Chromatography Forum

We are having some major flow problems with our Shimadzu QP-2010 GC FID system. A while back my boss and I were changing out the glass insert and septum in the injection port. The insert was shattered and the bottom of the injector port taken off so that all the glass shards could be cleaned out. Upon tightening everything back up and putting the system back to operating conditions, there was an unstable total flow reading in the GC Real Time Analysis software. My thought process was that maybe a glass shard got stuck in the column or that things weren't properly sealed. We switched out the column with another one (Both columns have been used previously for the same type of analyses without problem) and were still having the same flow problems. We switched back to our original column, and have been trouble shooting for quite some time now. We tested the injection port for leaks by closing up the purge and split vents, setting the purge flow rates to about 500 ml/min, and inserting a ferrule with a rod through it where the column would go. The flow rates were then turned off and the pressure held constant for over an hour. We have used a leak detector and checked all the joints at every connection point at least 20 times. We are running in splitless mode and the total flow should be about 6 ml/min. The software treats split and splitless modes the same until it's time for the actual analysis. So when a sample is run, the splitless mode takes over and is able to regulate the pressure to 6 ml/min by use of just the total flow controller, but as soon as the run is over the split flow control mode kicks back into play with the electronic split controller calling all the shots, and the total flow rate drops to about 1 ml/min below where it should be and constantly fluctuates. We have changed all the traps to ensure that there wasn't any broken shards clogging up the air flows. My boss thinks that one of the flow controllers went out, but it seems odd that it would happen right after the fact that we broken the inlet liner. Any suggestions out there?

Is your gc is along with MS. As you have mentioned the model is QP 2010 .

Vajjara

Our GC does have an MS system but we are plumbing directly into the FID since our method only requires GC analysis for these tests.

It sounds as though the Shimadzu inlet plumbing is different to what I know on Varians/Brukers and Agilents, but there are some things that you can try.

If the plumbing is the usual back-pressure regulated split-splitless set up; at 6 ml/min either the flow contoller that feeds gas into the inlet, or the back-pressure regulator that bleeds gas out of it may not have enough flow to work with. Do you have a setting for splitless purge flow - if so increase it to 20 ml/min - this should not affect the injection , because the split/splitless transition is effected merely by re-routing gas inside the plumbing, not by changing the total flow. Increase the split ratio - you want at least 20 ml/min going out of the split vent. Also check your septum purge (if you have one) it should be at 3-4 ml/min and with only 6 ml/min total flow (if that really is total flow) and 1 or 2 ml/min down the column there is nothing left over for the presure regualtor to work with.

Put a flow meter on the split outlet and check whether the flow is really fluctuating - if not it is an electronic problem. What is the inlet pressure doing - does it also fluctuate ?

Peter