I was wondering has anyone ever analysed span 60 (sorbitan monostearate) and tween 60 (polysorbate 60) quantitatively using instrumentation? I have a LC - UV, LC-DAD, GC-FID, and LC=ELSD available to me.
Both compounds are within the same matrix and while the fatty acid composition could be calculated, span 60 with after hydrolysis break into predominately stearic acid and palmitic acid acid, and these are also products that other excipients will break down to so it makes quantification quite difficult.
I was wondering if anyone knew if it was possible to do, I think LC-ELSD will probably be my best bet, however it is not an instrument that I am familiar with, so was wondering what configuration would be required.
Long time ago (1997), I analyzed this kind of compounds using LC-ELSD. Evaporative Light Scattering Detection is more suitable than UV here because most of your coupounds are lacking a chromophore group. However, some specific point have to be considered. Fristly, Span and Tween are very complex mixtures and you really need a resolutive chromatographic system to separate the different compounds and without any help of mass spectrometry you wil need standard to identify them. You will probably also need to develop a gradient elution. Secondly, the ELSD response is independant from the optical properties of the compounds (contrary to Beeer's law). Its responsi is is related to the quantity of analyte on-column but through a Log-Log relation. Thus two consecutive peaks having the same area are supposed to be at the same concentration... However it is a little bit less true in gradient elution.
To illustrate the difficulty and what kind of results (separation) is obtained on Tween samples (here Tweeen 80) you can have a look at this following recent paper: Analysis of Polysorbate 80 and its Related Compounds by RP-HPLC with ELSD and MS Detection, R. Zhang et al., Journal of Chromatographic Science 50 (2012) 598 – 607
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