Chromatography Forum

Hi everyone!

I'm using LC with ESI QQQ MS/MS mostly for plant phenolics analysis. Although we use bidistilled or deionized water, I have to admit it's not of the best quality. Our typical mobile phase is 1 % aqueous HCOOH / MeOH. Samples are dissolved in aq, MeOH or DMSO.

Recently, we've started getting quite high background noise with m/z=214 in positive and 213 in negative ionization. Does anyone know the source of these peaks?

Also, in positive mode, besides usual [M+H]+, [M+NH4]+, [M+Na]+ and [M+K]+ adducts, we're now getting additional [M+46]+. Any ideas about what it is? [M-H+2Na]+ sounds a bit weird...

In negative mode, we're also getting [M+98]-. Again, we're clueless. The same adduct is obtained with 0,1 % acetic acid as phase A.

Thank you in advance!

Hi everyone!

I'm using LC with ESI QQQ MS/MS mostly for plant phenolics analysis. Although we use bidistilled or deionized water, I have to admit it's not of the best quality. Our typical mobile phase is 1 % aqueous HCOOH / MeOH. Samples are dissolved in aq, MeOH or DMSO.

Recently, we've started getting quite high background noise with m/z=214 in positive and 213 in negative ionization. Does anyone know the source of these peaks?

Also, in positive mode, besides usual [M+H]+, [M+NH4]+, [M+Na]+ and [M+K]+ adducts, we're now getting additional [M+46]+. Any ideas about what it is? [M-H+2Na]+ sounds a bit weird...

In negative mode, we're also getting [M+98]-. Again, we're clueless. The same adduct is obtained with 0,1 % acetic acid as phase A.

Thank you in advance!

Have you tried looking for product ions of the background peak? That could yield some answers.

http://www.waters.com/webassets/cms/sup ... r_list.pdf
This document suggests n-butyl benzenesulfonamide which is a plasticizer. Have any of your organic components been coming in contact with plastics?

Could [M+46]+ be [2M + 2Na]2+? Edit: Duh of course not. I clearly need more sleep.

Just random guesses here.

No, I have to admit I haven't tried to fragment the 212/214 so far. It may give some answers. My water does come in contact with plastic (it is stored in plastic barrel - it's outside of our control, since some other lab produces it), but same as for the past 2 years (and we haven't had that problem until about a few weeks ago).

[M+46]+ couldn't be [2M+2Na]2+ - it would have the same m/z as [M+Na]+.

[M-H+2Na](+) does happen, but it's M+45, not M+46.
An increment of 46 over another ion (i.e. M+47 if you have M+1 as the hydrogen adduct) is sometimes a formic acid cluster ion, but I find this more common in negative mode, where formate adducts happen a lot in our ion trap.

And how about [M+98]-? Any suggestions?

I ran some MSn experiments on background ions. In positive mode, ion 214 gives 158, which gives 141, which gives 77. It is consistent with the assumption it's N-butyl benzenesulfonamide. Now just to find out where it comes from, and how to get rid of it.

Wow, I'm glad that helped. Apparently it's commonly present in nylon tubing if that helps.

Did you at any time insert a plastic pipet tip into an organic solution? Or squirt organic solvent out of a plastic bottle? That's a common one.

nylon tubings - don't know where do I have them (all HPLC tubing should be PEEK, I think)... maybe those people supplying us with bidistilled/deionized water

plastic pipet tips - we use micropipettes all the times, but I doubt they are the source - been using them for years

plastic bottles - not for ogranics, only (sometimes) for water

I an minimize my sources of contamination, but cannot influence the quality of water I get. Tried to purify it by passing through a couple of various SPE columns, N-butyl benzenesulfonamide dissapeared but some other peaks remained/appeared, and baseline is even worse.

Next week, I'll try something more drastic - cooking with KMnO4 and then distillation, maybe?

Why don't you get an analytical reversed phase column (one that does not dewet in 100% H2O) and run your water through it? Then run a gradient to get rid of all impurities that were stack in the column and discard everything. If that works I would dedicate a column for this...

Well, buying *any* column (actually, anything) is a bit of a problem in my lab. Anyway, I'm not sure if that would help - the N-butyl benzenesulfonamide and other impurities' ions are present during the entire run, from 90 % aqueous to 100 % MeOH.

We had this exact contamination and determined it was from the N2 generator. We installed an air scrubber/filter just before the mass spec and it cleared that peak right up. I was so happy too... my internal standard weighed 215+ m/z!

Good luck

Orcicdejan,

I think your [M + 98]- is an H2SO4 or H3PO4 adduct.

JMB

Well, JMB, [M+H2SO4] and [M+H3PO4] are [M+98], but they would be neutral, not anionic.

Kerry, it never popped into my mind N2-generator could also be source of impurities. And recently woman who serviced our instrument had removed the trap between generator and MS. So, one possible source of at least some ions!

Orcicdejan,

But you will see a 98 Da adduct in the negative ion mode, because you are usually looking at [M-H]-, not M neutral.; a phenolic is certainly going to be [M - H]-. If your m/z value is +98 above neutral MW, then I agree that it is not phosphate/sulfate. So, is your adduct [MW + 98]- or [M-H +98]- ???

JMB

[MW + 98]-, I'm afraid...