THF in mobile phase turns glass frit black

[Tim]

An analyst has just reported that a new method using THF in the mobile phase has caused the glass frits on the end of the mobile phase lines (Agilent 1100 system) to turn black. She was able to clean them by sonication in IPA and then in Nitric Acid, but wanted to know what causes this in the first place, if it will cause any problems with the system and if it can be prevented.

Thanks

[Chris Pohl]

Tim,

You don't say what the other components in the eluent are so here's one possibilty: oxidation of the stabilizer in "stabilized" THF. Since the stabilizer is a phenolic compound, it's possible that the black color is from oxidation of the BHT stabilizer. Phenolics generally generate dark oxidation products under mildly alkaline conditions. Of course, this wouldn't apply if the THF was "unstabilized" THF.

[khw]

An analyst has just reported that a new method using THF in the mobile phase has caused the glass frits on the end of the mobile phase lines (Agilent 1100 system) to turn black. She was able to clean them by sonication in IPA and then in Nitric Acid, but wanted to know what causes this in the first place, if it will cause any problems with the system and if it can be prevented.

Thanks

We were told in an Agilent service seminar __never__ to sonicate the glass frits. This could generate some small particles which could travel along the solvent line to the pump and cause there scratches.
Sorry, that was not your question, but I thought it worthwhile to share.

[Tim]

Mobile Phase is 0.05M Phosphate buffer:MeCN:THF 65:25:10 unbuffered. THF is stabilised. The chemist has indicated that there is some sediment in the MP bottle, but the MP was filtered (0.45um) and the MP bottle rinsed before use.

[Chris Pohl]

Tim,

My bet is that it's due to the stabilizer. I'd try unstabilized THF to see if this eliminates the problem.

[Tim]

Thanks Chris. I'll get the chemist to try that and report back if it doesn't work.

[Durk]

We also use stabilized THF. In one application we have THF as mobile phase and in another we have a mixture of THF and water. In both cases the frits supplied with our Agilent 1100 systems don't become black or even grey. So I think it is not the BHT in the THF.

Durk