Chromatography Forum

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!

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.