Hello, Mira,

it could be a simple contact problem or (and that would be more serious) a power supply problem. Do you have the possibility to measure the voltage at the pin with a multimeter? Then you could at least exclude that it is a problem with the power supply. Apart from that: Have you ever thought about APPI (Atmospheric Pressure Photo Ionization) instead of ESI/APCI? An APPI source is also available from Waters. At least in the case of the steroid it should deliver up to 10 times more intensity.

Regards

Markus

Hellow, Mira,

You can follow this paper, if you like.

Article A simple desorption atmospheric pressure chemical ionization...

Good luck!

Hi Mira.

I agree with Markus may be APPI source are avaible for your analysis, it's will be helpfull for you. Another test you colud be is inject reserpine standard ( when Water's filder service enginner made QO in your mass spectrometer he used this) and verify the signal and mass spectrometer reference.

Hope this help you

Is the matrix of your direct injection the same as the eluant mixture at the point where progesterone elutes from your column? I have an ESCI source as well, and have found that it is very sensitive to solvent effects as well as sample matrix effects; much more sensitive than ESI by itself. We see both signal suppression and signal enhancement when running through the LC as opposed to direct tuning. It's so pronounced that I have almost quit using direct tuning as an option on that source. I have another Waters system with ESI and a separate APCI source, and it is not nearly as sensitive to the flow and matrix.

In a normal APCI, its corona needle is sensitive to solvent. If the surface of the needle is coverd with wet solvent, the voltage which start discharge is higher in my experience. As a result, discharge becomes weak or unstable. So the solvent must be desolvated by the hot tube of APCI which the sample and solvent go through, when the APCI is connected with LC of ml order flow rate. If LC flow rate is low, desolvation is easy and corona discharge is maybe stable. I don't know ESCI structure, but I wonder if the desolvation of APCI mode in ESCI is gentler than standard APCI. So you may have some troubles you mentioned.

Update. The APCI is still not working properly, but with help of Waters technician, we managed to clean whole machine, (all cones, Ion optics, hexapole, quadrupole - some parts were pretty black) And now I can see my compounds in the ESI mode. So for now im good. I also measured the voltage at the pin and it seems its working. I also saw that the APCI needle is somehow wet from the solvent eluting from LC (I even saw small droplet of solvent forming on the very tip). As Dr. Motohide mentioned that could be heart of the problem. Ill try to play bit with the temperatures and I will try to position the needle or the ESI capilary bit better. Anyway I have upcoming advanced LC-MS training from guys from Waters so I will ask them. Thank you all for answers and tips.

Hi, Míra

I'm not coming with an answer, but because we are experiencing the same problem with our APCI. The chamber current and corona voltage are unstable and the signal falls. Everything seems to be ok but that. Sometimes the corona voltage and chamber current become stable and the signal returns ok, but only for a limited time.

Have you resolved the problem? And in that case, how?

Hi, José

sorry for the very late response. I didn't notice earlier. But maybe it would be helpful to someone else. We basically solved it by cleaning everything and changing ESI capillary. Also if you see droplets of solvent forming on the tip of corona needle, make sure you have enough heat, good flow of nebu/makeup gas and that your ESI capillary position is okay.

Hope that helps.