2011 Volume 60 Issue 3 Pages 229-237
National Metrology Institute of Japan has been developing certified reference materials (CRMs) for molecular weights of synthetic polymers : polystyrene, poly(ethylene glycol), poly(ethylene glycol) nonylphenyl ether. These CRMs are produced with the certified values of the mass and number fractions as well as the averaged molecular weights, for the first case in the reference materials. In the analyses of common synthetic polymers and oligomers, the molecular-weight distribution in a sample often makes it difficult to precisely measure the physical properties. In order to avoid the effects of polydispersity, which is an essential property of synthetic polymers, uniform oligomers having no molecular weight distributions were used. Uniform oligomers are quite useful in determining the exact molecular weight dependence of the sensitivity of detectors. Supercritical fluid chromatography (SFC) is one method to separate the uniform oligomers. First, we separated the uniform oligomers with various degrees of polymerization from commercial polymer samples by means of preparative SFC. Next, we prepared exact equimass mixtures of the uniform oligomers. The calibration curves for the detectors were determined for the molecular weight by using the equimass mixtures of uniform oligomers with various degree of polymerization indices. Through the use of the calibrated detectors, we are able to make accurate determinations not only of the averaged molecular weight, but also all of mass and number fractions of components. This CRM can be used to calibrate the measuring instruments, to control the measurement precision, and to confirm the validity of the measurement methods when determining the molecular-weight distributions and averaged molecular weights. Especially, it is suitable for calibration against both the masses and intensities for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.
