Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry Interlaboratory Comparison of Mixtures of Polystyrene with Different End Groups: Statistical Analysis of Mass Fractions and

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• 作者：Charles M. Guttman ; Stephanie J. Wetzel ; Kathleen M. Flynn ; Bruno M. Fanconi ; David L. VanderHart ; and William E. Wallace
• 刊名：Analytical Chemistry
• 出版年：2005
• 出版时间：July 15, 2005
• 年：2005
• 卷：77
• 期：14
• 页码：4539 - 4548
• 全文大小：132K
• 年卷期：v.77,no.14(July 15, 2005)
• ISSN：1520-6882

文摘

A matrix-assisted laser desorption/ionization time-of-flightmass spectrometry (MALDI-TOF MS) interlaboratorycomparison was conducted on mixtures of syntheticpolymers having the same repeat unit and closely matching molecular mass distributions but with different endgroups. The interlaboratory comparison was designed tosee how well the results from a group of experiencedlaboratories would agree on the mass fraction, and molecular mass distribution, of each polymer in a series ofbinary mixtures. Polystyrenes of a molecular mass near9000 u were used. Both polystyrenes were initiated withthe same butyl initiator; however, one was terminated with-H (termed PSH) and the other was terminated with-CH₂CH₂OH (termed PSOH). End group composition ofthe individual polymers was checked by MALDI-TOF MSand by nuclear magnetic resonance (NMR). Five mixtureswere created gravimetrically with mass ratios between95:5 and 10:90 PSOH/PSH. Mixture compositions wheremeasured by NMR and by Fourier transform infraredspectrometry (FT-IR). NMR and FT-IR were used tobenchmark the performance of these methods in comparison to MALDI-TOF MS. Samples of these mixtureswere sent to any institution requesting it. A total of 14institutions participated. Analysis of variance was usedto examine the influences of the independent parameters(participating laboratory, MALDI matrix, instrument manufacturer, TOF mass separation mode) on the measuredmass fractions and molecular mass distributions for eachpolymer in each mixture. Two parameters, participatinglaboratory and instrument manufacturer, were determined to have a statistically significant influence. MALDImatrix 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 acrossthe entire mass range, and poor data analysis methods(e.g., baseline subtraction and peak integration) seemedto be the greatest obstacles in the correct application ofMALDI-TOF MS to this problem. Each of these problemscan be addressed with proper laboratory technique.