Tiron wrote:Hi everybody! and thxs in advance for your valuable time and help
Could any of you give me some initial hints to develop a method for the determination of preservatives (classic ones, BIT, MIT pyrithione ...) in liquid soaps, and laundry detergents with the mínimum sample cleanup ?
I tried with a sort of SPE in C18 phases but recoveries were low and chroms stills pretty dirty...
many thanks!! Tiron
I make my living doing stuff like this!
We assay for MIT, CMIT, BIT preservatives by diluting the sample with water or methanol, then filtering; that's it, no SPE or clean up, over 30 years now.
We haven't modified our test methodology much over that time except to move to some more-modern (read: available/able to be purchased) C18 columns, nothing special needed. We do use gradient, starting at quite low organic, and with a 100% organic clean up step built in to the gradient (very important), before the requisite post-run equilibration. We've used both methanol and ACN as the organic, primary difference is lower pressure (duh !) using ACN. The aqueous phase has a little acid in it, but we've never had the need to study this. We use UV detection for these, with a higher wavelength used for BIT as it's more sensitive there than the wavelength used for MIT and CMIT (chlorinated MIT/Kathon). No, we don't use a nonspecific wavelength like 220nm either, and we typically inject 3µl.
As to pyrithione, we've only assayed for that in hair products at down to 0.1% level, or as sodium omadine in a different product (where it was fully degraded within 2 days). That's a tougher assay, but the higher detection wavelength helps with specificity there too.
We've done other preservatives too in consumer products, like parabens, phenoyxethanol, antioxidants.....puts food on the table....