Chromatography Forum

I'm running an Agilent 5975C and am trying to dissect the Autotune and Tune Evaluation printouts to get a better sense of what's happening inside the MS. I've come up with the following questions:


-What are the precursors to 69, 219 and 502 and why must they be below a certain threshold? (are the precursors parent ions for the listed masses? why aren't the precursor masses listed?)

-Why is the isotope ratio for each tuning mass measured and why must it be BELOW a certain level? (I understand the need for mass axis resolution, but why abundance?)

-Is abundance measured as detector counts per second or the area under the peak?

-Why does the 219/69 and 502/69 ratio have a lower limit but not an upper limit?

-When the ADC readout is displayed onscreen is it to prove that the signal is within a certain SD or are there corrections made based on the readings?



The troubleshooting and maintenance manual was very helpful but didn't go into specifics on these topics. My least favorite part about learning these systems is occasionally having to ask the ultra basic questions, any help would be much appreciated.

Precursers may indicate poor mass resolution - often due to too high a repellor setting.

Isotope ratios are a reflection of the natural abundance of carbon-13 and should not be too far off from the known abundances. This is opposed to 219/69 type requirements - these are a product of instrument design - not a materail property like, for example, an absorbance wavelength.