12 Replies Latest reply on Dec 14, 2017 6:06 AM by graettin

    Bad autotunes 1 week after cleaning

    etcb

      We have a 5977 that we use to analyze oil samples primarily in DCM or hexane. We have been having an issue with our tuning degrading rapidly after cleaning the source (our latest tune file is attached). EM volts are at around 1800 directly after cleaning and then quickly (in a matter of 1 week) the autotune produces an EM volts value as high as 2600. The repeller is also maxed out, although this does not seem to change after cleaning the source. Our autotune peak shapes look very jagged for 219 and 502, and the relative abundance of 219 keeps falling as the conditions deteriorate (it is now at 4.8%). Over the course of a run (of ~30 samples and standards) the sensitivity drops off markedly. It does not appear from the air and water backgrounds that we have a leak. We have replaced both filaments and cleaned the source twice. We have observed this behavior after both cleanings. Has anyone had a similar experience? Thank you!

        • Re: Bad autotunes 1 week after cleaning
          james_jenkins

          Hi etcb,

          I updated the tags on your post for better visibility. The problems you are having look like a dirty source. The fact it exhibits this behavior so quickly after a cleaning, also having a persistently high repeller leads me to think you need new insulators and a new repeller . I also see that you are running your transfer line very hot at 340 C. There is only a short segment of column in the interface, but depending on what column you have you could be coating source parts with stationary phase from the column until it is of course gone. I hope that helps. Let us know what you find.

          Regards

          James

            • Re: Bad autotunes 1 week after cleaning
              etcb

              Thank you for your reply, James! I cleaned the source again yesterday using the recommendations from the document "How to clean and Agilent GCMS Ion Source," which I found through this forum. The tune looks good and EM volts are back down to 1700, although the repeller is still at maximum. I have ordered the parts to replace the repeller and insulators, so I will let you know what effect these have. The GC column we are using is deactivated, and we use a fused silica capillary transfer line between the column and the MS; still yet the transfer line is at 325-340 C and the source is at 230 C. If we feel pretty confident that the stationary phase is not entering the source, why is the temperature difference a concern (sorry, I am a new user so I am just curious)? Additionally, is the falling 219 percentage characteristic of any specific problems?

               

              Thanks again!

                • Re: Bad autotunes 1 week after cleaning
                  james_jenkins

                  Hi etcb,

                  Sounds like you made some improvements. The repeller still at 35 reinforces that the other parts are most likely needed. The fused silica transfer capillary should be fine at the higher interface temperature. In most cases customers have the coulmn direct into the interface and at a high temp like you have , column dependent, it could bleed the stationary phase into the source. Using uncoated fused silica removes that concern. For your 219 failing, it may improve with the other parts when replaced. Let me know

                  Regards

                  James

                  • Re: Bad autotunes 1 week after cleaning
                    gchaplain

                    There is something that maybe causing it, even if the source is fine. The temperature of the transferline is high, and the expansion/contraction of the transferline/transferline ferrule would likely loosen slightly and potentially loosen its grip on teh column and push it slightly into the source a bit further than normal.

                    Was it just the MSD that was turned off whilst changing/cleaning the source or the whole instrument? If the whole instrument it maybe that the column slip into the bombardment path of the source maybe the cause of the problem.

                    1 person found this helpful
                  • Re: Bad autotunes 1 week after cleaning
                    etcb

                    So we installed the new insulators, repeller and washers yesterday. The tune is looking okay, and while the repeller is not at the maximum, it is still at about 31. Our ion percentages are looking a lot better and the EM volts are around 1800. It will be interesting to see how long it stays this way.

                     

                    Additionally, the GC column did also appear to be part of the problem. The source stability was greatly improved when we switched to a different (and newer) column, so this will likely need to be replaced as well. The diffusion pump oil, and rough pump oil for that matter, had been changed very recently, so I think that this was not part of our problem. I am planning to gently clean the ion source insulator with Methanol (I was told under no circumstances to use chlorinated solvents or to sonicate it), and to wipe out the radiator and surrounding area next time we have to take out the source.

                     

                    Thank you all very much for your helpful suggestions!!

                  • Re: Bad autotunes 1 week after cleaning
                    cbrown

                    Is the low high vac pressure a concern?

                      • Re: Bad autotunes 1 week after cleaning
                        james_jenkins

                        I looked at the tune report with the vac reading, I suspect you have a gauge tube that has failed or is failing. The pumping system isn't capable of readings into the -10 range. The gauge tube isn't a show stopper and wont prevent the instrument from running, but it should be replaced at some point, especially if you have a CI option.

                          • Re: Bad autotunes 1 week after cleaning
                            etcb

                            Yes, it appears that this has been a problem for our diffusion pump since sometime in 2015. Is there a way to fix the gauge tube without fully replacing it? Thank you!

                              • Re: Bad autotunes 1 week after cleaning
                                james_jenkins

                                Unfortunately, replacement is the only option. The part number is G3870-80030 if you are interested . The life of the gauge tube, once replaced, can be extended by turning it off during a run. This is done with a pre-run command macro gauge_off. I have tested this macro with the 5975 and can see no reason why it wouldn't work with the 5977 but have not tested. The macro turns the tube off at the beginning of a run and protects the tube filament from solvent vapor . Once the run is complete, the tube will come back on and supply a reading. This increases tube life. I have placed a graphic below to show where you place the macro.

                                I hope this helps.

                                Regards

                                James

                                • Re: Bad autotunes 1 week after cleaning
                                  paulsalverda

                                  If you need the transferline at 340, the source should probably be run hotter than the default 230 - like maybe 265 to 275 or so. What column is installed?  What is your final oven temperature? What is your injection port temperature?   What liner and O ring?   You would go into tune, change the source temperature, save the tune, wait long enough for thermal equilibrium, retune it at the new temperature, save the tune file, and change the source temperature setting in your acquisition method.

                                   

                                  If cleaning the source properly brings the system back a bit but only for a while, then the problem is contaminated repeller insulators, both of which should be replaced once a year or so, contaminated lens insulator (the brown one), or some other simple problem.   If your ion source and the rest of the vacuum chamber is contaminated from running samples and tuning, then the freshly cleaned source gets recontaminated by stuff coming off the parts that were not cleaned.    Every few source cleanings, while the source is still out of the analyzer, take a fresh lint-free cloth, wet it with the same solvent you use for cleaning the source, and wipe the source radiator - the place where the source is mounted when installed - and all around that area taking care not to damage anything, of course.  Wipe the side plate and the inside of the analyzer manifold near the source end.  Don't be surprised if the cloth gets black as wiping aluminum will always do that, even when it is really clean.

                                   

                                  How long has it been since the diffusion pump fluid was replaced?  What is the level of the fluid in the pump?  You can see it through the front cover with a flashlight if you know where to look. It is behind the grill below the source/analyzer window.  This is what you should see back in there.  With the pump hot, you should see the fluid meniscus in the dark FULL HOT area.   If it is too low, or too high, the high vacuum efficiency is poor and your source will get dirty faster.  When it is hot and running, the oil will dance around a bit.

                                   

                                  Diff pump fluid hot.jpg

                                   

                                  How long since the rough pump oil was replaced?  It should be done every six months as described in the manuals.  Make sure that the exhaust oil mist filter is replaced at least once per year as well. If it gets clogged it backpressures the rough pump which reduces its efficiency and prematurely wears the seals.

                                   

                                  and let us know what happens next.

                            • Re: Bad autotunes 1 week after cleaning
                              danots

                              If possible I would like to get a copy of the your tune history file.   This is locate in the d:\masshunter\gcms\1\5977 folder and named atune.csv

                              • Re: Bad autotunes 1 week after cleaning
                                graettin

                                I agree, I see the original atune.pdf which shows a bunch of symptoms of a dirty source. I would love to see a new atune.pdf report now that the source has been recleaned, and please do also send the atune.csv. This will let us look at how the source has been performing over time.