Standard Reference Material 2881 - National Institute of Standards ...

Yan et al. 12 have looked at mass ratios of two polydimethylsiloxane polymers (averagemasses 2200 u and 6140 u) by MALDI-TOF MS. After initially optimizing the laser power togive the strongest signal intensity for both the low and high molecular mass polymers, theyfound that the mass ratios estimated from MALDI-TOF MS were very close to those predictedfrom gravimetric ratios. Chen, et al. 13, 14 performed a similar experiment using polyethyleneglycols with a variety of end groups. They found for molecular masses from 800 u to 3300 u thegravimetric amount of polymer seemed to map well into the MALDI-TOF MS measured values.Li and coworkers 15-17 started by looking at equimolar blends of polystyrenes withmolecular masses below 20 000 u in order to optimize the instrument and sample preparationparameters. They did this by varying machine parameters as well as matrix and salt ratios andfinding where the M n best matched the M n expected of the equimolar mixtures. They made acareful study of PS of molecular mass 5050 u, 7000 u and 11 600 u and blends of the three.Fitting their polymer MMD to Gaussian distributions and using 5050 u and 11 700 u samples,they studied changes in the MMD of the polymer of 7000 u with blends of the 5050 upolymer. They found they could detect no systematic uncertainties within 0.5 % in the MMDor the moments of the MMD assuming MMD were Gaussian distributions.13