Are you sure you have the product?it looks like the ionization method you are using cannot allow for the molecular ion. You may select a characteristic fragment ion and monitor. Alternatively, you may try other ionization methods like MALDI-TOF or even FAB-MS

I agree with John - please supply us more information so we can try and assist you. Rather more information than not enough information and details ;-)

I generally agree with everyone that has posted before me. Diacylgymnemic acid being a natural product, or a slightly modified natural product, the batch to batch variability comes up as a question as well. In general and assuming that the instrument/method is stable apart from the trouble you are having with diacylglycemic acid, in my opinion that specific compound should fare better in negative ESI than positive, and possibly APCI would be a better choice for ionization. This is based on the fact that it has both a glucuronic acid moyety as well as a steroid-like moyety, both of which fare mostly better in negative ionization (with exceptions of course). Another thing to try would be positive or negative ionization mode but then use additives such as Li-salts (in positive) to create a more stable parent ion that would hopefully result in more stable product ions. A third possibility would be to go the derivatization route in the sample preparation. Both of the last two options have drawbacks that you need to be aware of, but you should be able to read up on them on your own in literature.

I agree with Sigurous, APCI should work much better, and do not be be surprised if no reasonable fragmentation will be possible, so SIR most likely in negative ionization mode would be an option.

Dear all,

thanks for your suggestions

as per your suggestion, I already try ESI and APCI source for ionization of deacylgemnemic acid.

we have LCMS 8030 of Shimadzu.

Actually I facing problem that during the parent scanning, mostly I found the highest instensity at 647.4 m/z in positive mode which I cant correlate with the structure. if possible than please suggest me probable moiety  formed from DAGA. ( 682.847 actual molecular weight).

I have attached certificate of analysis of my compound, from that I have procured.

some times I also found the 681.2m/z in negative mode but the intensity is very less and not coming to all solutions which were prepared at different times.

we are assure that our instrument is stable with all other analytes which were currently going on...

Your mass of 647 (NL of 36) is not consitent with DAGA, at least not at first glance, With you experimental data not fitting with the certificate of analysis, which is only stating their results but not showing any of the data, I would ask for the data behind their conclusions. Also since they claim mass information perhaps find out how they are measuring that? 

As this is the only analyte you are having trouble with, to me this points to the company you are buying it from. Is there any chance to get even a small amount from someone else?  

If that is not a posibility I would strongly suggest derivatization as the next thing to try.