Size-exclusion chromatography with multi-angle laser light scattering (SEC-MALLS) and
acid–base titration were used to determine the molecular weight of a polyethylene glycol
with low molecular weight. All potential uncertainty factors for each measurement were
evaluated using cause-effect diagrams. Weight analysis was applied to harmonize the two
different measurement results. It was found that the main uncertainty sources of SECMALLS
measurement arose from the dn/dc value, the calibration constant of the differential
refractive index (DRI) detector, and the intermediate precision of the instrument,
while the sample mass, the titration volume and the concentration of titrant contributed to
the uncertainty of titration measurement. The weighted mean value of the two
measurement results was taken as the molecular weight of the polyethylene glycol.