Hello,

In the many years of working on the API4000 - a wonderful and robust instrument which has served me and many research collaborations well - I have seen a number of issues. You are missing a variety of rather important information in order to provide adequate advice .... but .... nonetheless I will try to help, if I can ... One: Have you adequately cleaned Q1 and changed the electrode? You do not state which mode of ESI you are using (+) versus (-) mode. You may be experiencing a form of charging or an issue with one of the boards. You may have no other choice but to call the engineer for service. When was the last time you had a PM? I certainly understand the need to keep costs down ... hope that helps, at least somewhat - best - MFW

Hi Mchael F. Wempe, Thank you for your response I appreciate it! Apologies for my late response due to some family emergency.

Now answer your questions:

1. No, I did not try to clean the Q1 and electrode--I probably should try even though I never did that before.

2. I tried both positive and negative mod--the same issue

3. The instrument was donated to us just a couple of months ago and it was running well over there. They had the last PM on August 2023.

Yeah, I am running a teaching lab, running out of budget for 10k for an Engineer to come in, you know. So, that's why I am trying to see if I can fix it by myself. Thank you again.

Best,

MMH

Hi - yes, I very much understand your situation all too well. If the instrument was physically moved from one location to another, that can be very problematic. I am sorry that I am not independently wealthy and where you are to take a look at it for you. I do like problem solving on them up until I need an engineer.

You likely have no choice and really need a new PM (Performance Maintenace). If for teaching, which API4000 is a great instrument, then perhaps someone in your administration might see the value for students to get a PM. Depending upon amount of usage and types of samples you are injecting, 2 PM's a year is really a good idea. Very important to keep Q1 clean and make sure electrode is not clogged which you can check by running the HPLC part with the source off and visually see if you are getting a nice liquid flow. Many other settings are rather important too (heat, flow-rate, MS/MS settings, etc), but as I say above - likely need a PM that passes specs - wish you my best - Mike

Thank you, Mike! I appreciate your suggestions/comments. I will see if I can clean the Q1 by myself. I am also thinking, Is there a problem with the detector anyway?

Maybe - if detector was completely not working, then the software would not let you run an LC/MS-MS run. When was the last PM on this instrument? If it was a board, it too would not let you run a sample. A lot depends on what sort of samples you are running. Historically, I ran clinical samples (extracted blood, serum, plasma) and urine samples. But also did PK/PD and so did many different types of extracted tissues. Feces samples are the worst, and it can only take a few nasty samples to dirty the source.

Are you able to infuse a known small molecule drug (Molecular weight somewhere between 200 - 450 amu) and get a signal in ESI (+)? Did you check and see if the flow was moving through the electrode and that it is not clogged or impaired? This would help regarding information, but likely your source is dirty and time for an important PM. Do you have any PM paperwork from the past?

Regards,

Mike