Detection of High Molecular Weight Narrow Polydisperse Polymers up to 1.5 Million Daltons by MALDI Mass Spectrometry

Abstract

The detection of very high molecular weight narrow polydisperse poly(styrene) samples by MALDI time-of-flight mass spectrometry is reported. It is shown that accurate molecular weight determinations of samples up to 1 million can be achieved very rapidly from the singly charged polymeric species. For a poly(styrene) with a molecular weight of approximately 1.5 million, signals corresponding to the multiply charged ions of the principal distribution are observed. The molecular weights obtained by MALDI are in good agreement with classical molecular weight determination techniques. all-trans-Retinoic acid was used as the organic matrix for the laser desorption procedure, and the samples were analyzed as their silver cation adducts. This work demonstrates that, with proper matrix selection and sample preparation, MALDI can be a very useful tool for high molecular weight polymer sample analysis.

The analysis of polystyrene and polystyrene aggregates into the mega dalton mass range by cryodetection MALDI TOF MS

“…Compared with the studies of high mass polystyrene by Schriemer and Li [15], our data revealed enhanced high m/z signals that we believe are primarily due to the advantage of using a cryodetector. In their studies, using a conventional ionizing detector, the ϩ2 or ϩ3 charge states are the most abundant distributions in the spectrum for M n /z n n Ͼ 150,000.…”

“…Polystyrene, singly charged monomer ion distributions and doubly charge aggregates were observed up to ϳ2.2 MTh. Compared to a conventional ionizing detector, the cryodetector has revealed that there is indeed a higher proportion of high m/z (low z) ions produced in the MALDI process than previously reported for polystyrene [15] and these broad peaks can be made up of more than one charge state.…”

“…All-trans retinoic acid matrix was purchased from Sigma-Aldrich (St. Louis, MO) and stored in a cold, dark place. The THF solvent was distilled over Na metal to eliminate water which was found to have an adverse effect on the MALDI signal [15]. An optimal MALDI recipe for high mass polystyrene was developed by using a number of preparation methods based on early reports [28,29].…”

“…Even with an ideal detector, three reasons may explain the expected upper mass limit of the MALDI technique: (1) a less efficient molecule launch into the gas phase for macromolecules, (2) increased source fragmentation which is the result of the use of higher laser powers typically required to lift macromolecules into the gas phase, and (3) metastable decomposition, which can occur to a greater extent because of the higher laser power and longer flight times to the detector for massive ions [13]. Despite these limitations, Danis and Karr reported MALDI TOF MS of poly(methyl methacrylate) (PMMA) at a molecular weight of ϳ256 kDa [14]; Schriemer and Li have reported the detection of singly charged and multiply charged polystyrene for M n 900 kDa and 1.5 MDa at 900 kTh for [M ϩ Ag] ϩ1 and 750 kTh for [M ϩ 2Ag] ϩ2 , respectively [15], and Nelson et al reported the detection of human monoclonal immunoglobulin M (IgM) at ϳ1 MDa with charge states of ϩ2 to ϩ6 [16]. In all of these experiments, the researchers used conventional, secondary emission based detectors, which inherently show a decreased signal with increased mass [13].…”

“…Before this study, others have collected mass spectra of high mass polystyrene and PMMA [15,28,29]. The highest reported MALDI TOF distribution of polystyrene ions were observed at m/z 750 kTh for the ϩ2 charge state of the 1.5 MDa polystyrene [15]. In out study, we collected mass spectra of both polystyrene and PMMA, but focused our work on the analysis of polystyrene.…”