Elsevier

Journal of Chromatography A

Volume 1217, Issue 13, 26 March 2010, Pages 2070-2073
Journal of Chromatography A

Short communication
Determination of methylamines and trimethylamine-N-oxide in particulate matter by non-suppressed ion chromatography

https://doi.org/10.1016/j.chroma.2010.01.066Get rights and content

Abstract

An ion chromatography method with non-suppressed conductivity detection was developed for the simultaneous determination of methylamines (methylamine, dimethylamine, trimethylamine) and trimethylamine-N-oxide in particulate matter air samples. The analytes were well separated by means of cation-exchange chromatography using a 3 mM nitric acid/3.5% acetonitrile (v/v) eluent solution and a Metrosep C 2 250 (250 mm × 4 mm i.d.) separation column. The effects of the different chromatographic parameters on the separation were also investigated. Detection limits of methylamine, dimethylamine, trimethylamine, and trimethylamine-N-oxide were 43, 46, 76 and 72 μg/L, respectively. The relative standard deviations of the retention times were between 0.42% and 1.14% while the recoveries were between 78.8% and 88.3%. The method is suitable for determining if methylamines and trimethylamine-N-oxide are a significant component of organic nitrogen aerosol in areas with high concentration of these species.

Introduction

Organic nitrogen is ubiquitous in the environment, and yet a poorly characterized component of atmospheric aerosol [1], [2], [3]. With growing concerns of aerosol effects on health, climate and modification of the nitrogen cycle, it is crucial to identify sources as well as understand the composition of atmospheric aerosol, including the organic nitrogen component [4], [5], [6]. Previous studies of organic nitrogen in the atmosphere have concentrated on dissolved organic nitrogen [7]. Most of these were bulk studies where the total water soluble organic nitrogen was determined, and compound-specific studies of organic nitrogen aerosol remain rare [8], [9], [10]. Given the diversity of the organic nitrogen compounds, it has been difficult to define source-and-sink budgets and describe their atmospheric behavior. This knowledge demands both the quantitative determination of bulk organic nitrogen aerosol and the characterization of individual compounds.

Agricultural practices are known to input large amounts of nitrogenous species into the atmosphere [11]. Some of these compounds react using a number of pathways to form gas phase species as well as aerosol. Most studies have focused on the inorganic nitrogen chemistry, especially the contribution of ammonia in aerosol formation, but the organic nitrogen fraction of the aerosol is important as well. Recent work has shown that some organic species such as aliphatic amines may be present in concentrations as high if not greater than that of ammonia [12], [13]. These species could therefore undergo atmospheric reactions to form secondary organic nitrogen containing aerosol.

Several researchers have detected amines in aerosols during ambient air sampling [14], [15], [16]. Some of these studies have indicated that amine cations are present in aerosols as salts formed in secondary reactions in the atmosphere [14], [15]. One ambient study using aerosol mass spectrometry (AMS) showed significant particle mass loadings of up to 6 μg m−3 [16]. Smog chamber reaction studies focusing on amines have also been performed to characterize the types of amines present in aerosol products due to atmospheric oxidation [8], [16], [17], [18]. Amine-N-oxides were first hypothesized as a potential reaction product of tertiary amines in a smog chamber study using aerosol time-of-flight mass spectrometry (ATOFMS) [8]. Other reports have shown that the reaction products of amines can be a complex mixture of salt formation products and/or of secondary organic oxidation species [16]. Recent studies using the AMS have indicated that little of the aerosol product can be accounted for by the formation of salts [17], [18]. Clearly, a separation method that can sort through some of these proposed reaction products would be helpful to corroborate observations using mass spectrometry.

Trimethylamine-N-oxide (TMAO) is a natural osmolyte found in some marine creatures such as fish [19]. When fish rots, TMAO is enzymatically converted to TMA that gives the characteristic ‘fishy’ smell. It has been suggested that TMAO may also form in the atmosphere through oxidation of trimethylamine by ozone and other oxidants [8], [16]. This reaction would be important in areas where the mixing ratio of trimethylamine is thought to be high due to the presence of agricultural emissions such as the central valley of California and Cache Valley in northern Utah. There have been no attempts to measure TMAO in atmospheric aerosol.

An efficient and simple method is necessary for the quantitative determination of TMAO in air samples. Here we report a method that can be used to detect and quantify TMAO and methylamines in air samples using non-suppressed ion chromatography. The composition of the mobile phase was optimized and efficient separations between the analytes were achieved. A variety of analytical techniques have been developed to measure biogenic amines in food samples. For example, ion chromatography with suppressed conductivity detection with either integrated pulsed amperometric or conductimetric detection has been utilized to measure amines such as putrescine, cadaverine, histamine, and similar compounds in alcoholic beverages, fresh and processed meats, chocolate, fish, vegetables, and fermented foods [20], [21], [22], [23], [24], [25]. A gradient elution method coupled with suppressed ion chromatography was used to separate alkylamines, such as butylamine and diethylamine, from alkali and alkali earth metals [26]. A study of dimethylamine, trimethylamine and TMAO separation using non-suppressed conductivity applied to aquatic products was recently published [27]. To our knowledge, this study is the first application of IC non-suppressed conductivity detection to analyze TMAO in addition to methylamine, dimethylamine, and trimethylamine in aerosol samples.

The main goal of this study is to develop a method to determine whether TMAO is a quantitatively significant component of organic nitrogen aerosol in the atmosphere. This is done using aerosol collected from smog chamber reactions of trimethylamine with ozone and/or nitrogen oxide. The method is tested using a solution of laboratory-generated aerosol containing a mixture of the analytes.

Section snippets

Materials and chemicals

All the reagents used in this study were of analytical reagent grade. Water was purified using a Milli-Q system (Millipore, Bedford, MA, USA) to produce 18.2 MΩ water. Methylamine hydrochloride (98%, Sigma), dimethylamine hydrochloride (99%, Aldrich), trimethylamine hydrochloride (98%, Aldrich), trimethylamine-N-oxide dihydrate (98%, Acros), nitric acid (90%, Sigma), and acetonitrile (99.9%, Fisher) were all used as purchased.

Chromatography

Ion chromatography was performed using a Metrohm 761 Compact IC

Standard separation

A straight forward, rapid method has been developed for determination of organic nitrogen in aerosols using non-suppressed ion chromatography. A chromatogram of a standard solution of methylamines and methylamine-N-oxide is shown in Fig. 1. The analytes are well separated in less than 15 min. Separation selectivity of the TMA and TMAO was reversed in comparison to the work done by Li et al. due to the use of a different IC column [27].

Under optimized experimental conditions, all four analytes

Conclusion

A method for the simultaneous determination of methylamines and TMAO was developed using ion-exchange chromatography with non-suppressed detection. The method described here is simple and has low detection limits suitable for analysis of aerosols generated in smog chamber experiments and in ambient air where the concentration of these species is expected to be high. The smog chamber samples indicate that only minor amounts of particulate amines (1.5%) can be accounted for by the cation salts

Acknowledgments

This project was supported by the National Science Foundation under grants ATM-0735396, ATM-0449778, and DUE-0525574, and the Kenneth T. and Eileen L. Norris Foundation. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.

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