502 Isotope and its Ratio using Standard Tune

[msteele5k]

According to Agilent, the 502 Isotope should have a ratio of 7.9 to 12.3 after a Standard Tune has been performed. The instrument in question is a 5973N.

If the Ratio after a tune was 13.4 would that affect any data? If your instrument reports the ratio to 2 decimal places would you consider 12.37 to be within the specified criteria to say that instrument is working correctly? What is the importance of this ratio? What does the ratio mean? Are there any articles or other sources to learn more?

Thanks for any help!

Meg

[mckrause]

It really depends on what you are trying to accomplish. If you're trying to pass BFB, for example, then excess 502 might give you trouble (219 too high). If you're trying to maximize signal for heavy ions, then you want all the 502 you can get.

[msteele5k]

The Mass Spec is tuned daily to insure the instrument is working correctly prior to casework. We use the Agilent parameters to determine this. The isotope ratio parameter for Mass 503 (502) is 7.9 - 12.3%. If you are running compounds that have a molecular weight range of 125 to 325, would an isotope ratio above 12.3% (such as 13.3) negatively effect any compounds in that weight range? Would you expect to see full mass spectral data with no problems?

Thanks

Meg

[James_Ball]

It shouldn't be a problem. Usually when the ratio is high, it means that the mass peaks are narrow. If you widen the half height width a little the ratio will drop usually. The ratio of 69, 219 and 502 is more important in matching library spectra than the isotope ratios for the tune masses.

For EPA work the important check is the BFB ratio matches for volatiles and the DFTPP ratio matches for semivolatiles. The ion ratio would matter more depending on if you are doing some kind of research that requires that much accuracy.

[mckrause]

if I'm running compounds in the 125-325 dalton range I want all the 502 I can get!

One problem that you have to be wary of. Normally excess 502 indicates that your source temp is low. This leads to a dirty source rather quickly. Check your source temp; keep it stable but nice and warm.

[James_Ball]

Reading through again I am wondering about my reply. Are you talking about just mass 502 or the isotope ratio of 502/503 being out of spec. I replied as if you are asking about the isotope ratio not simply the mass abundance at mass 502.

[msteele5k]

Isotope Mass 503 with an Isotope Ratio up to 13.4 (13.13 in this particular Standard Tune)

I am interested in the isotope ratio specifically.

Also, I must make a correction the instrument is a 5975C.

Thanks!

[James_Ball]

Isotope Mass 503 with an Isotope Ratio up to 13.4 (13.13 in this particular Standard Tune)

I am interested in the isotope ratio specifically.

Also, I must make a correction the instrument is a 5975C.

Thanks!

That would normally be adjusted by peak width at half height. If you widen the mass peaks in tune then the ratio should fall, if you narrow the peaks then the ratio can increase. Peak widths of 0.5 to 0.75 are usually in the range you want. Autotune will get them close, but when within a certain deviation from the set target width the autotune will finish even if it is not exactly what you are wanting.

[msteele5k]

So, if the 503 isotope ratio is higher than 12.3 it will not impact any compounds that have an ion range of 38 to 325?

[James_Ball]

Most likely not. It could indicate that you may have a problem if you are looking at accurate isotope rations near the high mass end of that range, but I would believe the ratio of 219/220 would be more critical than 502/503.