MALDI FTMS ANALYSIS OF POLYMERS - IMPROVED PERFORMANCE USING AN OPEN-ENDED CYLINDRICAL ANALYZER CELL

Improvements in the matrix assisted laser desorption/ionization analys is of polymers are obtained with Fourier transform mass spectrometry b y using an open-ended cylindrical analyzer cell. These improvements in clude a reduced sensitivity to experimental parameters in determining the oligomer molecular weight distribution, and better mass accuracy. Ion trajectory calculations and experimental data show that the open-e nded cylindrical cell is less sensitive to changes in gated trapping t ime for capturing a range of masses. For poly(ethylene) glycol 1000, a shift of only 20 Da is observed for a 200 mu s change in gated trappi ng time and shift of 100 Da for the weight average is observed for a 5 40 mu s change. The mass accuracy for determinations of end-group and repeat unit masses are presented for internal and external calibration of polymer samples. Using a linear regression method, repeat group ma sses were determined to within 0.1 mmu and 0.7 mmu for internal and ex ternal calibration at 2000 Da. The mass accuracy at high molecular wei ght with external calibration was tested with poly(methyl) methacrylat e 6000, which yielded a mean squared error of 8.1 mmu for the repeat m ass and 23.6 mmu for the end-group mass. Space charge is shown to affe ct mass accuracy. By accounting appropriately for this effect, a root mean error of 1.4 ppm is obtained for nine peaks in an externally cali brated poly(methyl) methacrylate 6000 mass spectrum. (C) 1997 Elsevier Science B.V.