Dear Yasir,

I can answer if you give information regarding which standars used and elution time of your standards at 1500-200Da. The concentration your maitaining also seems very low.

Dear yasir, your polymer is linear or branched? if it is so,  you can not use a linear standard to determination of molar mass of a branched polymer. if your polymer is branched you have to use another method, such VPO.

The result of the GPC depends mostly on the detectors that you are using to do the calculation. Depending on the detector and the standards that you are using to calibrate the instrumentation, you can calculate the absolute molecular weight or an approximate 'depending -on-the -standards' one. 

You can find more details in 'A guide to multi-detector gel permeation chromatography' of Agilent: https://www.agilent.com/cs/library/primers/Public/5990-7196EN.pdf 

Try to use a concentration that is recommended by the GPC company for your specific instrumentation normally is between 1-10mg/ml, if you have a good response on your detectors I do not think that it affects your result.

Many thanks for your supports..

Dear yasir, I would like to know which company GPC your using. (like waters, shimadzu  etc.)

 Dear, Sreenath, Edwin and Eftychia

thank you so much for your help, i would like to add the following information to make my question clear

actually, since this is the first time i use GPC, i am not familiar to highlight  your points, however here are some useful information

my polymer is Tannin base ( as i read in the literature, it is polyphenolic compound) 

Model/Brand: VISCOTEK GPCmax/Malvern

Software: OMNiSEC

The column used is ViscoGEK I-Series Column CLM1013.

Method File: Polyphenolic 270116-0001.vcm

Date Acquired: Jan 27, 2016 - 11:11:54

Solvent: DMF

Column Set: CLM1013X1

Flow Rate - (ml/min): 1.0 ml/min

Inj Volume - (ul): 100

Volume Increment - (ml): 0.00333

Detector Temp. - (deg C): 35

Column Temp. - (deg C): 35

please find the attached file (result report)

your help is highly appreciated

looks like your polymer was oligomerized Yasir from the attached file.

Generally, GPC results depends on standards used for calibration and detectors.

you mentioned MW from literature plz let me know is it commercially purchased or prepared in by you. For low molecular weight samples we have to take higher concentration i.e, 5mg/ml.

All the best.

In the attached file we can clearly see that the response of the RI detector is good and you do not have any noise, so the concentration is not a problem for you.

Also we can see that you are using a conventional calibration, meaning that you are calculating the molecular weight of your polymer from a calibration of standard samples. If the standards used are not of the same nature (type of polymer, linear, branched etc) you have an estimation of the molecular weight and not the real one. I assume that you are using PS standards for the calibration? Since your polymer is a polyphenol, it is perfectly normal not to have the molecular weight that you were expecting. 

If you want to find the real molecular weight an easy method is vapor pressure osmometry or use a multidetector GPC system (UV, LS, visco).

Dear Yasir,

First of all I read all the answers given to your question and I noticed that the main concept of MW determinaton by GPC is overlooked. GPC separates on the principle of  difference in hydrodynamic volumes of polymer coils. You shold first run a series of primary standards soluble in your solvent DMF, and construct a primary calibration curve, you can do this by using most popular PS standards. Then you have to convert this primary calibration curve into so-called universal calibration by using the Mark-Houwink parameters of of both PS and your polyphenolic polymer in DMF. Based on my 35+ years of GPC experience I am afraid to tell you that you can hardly find M-H parameters for your polymer in the literature. Therefore you can not establish a universal calibration curve from which you would try to calculate the MW of your sample.Under existing conditions you can not use GPC to determine the MW of your polymer. Do not waste your time, people try to make DIRECT correlation wth the GPC curve of a sample with that of a standard which is WRONG.

I have another suggestion for you, since you expect a molecular weight of around 2000Da for your polymer, you can use any of the colligative property methods and if you can find nearby a Vapor-phase Osmometer, you can use it very reliably.

I repeat under your existing conditions by using GPC all you will get is a raw distribution curve of your sample from which you can not calculate MW unless you have Low Angle Laser Ligth Scattering and Viscometric detectors attached to your instrument.

Good luck.

Dear Yasir, I would also like to ask you if you are performing yourself the polymerization or if you have bought the polymer from a supplier. Could you please add more info on this? 

The determinatin of a molecular weight is based on a calibration carried out using standard polymers. If the structure of the calibration polymer is completely different from your polymer you can have sensitive deviation. I suggest to get information about the calibratio method. Regards

many thanks for all of my friends

Dear Eftychia and Billa, actually my polymer is commercially available under the name of (Tanfloc), attached the specification of this powder (also supplied as liquid, but i am using the powder).

thank you so much for your help

many thanks for all of my friends

Dear Eftychia and Billa, actually my polymer is commercially available under the name of (Tanfloc), attached the specification of this powder (also supplied as liquid, but i am using the powder).

thank you so much for your help

many thanks for all of my friends

Dear Eftychia and Billa, actually my polymer is commercially available under the name of (Tanfloc), attached the specification of this powder (also supplied as liquid, but i am using the powder).

thank you so much for your help

Dear yasir 

salam

did you sure you have a polymer?! your molecular weight is very very low!

every traditionla polymer have a more molecular weight

what is your POLYMER?

You need to check the columuns in the GPC, at least, you should have a column for small molecular weight ( 500 Da). For small molecular weight sample, the concentration of the sample should be higher than the high molecular weight sample. I recommended to run 2-5 mg/mL.

Hello,

What is the nature of the polymer you use? Are you sure you solubilize all of the solid? What the solvent you have used? if you filter the solution, you eliminate the high masses and therefore you will have low average masses.

Dear friends,

many thanks for all of you

i contacted the person who is running the GPC  to ask him about the standard which he used. He answered me that he used PS (Polystyrene) standard. 

Based on that i can say that this unreasonable results is due to this standard that is not the same like my polymer. however i will try to do the test again using higher concentration.

Salam Yasir,

Your issue is very interesting to me since I've been working on determining the Mn Mw and PD of oligomers from palm oil. I had the same dilemma when analyzing the samples using the conventional calibration with PS as standards. The Mn was comparable but the Mw and subsequently PD were too big for an oligomer.

My team has come up with an idea to use commercial polyether polyols with defined molecular weights as the calibration standard. It turned out that the Mn Mw and PD were much closer to our expectation compared to PS calibration. All these findings were published which you can take a look in my profile.

Hope this helps!