
MALDI-MS is widely used as an analytical tool for the characterization of synthetic polymer samples. However, in complex mixtures, the minor components may not be detected due to ion suppression by more abundant species also present in the sample. Gel Permeation Chromatography (GPC)-MALDI is an effective method for detailed analysis of such samples. In GPC-MALDI, complex samples are fractionated by GPC prior to MALDI-MS analysis. When preparing polymer samples for MALDI-MS analysis, the sample (e.g., an aliquot of a GPC fraction) must be mixed with MALDI matrix and a salt (to promote cationization of the analyte) prior to loading on to the MALDI target. To automate this process, we have developed an organic solvent-resistant fraction collector / MALDI spotting robot (AccuSpot), which mixes the GPC eluent with MALDI matrix solution on-line and then automatically deposits the resulting solution onto the MALDI sample target. The new AccuSpot provides a fully automated solution for the GPC-MALDI analysis of synthetic polymer samples.
The following figure is an example showing the analysis and detection of minor homo polymers in a complex synthetic polymer sample. A two component copolymer [poly(methilmethacrylate-b-n-butylmethacrilate) (poly(MMA-b-n-BMA)] was used as a model complex polymer sample. Fifty fractions were prepared on a MALDI sample target by spotting GPC eluted solution every 6 seconds (T = 8 min 20 sec to 13 min 20 sec). Automated MALDI-MS analysis of the fraction collected at T = 11 min 18 sec resulted in the detection of two polymer series which could not be easily detected in the unseparated sample (see figure below). The newly developed GPC-AccuSpot-MALDI system facilitates the detection of PnBMA and PMMA homo polymer components, present as minor components, in complex copolymer samples, allowing Polymer Analysis calculations to be performed.
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