M+56 adduct in ESI LC-MS

[Fredrick Skoog]

"Andrew Peters" <an...@ceh.ac.uk> wrote in message
news:9s6462$240$1...@news-int.gatech.edu...
} Dear All,
}
} I'm a newbie to LC-MS, so please excuse me if this is a "no brainer"
} question....
}
} We are developing a method to analyse 3-phenoxybenzyl alcohol (aka
} 3-phenoxybenzenemethanol) by LC-MS on a ThermoFinnigan LCQ Duo using ESI.
} We are infusing a neat standard solution directly into the source via a
} T-piece and a mobile phase of 70% MeOH and 30% H2O at 500 uL/min. We get
} a very strong peak at [M+56]+ and only a weak peak at [M+H]+ (M = 200.2
} for 3-PBA). Which adduct does M+56 represent? When we do an MS/MS
} experiment on the [M+56]+ ion we do see the product ion at m/z 183.1 as
} predicted for [M+H]+ by fragmentation software. Also, this adduct is
} formed when we are using either acetic acid or ammonium acetate as mobile
} phase modifiers. We do not see this adduct with any of the other
} compounds which we are looking at so I assume it to be compound specific
} (ie. not a contaminant in the system).
}
<snip>
[M+56]+ could be an iron adduct I guess, is it likely that your
3-phenoxybenzyl alcohol has some contamination? If the mass is slightly out
it might also be a sodium and methanol adduct (23+32=55) but I don't know
how likely that is.

[Peru,Kerry [NHRC]]

In reply to Andrew's question regarding the M+56 adduct ion. This ion is
most likely the M+H+Methanol+Na adduct. (201+32+23)=256

Kerry M. Peru
Senior Organic MS Research Technologist
Environment Canada
NWRI - NHRC
11-Innovation Blvd.,
Saskatoon, SK. S7N 3H5
ph: 306-975-4206
fax:306-975-5143
email: Kerry...@ec.gc.ca <mailto:Kerry...@ec.gc.ca>

"Andrew Peters" <an...@ceh.ac.uk <mailto:an...@ceh.ac.uk> >wrote:

}
}Dear All,
}
}I'm a newbie to LC-MS, so please excuse me if this is a "no brainer"
}question....
}We are developing a method to analyse 3-phenoxybenzyl alcohol (aka
}3-phenoxybenzenemethanol) by LC-MS on a ThermoFinnigan LCQ Duo using ESI.
}We are infusing a neat standard solution directly into the source via a
}T-piece and a mobile phase of 70% MeOH and 30% H2O at 500 uL/min. We get
}a very strong peak at [M+56]+ and only a weak peak at [M+H]+ (M = 200.2
}for 3-PBA). Which adduct does M+56 represent? When we do an MS/MS
}experiment on the [M+56]+ ion we do see the product ion at m/z 183.1 as
}predicted for [M+H]+ by fragmentation software. Also, this adduct is
}formed when we
}are using either acetic acid or ammonium acetate as mobile phase
}modifiers. We
}do not see this adduct with any of the other compounds which we are
}looking at so I assume it to be compound specific (ie. not a contaminant
}in the system).

}Does anyone know of any compilations (ie. tables, lists, etc.) of common
}and not-so-common adducts which are encountered in LC-MS?
}Thanks for any help you can offer.
}Andrew
}
}==========================================
}Dr. Andrew J. Peters
}Natural Environment Research Council
}Centre for Ecology and Hydrology
}Chemical and Molecular Ecology Section
}Winfrith Technology Centre
}DORCHESTER, Dorset, DT2 8ZD, United Kingdom
}e-mail: an...@ceh.ac.uk <mailto:an...@ceh.ac.uk>
}Tel: +44 (0)1305 213631 Fax: +44 (0)1305 213600
}==========================================

[Drew Gibson]

In an article about "M+56 adduct in ESI LC-MS", "Peru,Kerry [NHRC]"
<Kerry...@EC.GC.CA> wrote...

}In reply to Andrew's question regarding the M+56 adduct ion. This ion is
}most likely the M+H+Methanol+Na adduct. (201+32+23)=256

Not so sure about that. This would look like (M) + (H+) + (MeOH) +
(Na+), which would be a doubly charged adduct, and so m/z would be 128.
But see below !

Note that the sodium salt of the phenoxy anion can exist, but again, the
protonated MeOH adduct would only be 55 up i.e. ((M-H)-) + (Na+) +
(MeOH) + (H+) .

I suspect that the culprit is one of two things...

1) it really IS an iron adduct (see below !). note that 54Fe is approx
6% of 56Fe - do you see this in your spectrum ?

2) something else is up... you say...

} We get
}a very strong peak at [M+56]+ and only a weak peak at [M+H]+ (M = 200.2
}for 3-PBA). Which adduct does M+56 represent? When we do an MS/MS
}experiment on the [M+56]+ ion we do see the product ion at m/z 183.1 as
}predicted for [M+H]+ by fragmentation software. Also, this adduct is
}formed when we
}are using either acetic acid or ammonium acetate as mobile phase
}modifiers. We

this rings alarm bells - M+H for 3-PBA is 201 is it not ? If you are
seeing 200, and a loss of 17 in your MS/MS spectrum, then your compound
is a primary amino or amido compound, not an aliphatic alcohol. If M+H
really is 201, then m/z 256 is 55 up, and an iron adduct is NOT the
culprit - maybe the Na salt of the phenoxy anion methanol adduct comes
into play then.

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