Macromolecular Mass Spectrometry

The facility has a Bruker Reflex time-of-flight mass spectrometer (shown in top photograph) with the capability of mass measurements on synthetic polymers up to 250 ku. Isotope resolution may be obtained for polymers with masses less than 5 ku. Polymers of larger mass, depending on the repeat mass of the polymer, may be resolved at the repeat mass level. For example, polystyrenes with masses less than 40 ku, can be resolved by repeat units. As a consequence, copolymer compositions or end group distributions may be obtained as a function of molecular mass for polymers with total mass below 40 ku. Also, at low masses, studies may be made of polymer architecture and how it is affected by chemical synthesis.

The facility also has a Comstock/Atom Sciences RTOF-260 time-of-flight mass spectrometer with the unique capability of a heated sample stage. This allows for studies of crystalline polymers by heating them above their melting point. It also allows for the study of target temperature effects on the MALDI process. This instrument has a gentle 5kV ion-extraction voltage and delayed ion extraction with extraction times on the order of microseconds.

Sample preparation of synthetic polymers that will not dissolve at room temperature presents a significant obstacle to the MALDI analysis of such materials. Bill Blair has constructed a device in our laboratory for the electrospray deposition of polymer samples dissolved in solvent up to 150 °C. The electrospray apparatus, the MALDI target and a small reservoir of dissolved polymer are contained in a thermostated heated zone allowing the dissolved polymer to be electrosprayed onto the target without precipitation out of solution. To electrospray a sample, solvent delivered by a syringe pump operating at room temperature displaces hot polymer-solvent solution within the heated zone of the apparatus. We have found that electrospray MALDI sample preparation crucial for creating reproducible mass spectra, which is critical to our standards development effort.

The Division is actively pursuing research in the development of MALDI-TOF-MS as 1) a quantitative tool to obtain the overall molecular mass distribution of synthetic polymers, 2) a method to obtain the mass spectrum of hydrocarbon polymers, such as polyethylene and polypropylene, that have historically not been amenable to analysis by MALDI-MS, 3) a means to study polymers (particularly prepolymers) where, with the help other techniques, the unique structural or architecture properties of these polymers can be observed.

Additional information about current MALDI-MS research activities, please check with this link: MALDI Synthetic Polymer Project

MALDI Recipes page