Chromatography Forum

Dear all,
I'm using LCMS system for analyzing charantin (extracted form bitter melon). i always have problems with MS system because charantin's intensity decreased after a short time using. Before running, i infused the calibrant directly into the source to confirm the intensity. it's intensity was really high if i had washed the spray shield with pure water by LC pump (flow rate 0.5ml/min). I saw the water droplet drop from the spray shield look like a rain drop. After washing, the intensity of the calibrant increase pretty high, but it decrease if i keep infusing the calibrant until the calibrant was run out of.
The intensity increase again if i wash the spray shield with LC pump.
i don't know what happened with it! It's desperate if i don't know why ! Please help me! I need all your helps!

More details would help. For a start, what are you using as mobile phase? And what solvent for the infusion. It may help to know what kind of LC/MS you are using. More details, including instrument conditions, will help the LC/MS experts (of which I am not one) give you a good answer faster.

thanks!
I'm using Q-TOF with ESI interface (Bruker). Mobile phases are ACN, MEOH, EtOH and sometimes i use IPA, but i dissolve charantin in MEOH (100ppm) then i dilute to 1ppm in ACN and H2O (9:1). With calibrant, it is dissolved in ACN. some instrument conditions that i use to run charantin:
*SOURCE
End plate offset: -500V
Capillary voltage: -5500V
Nebulizer: 0.4 bar
Dry gas: 5l/min
Dry Temp: 300 centigrade
*TRANSFER:
Funnel 1 RF: 250Vpp
Funnel 2 RF: 350Vpp
ISCID: 0V
Hexapole RF: 500Vpp
* QUADRUPOLE:
Ion energy: 10.0 eV
*COLLISION CELL:
Collision Energy:10 eV
Collision RF: 600 Vpp
Transfer time: 120 us
Pre Pulse Storage: 10us
*DETECTOR:
Soucre: 0V

Are there any problem with my method ? Plz help me!
Waiting for your reply!