Chromatography Forum

Hello everybody,

I want to know pleas why in some compound I see two peaks.for example:
I'm monitoring compound called 'Metoxuron' (pesticide) using Water 2790 Alliance Autosampler couple with Water micromass tandem quadrupole mass spectrometry. my colon is kinetex 50x2.1mm 2.4micron
one peak appear in 0.7 and the other (usually with more intensity) in 5.26

Thanks

Rachamim

Without a bit more information it will be difficult to say why you see 2 peaks.

Are you scanning a specific mass or parent/fragment or a mass range?

What is your mobile phase and flow rate?
What is the sample prepared in?
How much are you injecting?
Is your sample in a strong organic and your initial mobilephase is low in organic?

Alp

Thank for replying

Are you scanning a specific mass or parent/fragment or a mass range?I'm scanning only the fragments(Daughters)

What is your mobile phase and flow rate? mobile phase A:water+0.1%FA mobile phase B:Methanol flow rate:0.2ml/min
What is the sample prepared in?Quechers procedure
How much are you injecting?10 micro liter
Is your sample in a strong organic and your initial mobile phase is low in organic? I'm not sure what do you mean , my sample actually extracted from vegetative source

I want to send an image of the chromatogram but i don't know how

Rachamim

Image posting instruction:
viewtopic.php?f=3&t=12660

"Is your sample in a strong organic and your initial mobile phase is low in organic? I'm not sure what do you mean , my sample actually extracted from vegetative source"

You inject on column non-diluted MeCN extract from sample ?

The peak at 0.7 min ist probably a bunch of matrix eluting at the dead time.

A few questions come to my mind:
Have you run a blank? If you see the peak at 0.7 min in the blank, than it is not your analyte.
Have you run your sample in scan-mode? Are the mass spectra of the two peaks similar?
Don't your peaks look terrible if you inject 10 µl of 100% ACN? You might want to dilute with some water...

The peak at 0.7 min ist probably a bunch of matrix eluting at the dead time.

Sorry, I want to correct my self ,I'm running standard. is the remark still relevant?

A few questions come to my mind:
Have you run a blank? If you see the peak at 0.7 min in the blank, than it is not your analyte.

Yes, its absolutely not there when running with blank,more then that, the peak sometime has linear behavior (I run it in 6 concentrations)

Have you run your sample in scan-mode? Are the mass spectra of the two peaks similar?
I'm running MRM mode

Don't your peaks look terrible if you inject 10 µl of 100% ACN? You might want to dilute with some water...

(Do you mean for the blank sample?)
I'm using water as solvent A and methanol as solvent B.(but ,indeed, in some compound I'm using 100 ACN as solvent B, is there an issue with that? its seems to work perfect)

I'm running standard. is the remark still relevant?

Probably not, if there is no matrix, you won't see any

Yes, its absolutely not there when running with blank

good

I'm running MRM mode

Sure, but you could switch to scan just to see what is happening.

> Don't your peaks look terrible if you inject 10 µl of 100% ACN? You might want to dilute with some water...

I'm using water as solvent A and methanol as solvent B.

ok and what is the solvent of your sample? Is it just water or an extract in some organic solvent

but ,indeed, in some compound I'm using 100 ACN as solvent B, is there an issue with that? its seems to work perfect

no

The only idea I have then is running a scan to see if the two peaks are really the same and/or checking the purity of your standard (solutions). Maybe they have been contaminated or have hydrolyzed?

If you run two MRMs, see both with similar ratio to the standard, then it is time for you to find out what's happening. If not the case, why care? Using dynamic/scheduled MRM can make you feel better.