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- Posts: 1
- Joined: Mon Sep 16, 2024 7:48 pm
- Location: Italy
Hello everyone,
In our research lab has recently arrived a Varian CP3800 with the following equipment
1079 PTV inlet
1177 split/splitless inlet, equipped with a Valco sampling valve upstream, for permanent gas analyses
OI analytical serial PID-FID detector
Varian PFPD detector
We use it for multiple analyses but i encountered a problem using the gas sampling loop for methane analyses, with a CarboPLOT column and FID detector
i made up a calibration diluting a standard mix from a standard cylinder and injecting with the loop. It works very well. Since the column is a 0.32mm ID 30m i must use a split minimal split ratio of 3 to maintain a good peak shape. I usually use it 5 or 10
Some acqueous samples arrived at the lab and I was thinking to use the static headspace method, manually or by CTC Pal autosampler.
I measured the loop volume by weight, after filling with water, and turns out to be 268 uL
Then i tried multiple injections with the gastight syringe (manually 280 uL, 268 uL by CombiPal, even if it will never be so accurate). I tried different injection types separates or in the same run after a loop injection maintaining constant the split ratio and i always obtain a lower area (50-60%) for the syringe injection. Only at 20mm penetration the area ratio reached 68%
- tried different injection speed and needle depts
- tried different split ratios
- in splitless, even if the peak broadens, i can reach a 90% of the area, which is good
- i work with the septum purge valve closed, tried even to open it and did not change
- the valve is leak-free and is placed just before the inlet head (i use H2 as carrier)
- the head pressure is low, few psi, i think that the syringe repressurization can't justify this loss in signal
- when using the standard cylinder, i let fews seconds of wait after dispensing, before pressing the start buttor and rotate the valve, to inject the mixture at ambiente pressure
- i let the HS syringe such directly from the pressure regulator with gas flowing
- valve oven and the gastight syringe when using the autosampler were at the same temperature (70°C), since we can predict an ideal 17% volume increase from 20°C to 70°C
- the difference in area changes with split ratios
Plus, i have tried also in H2S analysis, for which i have a 0.53 mm column that can work in splitless. injecting equal volumes of the standard from the loop and the syringe, in that case gives a comparable PFPD area (90-110% if i'm not wrong)
Do anyone know the detail of Varian EFCs? I can't figure out how using the same system, in a condition where splitting is ideal, i get so much difference changing the sample introduction mode/position, and the difference is particularly related on the splitting process. is the sample injected in the liner (2mm ID) preferably sent to the split vent, instead of the loop content that arrives on the top on the injector?
Thank you!
In our research lab has recently arrived a Varian CP3800 with the following equipment
1079 PTV inlet
1177 split/splitless inlet, equipped with a Valco sampling valve upstream, for permanent gas analyses
OI analytical serial PID-FID detector
Varian PFPD detector
We use it for multiple analyses but i encountered a problem using the gas sampling loop for methane analyses, with a CarboPLOT column and FID detector
i made up a calibration diluting a standard mix from a standard cylinder and injecting with the loop. It works very well. Since the column is a 0.32mm ID 30m i must use a split minimal split ratio of 3 to maintain a good peak shape. I usually use it 5 or 10
Some acqueous samples arrived at the lab and I was thinking to use the static headspace method, manually or by CTC Pal autosampler.
I measured the loop volume by weight, after filling with water, and turns out to be 268 uL
Then i tried multiple injections with the gastight syringe (manually 280 uL, 268 uL by CombiPal, even if it will never be so accurate). I tried different injection types separates or in the same run after a loop injection maintaining constant the split ratio and i always obtain a lower area (50-60%) for the syringe injection. Only at 20mm penetration the area ratio reached 68%
- tried different injection speed and needle depts
- tried different split ratios
- in splitless, even if the peak broadens, i can reach a 90% of the area, which is good
- i work with the septum purge valve closed, tried even to open it and did not change
- the valve is leak-free and is placed just before the inlet head (i use H2 as carrier)
- the head pressure is low, few psi, i think that the syringe repressurization can't justify this loss in signal
- when using the standard cylinder, i let fews seconds of wait after dispensing, before pressing the start buttor and rotate the valve, to inject the mixture at ambiente pressure
- i let the HS syringe such directly from the pressure regulator with gas flowing
- valve oven and the gastight syringe when using the autosampler were at the same temperature (70°C), since we can predict an ideal 17% volume increase from 20°C to 70°C
- the difference in area changes with split ratios
Plus, i have tried also in H2S analysis, for which i have a 0.53 mm column that can work in splitless. injecting equal volumes of the standard from the loop and the syringe, in that case gives a comparable PFPD area (90-110% if i'm not wrong)
Do anyone know the detail of Varian EFCs? I can't figure out how using the same system, in a condition where splitting is ideal, i get so much difference changing the sample introduction mode/position, and the difference is particularly related on the splitting process. is the sample injected in the liner (2mm ID) preferably sent to the split vent, instead of the loop content that arrives on the top on the injector?
Thank you!
