May 2015

We have been doing quite a bit of analytical work recently on epoxy resins and epoxy  systems. The GC MS has been great for this but it can only really handle resins up to a molecular weight of 400. It has to be able to volatilize the materials so that they can get through the GC. This is difficult  if the resins are too big and we can’t heat them up any more than 280°C or they  start to break down. The next technique available for this sort of work is HPLC. This is very similar to GC but instead of using a stream of gas to carry the sample through a column that separates the various components, we use a solvent. The problem that unlike GCMS where there is a pretty standard set up that most people can buy off the shelf and use, the HPLC has numerous options which are optimised for the materials that you are going to analyse. The first option is whether to go for a standard HPLC or a GPC (sorry about the acronyms High performance Liquid Chromatography, and Gel Phase Chromatography). As I explained HPLC is very much like GC where the column separates out the various components in the sample with the smallest molecules coming out first and the larger ones coming out later. GPC works the other way around as it uses a material in the column with pores . These pores accommodate the small components of the samples but not the larger ones. This means that the larger molecules come out first and the smaller ones come out later. This technique has been used extensively for looking at blends of epoxy resins and can handle some very high molecular weight oligomers. Unfortunately this is not so good at more general analysis and as many  of our samples will have other materials present apart from high molecular weight epoxies that we want to identify this could be a drawback of GPC.  There is also the problem of detectors. When use the MS as a detector on the GC it is amazing, as not only does it tell us when a material is coming out the end of the GC column, it tells us how much of it is there and 95% of the time will give us an identification. Unfortunately with HPLC there is no such universal detector ( apart from LC MS which at £100-£250K is not an option!). The normal detectors are all specific and will work well with some materials and not work with others eg. UV detectors great for UV active materials no good for materials with no chromophores).

So we are currently working through this and trying to specify a system that will fit our needs. It will be a compromise, on capability as we don’t have an unlimited budget, and even with it up and running there will be analytical tasks that will defeat us, but it will be a great help and fill a gap in our current capability and hopefully enable us to give our clients a better understanding of the nature of the materials that they use. For this we are talking to Agilent ( used to be called Hewlett Packard). They are the world leader in HPLC. They also supplied the GC MS which has been running faultlessly, and the software on both instruments is similar so that will make life easier.

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