11 Replies Latest reply on Jul 3, 2018 1:57 PM by alfausett

    GC-FID/MS

    huyenchalmers

      We have a GC-MS instrument and it works well. Recently we installed a new column which connected to FID detector. Now we want to run a method with GC-FID/MS.

      However, we observed the peaks only in MS spectrum without FID spectrum. We need help with the set up method and configure the column maybe.

        • Re: GC-FID/MS
          james_jenkins

          Hi huyenchalmers,

          Can you let us know what instrument and software you are using? The second signal is usually just a matter of setting it up in the signals page. I will be able to give you more info once I know what you have.

          Regards

          James

            • Re: GC-FID/MS
              huyenchalmers

              Hi James!

               

              We have GC (Agilent 7890A) and MS (Agilent 5975C), spectral interpretation by using the NIST MS Search programme version 2.0.

              It is very good if you can help us with this.

               

              Best regards,

              Huyen

                • Re: GC-FID/MS
                  james_jenkins

                  The FID is a two dimensional signal and NIST will not be able to read FID data. Perhaps we need more information here, can you see the FID signal in data analyses ?

                    • Re: GC-FID/MS
                      huyenchalmers

                      Hi!

                       

                      Yes, we see some peaks in FID signal which are not corresponding to MS spectrum.

                      I think we need to change the analytic method.

                      Do you have the same system like us? The sample is sent from inlet to splitter which splits it in two columns, one connects with FID and another with MS. It seems no sample goes to the column connected with FID.

                       

                      Best regards

                        • Re: GC-FID/MS
                          james_jenkins

                          Good morning,

                          I work for Agilent and support GCMSD and CFT splitters. Depending on how you are splitting, CFT plate, or simple union etc, back to basics checking connections is the place to start. Keep in mind that the MSD has a vacuum on the end of the column so with the same size columns more flow will go to the MSD. Are you splitting using a CFT splitter? Let me know more about the splitter input and I maybe able to make better suggestions.

                          Regards

                          James

                            • Re: GC-FID/MS
                              huyenchalmers

                              Hi,

                              Yes, we have CFT splitter (G3181 60500) in our system, and two same size columns (HP-5MS) (5m x 0.25mm x 0.25µm).

                              We actually do not know how to control splitter input. Could you suggest us the way to do it. Here is a part information of our method:

                              Column #1
                              Agilent 19091S-433: USF729013H
                              HP-5MS  5% Phenyl Methyl Silox
                              325 °C: 30 m x 250 µm x 0.25 µm
                              In: Front SS Inlet He
                              Out: Vacuum

                              (Initial)                                    45 °C
                              Pressure                                     7.3614 psi
                              Flow                                         1 mL/min
                              Average Velocity                             36.354 cm/sec
                              Holdup Time                                  1.3754 min
                              Flow Program                                 On
                                  1 mL/min for 0 min
                              Run Time                                     139.75 min

                              Column #2
                              Agilent 19091S-433: USF731114H
                              HP-5MS  5% Phenyl Methyl Silox
                              325 °C: 30 m x 250 µm x 0.25 µm
                              In: Front SS Inlet He
                              Out: Front Detector FID

                              (Initial)                                    45 °C
                              Pressure                                     7.3614 psi
                              Flow                                         0.5561 mL/min
                              Average Velocity                             15.963 cm/sec
                              Holdup Time                                  3.1321 min
                              Pressure Program                             On
                                  7.3614 psi for 0 min
                              Run Time                                     139.75 min

                              Front Detector FID
                              Heater                                       On    250 °C
                              H2 Flow                                      On    25 mL/min
                              Air Flow                                     On    400 mL/min
                              Makeup Flow                                  On    25 mL/min
                              Const Col + Makeup                           Off
                              Flame                                        On
                              Electrometer                                 On

                               

                              Best regards,

                                • Re: GC-FID/MS
                                  james_jenkins

                                  I see that your run is over 2 hours long? This maybe difficult to determine the issues you are having through the Agilent community.  Do you see a solvent peak on the FID after injection?

                                  James

                                    • Re: GC-FID/MS
                                      huyenchalmers

                                      Hi!

                                      We have run the same sample with short time (about 14 min long) but the observation is more or less same with long time (about 2 hours long). That is why we can not discover what is wrong.

                                      We set up solvent delay at 3 min. So we can not see the solvent peak in MS. But we see a big peak after 3 min in FID detector which is not observed in MS spectrum. I have no idea what this big peak is actually.

                                      Best,

                                      Huyen

                                    • Re: GC-FID/MS
                                      alfausett

                                      Hi, huyenchalmers~

                                       

                                      Because your detectors have two different exit pressures (ambient - FID and vacuum - MSD), you will not have retention time alignment with equal lengths of the same column after the splitter.  You need to calculate different lengths/inner diameters to provide equivalent restriction between the two detectors.  If both of your detectors had ambient exit pressures, this approach would be correct. 

                                       

                                      Separations are typically done pre-splitter, so many people choose to use uncoated column (restrictors) with sub-250 micron inner diameters between the splitter and the detectors to minimize the amount of column in their GC oven.   Other factors worth considering are holdup time (how long it will take your sample to travel the additional length of column) and the split ratio between detectors.  If an equal split is desired, your calculations will be different that the case of a 10:1 FID/MS split. 

                                       

                                      Un-purged splitters ship with a disk that contains a spreadsheet to help you balance the restrictors along with selections of restrictors lengths with 4-5 different inner diameters.  While we generally recommend a purged splitter with MS detectors, an unpurged one will work well once the restrictors are balanced and all connections are leak-free. 

                                       

                                      Best of luck, and keep us posted!

                                       

                                      Abbey

                                        • Re: GC-FID/MS
                                          huyenchalmers

                                          Hi Abbey!

                                          Thanks for information!

                                          Since our two columns have the same length/inner diameter, should we use the flowrate for calculation to provide equivalent restriction between the two detectors?

                                          How to input the split ratio between detectors and a purged splitter?

                                          This is the reason why we need help with the setup of method for GC-FID/MS.

                                          Best,

                                          Huyen

                                            • Re: GC-FID/MS
                                              alfausett

                                              Of course,  Happy to help.

                                               

                                              You will not be able to achieve an equal split with an MS and FID using the same length/ID columns.  You will need to use the excel spreadsheet on the software disk that shipped with your splitter.  You more restriction to the MS when compared to the FID.   A pressure is applied from the inlet, and the restriction of the two columns will create the split. 

                                               

                                              Abbey