Trying to develop a robust method

[brendandamm]

Hello,

Currently I am studying the preservatives left over in customer samples that I am receiving. The two preservatives that I am looking at are methylisothiazolinone and benzisothiazolinone. As of right now I have to run two different methods, one for each preservative, and it is incredibly time consuming. So I'm curious as to if there is a way that I can use one method for both compounds. Is there a way for me to only prep the sample once and then run it through the column looking at both wavelengths and cut my time in half? I've tried prepping the BIT samples with H2O(current prep for MIT) but the BIT does not solubilize very well and my data is inaccurate. The same thing happens when I try to prep the MIT samples in Ethanol(current prep for BIT). Any helpful advice would be much appreciated!

[Consumer Products Guy]

Brenda: we've assayed for both those preservatives here, but never have had a mixture. Typically we have used methanol solvent for samples containing BIT, and water for samples containing MIT. We haven't experimented with methanol as solvent for MIT, but since we use gradient for that and start out with low organic, we don't want to really inject sample in a strong solvent there.

We use 273nm for MIT and 320 nm detection for BIT, C18 column for each. For MIT, we do add some acetic acid to the mobile phase, and run an aqueous-methanol gradient, starting at low methanol percent.

For BIT, we do isocratic, with just water and acetonitrile.

So if I was looking into this as a single assay myself, I'd start with trying methanol or methanol-water as solvent, and try a gradient with wavelength switching, starting at 272nm for the MIT and going to 320nm for the BIT.

[brendandamm]

Yeah that's basically the same exact thing I'm doing right now except 318nm for BIT and 275nm for MIT. I read one article that suggested a 5%ACN prep with a slight gradient in the method so I am going to give that a whirl but I am not too optimistic about it. Thanks!