Hello, I'm currently working with a G1888 Headspace Sampler connected via to a 6890N GC. The transfer line connects to the GC via needle punctured through the septum on a split/splitless inlet. The 6890N does not have an auxillary EPC module so I unfortunately can't run the G1888 in EPC mode. I found the guide for cutting into the inlet line and using zero dead volume couplings to re-route the inlet carrier gas line to the EPC connection in the back of the G1888, and then connect the G1888 transfer line to the other end of the cut inlet carrier line, but that's a bit more invasive than I am looking to do right now.
For the meantime, I'm just trying to get the MPC mode to work correctly. The system was running properly and reliable with only one issue; the split ratio wasn't even remotely proportional. For example, a split ratio of 10:1 might have a response of 300 counts, 20:1 would have 295 counts, and 40:1 would have 290 counts. I discovered that the carrier gas flow rate on the G1888 was set really high (on a 2:1 split, 5ml/min column flow rate, the as-found split vent flow rate was in excess of 50ml/min), so I attempted to correct it according to the User Manual (the directions below), but the resulting chromatograms were horrendous. Extremely decreased signal with broad ugly peaks. I then found another set of instructions for setting the mpc carrier flow rate in the G1888 Site Prep Manual, also below, however they instructions don't make sense to me. Step 2.b seems to contradict step 2.c
User Manual MPC Carrier Flow Rate Guide
Setting the carrier gas flow rate using MPC
Set the carrier gas flow as follows:
1. Set the GC parameters shown in per the method. Use a split
ratio of 1:1.
2. Set the split flow to 4 mL/min. The GC total flow reads
11 mL/min.
3. Press Menu and choose Pressure from the menu. Use the
cursor keys to scroll to Carr. (PSI). The actual carrier gas
pressure displays in the right side of the window. See
page 62.
4. Connect an electronic flow meter to the GC split vent. Turn
up the headspace carrier gas flow until the flow rate out the
split vent equals the flow rate desired in the column. The
split ratio is 1:1. This flow rate equals the column flow rate.
Site Prep Manual Checkout Sample Gudie
Run the checkout sample
1. Set the method parameters on the GC and Headspace
sampler. See Table 5 on page 58 for checkout settings or load
the stored checkout method as described in “6850/6890 GC
checkout method” on page 58. If needed, install the checkout
column and liner.
2. If using MPC, set the carrier gas flow as follows:
a) Set the GC inlet split ratio and column head pressure to
the values given in Table 7 on page 61. (the split ratio in this table is 20:1 and the column pressure is 19.5psi)
b) Set the split flow to 4 mL/min. The total flow will read
11 mL/min.
c) With an electronic flow meter connected to the GC split
vent, turn up the headspace carrier gas flow until the flow
rate out the split vent is approximately 80 mL/min.
Remove the flow meter. See Figure 24.
My primary frustration right now is that I can't get the manual's instructions to work properly, and have to jack up the MPC carrier flow rate on the G1888 to get any decent peaks. Does it seem like I'm missing anything, or does anyone have any decent tips or tricks for adjusting the MPC Carrier on a G1888?