Capillary electrochromatography-mass spectrometry of nonionic surfactants.
The Triton X (TX)-series are alkylphenol polyethoxylates -type nonionic surfactants of varying numbers of ethylene oxide units. Applications include industrial and household detergent formulations as well as emulsifying agents. For analysis of these surfactants, capillary electrochromatography-electrospray ionization-mass spectrometry (CEC-ESI-MS) offers several unique advantages over the traditional hyphenation methods based on HPLC-MS. These include higher plate numbers attainable in CEC-MS, as well as more compatible flow rate (submicroliter) when coupled to ESI-MS and, perhaps most importantly, less consumption of toxic and costly organic solvents. In this work, different CEC-ESI-MS parameters such as mobile-phase composition, sheath liquid, and spray chamber parameters were optimized to provide suitable and sensitive analysis of short-, medium-, and long-chain length (e.g., n = 1-16) TX-series nonionic surfactants. The optimized CEC-ESI-MS conditions were mobile phase containing 90/10 ACN/2.5 mM Tris, pH 8, sheath liquid containing 50/50 MeOH/10 mM HCO(2)NH(4) delivered at 5 microL/min, spray chamber set to drying gas flow of 6 mL/min, nebulizer pressure of 5 psi, and drying gas temperature set to 200 degrees C. This optimization is followed by the more challenging separation of very long chain TX-series with a large number (n = 30-70) of ethoxy units, which were initially found to exhibit extreme retention using the developed method. It was observed that through the addition of small volume fraction of polar-aprotic tetrahydrofuran solvent to the running buffer, the retention time could be significantly reduced thus enhancing the feasibility for CEC-ESI-MS analysis of these very long chain nonionic surfactants for the first time. The detection limit was approximately 37 microg/mL total octylphenol ethoxylate for TX-45; acceptable precision of migration time (<1% RSD, n = 3) and peak area ( approximately 4% RSD, n = 3) were achieved.
Norton
Dean
D
Department of Chemistry, Center of Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia 30303, USA.
Shamsi
Shahab A
SA
D002021:Buffers; D053801:Capillary Electrochromatography / Q000379:methods*; D007202:Indicators and Reagents; D008722:Methods; D017830:Octoxynol / Q000032:analysis*; D012997:Solvents; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D013501:Surface-Active Agents / Q000032:analysis*
D002021:Buffers; D007202:Indicators and Reagents; D012997:Solvents; D013501:Surface-Active Agents; D017830:Octoxynol