LETTER TO THE EDITOR Carbamate Chemistry at Interfaces: Practical Considerations and Challenges of Studying Amine Surfactants Anna-Karin Hellström 1 · Lars Nordstierna 1 · Romain Bordes 1 Received: 23 October 2018 / Revised: 10 February 2019 / Accepted: 18 March 2019 © 2019 AOCS Abstract It is well known that CO 2 reacts with pri- mary and secondary amines in aqueous solutions and forms carbamates. This reaction can have consequences when studying the self-assembly of amines. In this arti- cle, we discuss the practical challenges when working with an alkyl Y-shaped amine (Y12-amine) and demon- strate how the formation of carbamate species influences the physicochemistry of the amine-based surfactant. A drift in dynamic surface tension was observed for Y12-amine at pH above pKa due to the reaction with the naturally occurring CO 2 from the atmosphere. The drift in dynamic surface tension was more pronounced at pH above pKa, than at and below pKa. Furthermore, the drift in dynamic surface tension of Y12-amine at pH 12 also affected the surfactant’s critical micelle con- centration (CMC). CMC of Y12-amine determined by the pendant drop at the air/water interface was almost five times higher than at the N 2 /water interface. The lat- ter result was in agreement with the one determined by monitoring the change in chemical shift of 1 H NMR in aN 2 atmosphere. Moreover, it was also shown that the adsorption of the amine at different interfaces influences carbamate formation. Keywords Carbamate  Surfactant  CO 2  Dynamic surface tension J Surfact Deterg (2019). Introduction Fatty amines and by extension amine-based surfactants are commonly used in a wide range of applications, such as those related to enhanced oil recovery, corrosion inhibition, and agricultural applications. The amines act as dispersants, stabilizers, bioactive components, or surface modifiers, among other roles. Furthermore, they are often regarded as starting materials in the preparation of a more complex sur- factant structure. A well-known example is fatty amine ethoxylate where the amine group serves as a nucleophile to react with ethylene oxide (Holmberg and Lindman, 2003). However, in many cases, the amine remains the functional group of interest for surface-related application and it is, therefore, central to keep the NH 2 form intact. Alkyl primary and secondary amines are well known to readily react with CO 2 and form alkyl ammonium-carba- mate. This reaction has been employed in the industry for decades for the capture of CO 2 (Rochelle, 2009). However, the spontaneous formation of carbamate can be a disadvan- tage when alkyl amine reacts in an undesired and uncon- trolled manner with CO 2 naturally present in the air (Blain et al., 2016; Mills, 2008). Carbamate formation involves a multifaceted pattern of several parallel reactions that is highly dependent on pH. The carbamate formation is facilitated at high pH, i.e., when the amine is deprotonated (McCann et al., 2009). At neutral pH, close to pKa of the amine, the amine is only partly deprotonated and the formation of ammonium- carbamate species is dominating (see Fig. 1). This is favored by the van der Waals interaction between the alkyl tails. At pH well below pKa of the amine, the alkyl amine is fully protonated and not susceptible to react with CO 2 . Additionally, CO 2 not only reacts with the amines in * Romain Bordes bordes@chalmers.se 1 Department of Chemistry and Chemical Engineering, Chalmers University of Technology, Göteborg, Sweden J Surfact Deterg (2019) J Surfact Deterg (2019) DOI 10.1002/jsde.12285