Hi,

Currently, we are developing method for analysing Si contamination in lube samples using GCMSD. Before we started the project, we make sure that there is no contamination from inlet (new septa, liner etc), column and the MSD tune doesn't show any leakage problem. However, when we run blank (without any injection), we can see small silicone peaks (confirm from the library searching) even though no injection has been made. I try to reduce the injection temperature to 100 cel and rerun the blank. Problem still persist. The new column had been conditioned overnight at 20 cel above the final temperature used for the oven programming.
I also did try to inject DCM several times and at least the Si peak is missing for few injections before it reappeared again.
The question is : is it normal for column to bleed significantly?/ IS there any way to overcome this problem, especially we need to monitor Si presence in our samples. I would be appreciate if someone can shed a light on this.

regards and best wishes,

Steven

Column bleed generally does not appear as peaks. I would suspect contamination of the inlet from the septum, as shown by no peaks after cleaning by DCM. You might want to try a different septum, maybe one with a higher temperature rating. Different septa will show different bleed levels. Also, what are the primary ions in your peaks? 207 is usually column, while 73 is usually septum.

Hi,

The primary ion is 207. If it is originated from the septum, then the peak should disappear/reduce if i reduce the inlet temperature. If it is from the column (since the 207 ion is detected), what will be the normal lifespan of the column before we need to replace with new column. Currently, we are injecting lube solvent for hard disk contamination control purpose. Is there any SOP/suggestions (e.g. sample preparation) to overcome/minimized the problem?? Please guide me if i am wrong. THank you again.

Regards,

Steven

hi
I am Dr. Vivek K Gaur.I have GCMSD (PolarisQ)model. We are dealing with the Decabromodiphenyl ether in Plastic tubing. The molecular weight of the above compound is 800. our analysis is in trace level. I would like to ask that either it has possibility to retain the OBDE on column or not because of high molecular weight.

Hi,

Usually, the upper MW range for GCMSD analysis is 500 amu. Have you tried to run that compound using the GCMSD and able to see any peak?? Instead, it would be advisable to use LC system instead.

regards,
Steven