Chromatography Forum

Hello

I finally cleaned my API stack. The lens wasn't that dirty but the skimmer was. I reinstalled the stack but unfortunately, nothing has changed as I infused methanol today and the NL was still between 1++02-1++04.

While the MS was ON, I ran the diagnostics. Everything passed except the capillary voltage which is out of range. I set my value to 13V this time but the readback is always around 140V. Anyone knows how to explain this?

Many thanks

This is getting way outside my expertise, but it does worry me that the capillary voltage is so far too high. Either the read-back is wrong, or something is giving it too high a voltage. I can't imagine that its own power-supply would be capable of getting that high, but a Thermo engineer would know for sure. The only other option is that something, somewhere, is shorting the capillary to some other part of the system that's at a higher voltage. I can't think what it could be, though! A decomposed capillary heater cable?? No idea, sorry! If you can possibly afford to get a Thermo engineer to take a look, it may be that a few hours' of his/her time will save you weeks.

Hi lmh

I definitely need an engineer to come. I am getting quotes from service companies in the area. In the meantime, I try to find out the price of an ion transfer tube. May be if i replace it with a new one, it could solve the problem.

Many thanks for the discussion we had here, it was all relevant to me.

Hi

I have a question about the ion transfer tube and the Kalrez O-ring. How often do you change it? I plan to buy these two parts and hope it will help with the capillary high voltage. I send a quote request to thermo.

Many thanks

Hello

A quick update of my situation.

I finally spoke to an engineer about the high capillary voltage. It is definitely a fault on the instrument (he suggested the main system board). My company has subscribed for a service contract. I am waiting for the paperwork to be done and for someone to come in to fix it.

Sorry haven't been here lately. Good, with a contract they're obliged to fix it, whatever the problem is!

As regards the Kalrez ring and ion transfer capillary, I only replace the ring when it fails obviously (usually it turns into gooey mess stuck to the capillary, and one day when I try to take the capillary out for cleaning, I find myself scraping it off with a spatula! Otherwise they can also just go hard, crack, and again break when changing capillary).

I work in a lab with fairly clean samples, so I only clean the capillary fairly rarely - unless you run a lot of dirty samples, you don't need to do it more than every few months. I find it enough to sonicate it in water/formic acid (I just use some spare running solvent!) followed by methanol, poke the cleaning-wire through a few times, and use some micro-grit paper on the conical end.

An update on my situation

After nearly 3 long and horrible months, my LCQ Deca XP has been returned to me yesterday. The default was an electric problem, the main system board was changed. The diagnostic, tune and calibration are all good.

This morning I start working with the chloro-compound Alachlor. Using a tee-union, it is impossible for me to infuse my analyte throught the mass spec with a LC flow. I have a back pressure from the LC and my gastight syringe is leaking.

I decide to optimise the tune method for the analyte using the LC. I am able to inject my analyte but unfortunately, I don't see my parent ion. and my TIC is completely flat. I am desperate. My HPLC solvent weren't degassed. A helium pipe will be installed tomorrow, I have to try with it as well.

Hello All,

Me again.

My LCMS is working fine now. The problem was the HPLC system, the syringe wasn't taking the sample, so there was nothing injecting.

I have a chromatogram but with a hedgehog profile, i will try and see if i can reduced the number of scans.

When scanning the solvent only, I have a contaminant at m/z 278. Any idea what that could be? It is not a problem when the ion 278 is not in my mass range. When it is, then I dont see a pic at all. For example for a pesticide, when I do a SIM (m/z 241, width 3), I see my pic. When I do a full scan with the same pesticides (range 90-390), the 278 pic is predominant throughout the running and I have a flat spectrum.

Any idea how to solve this problem?

Thank you for any suggestions

Are you sure it's 278 and not nearly 279? 279 would have been a common phthalate contaminant of solvents, a plasticizer. The ion trap isn't very accurate, so it might come out at 278.9

If you've got a surveyor hplc system, the injection mechanism can be a bit difficult. It's almost impossible to remove all bubbles from it, and it tolerates a few bubbles, but if it runs out of needle wash it stops injecting altogether. If the needle ever gets partially blocked, or the drive mechanism on the syringe gets dirty, the drive motor will slip a bit, and it loses coordination of how far up or down it is. This matters because it uses a double-plunger concentric syringe, and how far up or down it is determines which plunger is moving. If it thinks it's pipetting with the middle bit but is actually using the larger bit, it will think it's pushing the sample neatly into the sample loop, but actually it's pushing it straight out the other side and into the waste!

According to wikipedia, Alachlor has a neutral mass of 269... it's not got huge numbers of easily ionised groups, so it might not give a huge signal? If I were you, I'd go back to syringe injection, but if you can't do the teeing thing because your syringe is too leaky, just inject directly into the source at 5uL/min or so, and see if you can detect it at all. You'll need to reduce the sheath gas substantially at this low flow rate, and no aux gas, but otherwise the tune parameters can stay the same.

lmh, my apologies. Indeed the m/z is 279. It is written in big on my notes but I write 278 in this forum and I google the wrong ion as well.
I was able to detect the (M+H)+ of Alachlor (270) and two triazines (272 and 241). What puzzled me is that I absolutely need not to restrict my mass range not to include the m/z 279.

I am reading some documentation on how to avoid this contamination.

Many thanks

buy good quality solvents (ideally LC-MS grade), avoid plastic bottles, and you will probably find that once you've got a reasonable throughput of work, the 279 ion will shrink. Yes, in an elderly ion-trap it will limit your sensitivity a bit because the instrument isn't very good at filling its trap while rejecting other ions (you can try the two injection waveforms in the trap part of the tune-file, but I haven't had much success with them), and sensitivity is limited by the number of the "right" ions in the trap when it's filled. But it's rarely catastrophic with these plasticisers. In fact Orbitrap people sometimes use them, and other contaminants, as lock-masses!
Good luck!

lmh,

Many thanks for your advices and tips. I got rid of every plastic in my standard preparation and eventually the m/z 279 has shrinked. My system is working fine now and I can really start my work. I am quite excited by all this.

I have injected a mixture of 23 organonitrogen pesticides, with a SIM method using multiple scan events. I am processing them at the moment and it seems as everything went fine. Even though I have to differenciate compounds with the same m/z by injecting them individually.

Many many thanks