Guttman Charles M, Wetzel Stephanie J, Flynn Kathleen M, Fanconi Bruno M, VanderHart David L, Wallace William E
Polymers Division, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899-8541, USA.
Anal Chem. 2005 Jul 15;77(14):4539-48. doi: 10.1021/ac050298h.
A matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) interlaboratory comparison was conducted on mixtures of synthetic polymers having the same repeat unit and closely matching molecular mass distributions but with different end groups. The interlaboratory comparison was designed to see how well the results from a group of experienced laboratories would agree on the mass fraction, and molecular mass distribution, of each polymer in a series of binary mixtures. Polystyrenes of a molecular mass near 9000 u were used. Both polystyrenes were initiated with the same butyl initiator; however, one was terminated with -H (termed PSH) and the other was terminated with -CH2CH2OH (termed PSOH). End group composition of the individual polymers was checked by MALDI-TOF MS and by nuclear magnetic resonance (NMR). Five mixtures were created gravimetrically with mass ratios between 95:5 and 10:90 PSOH/PSH. Mixture compositions where measured by NMR and by Fourier transform infrared spectrometry (FT-IR). NMR and FT-IR were used to benchmark the performance of these methods in comparison to MALDI-TOF MS. Samples of these mixtures were sent to any institution requesting it. A total of 14 institutions participated. Analysis of variance was used to examine the influences of the independent parameters (participating laboratory, MALDI matrix, instrument manufacturer, TOF mass separation mode) on the measured mass fractions and molecular mass distributions for each polymer in each mixture. Two parameters, participating laboratory and instrument manufacturer, were determined to have a statistically significant influence. MALDI matrix and TOF mass separation mode (linear or reflectron) were found not to have a significant influence. Improper mass calibration, inadequate instrument optimization with respect to high signal-to-noise ratio across the entire mass range, and poor data analysis methods (e.g., baseline subtraction and peak integration) seemed to be the greatest obstacles in the correct application of MALDI-TOF MS to this problem. Each of these problems can be addressed with proper laboratory technique.
对具有相同重复单元、分子量分布相近但端基不同的合成聚合物混合物进行了基质辅助激光解吸/电离飞行时间质谱（MALDI-TOF MS）实验室间比对。该实验室间比对旨在考察一组经验丰富的实验室对一系列二元混合物中各聚合物的质量分数和分子量分布的结果一致性如何。使用了分子量接近9000 u的聚苯乙烯。两种聚苯乙烯均由相同的丁基引发剂引发；然而，一种以-H封端（称为PSH），另一种以-CH2CH2OH封端（称为PSOH）。通过MALDI-TOF MS和核磁共振（NMR）检查了各聚合物的端基组成。通过重量法制备了五种质量比在95:5至10:90之间的PSOH/PSH混合物。通过NMR和傅里叶变换红外光谱法（FT-IR）测量混合物组成。与MALDI-TOF MS相比，NMR和FT-IR用于评估这些方法的性能。这些混合物的样品被发送给任何有需求的机构。共有14个机构参与。采用方差分析来考察独立参数（参与实验室、MALDI基质、仪器制造商、TOF质量分离模式）对每种混合物中各聚合物测量的质量分数和分子量分布的影响。确定参与实验室和仪器制造商这两个参数具有统计学上的显著影响。发现MALDI基质和TOF质量分离模式（线性或反射模式）没有显著影响。质量校准不当、在整个质量范围内未针对高信噪比进行充分的仪器优化以及数据分析方法不佳（例如基线扣除和峰积分）似乎是将MALDI-TOF MS正确应用于该问题的最大障碍。这些问题中的每一个都可以通过适当的实验室技术来解决。
