Hi,
I'm going to work on a GPC system that produce only raw data (RI signal vs elution time), and I found out the way to produce the graph of dwt/d(LogM) against log M, according to the thread posted by Mostafa. I would like to know how can I manually obtain the values of Mw and Mn for a sample after I produced the mentioned graph. Thanks.
https://www.researchgate.net/post/What_is_the_relation_between_the_RI_detector_signal_in_raw_data_and_dwt_dLogM_in_MWD_in_the_GPC
The area increment under such a curve gives you the weight fraction, so that the log M that separates the curve into two equal parts (i.e. when cumulative weight fraction = 0.5) is your M_w.
(area increment from log M to log M + d(log M) is: Area increment = dw/d(log M) * d(log M) = dw)
Yes, easily - but only if you have the calibration equation. If not it's essentially impossible.
If you have the equation and a flat baseline at zero then make an excel spreadsheet thus -
Col A - retention time (of the slice)
Col B - RI response
Col C - delete (zeroise) all signals outside of the peak of interest
Col D - normalise the signal to 1 (sum col C and divide each slice of col C by the total)
Col E - use the calibration equation to calculate the MW of the slice
Col F - D x E - sum them to get Mn
Col G - D x E^2 - sum them and divide by Mn to get Mm (Mw in old terminology)
Dispersity = Mm/Mn
If the baseline isn't flat you need to calculate the baseline gradient and perform a correction (easily done, calculate the change in height per slice (R), then add/ deduct R x Col A). If the baseline isn't at zero you'll need to do simple addition/ subtraction to make the base zero.
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