Naproxen Sodium Impurities Method---Carryover

[edrigger]

Has anybody ran a Naproxen Sodium Impurities method? If so, please help. I have had to go back to development because we cannot eliminate or effectively reduce carryover I am seeing in the impurities analysis. High spl concentration, lower std concentration, phenyl column, ACN:MeOH:Na Phos buffer. Carryover is not from the high spl concentration, and we have tried all the common techniques. Anyone seen this before?

[shaun78]

It could be nonspecific analyte binding to the head of your column. I have seen this before in an assay I delt with years ago.

There are two options:

1. Introduce the use of a post run column wash. If you are using reverse phase, then the wash would be very strong organic solvents.

2. Screen similar columns by different manufacturers. By this I mean if you are using a Symmerty C18 column, look at Luna C18(2), Gemini, XTerra, etc.

I hope this helps.

[edrigger]

I have tried extensive variations of post column wash. I've even gone overnight washing, only to inject fresh,clean blank and find a naproxen peak. Even did 6N nitric on the system, and THF wash on the column.

In the original validation, alternative manufacturers of the phenyl column we're using did not pass ruggedness. I'm using waters nova-pak phenyl 3.9x150, 4u.

[Mark Tracy]

You probably have a subtle hardware problem in your autosampler. What kind is it, and what have you done with it?

[Uwe Neue]

My bet is also on the autosampler. Consider seal materials.

The analytical column commonly has the packing material and steel frits. The analytes elute from the packing, so we can throw this out as a source of the problem. The frits are commonly stainless steel. This is also only rarely a problem.

[edrigger]

Sorry I didn't post all the info originally, but I have tried so many things, you tend to forget some.

Autosampler-Waters 717 (old, but injector is replaced ea. year)

We believe the carryover is from 2 sources:
1) There is some salting out of the Naproxen Na in the system, as evidenced by blank inj's on a new column on a system that has been thoroughly cleaned. These blanks still show Naproxen peaks.

2) We also think there is potentially some salting out of the Naproxen Na in the column, and have played w/buffer conc's to try to force the Naproxen to stay in the ion form, but no luck. Seemed to stabilize the results, but not eliminate.

[Mark Tracy]

Can you find a manual injector valve somewhere? Install it and see if there is still carryover. I'm still betting on the 717; when the seal go out, all kinds of weird things happen.

[edrigger]

We may go that route, that has been discussed. What I can add though, is that I have seen this on all our 717's, and I also ran a test where I injected acetone followed by water inj's and saw no carryover.

[Uwe Neue]

Mark suggestion is OK. Also, check with the Waters service. There are different seal materials available for the 717. Naproxen is a sufficiently common compound that a compatibility issue with a particular seal material would certainly be known already.

[edrigger]

Will check w/Waters. That's pretty much where I'm at now, consulting outside sources, as I've exhausted all other options. Thanks