ELSD for Polymers? [August 17, 2004]
Posted: Sun Aug 29, 2004 6:59 pm
By cytw98 on Tuesday, August 17, 2004 - 08:27 am:
Hello,
I wonder anyone has used ELSD for polymers (Mw & Mw distribution).
Also, I know that the mobile phase needs to be volatile. But can I analyse samples in aqueous solution (release study of gentamicin in PBS) as long as I choose a volatile mobile phase?
Thanks!
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By A on Tuesday, August 17, 2004 - 09:25 am:
Do not use ELSD for the calculation of Mw & Mw distributions, the results will be significantly skewed. This is because of the non-liniar response to concentration that ELSD provides.
Of course you can analyse a sample by ELSD in an aqueous solution. You just need to stay away from non-volitile mobile phase components (phosphate buffers and some ion-pairing agents for example.
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By cytw98 on Tuesday, August 17, 2004 - 10:02 am:
Thanks for the input! That's exactly what I wanted to know.
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By yiya on Tuesday, August 17, 2004 - 01:20 pm:
Although it's non-liniar response to concentration, you can use log response vs log conctration to plot calibration curve, which will be linear.
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By user on Tuesday, August 17, 2004 - 07:13 pm:
I am using ELSD with Waters Empower software. The calibration type used is 3rd order fit. So whether you use RI or ELSD detector to calculate Mw, the outcome should be the same since GPC do not have linear fit calibration.
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By cytw98 on Wednesday, August 18, 2004 - 05:29 am:
Thanks yiya and user for the input. I will contact ELSD vendors for more information.
To user: do you use ELSD for polymers?
Thanks!
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By A on Wednesday, August 18, 2004 - 11:47 am:
To User:
Wrong Wrong Wrong
It is not the curve fit to concentration that determines the Mw calculation. Far from it. You can use ELSD to calculate concentration, no problem. You can use a log/log or quadratic fit for these calculations. Some compounds over relativly narrow concentration ranges even fit fairly well to linear curves. You simply can not used an ELSD to correctly calculate Mw. If you are doubtful, do the experiment with a known Mw standard.
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By cytw98 on Wednesday, August 18, 2004 - 01:01 pm:
Hello A, thank you so much for your input! (and your response to another post of mine). I already sent an email to Alltech's tech support to see whether they could offer me any information useful.
To A and Everyone who has used or researched on ELSDs: which vendor in your opinion makes the best ELSD: Alltech, Sedere, Waters, Polymerlabs, etc.
Thanks!
-------------------------------------------------------------------------------------------------------
By Kostas Petritis on Wednesday, August 18, 2004 - 05:07 pm:
I think that some times people confuse the evaporative light scattering detector (ELSD) with the static and dynamic light scattering detectors which can actually being used for the approximate calculation of MW and MW distributions. I am not going to enter in to details about their foundamental differences...
About your second question cytw98 there have been extensive discussions in the past in this forum. Most of the vendors comes with new models now and then.
As an update:
Waters just recently got in the ELSD market with the Waters 2420.
SEDERE came up with the SEDEX LT-ELSD 85 model which is totally redesigned outside and inside. The detector has now a modern look (it was about time), and has now a very small footprint. Further improvements resulted to further increase in the sensitivity and better peak shapes due to internal modifications.
Alltech introdced the ELSD 2000ES. They claim that they use a patent pending technology for noise reduction which increase S/N about 10 fold.
Finally, Polymer Labs introduced the PL-ELS 2100 which claims improvements like programable gain factor and time constant, low temperature operation etc (exactly the same improvements were announce by SEDERE 4 years ago when they introduced the SEDEX 75).
There is a comparative ELSD study in terms of sensitivity made by Alltech (see: www.alltechweb.com/ELSD.compare) which compares all the above detectors and (what a suprice) Alltech is the winner (according Alltech of course).
They refer on the other detectors as Competitor A, B, C but as they give the settings they used and if you are experienced with these models you can understand that A is Waters, B is Sedere and C is Polymer Labs. So according Alltech in terms of sensitivity these models are rated:
Alltech>Sedere>Waters>Polymer Labs.
Personally I think that the results are biased in one way or another and your best bet always is to require a demo in your labs of these detectors (I am not sure if they still doing it).
Anyway, personally I believe that the best model among them is the Sedere one, but all the new models have decent performances.
Kostas
-------------------------------------------------------------------------------------------------------
By cytw98 on Thursday, August 19, 2004 - 05:35 am:
Hi Kostas,
Thank you so much for the in depth information! It is really helpful. I was confused by ELSD and regular light scattering, since I had never run LC for polymers before.
I will contact the vendors mentioned here to see what they can offer.
Thanks again!
Hello,
I wonder anyone has used ELSD for polymers (Mw & Mw distribution).
Also, I know that the mobile phase needs to be volatile. But can I analyse samples in aqueous solution (release study of gentamicin in PBS) as long as I choose a volatile mobile phase?
Thanks!
-------------------------------------------------------------------------------------------------------
By A on Tuesday, August 17, 2004 - 09:25 am:
Do not use ELSD for the calculation of Mw & Mw distributions, the results will be significantly skewed. This is because of the non-liniar response to concentration that ELSD provides.
Of course you can analyse a sample by ELSD in an aqueous solution. You just need to stay away from non-volitile mobile phase components (phosphate buffers and some ion-pairing agents for example.
-------------------------------------------------------------------------------------------------------
By cytw98 on Tuesday, August 17, 2004 - 10:02 am:
Thanks for the input! That's exactly what I wanted to know.
-------------------------------------------------------------------------------------------------------
By yiya on Tuesday, August 17, 2004 - 01:20 pm:
Although it's non-liniar response to concentration, you can use log response vs log conctration to plot calibration curve, which will be linear.
-------------------------------------------------------------------------------------------------------
By user on Tuesday, August 17, 2004 - 07:13 pm:
I am using ELSD with Waters Empower software. The calibration type used is 3rd order fit. So whether you use RI or ELSD detector to calculate Mw, the outcome should be the same since GPC do not have linear fit calibration.
-------------------------------------------------------------------------------------------------------
By cytw98 on Wednesday, August 18, 2004 - 05:29 am:
Thanks yiya and user for the input. I will contact ELSD vendors for more information.
To user: do you use ELSD for polymers?
Thanks!
-------------------------------------------------------------------------------------------------------
By A on Wednesday, August 18, 2004 - 11:47 am:
To User:
Wrong Wrong Wrong
It is not the curve fit to concentration that determines the Mw calculation. Far from it. You can use ELSD to calculate concentration, no problem. You can use a log/log or quadratic fit for these calculations. Some compounds over relativly narrow concentration ranges even fit fairly well to linear curves. You simply can not used an ELSD to correctly calculate Mw. If you are doubtful, do the experiment with a known Mw standard.
-------------------------------------------------------------------------------------------------------
By cytw98 on Wednesday, August 18, 2004 - 01:01 pm:
Hello A, thank you so much for your input! (and your response to another post of mine). I already sent an email to Alltech's tech support to see whether they could offer me any information useful.
To A and Everyone who has used or researched on ELSDs: which vendor in your opinion makes the best ELSD: Alltech, Sedere, Waters, Polymerlabs, etc.
Thanks!
-------------------------------------------------------------------------------------------------------
By Kostas Petritis on Wednesday, August 18, 2004 - 05:07 pm:
I think that some times people confuse the evaporative light scattering detector (ELSD) with the static and dynamic light scattering detectors which can actually being used for the approximate calculation of MW and MW distributions. I am not going to enter in to details about their foundamental differences...
About your second question cytw98 there have been extensive discussions in the past in this forum. Most of the vendors comes with new models now and then.
As an update:
Waters just recently got in the ELSD market with the Waters 2420.
SEDERE came up with the SEDEX LT-ELSD 85 model which is totally redesigned outside and inside. The detector has now a modern look (it was about time), and has now a very small footprint. Further improvements resulted to further increase in the sensitivity and better peak shapes due to internal modifications.
Alltech introdced the ELSD 2000ES. They claim that they use a patent pending technology for noise reduction which increase S/N about 10 fold.
Finally, Polymer Labs introduced the PL-ELS 2100 which claims improvements like programable gain factor and time constant, low temperature operation etc (exactly the same improvements were announce by SEDERE 4 years ago when they introduced the SEDEX 75).
There is a comparative ELSD study in terms of sensitivity made by Alltech (see: www.alltechweb.com/ELSD.compare) which compares all the above detectors and (what a suprice) Alltech is the winner (according Alltech of course).
They refer on the other detectors as Competitor A, B, C but as they give the settings they used and if you are experienced with these models you can understand that A is Waters, B is Sedere and C is Polymer Labs. So according Alltech in terms of sensitivity these models are rated:
Alltech>Sedere>Waters>Polymer Labs.
Personally I think that the results are biased in one way or another and your best bet always is to require a demo in your labs of these detectors (I am not sure if they still doing it).
Anyway, personally I believe that the best model among them is the Sedere one, but all the new models have decent performances.
Kostas
-------------------------------------------------------------------------------------------------------
By cytw98 on Thursday, August 19, 2004 - 05:35 am:
Hi Kostas,
Thank you so much for the in depth information! It is really helpful. I was confused by ELSD and regular light scattering, since I had never run LC for polymers before.
I will contact the vendors mentioned here to see what they can offer.
Thanks again!