Page 1 of 1
(M+17)- in NEGATIVE ionization?
Posted: Fri Mar 18, 2011 12:58 pm
by Katrina
Hello,
I am working in a Shimadzu LC-MS 2010EV, recently I' ve observed, in the negative mode an adduct M+18,
The probe is APCI, my column is new (Purospher RP8), my mobile phase is ACN/H2O (9:1), I use buffers (CH3COONH4) very often, I always wash the system and our samples are free from contaminants. My exact mass is 1483, i see the 1484 (M+1) in the possitive mode and a major peeak (100%) of 1500 (M+17) in the negative mode, {I also see 1518 (M+35), which is the Chloride adduct} The particular molecule has a Bromine and an Boronic ester, its generally non-polar (that's why i am using APCI, with the ESI probe the ionization could't take place), the sample is dissolved in DCM and then to ACN.
If someone has any suggestions....
Thank you in advance
Re: (M+17)- in NEGATIVE ionization?
Posted: Fri Mar 18, 2011 1:37 pm
by Katrina
Hello again,
Complementary information always help:
I make a run in which I replaced the H20 of my mobile phase with buffer CH3COONH4 10mM PH=4.5, everything else remained the same.
This time I obtain in the possitive mode a major peak 100% of m/z 1501 (M+NH4)+ and in the negative mode a major 1500 (M+17)- 100% , a 1518 (M+Cl)- 40% , and a 1542 (M+Acetate)- 26%
I' ve googled the negative adduct of M+17, but I couldn't find nothing mentioned before,
I am looking forward for an answear
Thanks
Re: (M+17)- in NEGATIVE ionization?
Posted: Fri Mar 18, 2011 2:04 pm
by bhuvfe
Do you have any reason to suspect an electron capture mechanism (since you have a Br)?
Is there a chance that you have an extra ionizable group that can form a ammonium salt, a COOH and SO3H, etc?
Re: (M+17)- in NEGATIVE ionization?
Posted: Fri Mar 18, 2011 2:08 pm
by sav
1500: adduct [M+H2O-H]- or not adduct [M+OH]- or [M+X-Y]-* and ...
1518: + Cl? Why?
Can you post some mass spectrum and "picture"(or CxHyOz...) of molecule?
Re: (M+17)- in NEGATIVE ionization?
Posted: Fri Mar 18, 2011 2:29 pm
by Katrina
1499.45: adduct [M+NH3-H]- or not adduct [M+OH-H]- or [M+X-Y]-* and ...
1518: + Cl? Why?
Can you post some mass spectrum and "picture"(or CxHyOz...) of molecule?
Can you be more spesific in your answear?
C71H124BBrO26, this is the molecular formula, I can not post you the structure (industrial regulations),
but the molecule has a basic core of fluorene, and two extra long etheric chains
Re: (M+17)- in NEGATIVE ionization?
Posted: Fri Mar 18, 2011 5:27 pm
by southp
Maybe these are water adducts of the [M-H]-? Sav seemed to be thinking along that line too. If so, the Br isotope should give also 1502 and 1520.
1500 m/z = [M-H+H2O]-
1518 m/z = [M-H+2H2O]-
You didn't mention adding a source of chloride or seeing extra 1520 m/z, which you'd expect if 1518 were a chloride adduct.
Re: (M+17)- in NEGATIVE ionization?
Posted: Fri Mar 18, 2011 9:35 pm
by sav
I think...
1500: [(RO)3B(-)OH]-
1518: [(RO)3B(-)OH+H2O]- (may be, cheсk isotope model)
+APCI: Isotope peak with 100% rel. abundance (rel. int.) [М]+* (radical ion) for C71H124BBrO26 is 1484.77 amu, [M+H]+ is 1485.77 amu
Without structure of molecule, MS parameters and mass spectra is very difficultly to predict [M+X-Y]- or...
Bororganic compounds often give some unpredictable results with ESI, APCI.