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Lois Weyer (lois_weyer)
Senior Member
Username: lois_weyer

Post Number: 27
Registered: 7-2002
Posted on Thursday, August 20, 2009 - 3:19 pm:   

I suggest that you try mid IR first,as the anhydride, acid, and acid salt carbonyl absorptions are in different locations and are strong absorbers. I once developed a method for acid and acid salt end groups of a cellulosic polymer, I think with thin films deposited from o-xylene. You might be able to prepare thin films which would avoid your solubility issues. You may need model compounds to simulate the carbonyls and perhaps use chemometrics to help sort them out. Carbonyls are weak in the NIR, although there may be some combination bands in the high wavelength region that may be helpful. If you work in the NIR, you could use thicker films, but you wouldn't have the isolated carbonyl absorptions you would have in the mid IR.
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Sam Keegan (sam_keegan)
New member
Username: sam_keegan

Post Number: 1
Registered: 8-2009
Posted on Thursday, August 20, 2009 - 9:23 am:   

Hi

As part of a larger project i am looking for a method of quantifying the relative and/or absolute levels of a polymeric anhydride and it's conjugate acid and ester. Each form has differing solubility (in aqueous and lipid phases) and each is embedded within a matrix of other polymers and rubbers.

Further information is included in the technical statement from the project leader, below:

An analytical method is required to quantify each of the possible different forms of a polymeric ingredient present at 1% � 3% (in total of all possible forms) in a complex matrix. The matrix includes a range of other organic and inorganic ingredients, including polymers such as polyvinyl acetate and rubbers. As added, the polymeric ingredient which requires quantification has cyclic carboxylic anhydride groups as part of its chemical structure.

Over time, in the matrix, these anhydride groups may be hydrolysed to free acid groups which may then be further converted into salt forms (predominately calcium and/or sodium salts are believed to be produced). A reaction of the polymeric anhydride-containing component with polyols present in the formulation (to yield esters) may also occur.

Even in the anhydride form, the polymeric component is difficult to dissolve and an apparent solution may in fact contain sub-visible particles of the component which do not pass through, for example, the filters in HPLC systems. Furthermore, in some solvents, slow conversion of the anhydride into the acid form occurs, making identification of the original form of the polymer difficult. A chromatography (e.g. GPC) based approach does, therefore, present severe problems. The different forms of the polymer (anhydride, acid, and ester) are not all soluble in the same solvents, and in some cases are not soluble at all.

The approximate molecular weight range of the polymeric ingredient (as added to the formulation) is one million to five million Daltons.


The challenge is to measure the levels of polymeric anhydride, acid and ester; each of which has different solubility and reactivity to solvents.

Can NIRS give us an answer?

Many thanks

Sam Keegan

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