Septum
Proper Use of the Septum
The septum is used to inject quantities of gas into the analyzer.
Do not use the septum at pressures above ambient. Gas may escape at elevated pressures. |
Accuracy of data is diminished when poor techniques are used for injecting gas through the septum.
Injecting the gas through the septum causes a peak to appear, but it also causes a perturbation in the flow of gas through the analyzer. This perturbation is visible in the peak data. To minimize this perturbation, inject the gas more slowly into the septum. Prolonging the injection causes the peak to spread.
An injection method should be developed to balance the need to minimize the perturbation with the need for sharper peaks. See Peak Editor to adjust peak data to reduce the effects of perturbation.
- Always hold the syringe by its metal parts away from the needle. Holding the syringe by the glass allows body heat to affect the volume of gas in the syringe.
- After filling the syringe, allow the syringe to lie on a room temperature surface for about a minute. This ensures that the syringe and its contents are at room temperature.
- If the gas used is lighter than air, do not allow the filled syringe to remain in a vertical position (needle up) — the gas will diffuse out and the total volume will be reduced.
To fill the syringe:
- Empty the syringe completely.
- Insert the syringe into a septum accessory installed on the gas regulator.
- Draw the syringe plunger back until the syringe is completely filled with gas.
- Remove the syringe from the septum and allow it to return to room temperature as described previously.
- Press the plunger into the syringe until the correct amount of gas is contained in the syringe.
An alternate method to fill the syringe with nitrogen (evaporating from liquid nitrogen):
- Empty the syringe.
- Hold the tip of the needle just above the surface the liquid nitrogen.
- Draw the syringe plunger back until the syringe is filled with nitrogen gas.
- Allow the syringe to stabilize at room temperature.
- Push the plunger into the syringe until the correct amount of gas is contained in the syringe.
To inject gas into the analyzer:
The system must be at atmospheric pressure to safely use the septum. Attempting to use the septum at a higher pressure may cause the septum to eject from the analyzer, resulting in damage to the septum and, possibly, bodily injury. |
- Turn the septum closure cap counter-clockwise to loosen, then remove the nut.
- Insert the needle fully into the septum .
- Press the plunger into the syringe completely to ensure that the entire quantity of gas is injected from the syringe.
- Remove the syringe.
- Replace the septum cap and tighten finger-tight.
Septum Replacement
The septum usually requires replacing after approximately 100 injections when using the 1 mL syringe.
- Turn the knurled nut counterclockwise and remove it from the injection port.
- Tap the nut into the palm of your hand to remove the septum and discard the used septum.
- If the washer came out when the septum was removed, place the washer back into the knurled nut first. Place a new septum into the knurled nut.
- Place the knurled nut back onto the injection port. Turn the nut clockwise to finger-tighten.
Do not use a wrench to tighten the septum retaining nut. Do not overtighten the retaining nut. Doing so may damage the septum or the fitting. |
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