Molecular weight determination

Molecular weight determination

For customers who require guidance regarding molecular weight characteristics of their products, we can offer analysis with gel permeation chromatography (GPC)– also known as size exclusion chromatography (SEC). We can resolve dextrans and other polysaccharides, for example, polysucrose, hyaluronic acid, or derivatives of these, in the MW range from 1000 to 5 million Da. Our system is adapted for derivatives of dextran, polysucrose and other water-soluble polymers. The chromatography is performed using specially selected gels which are run in series according to the molecular weight range in question. The parameters for the system including flow rates, eluents, and sensitivity are carefully controlled to obtain optimal resolution.

The following data can be obtained:

  • Weight average molecular weight (Mw)
  • Number average molecular weight (Mn)
  • Peak molecular weight (Mp)
  • Polydispersity (PD)
  • Ranges (e.g. percentage of product within defined molecular weight ranges)

The columns are calibrated with dextran standards and the optimal polynomial fits are calculated.

Our analytical method is based on Ph.Eur 2.2.30 (European pharmacopoeia) and it is validated according to ICH guideline Q2(RI). We therefore can offer GPC/SEC analyses complying with GMP requirements.

We perform the standard molecular weight determination (non-GMP) within two working days after we have received the sample. Our customers will receive an analytical report and a chromatogram along with the test results.

Please contact us  at info@tdblabs.se if you need specialised expertise in this area.

Getting to grips with molecular weight

For those that are working with polysaccharides or their derivatives, an understanding of mean molecular weight and polydispersity is essential. The most common parameters for defining polymer products are:

  • Weight average molecular weight (Mw) - a calculation with emphasis on the molecular weight of each molecule in the fraction.
  • Number average molecular weight (Mn) - a calculation with emphasis on the number of molecules of a given molecular weight in the fraction
  • Polydispersity (PD) - as expressed by the ratio of Mw/ Mn
  • Peak molecular weight (Mp) – the molecular weight at the peak of the distribution curve.

The parameter PD is valuable as it reflects the broadness in the distribution (polydispersity) of the fraction. Whereas a normal fraction may have a value of 1.5, a very broad fraction may have values over 5. If the sample only consisted of one molecular species, the PD would be 1. For purposes aimed at establishing the permeability of a membrane or cell, it is desirable to have a narrow fraction.

TdB Consultancy has provided us with expert analytical service. They were able to assist us with molecular weight determination for release and stability GPC testing according to GMP requirements. The efforts and support from TdB Consultancy were a key component in reaching regulatory approval.

Dr. Leighton Jones, Director of PD & Clinical Supply, Norgine B.V, United Kingdom

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