Chromatography Forum

A peak of m/z 282 always appears on the full mass Q1 scan (+) spectra even when I infused solvent only such as ACN, MeOH, ACN/H2O with 0.1% formic acid. What could this peak be - solvent cluster or contamination? Please help.

WW

There's numerous possible sources.

We have had contaminant peaks from our system from brighteners in the tissues used to clean the spray chamber (so changed from white to dark blue and the contamination disappeared.)

We also had intermittent contamination which we couldn't pin down, happened on Tuesday morning first Tuesday of every month. Turned out to be a cleaning spray that the cleaner used to dust and clean the work surfaces first Monday of each month.

I like that one - I'll add it to my collection

Regards,

Ralph

I feel it may be a solvent cluster.

It may come from the nitrogen. Some N2 generator contaminate the gas. You can connect a bottle of N2 and try to see if the ion disappear.

WW,

For interpretation of m/z 282, we need to know whether this is a fragment ion (possible, but unlikely for ESI; more possible for APCI) or a molecular ion e.g. [M+H]+or a cluster ion MH+ with NH4/Na/H2O/MeCN etc.....

If [M+H], do you see [M+Na] at m/z 304, [M+K] at m/z 320 ???

If m/z 282 is [M+H], then MW 281, and N count is odd--do you use ammonium acetate/formate; if not then the N is derived from MeCN or an N-containg contaminant----

Can you change cone voltages etc. to fragment the m/z 282 ???

JMB

Thank you all for your help. It took me a long time to figure out the problem. Instead of identifying what was m/z 282 I tried to remove it from the system. I connected LC bypass the column to the MS and run 0.1% FA in 80% ACN at 100 ul/mL for more than 24 hours. Then I infused ACN to check m/z 282 - it had finally gone.

M/Z 282 was one of starting material for our discovery compounds, which was very sticky to MS. The solution for not to get too much of m/z 282 in the system is to infuse discovery cpds at very low conc., just enough to acquire the cpd peak.