contaminants in UPLC MS/MS

[betox]

For anyone in this interesting forum.

I am using a UPLC MS/MS analyzing biological samples, our methods work.

When uisng clonazepam and cocaine separately as standars they stand as contaminants even for blanks, I had to wash several times the system until they disappeared.I thought it was the method, maybe when change the solvent the peak appears, I enlarge the time, then disappeared the contaminant, it seem resolve but again appeared.

Someone can help me?

Many thanks.

[sam.pedraglio]

Which solvents are you using for the strong and wash solvent of the UPLC? And how much solvent do you use in the washing steps?
Waters people told us, at the beginning of our UPLC adventure to use Water/MeOH/ACN/iPr-OH 25/25/25/25 as strong wash but, of course, with the experience we modified it many times accordingly to analyte solubility.
Take care of it in your work.

[betox]

About the solvents we use:
1.strong needle wash:
ACN 9, water 1, formic acid 0.1%
2.weak needle wash:
water : 8, ACN 2, formic acid 0.1%
3.we found a mixture LC mixture 2, in Controlling Contamination in Ultra Performance LC/MS and HPLC/MS systems:
ACN 25% ,methanol 25%,2-propanol 25%,water 25%, formic acid 0.1%
(the doc says 0.2%) we used it but somo papers say that it is not good for the MS/MS detector, what do you think?
4.As movil sytem we usually use :
4.1 water and formic acid 0.1%
4.2 metanol and formic acid 0.1%
at 0.1 or 0.2mL/min

Maybe we can use the mixture 3 to wash the needle, can`t we?

I want to know your opinion..

best regards,

Thanks

betox

[sam.pedraglio]

The solution 3 is more or less the same we started from.
Adding some acid could help in increasing the compounds solubility in water, so you could increase a little bit the water content of the mix.
I don't think you could dmage the detector. The same if you increase it to 0.5%.

[betox]

Dear Samuele:

We have prepared solution 3 with more methanol, 2-propanol and ACN to eliminate cocaine and benzos.With this we eliminated the analytes.

Many thanks for your suggestion.

betox