Chromatography Forum

Hi,

I struggling to identify an extractable from a rubber stopper by LC/MS (ESI, QTOF, positive mode, with lockspray)

The unknown has mass of 269.104 [M+H] and fragments into 135.06, 107.06, 92.05 and 80.04.
It has UVmax at 228 and 277 nm (aromatic)

Has anyone seen this one before?

Mattias,

What is the accurate mass of m/z 269, and from that the possible elemental compositions ?

Possibly m/z 135 is [CH3OC6H4C=O]+
and m/z 107 [CH3OC6H4]+

JMB

This probably isn't it, but I notice there are some masses in common (or off by 1) with the the rubber additive benzothiazole. Prominent molecular ion 135 on GC-EI-MS, and fragments 108, 91, 82 and 69.

Hi,

I struggling to identify an extractable from a rubber stopper by LC/MS (ESI, QTOF, positive mode, with lockspray)

The unknown has mass of 269.104 [M+H] and fragments into 135.06, 107.06, 92.05 and 80.04.
It has UVmax at 228 and 277 nm (aromatic)

Has anyone seen this one before?

This raises the issue of whether m/z 269 is indeed [M+H]+ or is [2M+H]+ ?????

JMB

Also, 2-mercaptobenzothiazole is used as a vulcanization agent for rubber (Wikipedia).

Can you detect presence of S in m/z 269 ion, i.e. enhanced signal intensity at m/z 271 ??

JMB

This raises the issue of whether m/z 269 is indeed [M+H]+ or is [2M+H]+ ?????

JMB

That is a good question! Even without MS/MS the 135.05 peak is much larger than the 269.10 peak. I also see some 291.1 peak which then would be [2M+Na].

But [M+H] of benzothiazole should weigh 136.0 and [2M+H] should weigh 271? Could it be possible to knock of an electron from the aromatic ring and get the [M+] ion instead?

Also, when I perform fragementation on m/z 269, I do not see any fragments between 269 and 135.

So my molecular ion is most probably 135 (and not 269).

The closest hit on 135.0552 (determined with accurate mass) is

C7H7N2O (protonated), calculated mass 135.0558.

Google on C7H6N2O + rubber chemical = 2-hydroxybenzoimidazole. I cannot find any ms/ms data on this one, but I have just ordered it

Mattias,

2-OH-benzimidazole is a good possible, although I cannot get m/z 80 from it.

Do you have these two sources; Massbank is very nice.

http://www.massbank.jp/index.html

http://www.lc-ms.nl/contaminants.htm

Regards,

JMB

http://www.massbank.jp/jsp/Dispatcher.j ... 116&site=0

This is the fragmentation of 2-amino benzimidazole. It weighs one mass unit too little, but it fragments into 65, 80, 92 and 107. Exactly the fragments that I observe.

Will be very exciting when I get the reference substance

http://rd.springer.com/article/10.1007% ... 11-1104-0#

In the bottom of page 305 the fragmentation of 2-OH-benzimidazole in ESI-MS is described. It fits perfectly to my observations.

But I assume that the fragmentation of small molecules can be quite similar, final confirmation will have to be done with retention time, UV-spectrum and MSMS fragmentation.

It is fun to work

I retired a couple of years ago, but still try to keep my brain ticking over by looking at these MS problems.
So much for..............
"Possibly m/z 135 is [CH3OC6H4C=O]+
and m/z 107 [CH3OC6H4]+"

Enjoy your work !!

JMB

I have now confirmed that the peak is 2-hydroxybenzimidazole

It was a great help that you (JMB) made me aware that the 269.1 peak was not the molecular ion! Otherwise I would probably be still stuck in this problem.

Mattias,

Excellent, that was your starter question for 10 points..............

Regards,

JMB