Liang Z M, Marshall A G, Westmoreland D G
Department of Chemistry, Ohio State University, Columbus 43210.
Anal Chem. 1991 Apr 15;63(8):815-8. doi: 10.1021/ac00008a016.
Triton polymers are commercial surfactants whose molecular weight distributions are conventionally determined by means of high-performance liquid chromatography (HPLC). However, in the case of the important octylphenol ethoxylates [p-C8H17-C6H4-O-(CH2CH2O)n-H], HPLC cannot resolve individual oligomers of high molecular weight Triton surfactants (e.g., greater than 2000 u or so; u = unified atomic mass unit). In this paper, we show that laser desorption Fourier transform ion cyclotron resonance mass spectrometry (LD/FT/ICR/MS) provides a simple and accurate measure of such Triton surfactant molecular weight distributions up to at least 3500 u, based on a single-shot laser pulse measurement of a few seconds duration. Comparison of LD/FT/ICR/MS and HPLC molecular weight distributions of low molecular weight surfactants shows that laser desorption/ionization produces minimal fragmentation and thus offers an accurate measure of the relative abundances of the neutral oligomers, without the need for prior chromatographic separation of the components. Moreover, for all Triton polymer molecular weight distributions (700-3000 u), LD/FT/ICR/MS provides much more highly resolved profiles of oligomer relative abundances. Finally, LD/FT/ICR/MS reveals the presence of poly(ethylene oxide) side products of the polymerization process, which are not observed by HPLC with conventional ultraviolet absorption detection.
Triton聚合物是商业表面活性剂，其分子量分布通常通过高效液相色谱法（HPLC）来测定。然而，对于重要的辛基酚乙氧基化物[p-C8H17-C6H4-O-(CH2CH2O)n-H]，HPLC无法分辨高分子量Triton表面活性剂的各个低聚物（例如，大于2000 u左右；u =统一原子质量单位）。在本文中，我们表明，基于持续几秒钟的单次激光脉冲测量，激光解吸傅里叶变换离子回旋共振质谱法（LD/FT/ICR/MS）能够简单而准确地测量此类Triton表面活性剂的分子量分布，直至至少3500 u。低分子量表面活性剂的LD/FT/ICR/MS和HPLC分子量分布的比较表明，激光解吸/电离产生的碎片化最小，因此无需对组分进行预先色谱分离就能准确测量中性低聚物的相对丰度。此外，对于所有Triton聚合物的分子量分布（700 - 3000 u），LD/FT/ICR/MS能提供分辨率更高的低聚物相对丰度图谱。最后，LD/FT/ICR/MS揭示了聚合过程中聚环氧乙烷副产物的存在，而这在使用传统紫外吸收检测的HPLC中是观察不到的。
