Your concern is ambiguous. You can run sec using an hplc. Please be more specific regarding type of polymers and stationary phases.
Thank you! I got it, regardless of the separation mechanism I can choose the appropriate column (in my case the most appropriate one is SEC). I am going to analyse Polymethylphenylsiloxane, the phenyl groups are absorb in UV‑spectrum and it will allow me to determine the Mw using the SEC. Am I right?
Your question is incomplete and ambiguous. "Chromatography, SEC or HPLC". We can best help others when they help us to understand both what they are doing and what they hope to measure or accomplish.
"SEC" is HPLC. SEC stands for "Size Exclusion Chromatography" and simply expresses the mode of chromatography (HPLC in this case) being used. IOW: Molecules are sorted based on diameter in solution. There are many types of supports and methods which come under this subject.
The mode of chromatography best suited for a particular sample will depend on specific properties such as its solubility (*the mobile phase you use would need to be dissolve the compound fully AND not absorb the wavelengths of light used for UV/VIS detection. You may want to consider RID, ELSD or CAD which do not have this limitation) and also what other compounds may be present which require resolution away from the main compound.
What is your goal? Are you simply trying to measure a particular sample's molecular weight distribution? GPC would provide you with a straightforward method to characterize them. Viscosity measurement, sedimentation rates and LALLS could also be used, depending on the type of information you need.
Thanks! I just never did it, the chromatography I mean, it is good to be informed properly.
I depolymerizied the polymethylphenilsiloxane at different temperatures and now want to detect the Mw of each fraction to see the influence of temperature on degree opf polymerization/molecular weight. Therefore, yes, I am going to measure a particular sample's Mw.
Thanks very much!
it would be better to explain the question regarding your objective?
Regards
I would assume when you refer to HPLC you are referring to either normal phase or reverse phase chromatography. Molecular weight determinations by chromatography are done by size exclusion chromatography. There are a number of levels of molecular weight information that can be determined using size exclusion chromatography depending upon the complexity of the instrument. For example coupled with the appropriate standards and the appropriate conditions RI will provide relative molecular weight values. On the other hand a triple detection system will provide molecular weight, polydispersivity and a great deal more information. To make things easy, send the samples out for analysis.
Indeed, GPC/SEC is a specifiy type of HPLC. Therefore in polymer chromatography we usually differentiate between GPC/SEC a truly size based separation, free of interaction with the stationary phase and IC (LA) interaction chromatography or adsorption chromatography, where specific interactions are used for separations.
GPC/SEC separates by molecular size, which is for linear homopolymers related to molar mass. That is, why GPC/SEC is the standard method to determine molar masses. However, GPC/SEC is a relative method as a calibration with standards is required. The molar masses are only correct, if the standards are of identical chemical composition as the sample to be analyzed. If no adequate standards are available, there are several other calibrations methods e.g. calibration using braod standards, or GPC/SEC with light scattering or viscosity detection.
Interaction chromatography (I assume that is, what you assume under HPLC) is more suited to separate by other features e.g. chemical composition or end groups. In particular there are problems with recovery when running isocratic interaction chromatography, That is why usually gradients are employed.
For your problem SEC/GPC seems to me the appropriate method. The main question is, whether you need true molar masses or whether you can live with relative molar masses (relative to the standards applied) as well. Even with relative molar masses you should be able to identify degradation by the decreasing relative molar masses.
My polymer is polymethylphenylsiloxane, I depolymerized it and need to measure the molecular mass of the obtained fragments.
GPC, with whichever detection mode you desire to provide the type of data you desired (which you did not specify). Keep in mind you would only be measuring approximate "Mw" by hydrodynamic volume. You will need standards and/or othogonal techniques to do so.
*BTW: You would benefit from a class on basic polymer chemistry as it would answer many of your basic questions.
- Badges
- Science method