Elsevier

Journal of Chromatography A

Volume 1319, 6 December 2013, Pages 80-87
Journal of Chromatography A

Characterization of polyoxyethylene tallow amine surfactants in technical mixtures and glyphosate formulations using ultra-high performance liquid chromatography and triple quadrupole mass spectrometry

https://doi.org/10.1016/j.chroma.2013.10.032Get rights and content

Highlights

  • Polyoxyethylene tallow amine (POEA) is a surfactant in many glyphosate formulations.

  • POEA is toxic to many species of aquatic organisms.

  • Reverse phase chromatography separates POEA into peaks by tallow moieties.

  • POEA is available in technical mixtures with different ethoxylate distributions.

  • Different POEA technical mixtures are in commercial glyphosate formulations.

Abstract

Little is known about the occurrence, fate, and effects of the ancillary additives in pesticide formulations. Polyoxyethylene tallow amine (POEA) is a non-ionic surfactant used in many glyphosate formulations, a widely applied herbicide both in agricultural and urban environments. POEA has not been previously well characterized, but has been shown to be toxic to various aquatic organisms. Characterization of technical mixtures using ultra-high performance liquid chromatography (UHPLC) and mass spectrometry shows POEA is a complex combination of homologs of different aliphatic moieties and ranges of ethoxylate units. Tandem mass spectrometry experiments indicate that POEA homologs generate no product ions readily suitable for quantitative analysis due to poor sensitivity. A comparison of multiple high performance liquid chromatography (HPLC) and UHPLC analytical columns indicates that the stationary phase is more important in column selection than other parameters for the separation of POEA. Analysis of several agricultural and household glyphosate formulations confirms that POEA is a common ingredient but ethoxylate distributions among formulations vary.

Introduction

Polyoxyethylene tallow amine (POEA) is a non-ionic surfactant related to alkylamine ethoxylates (ANEOs). POEA is composed of a tallow amine moiety, as opposed to the more general alkylamine, and two chains of repeating ethoxylate units (Fig. 1). The tallow amine moiety is a mixture of amines derived from palmitic acid (C16 saturated carboxylic acid), oleic acid (C18 mono-unsaturated carboxylic acid), stearic acid (C18 saturated carboxylic acid), and other minor components [1]. The length of the ethoxylate chains vary in different technical mixtures and can give different physical properties. Although POEA is a non-ionic surfactant, the tertiary amine can act as a base and become protonated in neutral to acidic conditions; the acid dissociation constant (pKa) of POEA has been reported as a range of 6.5–7.0 [2]. Specific POEA molecules will be described herein by the number of carbon atoms in the tallow amine moiety (Cz), whether the tallow amine moiety is saturated or is mono-unsaturated (s/u), and by the combined number of ethoxylate units (EOn).

Toxicity studies have shown POEA to be harmful to a variety of aquatic wildlife. A compilation of acute toxic levels of POEA for several species is shown in Table 1 [3], [4], [5], [6], [7], [8], [9], [10], [11]. Lethal concentration for 50% of the population (LC50) values have been observed from 0.097 mg/L for Daphnia magna (water fleas) to 13 mg/L for Ictalurus punctatus (channel catfish) and Chironomous plumosus (midge larvae).

One of the primary uses of POEA is as an additive for use with glyphosate formulations, the most widely applied herbicide in agriculture and urban environments. The terminology in the literature regarding pesticide additives is inconsistent. The US Environmental Protection Agency (EPA) defines an additive to pesticide formulations by the manufacturer before purchase as “inert ingredients” while those that are added by the user before application as “adjuvants” [12]. Surfactants are used in herbicide formulations to change various physical properties and may be added as wetting agents, emulsifiers, or dispersants [13]. While POEA may be added to glyphosate formulations for such physical benefits, studies have also shown that POEA increases the efficacy of glyphosate and does so more effectively than other surfactants [14], [15], [16], [17], [18], [19]. Glyphosate has been described as a “once-in-a-century herbicide” because it is considered environmentally benign to non-target organisms, effective at controlling weeds, and can be applied directly to crops that are genetically modified to be glyphosate resistant [20]. Available glyphosate resistant crops include corn, soybeans, cotton, alfalfa, and canola [21]. According to an estimate from the EPA, over 81,000 metric tons (180 million pounds) of glyphosate was applied in the agricultural sector in 2007, which is more than the next five most applied herbicides combined (atrazine, metolochlor-S, acetochlor, 2,4-D, and pendimenthalin) [22]. Glyphosate is also used in urban settings to control weeds and is often applied to hard surfaces such as roads and sidewalks [23]. Most manufactures consider the composition of their glyphosate formulations to be proprietary information, making it difficult to determine what the actual composition of the formulation is beyond the active ingredient. One exception is the product literature for Glyfos X-TRA, which states on the product label that it contains 14.5% surfactant (compared to 41% glyphosate), which the MSDS identifies as a POEA mixture (CAS no. 61791-26-2).

The use of POEA in glyphosate formulations may change the sorption/desorption characteristics of the soil with respect to glyphosate. This effect has been shown in other surfactant/pesticide systems [24]. The transport of glyphosate has been studied [25] but has not taken into account the presence and effect of surfactant additives. Characterizing POEA will deepen the understanding of the transport of glyphosate in the environment.

There are other uses for POEA beyond glyphosate formulations. Searches of material safety data sheets reveal POEA listed as an ingredient in cleaners, degreasers, and wire pulling lubricants. Marketing materials indicate that some distributors of POEA suggest it can be used as an antistatic agent, a corrosion inhibitor, a dye leveler, an emulsifier, a metal lubricant, and more. Without further information or study, the potential environmental impact from POEA from uses other than glyphosate formulations is difficult to predict.

Published analytical methods for the detection and quantification of POEA or other ANEOs are sparse. Research by Krogh et al. [26] describes a liquid chromatography–mass spectrometry (LC–MS) method and a soil extraction method for POEA, but only included the C16s and C18s homologs. Corbera et al. [27] also reported on an LC–MS method, one that accounts for the primary components of the tallow amine moiety but only examines the range of EO13–17. A full characterization of POEA technical mixtures present in glyphosate formulations is an important extension of previous efforts.

The lack of published methods also shows that little work has been done with environmental samples to study the fate and transport of POEA. Other surfactants in environmental samples have been shown to transport via surface waters. A study of the Cuyahoga River in Ohio showed concentrations of nonylphenol ethoxylates and octylphenol ethoxylates of 5.1 μg/L and 0.19 μg/L, respectively [28]. In Spain, a study showed concentrations of linear alkylbenzene sulfonates, alkyl ethoxysulfates, alkyl sulfates, nonylphenol polyethoxylates, and alcohol polyethoxylates of 38.7, 3.0, 2.9, 5.0 and 1.2 μg/L, respectively [29]. While these studies show surfactants in the environment below the LC50 levels of POEA, it is important to note that these surfactants have different applications and likely have different transport characteristics than POEA. POEA applied in agriculture may be transported in higher concentration pulses in surface waters due to precipitation events after application. This phenomenon has been reported for pesticides and is referred to as the “spring flush” [30]. Even if concentrations of POEA do not reach acute toxic levels, there may be unexplored chronic effects.

There has been a drive to use smaller diameter stationary phase particles in analytical columns to increase the number of theoretical plates and these smaller particles in turn require instruments capable of maintaining higher pressures. Typical high performance liquid chromatography (HPLC) packing materials are 3 μm or larger in diameter and are useable at pressures up to approximately 400 bar. Ultra-high performance liquid chromatography (UHPLC) uses particles with diameters smaller than 3 μm and can support pressures of over 1000 bar. There has been no systematic chromatographic assessment on the ability of different stationary phases, particle sizes, and pressure limits to separate POEA in the literature.

The purpose of this research is threefold: to characterize POEA mixtures using UHPLC and mass spectrometry, to compare the chromatographic ability to separate POEA for a variety of analytical columns, and to examine commercial glyphosate formulations for the presence and nature of POEA included as an inert ingredient. Because POEA may have a deleterious effect on the environment, this research is important as a foundation to build quantitative methods to determine the scope of POEA's environmental relevance through future studies on degradation, transport, co-transport, and occurrence.

Section snippets

Reagents and materials

Nitrogen gas (generated from liquid nitrogen) and argon gas for mass spectrometry were supplied by Praxair Inc. (Danbury, CT, USA). The mobile phase for chromatography experiments consisted of LC–MS grade acetonitrile (Burdick & Jackson, Muskegon, MI, USA), deionized water from a Nanopure DIamond TOC Life Science system (Barnstead|Thermolyne, Dubuque, IA, USA), and Optima acetic acid (Fisher Scientific, Fair Lawn, NJ, USA). Four different POEA technical mixtures were investigated. POE (2)

Characterization of POEA

The POEA technical mixtures were examined with two different mass spectrometry experiments. The first was a single quadrupole scan performed while infusing with a syringe pump and the second was a LC–MS method using an Acquity BEH column to provide separation for a single quadrupole scan. An example of a tandem mass spectrometry experiment, a product ion scan, was also performed by infusing with a syringe pump for a single homolog of POE (15) tallow amine.

Conclusions

POEA is a surfactant additive in glyphosate formulations that has been shown to have deleterious effects on a variety of aquatic species. Characterization of the composition, distribution, and separation of POEA mixtures in technical and commercially available pesticide formulations was a first step before research on the extraction, degradation, sorption, and environmental occurrence of POEA can be conducted. Several glyphosate formulations were found to contain POEA but with varying

Acknowledgments

This research was funded by the U.S. Geological Survey Toxic Substances Hydrology Program. The use of trade, firm, or brand names in this paper is for identification purposes only and does not constitute endorsement by the U.S. Government.

References (33)

  • M.T.K. Tsui et al.

    Chemosphere

    (2003)
  • L.J. Moore et al.

    Ecotoxicol. Environ. Saf.

    (2012)
  • F. Botta et al.

    Chemosphere

    (2009)
  • P.A. Lara-Martin et al.

    J. Chromatogr. A

    (2006)
  • P.L. Ferguson et al.

    J. Chromatogr. A

    (2001)
  • F. Adas et al.

    J. Chromatogr. A

    (1998)
  • S.A. Lawrence

    Amines: Synthesis, Properties and Applications

    (2004)
  • D.G. Thompson et al.

    Ann. For. Sci.

    (2003)
  • J.M. Brausch et al.

    Bull. Environ. Contam. Toxicol.

    (2007)
  • R.B. Bringolf et al.

    Environ. Toxicol. Chem.

    (2007)
  • L.C. Folmar et al.

    Arch. Environ. Contam. Toxicol.

    (1976)
  • C.M. Howe et al.

    Environ. Toxicol. Chem.

    (2004)
  • J.A. Servizi et al.

    Bull. Environ. Contam. Toxicol.

    (2000)
  • J.M. Brausch et al.

    Arch. Environ. Contam. Toxicol.

    (2007)
  • P.J. Perkins et al.

    Environ. Toxicol. Chem.

    (2000)
  • U.S. Environmental Protection Agency, Pesticide Registration Manual, www.epa.gov/pesticides/bluebook/chapter1.html...
  • Cited by (39)

    • Unravelling plant protection product analysis: Use of chromatography techniques (GC and LC) and high resolution mass spectrometry

      2023, Trends in Environmental Analytical Chemistry
      Citation Excerpt :

      Despite that, PPPs impurities and additives are not normally monitored in fruits or vegetables, so the real extent of their hazard remains unknown. In the past, analytical methods that used liquid chromatography (LC) [13–16] and gas chromatography (GC) [17–21] coupled with mass spectrometry (MS) were employed, predominating the use of low-resolution mass spectrometry analyzers (LRMS) versus high resolution MS (HRMS) [9,22]. In addition, classic detectors as ultraviolet-visible (UV) or flame ion detector (FID) were also used [20,23].

    • Glyphosate-based herbicides alter soil carbon and phosphorus dynamics and microbial activity

      2022, Applied Soil Ecology
      Citation Excerpt :

      Within the ANEOs, one of the most used surfactants in glyphosate herbicide formulations is polyoxyethylene tallow amine (POEA). This non-ionic surfactant consists of a mixture of polyethoxylated long-chain alkylamines (Tush et al., 2013), synthesized from fatty acids derived from animals (Williams et al., 2000). Studies about the mobility of this compound in soil are limited.

    View all citing articles on Scopus
    View full text