Zero counts in positive ESI, good negative mode signal

[djacqo]

Hi everyone,

I've never seen this problem before. I'm using an Agilent 6130 multimode MSD coupled to a 1200 Series HPLC. All of a sudden, I am seeing no signal whatsoever in positive mode, not even background ions. I'm talking ZERO counts of any ions with a totally flat TIC. Negative mode background looks typical, with random noise fluctuations in the baseline (~15,000 counts) and strong signal when an analyte elutes and is introduced into the detector.

I also get no observable ionization in positive mode even when using the autotuning program.

My current spray chamber settings have been used successfully with this method many times and are:

MultiMode dual ESI/APCI
Scan range: 100-1000 amu
Fragmentor: 70, Gain 1.00, Threshold 150, Step size 0.10
Drying gas flow: 5 L/min
Nebulizer: 40 psig
Drying Gas Temp: 350 C
Vaporizer Temp: 200 C
Capillary Voltage: 2000 V both positive/negative
Corona Curent: 5 µA both positive and negative
Flow rate: 1 ml/min


The only recent change to the instrument that I'm aware of is that we've recently installed EasyAccess walk up software. I'm worried I may have a serious electronics problem in the MSD. I've tried resetting the board but without any luck. Has anyone come across anything like this before?

I appreciate the help. Thank you!

DJA

[sav]

1. Electronics trouble (capillary HV, lens voltage etc.).

2. MS parameters (voltages, gas flow etc.). Check it or/and try to reload default parameters.

[djacqo]

Thanks for the reply!

Everything is good now. All MSD electronics diagnostics tests passed (except for ion optics test since I couldn't generate ions) so I focused on the ion source. I cleaned the ion transfer capillary, spray shield, and everything inside the spray chamber. After that, I went to retune and started to see some small counts with some very wide peaks, some over 10 amu. Fortunately, I was finally able to retune on this and I have strong peaks at ~0.6 amu peak width.

In the end I'm not sure if cleaning the source provided much help since the tuning seemed to be so far off (out of nowhere). In any case I learned that one can observe zero counts from an improper MSD setup. The more you know.

DJA