Switching from py-GC-MS to auto-sampler liquid injection

[Verdegreen]

Hi All,

We have a py-GC-MS. Thy pyrolyzer is Frontier 3030D, GC is Agilent 7890B, and MS is Agilent 5977. We recently switched pyrolyzer to Agilent auto-sampler because we'd like to analyze liquid samples. However, since we switched from pyrolyzer back to auto-sampler, the signal of peaks is significantly reduced. The column used is a UA5 metallic column.

We suspect that this is related to a selective sampler that comes with the pyrolyzer. Even when we turn off the sampler, there might be He back flushed to the GC injector (please see more details here, https://www.frontier-lab.com/assets/fil ... T-036E.pdf)

I wonder if anyone could give us some suggestions? Would increasing the gain factor be a good idea?

Below is the method we used:
GC
GC Summary
Run Time 65 min
Post Run Time 20 min

Oven
Temperature
Setpoint On
(Initial) 50 °C
Hold Time 5 min
Post Run 350 °C
Program
#1 Rate 5 °C/min
#1 Value 350 °C
#1 Hold Time 0 min


Equilibration Time 3 min
Max Temperature 350 °C
Maximum Temperature Override Disabled
Slow Fan Disabled

ALS
Front Injector
Syringe Size 10 μL
Injection Volume 1 μL
Solvent A Washes (PreInj) 3
Solvent A Washes (PostInj) 3
Solvent A Volume 8 μL
Solvent B Washes (PreInj) 3
Solvent B Washes (PostInj) 3
Solvent B Volume 8 μL
Sample Washes 3
Sample Wash Volume 8 μL
Sample Pumps 3
Dwell Time (PreInj) 0 min
Dwell Time (PostInj) 0 min
Solvent Wash Draw Speed 300 μL/min
Solvent Wash Dispense Speed 3000 μL/min
Sample Wash Draw Speed 300 μL/min
Sample Wash Dispense Speed 3000 μL/min
Injection Dispense Speed 6000 μL/min
Viscosity Delay 0 sec
Sample Depth Disabled
Injection Type Standard
L1 Airgap 0.2 μL
Solvent Wash Mode A, B

Sample Overlap
Mode Sample overlap is not enabled

ALS Errors Pause for user interaction

Front SS Inlet He
Mode Split
Heater On 250 °C
Pressure On 12.024 psi
Total Flow On 147.39 mL/min
Septum Purge Flow On 3 mL/min
Gas Saver Off
Split Ratio 100 :1
Split Flow 142.96 mL/min
Liner A Liner has not been selected.

Thermal Aux 2 (MSD Transfer Line)
Temperature
Setpoint On
(Initial) 250 °C


Column
Column #1
Pressure
Setpoint On
(Initial) 12.024 psi
Post Run 12.024 psi

Temperature Range -60 °C—360 °C (380 °C)
Dimensions 30 m x 250 μm x 0.25 μm
Column lock Unlocked
In Front SS Inlet He
Out MSD
(Initial) 50 °C
Pressure 12.024 psi
Flow 1.4296 mL/min
Average Velocity 43.575 cm/sec
Holdup Time 1.1475 min
Control Mode Constant Pressure

Column Outlet Pressure 0 psi

Signals
Signal #1: Test Plot
Description Test Plot
Save Off
Data Rate 50 Hz

Signal #2:
Description None

Signal #3:
Description None

Signal #4:
Description None




MS Information
-- -----------


General Information
------- -----------


Acquisition Mode : Scan
Solvent Delay (minutes) : 4
Tune file : D:\MassHunter\GCMS\1\5977\ATUNE.U
EM Setting mode Gain : 1.000000

Normal or Fast Scanning : Normal Scanning
Trace Ion Detection : Off
Run Time (if MS only) : 45 minutes

[Scan Parameters]
Start Time : 4
Low Mass : 30
High Mass : 800
Threshold : 150
A/D Samples: : 4


[MSZones]

MS Source : 230 C maximum 250 C
MS Quad : 150 C maximum 200 C

Timed Events
----- ------
Number Events= 0



END OF MS ACQUISITION PARAMETERS


TUNE PARAMETERS for SN: US1513L405
---------------------------------

Trace Ion Detection is OFF.

34.593 : EMISSION
70.007 : ENERGY
31.911 : REPELLER
90.331 : IONFOCUS
15.136 : ENTRANCE_LENS
1266.252 : EMVOLTS
1335.1 : Actual EMV
1.00 : GAIN FACTOR
993.000 : AMUGAIN
100.250 : AMUOFFSET
1.000 : FILAMENT
0.000 : DCPOLARITY
13.566 : ENTLENSOFFSET
0.000 : Ion_Body
0.000 : EXTLENS
-756.000 : MASSGAIN
-43.000 : MASSOFFSET


Thank you so much for your help in advance!

[James_Ball]

What solvent are you injecting?

Unless the samples are very dirty, you could try to reduce the split ratio to improve sensitivity. Maybe try 50:1 split ratio, it could double the peak sizes compared to the 100:1 listed in the method you posted.

If the samples are clean enough and the solvent isn't tailing past the solvent delay, the split ratio is where I would begin.