Pressure of inlet lower than setting point - EPC problem?

Hi thanhlong,

I updated the tags on your post for better visibility. What mode are you operating in with your inlet? It sounds like splitless and you may not have enough total flow supplying the inlet, or perhaps a leak. If you respond with your inlet parameters such as flow, mode etc, I may be able to get a better idea what is happening.

James

Hi James,

The mode I am using is split with ratio 30:1 and the temperature of inlet is 250oC. Actually, I haven't changed the pressure of supplier and GC has worked with the current supplier. This morning, that symptom happened again and after applying above way, it is running now and 2 samples were completely analysed.

Long.

Yes, it is the constant flow mode. The following is the method I am using:

Carrier gas: Helium

Carrier gas flow rate: 1 mL/min (constant flow)

Injection volume: 1 μL

Injection port temperature: 250 °C

Split injection ratio: 30:1

Initial oven temperature: 45 °C, 10 min hold time

Oven ramp rate: 3 °C/min

Final oven temperature: 250 °C, 5 min hold time

FID: 280oC.

Column: DB-1710 60m x 0.25mm x 250um

This morning, the maximum of inlet pressure was 1.2 psi while the calculated pressure was around 20 psi. When the flow rate was reduced at 0.04 ml/min, the calculated pressure was down to 1.2 psi. After 30-min holding, the flow rate was increased again and the inlet pressure reached the desired value.

Long.

P/S: Can you tell me the suitable temperature of environment that GC works properly? I mean temperature of room in which GC is located.

Working in constant flow? Possible this is a small leak at the septa or other connection. With a 30 to 1 split I don't see it being a total flow issue. If it happens again, post your method parameters so those can be ruled out. I hope it keeps working for you .

James

Working in constant flow? Possible this is a small leak at the septa or other connection. With a 30 to 1 split I don't see it being a total flow issue. If it happens again, post your method parameters so those can be ruled out. I hope it keeps working for you .

James

Yes, it is the constant flow mode. The following is the method I am using:

Carrier gas: Helium

Carrier gas flow rate: 1 mL/min (constant flow)

Injection volume: 1 μL

Injection port temperature: 250 °C

Split injection ratio: 30:1

Initial oven temperature: 45 °C, 10 min hold time

Oven ramp rate: 3 °C/min

Final oven temperature: 250 °C, 5 min hold time

FID: 280oC.

Column: DB-1710 60m x 0.25mm x 250um

This morning, the maximum of inlet pressure was 1.2 psi while the calculated pressure was around 20 psi. When the flow rate was reduced at 0.04 ml/min, the calculated pressure was down to 1.2 psi. After 30-min holding, the flow rate was increased again and the inlet pressure reached the desired value.

Long.

P/S: Can you tell me the suitable temperature of environment that GC works properly? I mean temperature of room in which GC is located.

Thank you James.

I will check it tomorrow.

Long.

This sounds like the inlet pressure and flow were  off . If set point was 20 and actual is 1.2 , the inlet is either off or is in shutdown from an inability to maintain pressure. I would check for leaks, typical areas like septa, liner oring, column connection etc.

GC enviornmental conditions for a 7820 are below. These are the operational conditions.

Hi James,

After tightening the nuts between column and FID/inlet and also replacing the new septa, the pressure of inlet is stable and reach the setting point quickly.

Thank your for your suggestion.

Long.