Capillary Electrochromatography-Mass Spectrometry of Nonionic Surfactants
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- 作者：Dean Norton ; Shahab A. Shamsi
- 刊名：Analytical Chemistry
- 出版年：2007
- 出版时间：December 15, 2007
- 年：2007
- 卷：79
- 期：24
- 页码：9459 - 9470
- 全文大小：324K
- 年卷期：v.79,no.24(December 15, 2007)
- ISSN：1520-6882
文摘
The Triton X (TX)-series are alkylphenol polyethoxylates-type nonionic surfactants of varying numbers of ethyleneoxide 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 thetraditional 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. Inthis work, different CEC-ESI-MS parameters such asmobile-phase composition, sheath liquid, and spray chamber parameters were optimized to provide suitable andsensitive analysis of short-, medium-, and long-chainlength (e.g., n = 1-16) TX-series nonionic surfactants.The optimized CEC-ESI-MS conditions were mobile phasecontaining 90/10 ACN/2.5 mM Tris, pH 8, sheath liquidcontaining 50/50 MeOH/10 mM HCO2NH4 delivered at5 L/min, spray chamber set to drying gas flow of 6 mL/min, nebulizer pressure of 5 psi, and drying gas temperature set to 200 C. This optimization is followed by themore challenging separation of very long chain TX-serieswith a large number (n = 30-70) of ethoxy units, whichwere initially found to exhibit extreme retention using thedeveloped method. It was observed that through theaddition of small volume fraction of polar-aprotic tetrahydrofuran solvent to the running buffer, the retention timecould be significantly reduced thus enhancing the feasibility for CEC-ESI-MS analysis of these very long chainnonionic surfactants for the first time. The detection limitwas ~37 g/mL total octylphenol ethoxylate for TX-45;acceptable precision of migration time (<1% RSD, n =3) and peak area (~4% RSD, n = 3) were achieved.