GPC (gel permeation chromatography a.k.a. SEC (size-exclusion chromatography)) is a fairly common technique for measuring the molecular weight distribution of a polymer. A colleague had some results yesterday and in discussing them, it hit me that despite the technique producing quantitative results, I always look at the results qualitatively.
Here's why: the report we were discussing gave several measure of the molecular weight distribution - Mn, Mw and Mz. The first two have a physical;y intuitive meaning, while the last one doesn't. I've seen other reports that even include Mz + 1, also not a physical quantity. The string of all four of these are simple the first through the fourth moments of the distribution.
So the report had a nice set of numbers for all these moments, calculated out to 3 or 4 significant figures and my colleague was trying to make sense of the numbers. That's when it hit me. I only look at the numbers in a "relative" sense (there are two meanings to that phrase - see below). I seldom care about what the exact number of the molecular weight is, only what the changes are between one sample and the next. Yes, the polydispersity index (Mn/Mw) is a helpful as a measure of the distribution's width, but still, I'm only looking for qualitative changes in the distribution, not exact numbers that I can run calculations with. My colleague seemed a little disappointed with this, as certainly we all take strength from numbers, but to me, the numbers do not add anything.
Back to my double entendre on the "relative" results. The paragraph above gave one meaning, but even the quantitative values are relative in that the instrument is calibrated with polystyrene standards and so the results are always relative to this. (Polystyrene can be easily polymerized anionically, so that the molecular weight distribution is tightly controlled.) There are ways to make the measurements absolute (Wyatt's light scattering technique is prominently advertised), but that is still not something I've ever felt the need for.
In this case, we had samples which we were examining for UV degradation and the associated drop in molecular weight. We found this (qualitatively) so we didn't go any further.
And that's unusual for me. One skill that I learned from my advisor during grad school was to get as much information as possible from each experiment and measurement. It's a skill that I now greatly cherish, although I certainly didn't when I was trying to finish up and he kept wanting me to get more info out of my data! It's a skill that my clients always value, but this is one case where just I don't go any further.
I would like to comment that despite the claim that with light scattering absolute molar masses can be obtained, this is rarely really the case, since i) too many parameters need to go into the calculation which are typically assumed and ii)light scattering is stronly discriminating between larger and smaller polymers. Probably most users of GPCs with light scattering detectors are not aware of this, they just believe the stuff companies tell them to buy their equipment. At least that is my impression.
Definitely good points. I've only been exposed to light scattering in undergraduate classwork. The same goes for neutron scattering, x-ray scattering and any other scattering. Some day I'd like to dive in further, but the need hasn't been there yet.
But I have plenty of experience in being scatter-brained ;)
What a superb post! I have no words to describe this post because everthing is clear with your wonderfull words. I really feel out of world reading your post, it is full of fresh and usefull. I really appreciate, keep the work continue.
norton.com/setup ! norton.com/setup
A genuinely normal method for estimating the atomic weight conveyance of a polymer. A partner had a few outcomes yesterday and in talking about them, it hit me that regardless of the procedure creating quantitative outcomes.
The initial two have a physical;y natural significance, while the last one doesn't. I've seen different reports that even incorporate mz + 1, additionally not an actual amount.
I just glance at the numbers from a "Relative" perspective (there are two implications to that express - see underneath). I rarely care about what the specific number of the sub-atomic weight is, just what the progressions are between one example and the following.
The section above gave one significance, however even the quantitative qualities are relative in that the instrument is adjusted with polystyrene norms thus the outcomes are consistently comparative with this.
The segment above gave one importance, anyway even the quantitative characteristics are relative in that the instrument is changed with polystyrene. A really ordinary technique for assessing the nuclear weight movement of a polymer. An accomplice had a couple of results yesterday.
How much do you charge for a Statistics Assignment Help task? Take, for my case, where I need you to provide me with the Statistics Homework Help on plotting a scatter plot with a regression line? How much should that cost? Do you charge on the basis of the workload or have a constant payment?
Hello. Please check the task I have just sent and reply as soon as possible. I want an adjustment assignment done within a period of one week. I have worked with an Accounting Homework Help tutor from your team and therefore I know it’s possible to complete it within that period. Let me know the cost so that I can settle it now as your Accounting Assignment Help experts work on it.
That is a huge number of students. Are they from the same country or different countries? I also want your math assignment help. I want to perform in my assignments and since this is what you have been doing for years, I believe you are the right person for me. Let me know how much you charge for your math homework help services
Hey there, I need an Statistics Homework Help expert to help me understand the topic of piecewise regression. In our lectures, the concept seemed very hard, and I could not understand it completely. I need someone who can explain to me in a simpler way that I can understand the topic. he/she should explain to me which is the best model, the best data before the model and how to fit the model using SPSS. If you can deliver quality work then you would be my official Statistics Assignment Help partner.
I liked your article very much. It is really interesting and clearly gives the boundary between true competition and the solo performances. Check out white paper writing assistance to get better future articles.
Very interesting article. As I study chemicals at my University, this post very helpful for me. I need to write a review. With things to write reviews about it will be easier.
I was reading some of your material on this website and I think this internet site is really informative!!! Keep on putting up. You can apply for a visa on arrival Turkey, or you can apply visa to Turkey. Eligible citizens are required to complete a simple online visa application form Turkey with personal and passport information.
The process to set up PIXMA ts3122 starts from ij.start.canon/ts3122 and download the latest full driver & software package for PIXMA TS3122. You can learn to set up this multifunction printer model. Instructions on this page include everything from printer unpacking, installation, configuration, WiFi network establishment to complete canon printer drivers setup. Let’s get started.ij.start canon is the manufacturer site to download Canon printer drivers. Install and set up Canon Printer from ij.start.canon | canon.com/ijsetup | cannon/ijsetup | Cox High-Speed Internet provides its users with COX Communications..Cox webmail Login
What a top notch information you’ve shared.. Thank you for this. Apply online for Azerbaijan online visa to travel Azerbaijan. Get visa online with 24/7 customer support.
Wow! Nice article. Good Information Shared by the Author. Donate Zakat to irredeemable vagrants and widows and assist with giving them a more joyful and better life. Penny Appeal has a 100 percent Zakat strategy, which implies each penny of your Zakat gift will go straightforwardly to the people who need it most. Give today!
Shafi Dropship helps you to launch your turnkey dropship store without hiring designers. shopify dropshipping store Get your own money making dropshipping stores in USA, UK & Canada.
Thanks for sharing this great and useful information in your blog. It is really good and interesting. My colleague seemed a little disappointed with this, as certainly we all take strength from numbers, but to me, the numbers do not add anything fatal motorcycle accident virginia. Keep sharing more useful blogs.
Post a Comment