Problems with the TOGA method!

[vh_tc]

Hello,

We recently acquired a new Agilent 7820A gas chromatographer (adapted with an Agilent G4367A Auxiliary Electronic Pressure Control (Aux EPC) Module) with a 7697A Headspace, with the following specification (according to ASTM D3612 Method C):

• Carrier: Argon
• Detectors:
o thermal conductivity detector (TCD)
o flame ionization detector (FID)
• Columns:
o PLOT 5 A Mol. Sieve Column
o Carboxen-1006 PLOT Column

We verify our gas supply to be 99.999% pure, Nitrogen, Hydrogen, Argon and Air.
Using the standard gas references (100 ppm, 1000 ppm and 5000 ppm) we perform regular calibrations in order to obtain accurate results.

Using the ASTM D3612 method C we have set up the correction equation to obtain the corrected results at 760 torr and 273 Kelvin. We use a multiplier for the data acquisition of 1/Lab temperature (°K).

PROBLEM: We have recently performed an interlaboratory and found that our results vary significantly. Mostly in our H2, N2, CO2, CO and O2 results with differences of over 70%. I have checked all the formulas and the method itself and its all as it should be, however our results do not fall within the 2 standard deviation.

I would like any opinions/ suggestions as to what I can do to correct this.

Thank you,

V.H

[GasMan]

I would be very interested to know which company supplied you with a 7820A with a specification to follow the ASTM D3612 method.

Gasman

[vh_tc]

I would be very interested to know which company supplied you with a 7820A with a specification to follow the ASTM D3612 method.

Gasman

Hello,

Our lab is located in South America, and the company that provided us with the gas chromatographer is the official distributor of Agilent in this area, Khymos. It was recommended by one of our close associates.

[GasMan]

I presume that the fact that you have the 7820A, you have the 12 vial version of the 7697A and not the 111 vial version. If my presumption is correct, you will have a problem as the 12 vial version will not allow the 7697A oven to go to the temperature that the method asks for.

The biggest problem in TOGA analysis is sampling, especially with methods A and C. I have no experience with method B. How are you doing your calibration?

Gasman

[vh_tc]

We do have the 111 vial set up for the 7697A HSS, as well as the auxiliary Electronic Pressure Control.
Here is the method that we set up:

--7820A—
GC Oven
Temperature set point:…………….On
Initial:……………………………………….40°C
Hold time:…………………………………3 min
Post run:……………………………………50°C

Program
#1 Rate:…………………………………….24°C/ min
#1 Valve:…………………………………..170°C
#1 Hold time:…………………………….2 min
#2 Rate:…………………………………….24°C/ min
#2 Valve:…………………………………..250°C
#2 Hold time:…………………………….4.25 min

Equilibration Time…………………….0.5 min
Max temperature:…………………….250°C
Max. Temperature override:…….Disabled
Slow fan:…………………………………..Disabled

Thermal Aux 1 (Nickel Catalyst)
Temperature (Set Point):…........350°C
Post run:…………………………………… 0°C

Column
Column pressure set point:……….22 psi
Post run:…………………………………...0 psi

Tamiz+Carboxen
-60°C-250°C (250°C): 30m x 320 µm x 0 µm
In:……………………………………………..Aux PCM A N2
Out:…………………………………………..Back detector TCD
Initial:………………………………………..40°C
Pressure:…………………………………..22psi
Flow:………………………………………….7.0522 mL/min
Average Velocity:……………………..82.734 cm/ sec
Hold Up time:…………………………….0.60434 min
Outlet pressure:………………………..0 psi

Front Detector FID
Heater:……………………………………..On 250 °C
H2 Flow:..………………………………….On 30 mL/ min
Air Flow:………………………………….. On 400 mL/ min
Make up Flow:…………………………. On 25 mL/min
Carrier Gas Flow correction:…….. Does not affect make up or fuel flow.
Flame:………………………………………. On

Back Detector TCD
Heater:……………………………………..On 250 °C
Reference Flow:.……………………….On 10 mL/ min
Make up Flow:.……………………….. On 5 mL/ min
Negative polarity:………………….….On
Filament:…………………………………..On

Valve 1
Other………………………………………..Off

PCM A
PCM A N2
Pressure set point:…………………….Off
Initial:………………………………………. 22 psi
Post run:………………………………….. 0 psi

Aux PCM A N2 ***Excluded from affecting GCsreadiness state** Supplies Column 1.

Valve Box
Heater:…………………………………….. On 120°C

Signals (#1 and #2)
Zero signal:………………………………. Zero @ 0 min.

--7697A—

Transfer line type:…………………….Fused Silica
Transfer line diameter (mm):……0.53

Temperature settings:
Oven temperature:…………………..70°C
Loop temperature:……………………150°C
Transfer line temperature:………..150°C

Timing settings:
Vial equilibration:………………………30.00 min
Injection duration:…………………….0.90 min
GC cycle time:………………………….26.00 min

Vial and loop settings
Vial size:……………………………………20
Vial shaking:……………………………..Level 5, 71 shakes/min (acceleration 260 cm/s^2)
Fill pressure:……………………………..20 psi
Loop ramp rate:………………………..199 psi/min
Loop equilibration time:……………0.25