., 2011; Schade and Crutzen, 1995). Atmospheric measurements made during new particle formation events have further confirmed that alkylamines participate in particle formation at ambient concentrations and that these species may be present in most atmospheric particles (Creamean et al., 2011; Dall'Osto et al., 2012; Hodshire et al., 2016; Kulmala et al., 2013; Kürten et al., 2016; Ruiz-Jimenez et al., 2012; Smith et al., 2010; Tao et al., 2015).
Alkylamine emissions to the atmosphere arise from both natural and anthropogenic sources (Ge et al., 2011). Short-chain alkylamines such as the methylated and ethylated amines are predominantly reported in emission estimates. Measurements show that atmospheric alkylamines are prevalent in ambient air across the globe, especially in the particle phase (Ge et al., 2011). For example, methyl- and ethylamines were measured by an aerosol time-of-flight mass spectrometer at both rural and urban sites all across Europe (Healy et al., 2015). In particular, these amines have been measured in substantial quantities near animal husbandry operations (Kuhn et al., 2011; Lunn and Van de Vyver, 1977; Rabaud et al., 2003; Schade and Crutzen, 1995; Sorooshian et al., 2008), fisheries (Seo et al., 2011), and sewage-waste treatment facilities (Leach et al., 1999). Other anthropogenic sources include tobacco smoke (Schmeltz and Hoffmann, 1977), automobiles (Cadle and Mulawa, 1980), and cooking (Rogge et al., 1991; Schauer et al., 1999). The ocean is estimated to be the largest natural source of alkylamines, where they are released as volatile degradation products (Ge et al., 2011; Gibb et al., 1999a, b). Aliphatic amines have also been detected in smoldering stage biomass-burning (BB) plumes. These have been estimated to represent a quarter of global methylated amine emissions (Lobert et al., 1990; Schade and Crutzen, 1995).
Real-time in situ speciation and quantitation of atmospheric amines in the particle and gas phase can be difficult because alkylamines are commonly found at or below parts per trillion by volume (pptv) mixing ratios in the atmosphere (Ge et al., 2011). Furthermore, the atmospheric matrix can be complex and ubiquitous atmospheric species can cause matrix effects for various analytical methods targeting these reduced nitrogen species. Being able to chromatographically resolve alkylamines from the dominant base, ammonium, represents a major challenge when sampling the gas phase (Chang et al., 2003; Ge et al., 2011; Schade and Crutzen, 1995). Quantifying amines in particle samples, for example by ion chromatography (IC), presents a greater challenge due to possible interferences from sodium, potassium, ammonium, magnesium, and calcium whose concentrations are dependent on the particle source characteristics and the measurement location (Ault et al., 2013; Kovac et al., 2013; Sobanska et al., 2012; Sun et al., 2006). Particles frequently contain complex organic mixtures, such as high molecular weight organic compounds, which can cause further matrix effects during separation or direct analysis (Di Lorenzo and Young, 2016; Saleh et al., 2014).
Achieving full speciation of alkylamines is important because the nucleation potential of amines has been shown to increase with basicity (Berndt et al., 2014; Kurtén et al., 2008; Yu et al., 2012). For example, although monopropylamine (MPA) and trimethylamine (TMA) are structural isomers of one another, MPA is likely to be a more potent nucleator due to its stronger basicity. The suite of alkylamines that have been commonly detected in the atmosphere contains multiple structural isomers (e.g. monoethylamine, MEA, and dimethylamine, DMA), making it difficult to speciate the amines using mass spectrometry (MS) without prior separation. Multiple field investigations sampling atmospheric particles using MS analysis have reported the detection of amine ion peaks but have been unable to assign them to a specific amine (Aiken et al., 2009; Denkenberger et al., 2007; Silva et al., 2008; Yao et al., 2016). Derivatization of alkylamines coupled with HPLC or GC separation has been reported to aid in separation and quantitation of amine species (Akyüz, 2007; Huang et al., 2009; Fournier et al., 2008; Key et al., 2011; Possanzini and Di Palo, 1990). However, these approaches are time consuming, require optimization of reaction conditions, and employ phase separations, which use large quantities of consumables, reagents, and solvents. Capillary electrophoresis has also been employed for aqueous amine separation, but in either case derivatization was required (Dabek-Zlotorzynska and Maruszak, 1998) or the separation of atmospherically relevant cations was not addressed (Fekete et al., 2006). The use of ion chromatography to directly separate and quantify atmospheric alkylamines has been demonstrated (Chang et al., 2003; Dawson et al., 2014; Erupe et al., 2010; Huang et al., 2014; Li et al., 2009; Murphy et al., 2007; VandenBoer et al., 2012; Verriele et al., 2012), yet the established IC methods struggle with coeluting cations (Huang et al., 2014; Murphy et al., 2007; VandenBoer et al., 2012; Verriele et al., 2012) or they do not address a full suite of atmospherically relevant alkylamines and inorganic cations (Chang et al., 2003; Dawson et al., 2014; Erupe et al., 2010; Li et al., 2009).
In this work we demonstrate the separation and quantitation of the nine most abundant atmospheric alkylamines, two alkyl diamines, and six inorganic cations through the use of ion chromatography. We show (i) the separation method approach to maximizing peak resolution in the context of real-time atmospheric sampling and analysis; (ii) the effects of column temperature on amine coelution; (iii) the method precisions, accuracies, sensitivities, and limits of detection (LODs) for all alkylamine and inorganic cations; and (iv) application of the method to the complex matrix of atmospheric BB particle extracts to demonstrate method sensitivity and robustness.
Inorganic cation stock solutions were prepared from a primary mixed cation
standard concentrate (Dionex six-cation II, lot no. 150326, Thermo
Scientific, Waltham, MA, USA) consisting of Li
A Thermo Scientific ICS-2100 Ion Chromatography System (Thermo Scientific,
Mississauga, ON, Canada) utilizing Reagent-Free Ion Chromatography
(RFIC™) components was used to develop the separation of the selected
amines and inorganic cations. A Thermo Scientific methanesulfonic acid (MSA)
eluent generator cartridge (EGC III, P/N: 074535) was used in conjunction
with an ultrapure deionized water reservoir to supply the eluent mobile
phase with H
The gradient program used for the separation of methylamines, ethylamines,
other alkylamines, and six inorganic cations on the CS19 cation-exchange
column was optimized by combining analyte separation parameters from
multiple isocratic elution runs at varying MSA concentrations (1–16 mM)
and mobile-phase flow rates (0.75–1.25 mL min
Optimal separation of a suite of 15 cations was achieved using a mobile-phase flow rate of 1.25 mL min
Standards were prepared using Class A Corning polymethylpentene 50
(
Method precision for each methyl- and ethylamine cation was determined using
standard calibration curves (
To assess the method robustness in the presence of a complex matrix the gradient method standard addition was performed on a subsample of a size-resolved BB particle extract (320–560 nm; see Sect. 2.5). Standard addition was performed by adding known quantities of methyl- and ethylamine solution to a 0.5 mL subsample of the extract followed by dilution to 5 mL. The amount of the methyl- and ethylamines added to the internal calibration matched that of the external calibration. The slope and retention times for the methyl- and ethylamines from the internal calibration were calculated and compared to those performed externally to quantify matrix effects. Discussion of the analytical performance of the CS19 gradient program is presented in Sect. 3.1.2.
A size-resolved particle sample from a BB plume was collected using a
nanoMOUDI II (nano micro-orifice uniform-deposit impactor, model 122-R, MSP
Corp., Shoreview, MN, USA) in St. John's, Newfoundland, on 6 July 2013.
Satellite images of the plume smoke, HYSPLIT back trajectories, and
measured PM
The full method for the collection and extraction of BB particle samples
collected during July wildfires in British Columbia is detailed in Di
Lorenzo et al. (2017). Briefly, PM
Our approach to separation involved injecting the highest mixed inorganic
cation and mixed amine standards for the expected working range (0.1–2.5
Separation characteristics and statistics for the CS19 gradient
method. The retention time (
Separation of amine and inorganic cation standards with the
highest-resolution gradient program at
All gradient methods that were tested started with a 1 mM hold, followed by
a stepwise increase and/or ramp to higher eluent concentrations at a column
temperature of 30
Separation of 1
The separation method produced in this work is able to overcome previously
reported IC coelution difficulties between DEAH
The performance statistics of the CS19 gradient method for each cation are
summarized in Table 1. The method shows high reproducibility, with method
precisions better than 10 % for most analytes. Although the instrumental
response varied from month-to-month for each analyte, this variability was
random and the calibration curve slopes for each analyte showed no
systematic decrease over time. The larger variability in the TMAH
The LODs for each analyte are reported in Table 1 as
both a range and as the average LOD (
To further test the efficacy of the separation method, a standard addition calibration was performed in the presence of the complex BB matrix. The calibration slopes and retention times for each analyte from the standard addition and external calibration performed on the same day are listed in Table S1. The slopes for the two calibrations varied between 0 and 8 %, which is within the method calibration precisions presented in Table 1. Thus, the BB sample extracts did not exhibit matrix effects. However, increasing retention times of approximately 0.3–0.5 min were observed for all cation analytes when performing the standard addition. This is an effect inherent in IC when samples with higher total quantities of cations are preconcentrated, resulting in a sample plug filling a greater quanitity of the stationary-phase capacity. The initial weak mobile phase of the gradient method will therefore take a greater amount of time to elute all of the analyte cations from the preconcentration and analytical columns. This same increase in retention times is present in the external calibration with increasingly concentrated standards (Table 1).
Previous IC instrumental precisions reported for use in quantifying the six
atmospheric methyl- and ethylamines range from 0.4 to 17.2 %, which is
comparable to our method (Table S2; Chang et al., 2003; Dawson et al., 2014;
Erupe et al., 2010; Huang et al., 2014; Li et al., 2009; VandenBoer et al.,
2012; Verriele et al., 2012). Our separation method shows greater average
variability than others due to our numerous assessments (
Employing a method that is capable of quantifying amines at very low mixing
ratios is valuable since recent work has shown that parts per quadrillion by
volume (ppqv) concentrations of gaseous amines can lead to particle
formation and growth (Almeida et al., 2013). If our method were applied to
online atmospheric ambient sampling of gases or particles the method could
be used to detect amines at ppqv mixing ratios. For example, a detectable
signal for 100 ppqv mixing ratios could be attained by sampling through a
bubbler, filter, or denuder at a low flow rate of 3 L min
The separation method developed was further investigated to elucidate its
utility in quantifying MPA, iMPA, and
MBA, three amines that have been frequently
detected in ambient air (Ge et al., 2011). In particular, this test
was performed to assess their potential coelution with the fully separated
methyl- and ethylamines. Without modification of the gradient method, we
observed separation of these three amines from the original
12 cations with
Since diamines have recently been shown to be potent sources of new particle
formation and have been detected in field campaigns across the USA (Jen
et al., 2016b), as well as near livestock, food processing factories, and
sewage facilities (Ge et al., 2011), quantitation of DABH
As mentioned previously, IC methods in the literature have been unable to
separate potassium from the methyl- and ethylamines (Huang et al., 2014;
VandenBoer et al., 2012), and in our current method K
Over the course of 5 months, peak retention times noticeably decreased
and peak broadening of approximately 50 % occurred for all analytes.
After more than 1000 sample and standard injections retention times had
decreased by 1.9
During the course of method development severe peak broadening and
subsequent peak-to-peak resolution loss of Mg
BB particles often contain a complex mixture of water-soluble
ions, organics, elemental carbon, and other insoluble components, making them
nonpareil for testing the robustness of an atmospheric measurement
technique. Ions such as NH
In Fig. 5a we show the molar ratio of the sum of the methyl- and ethylamines to ammonium which is considered to be the main atmospheric base, as a
function of the size-resolved particles collected. The summed amine moles
exceeded ammonium in the particle diameter range from 100 to 560 nm, and the
ratio ranged from 0.50 to 1.9 in the fine mode (PM
Overlaid chromatograms of MOUDI size-fractionated particle samples
collected in St John's on 6 July 2013 during the intrusion of a
biomass-burning plume that originated from northern Labrador and Québec. The
robustness of the separation method for MMAH
Our method was also applied to a time series of PM
A time series of the amine-to-ammonium molar ratio as the smoke plume
intrudes into both the BKP and NVSN sites is presented in Fig. 5b. There
were either no amines present or they were present in concentrations below
our detection limits in the ambient particles collected on the front edge of
the plume intrusions. When the maximum PM
We developed an ion chromatographic method that can separate and quantify
the nine most abundant atmospheric alkylamines and two alkyl diamines from common
inorganic atmospheric cations. Ion chromatography methods reported in the
literature cannot fully resolve alkylamine peaks nor separate
interferences from K
The IC method is robust. Two sets of BB particle samples collected at two
different locations in Canada were injected onto the IC column and the
method detected and quantified amines in the presence of a complex matrix
where inorganic analytes, such as K
Overall, the developed IC method shows promise for (i) adoption into standard analysis of water-soluble atmospheric extracts; (ii) incorporation into online instrumentation already using ion chromatography for near real-time analysis of water-soluble atmospheric samples; and (iii) interfacing with mass spectrometry for even higher analytical sensitivity, particularly where supporting measurements for ppqv levels of amines may be stimulating new particle formation in the atmosphere.
To access the data sets presented and discussed, please see the Supplement or contact the corresponding author.
Trevor C. VandenBoer designed the experiments and Bryan K. Place, Aleya T. Quilty, and Robert A. Di Lorenzo carried them out. Bryan K. Place prepared the manuscript with contributions from all coauthors.
The authors declare that they have no conflict of interest.
The authors thank Geoff Doerksen at the Lower Fraser Valley Air Quality Monitoring Network in British Columbia for supplying biomass burning samples. Thanks to Joseph Bautista for help collecting biomass burning samples in St. John's, as well as Jamie Warren and Kathryn Dawe for their assistance in method development. Finally, the authors would like to thank Cora Young for her helpful comments in the writing of the manuscript. TCV was supported by a Government of Canada Banting Postdoctoral Fellowship and the ICS-2100 was procured through the Canadian Foundation for Innovation. Funding for this work was provided by the Government of Newfoundland and Labrador Department of Forestry and Agrifoods through a Centre for Forestry Science and Innovation grant (project no. 221269). Edited by: P. Herckes Reviewed by: three anonymous referees