5 Replies Latest reply on Jan 10, 2019 4:55 PM by kelint

    inlet and column pressure

    kelint

      The inlet and column is able to hold the pressure when no samples are being run. However, once a sample is injected and analysis begins, the front inlet and column pressure immediately decrease. How can I fix this?

      1. Thanks.
        • Re: inlet and column pressure
          kelint

          The front inlet is able to hold the pressure when GC is idle. However, once a sample is injected and analysis begins, the front inlet pressure and column flow rate immediately decreases. How can I fix this?

           

          Many thanks.

          • Re:  inlet and column pressure
            james_jenkins

            Hi kelint,

            Can you provide a few more details such as the inlet type and the method parameters that you are running?

            Regards

            James

              • Re:  inlet and column pressure
                kelint

                Hi James,

                 

                The inlet liner we are using is an Ultra Inert, split, low pressure drop, glass wool. Product number 5190-2295. This is a newish liner (it has never been used before but I think it is really old). It was installed only last month.

                 

                Even when I do blank runs (no sample is inserted, initial oven temp is 70 degrees Celsius), the pressure drops immediately. However, when I ramp up the temperature to 230 degrees Celsius, the GC is able to hold pressure and flow rate.

                 

                See below for method parameters (we are analysing volatile fatty acids and have been using this method for a while):

                 

                 

                Split/Splitless Inlet

                Heater Temperature

                150°C

                Pressure

                20 psi

                Total Flow

                1. 8.3642 ml/min

                Septum Purge Flow

                3 ml/min

                Mode

                Split

                Split Ratio

                2:1

                Split Flow

                1. 3.5762 ml/min

                Flow after 2 minutes

                40 ml/min

                 

                 

                Column

                Brand/material

                Agilent, ZB- WAX plus

                Length

                30m

                Internal Diameter (ID)

                250 um

                Film Thickness

                1. 0.25 um

                Temperature Limits

                0°C - 250°C

                Flow (He)

                1. 1.7881 ml/min

                Pressure

                20 psi

                Average velocity

                1. 39.584 cm/sec

                Holdup time

                1. 1.2631 minutes

                Constant Flow

                Yes

                Post run flow

                1. 0.44912 ml/min

                 

                 

                Oven

                Temperature

                70°C

                Equilibration time

                1. 0.5 minute

                Maximum oven temperature

                260°C

                 

                 

                Temperature Program

                 

                Rate °C/min

                Value °C

                Hold time (min)

                Run time (min)

                Initial

                 

                70

                1

                1

                Ramp 1

                15

                220

                1

                12

                 

                 

                Flame Ionisation Detector

                Heater

                250°C

                Air Flow

                450 ml/min

                H2 Fuel Flow

                45 ml/min

                Makeup flow (N2)

                5 ml/min

                 

                Many thanks!

                • Re:  inlet and column pressure
                  kelint

                  Just fixed a few formatting issues with the table contents. Here is the revised method parameters table, Thanks!

                   

                  Split/Splitless Inlet

                  Heater Temperature

                  150°C

                  Pressure

                  20 psi

                  Total Flow

                  • 8.3642 ml/min

                  Septum Purge Flow

                  3 ml/min

                  Mode

                  Split

                  Split Ratio

                  2:1

                  Split Flow

                  • 3.5762 ml/min

                  Flow after 2 minutes

                  40 ml/min

                   

                   

                  Column

                  Brand/material

                  Agilent, ZB- WAX plus

                  Length

                  30m

                  Internal Diameter (ID)

                  250 um

                  Film Thickness

                  • 0.25 um

                  Temperature Limits

                  0°C - 250°C

                  Control Mode

                  On

                  Flow (He)

                  • 1.7881 ml/min

                  Pressure

                  20 psi

                  Average velocity

                  • 39.584 cm/sec

                  Holdup time

                  • 1.2631 minutes

                  Constant Flow

                  Yes

                  Post run flow

                  • 0.44912 ml/min

                   

                   

                  Oven

                  Temperature

                  70°C

                  Equilibration time

                  • 0.5 minute

                  Maximum oven temperature

                  260°C

                   

                   

                  Temperature Program

                   

                  Rate °C/min

                  Value °C

                  Hold time (min)

                  Run time (min)

                  Initial

                   

                  70

                  1

                  1

                  Ramp 1

                  15

                  220

                  1

                  12

                   

                   

                  Flame Ionisation Detector

                  Heater

                  250°C

                  Air Flow

                  450 ml/min

                  H2 Fuel Flow

                  45 ml/min

                  Makeup flow (N2)

                  5 ml/min