I would like to split my analytes from a GC column simultaneously to a FID and a MS. I am using a 6890 GC and is aware that by using constant flow the split will stay unchange during the oven temperature program. However, I am interested in using the locking software from Agilent, but for this I have to operate the GC in the constant pressure mode. I suspect that the flow to the FID will change because the transfer line to the MS stays at a constant temperature. Someone proposed an open split to solve this problem, but I can not find any commercial open split interfaces suitable for capillary columns (0.1mm or 0.25mm i.d.). I anticipate a remark as to the capacity of a 0.1mm column, but I intend to use a 0.2um film in the 0.1mm column...the whole idea is to perform fast GC separations. Any comments please.

It would be easier to simply do dual column, using your single injector, splitting at the head of the column instead of at the outlet end. The biggest problem with splitting at the outlet end is prevention of pulling from the FID into the MS. You need high enough pressure and flow using either an open split or Y-connector to keep flow going into a detector at atmospheric pressure and one operating at high vacuum. This can be done easily with a 0.32 column, is possible with a 0.25 column, and would be very difficult with a 0.1 column. Using a splitter with a variable restriction would make the interface easier. Aviv Amirav published a paper 3 or 4 years ago about splitting the column effluent between a MS and a PFPD, and you might check that paper for some ideas on how other people have handled the problem. Sorry I don't have the the complete reference.

Thanks Anonymous for the dual column suggestion. I thought about this initially and rejected this idea because I suspect different retention times on the 2 columns (because the end of the one column will be under the influence of the vacuum from the ms). I even suspect that the elution order for some analytes may change because of the vacuum.