Identification of Surfactants in Commercial Products by Mass Spectrometry
This section describes techniques we find useful for the identification of a wide variety of surfactants in commercial products. The monomeric surfactants could be identified by either our SciFinder or ChemSpider using “known unknowns” approach. However, the oligomeric ones containing polyethylene glycol (PEG) are often more challenging since it is difficult to determine their lipophilic end groups. We have employed two different approaches for these types of surfactants.(New Nov 2013) Accurate and Nominal Residual Molecular Weight for Identifying PEG-Containing Surfactants: We use a technique to calculate a residual molecular weight (RMW) index for PEG-containing surfactants. The RMW index is then used to find candidate structures from Excel spreadsheets. The candidate structures are refined with other data such as MS/MS or in-source collision-induced dissociation data to arrive at an exact identification. This method is based on nominal molecular and accurate molecular weight data. The following example shows how one would calculate either the nominal and accurate mass RMW index from electrospray mass spec data. The RMW indices can also be calculated automatically using the Microsoft Excel MOD function.
Kendrick Mass Defect for Identifying PEG-Containing Surfactants:More recently, I became aware of the work of Michael Thurman and Imma Ferrer. They later published their work in the Journal of Analytical Chemistry and also as an Agilent Applicaton Note. Their approach used Kendrick mass calculations [1,2] and accurate mass data. I updated my Excel spreadsheets to include Kendrick mass defects. The example shows how one would calculate the Kendrick mass defect from accurate mass data.
General Information for PittCon Class on Surfactant Identification: Other general information from the class for surfactant characterization using mass spectrometry is included in the links below. The information was prepared for a class I taught at Pittcon in 2006 and for an American Society for Mass Spectrometry (ASMS) poster session. We had originally developed the approaches for the identification of surfactant packages in commercial latex paints.
Calculating Residual Molecular Weight (RMW) and Kendrick Mass Defect for Identification of PEG Containing Surfactants:
Spreadsheet of Surfactants, Kendrick Mass Defects and RMW’s with Structures:
Pittcon Class Powerpoint presentation:
Pittcon Class Notes:
TSCA Monomer List with Nominal and Accurate Mass
Creating MS/MS Libraries of Surfactants:
ASMS Poster 2004: