Chromatography Forum

I am running MSD Environmental Chemstation E.02.02.1431 and experiencing problems with column flow. When I edit instrument parameters, Chemstation changes my column flow rate, usually be 0.1ml/min. I am developing a micro-extraction/large volume injection method for PAH analysis and I tweak the method to optimize chromatography and response. I usually make the changes to the inlet panel and don't touch the column section. I want the flow at 1.3ml/min but Chemstation changes the flow to 1.2ml/min on its own. Today, the flow changed twice and was reduced to 1.1ml/min. Has anyone else experienced this problem and if so, what is the cause and can it be fixed. Agilent did not have anything regarding this on their website and I can't seem to find anything on the web either.

Thanks!!

I usually make the changes to the inlet panel and don't touch the column section.

If you change the inlet pressure in the inlet panel it will cause a change in column flow. The column flow is not measured but calculated based on temperature, column dimensions and head pressure. If you set flow in the column panel it will adjust the pressures in the inlet panel and vice versa. Inlet temperature and split flows may also cause changes in column flow calculations.

What I do is get my inlet setting in place then set flow in the column window and save the method.

I have noticed a glitch a few times when you will set the flow, then it will change when you click onto another panel, but if you set it again then save the method it should lock it in.

Thanks for the reply. I have not been changing the pressure with the column itself. I am using a Gerstel PTV and I have been adjusting Solvent Time and inlet temperature. This morning, I made three consecturive runs with the same method and again Chemstation changed the flow from run 2 to run 3 from 1.3 to 1.2ml/min during an uninterrupted sequence.

My next move is to rebuild my method from scratch. Method file may be corrupt.

Thanks.

I am also developing a micro extraction for PNA's and I'm using LVI. Are you seeing any carryover in the blanks? What calibration range are you using? Any help would be appreciated

The only carry-over or memory-effect I am seeing is in a blank or low-level sample following a high calibration standard or "hot" sample. I am using a Gerstel PTV in solvent vent mode.

As far as calibration range goes, I run my cal from 0.2ng/ml through 200ng/ml in full scan mode. I could probably extend the upper linear range but I don't believe that it's necessary. My standard PAH calibration range is 20ng/ml to 8000ng/ml in full scan mode.

Cheers.

Thanks for the reply. I have not been changing the pressure with the column itself. I am using a Gerstel PTV and I have been adjusting Solvent Time and inlet temperature. This morning, I made three consecturive runs with the same method and again Chemstation changed the flow from run 2 to run 3 from 1.3 to 1.2ml/min during an uninterrupted sequence.

My next move is to rebuild my method from scratch. Method file may be corrupt.

Thanks.

Good idea. Sometimes the methods in MSDChemstation do get corrupted and the only way to fix a glitch is to start from the Default method. We had one recently that if you used splitless it would not advance to prep-run. Rewriting it from scratch fixed it.

I am also using the Gerstel PTV. My curve range is 0.01ug/L through 0.5ug/L. On column it would be 0.1ug/L-5ug/L. Gerstel has told me my curve was too high, so I am trying the above curve. My last few PNA's are really the ones that are hanging around.