Carry Over

[NoNameLCMS]

Hello All

As the title suggest i am attempting to pinpoint sources of Carry Over on my LC-Ms experiments.

The Specs are

Sciex 4500 system with a Turbo V source (ESI mode) and diverter valve
Shimadzu HPLC System
LC-20AD Binary pumps
Sil-20AC/HT AutoSampler with 105 1.5mL vial sample rack
CTO-20A Column Oven

Column

Phenomenex Kinetex Biphenyl 2.6um, 4.6*50mm (P/N 00B-4622-E0)

The experiment consist of running Urine Analysis of Drugs and thier metabolites, around 55 to be exact. My Mobile phases are 0.1% Formic Acid in HPLC Water, 0.1% Formic Acid in Methanol. My Needle Rinse is a solution of IPA/Methanol/Acetonitrile in a ratio of 60/20/20.

Preventative Maintenance was done on both the LC and MS about a year ago, we have had an engineer swing by to perform more maintenance after we noticed a consistent source of contamination from different benzodiazepines, after our sample runs. To be more Precise after the Cal 7 runs into our solvent blanks then the rest of the run. We changed the times of the needle rinse before and after injections.

List of Maintenance done recently

New Column
New Guard Column
New PEEK tubing from MS to LC
New Needle in the Auto Sampler
New HPV Seal
New HPV Stator
New LPV Seal

Any and all suggestions would be appreciated.

[wss]

Do you have a suitably long postrun/flush time between runs?

If you run a high standard as per normal, then bypass the columns with a union and run a blank, do you still see ions from the offending compounds in the resulting mass specs?

If so, you could try replacing the sample loop and/or tubing from autosampler to the column.

[DR]

I'd try a needle wash solution that is a lot more aqueous... maybe just 10-20% organic.