Hi,have a look into the link its might be helpful and also attach a pdf file.....

https://www.agilent.com/cs/library/slidepresentation/public/1-Conventional_GPC_-_Polymers_ans_Molecular_Weight.pdf

It is easy to calculate the moments of the molecular weight distribution of samples using an excel spreadsheet.

(1) Define the 'envelope limits' of the elution [i.e. start and stop values for the peak]

(2) Measure peak heights above baseline [uniformly spaced, and at least 30].

(3) Define the relationship between elution time and molecular weight by calibration with standard(s).

(4) set up a series of columns in an excel spreadsheet.

Time peak height molecular weight N NM NM^2 NM3

The relationships in this table are:

molecular weight at each elution time from calibration curve

N = peak height /molecular weight

NM is peak height

nm^2 is peak height times molecular weight

nm^3 is peak height times molecular weight squared

Sum each column downward.

Divide the various sums gives the molecular weights (a.k.a. 'moments of the distribution')

sum of mol weights/ sum of peak heights = Number average molecular weight (called Mn)

sum of NM^2/ sum of NM = weight average molecular weight (called Mw)

sum of NM^3/sum of NM^2 = Z average molecular weight (called Mz)

There are a few important steps to take first: Have a good calibration curve for molecular weight versus elution volume (or time at constant flow rate), Choose a valid start and stop time. Carefully define baseline and correct for drift.

Dear Nidhi Joshi,

it is hard because you cannot calibrate with the same polymer. Therefore you have to make an universal calibration (calibration based on M[η] vs. Ve because M[η] is related to the hydrodynamic volume) than measuring the samples.

Here is a short description about the different calibrations: http://www.waters.com/waters/en_US/Calibration-of-the-GPC-System/nav.htm?cid=10167839&locale=en_US

You can surely find other ones on the net.

Actually, the Viscosity average molecular weight is related to the average size in solution of macromolecules- NOT Mn.Mn is the Number Average Molecular weight. Generally, the viscosity average molecular weight in a sample lies between Mn and Mw. See Yau's book on GPC. ( Wallace Yau and I invented the series capillary viscosity detector, which works well in GPC applications. Universal calibration with a viscosity detector is a good way to go, since it provides a window into the nature of the molecules in solution.

Without anything except a good linear column set and a reliable pump and detector, much simple way is get a single sample of the polymer of interest with known Mw and Mn and do a broad standard calibration technique. I l published a simple broad standard calibration technique (J Apl. Polymer chem ) about 30 years ago. [ October 1995 Journal of Applied Polymer Science 58(1):191 - 195 ].

The determination of Mn can be problematic, depending on the kind of sample. Mn is often prone to errors because the lower molecular weight portion of the elution profile contributes so greatly to the calculations, With some broad range samples, sometimes one must put an arbitrary limit on the lower eluted portion of the curve value to be used in the calculations. If one has a series of oligomers, partition chromatography can produce better results than GPC.

.

Dear Nidhi Joshi,

Calculation of molecular weight of polymers by GPC graph needs the standard curve of polymer which is used for calibration.

Good question, follow

Molecular weight can be calculated against the standard curve plot.