Optimization of the thermal modulation in

comprehensive two-dimensional gas-chromatography Authors:

Gianluca Stani¹, Armando Miliazza¹

¹SRA Instruments Italia S.r.l., Viale Assunta 101, 20063 Cernusco sul Naviglio (MI), Italy - e-mail: info@srainstruments.com – stani@srainstruments.com

Introduction

The two-stage thermal modulator is one of the most efficient

device to produce sharp modulated peaks in GCXGC [1][2][3].

The thermal modulation uses hot and cold jets of gaseus nitrogen

to continuously and efficiently trap and inject portions of eluting

peaks from the primary column into the secondary column. The

thermal processes are determined by the nitrogen cold flow and

the temperature/time of the hot pulse, furthemore a high gas and

liquid nitrogen cosumption is requested for operation. In order to

obtain an optimal modulation ratio of 3-4 [4], the cold jet flow [5]

and the activity time of the hot jet pulse must change during the

GC run for such application that requires the simultaneous

determination of either very volatile compounds and high boiling

compounds. The optimized combination of these two parameters

improve the modulator operation: the efficiecy of the modulation

in terms of preventing break-through of the high volatility

compounds and avoid the trapping for semi-volatile compounds

causing increase contribution on the modulation ratio and peak

tailing.

In this experiment an independent programmable device is used

as accessory for the thermal modulator to control, with a mass

flow controller, the cold flow during and after the GC run. An

additional feature controls and programs the hot pulse valve

activity.

An hydrocarbons mixture with wide range of boiling compounds

was used to demostrate the contribution of the modulator on the

modulated-peaks and how an optimized combination of cold

flow and hot pulse time jet can allow a proper modulation.

Experimental

GC Agilent Technologies mod. 6890N

Inlet: Split/Splitless with EPC, Pressure: 205KPa He const flow

Column 1: HP-1, 30 mt x 0.32 mm ID df: 0.25 µm

Column 2: BPX-50, 2.5 mt x 0.1 mm ID df: 0.1 µm

Oven: 45°C (5min) to 320°C, rate 2.5°C

2nd Oven: 60°C (5min) to 340°C, rate 2.5°C

Software MSD Agilent Chemstation

Zoex KT-2005 GCXGC Dual Stage Thermal Modulator

Zoex GC-Image Software

Hot Jet temp.: 145°C (5min) to 320°C, rate 2.5°C

Modulation Period: 4 sec and 8 sec

Modulation tube: 2 mt X 0.18 mm ID uncoated fused silica

Liquid Nitrogen cooling system

Bronkhorst Hi-Tech Mass Flow Controller 0-30 Nlt/min Nitrogen

Programmable Logic Controller Horner

qMSD 5975B Inert Agilent Techonologies

Fast Scan 45-420 amu

Sample: nC5-nC28 p/n 25950.200 Analytical-Controls BV, NL

Cold Jet conditions tested

and their effect on the modulation

•STAND-BY-FLOW: a minimum N2

flow is maintained between each

run or after the modulation time

within an analysis. It reduces the N2

gas flow from operation rate (flow

30-15 lt/min) to about 3 lt/min,

without transfer-line iceing.

Reduced use of gas & liquid N2.

•N2 COLD FLOW controlled by MFC,

reproducible run by run

•PROGRAMMABLE N2 COLD FLOW allows proper trapping of a wide

range of volatility components in a

sample: high rate for very volatile

and low rate for heavy compounds

within a run.

Cold Jet

*Cold Jet: immobilize

and trap the compounds by rapid cooling

2 5 .0 0 2 5 .2 0 2 5 .4 0 2 5 .6 0 2 5 .8 0 2 6 .0 0 2 6 .2 0 2 6 .4 0

5 0 0 0 0

1 0 0 0 0 0

1 5 0 0 0 0

2 0 0 0 0 0

2 5 0 0 0 0

3 0 0 0 0 0

3 5 0 0 0 0

4 0 0 0 0 0

4 5 0 0 0 0

5 0 0 0 0 0

5 5 0 0 0 0

6 0 0 0 0 0

T im e -->

A b u n d a n c e

T IC : C 9 C 2 5 R A T E 8 M O D 4 S _ 3 .D \ d a ta .m s

Peak width at baseline 9.12s with 4 sec

modulation = 2.28 theorical modulated

peaks

Un-modulated n-C25

2 5 . 5 0 2 5 . 6 0 2 5 . 7 0 2 5 . 8 0 2 5 . 9 0 2 6 . 0 0 2 6 . 1 0 2 6 . 2 0 2 6 . 3 0 2 6 . 4 00

5 0 0 0 0

1 0 0 0 0 0

1 5 0 0 0 0

2 0 0 0 0 0

2 5 0 0 0 0

3 0 0 0 0 0

3 5 0 0 0 0

4 0 0 0 0 0

4 5 0 0 0 0

5 0 0 0 0 0

5 5 0 0 0 0

6 0 0 0 0 0

6 5 0 0 0 0

7 0 0 0 0 0

7 5 0 0 0 0

8 0 0 0 0 0

8 5 0 0 0 0

9 0 0 0 0 0

9 5 0 0 0 0

1 0 0 0 0 0 0

1 0 5 0 0 0 0

1 1 0 0 0 0 0

1 1 5 0 0 0 0

1 2 0 0 0 0 0

1 2 5 0 0 0 0

1 3 0 0 0 0 0

1 3 5 0 0 0 0

1 4 0 0 0 0 0

1 4 5 0 0 0 0

T i m e - - >

A b u n d a n c e

T I C : C 9 C 2 5 R A T E 8 M O D 4 S _ 1 . D \ d a t a . m s

2 5 .5 02 5 .5 52 5 .6 02 5 .6 52 5 .7 02 5 .7 52 5 .8 02 5 .8 52 5 .9 02 5 .9 52 6 .0 02 6 .0 52 6 .1 00

2 0 0 0 0 0

4 0 0 0 0 0

6 0 0 0 0 0

8 0 0 0 0 0

1 0 0 0 0 0 0

1 2 0 0 0 0 0

1 4 0 0 0 0 0

1 6 0 0 0 0 0

1 8 0 0 0 0 0

2 0 0 0 0 0 0

2 2 0 0 0 0 0

2 4 0 0 0 0 0

2 6 0 0 0 0 0

T im e -->

A b u n d a n c e

T IC : C 9 C 2 5 R A T E 8 M O D 4 S _ 5 .D \ d a ta .m s

7 modulations vs 2.28 theorical modulations = Modulator trapping effect

nC25 @ 6 lt/min cold flow 2-D view

0.25 sec Hot Pulse Time

nC25 @ 3.6 lt/min cold flow

0.25 sec Hot Pulse Time

2-D view

2+ modulations vs 2.28 theorical modulations = Any modulator contribution

Hot Jet conditions tested

and their effect on the modulation

Hot Jet

•VALVE PULSE & POWER controlled externally from the GC

•HOT PULSE TIME PROGRAMMABLE for proper carryover of heavy

compounds

•TWO PULSE TIME programmable

within a run

•TWO MODULATION PERIOD TIME programmable within a run

2 5 .0 0 2 5 .2 0 2 5 .4 0 2 5 .6 0 2 5 .8 0 2 6 .0 0 2 6 .2 0 2 6 .4 0

5 0 0 0 0

1 0 0 0 0 0

1 5 0 0 0 0

2 0 0 0 0 0

2 5 0 0 0 0

3 0 0 0 0 0

3 5 0 0 0 0

4 0 0 0 0 0

4 5 0 0 0 0

5 0 0 0 0 0

5 5 0 0 0 0

6 0 0 0 0 0

T im e -->

A b u n d a n c e

T IC : C 9 C 2 5 R A T E 8 M O D 4 S _ 3 .D \ d a ta .m s

Un-modulated n-C25

Peak width at baseline 9.12s with 4 sec

modulation = 2.28 theorical modulated

peaks

2 5 . 5 0 2 5 . 6 0 2 5 . 7 0 2 5 . 8 0 2 5 . 9 0 2 6 . 0 0 2 6 . 1 0 2 6 . 2 0 2 6 . 3 0 2 6 . 4 00

5 0 0 0 0

1 0 0 0 0 0

1 5 0 0 0 0

2 0 0 0 0 0

2 5 0 0 0 0

3 0 0 0 0 0

3 5 0 0 0 0

4 0 0 0 0 0

4 5 0 0 0 0

5 0 0 0 0 0

5 5 0 0 0 0

6 0 0 0 0 0

6 5 0 0 0 0

7 0 0 0 0 0

7 5 0 0 0 0

8 0 0 0 0 0

8 5 0 0 0 0

9 0 0 0 0 0

9 5 0 0 0 0

1 0 0 0 0 0 0

1 0 5 0 0 0 0

1 1 0 0 0 0 0

1 1 5 0 0 0 0

1 2 0 0 0 0 0

1 2 5 0 0 0 0

1 3 0 0 0 0 0

1 3 5 0 0 0 0

1 4 0 0 0 0 0

1 4 5 0 0 0 0

T i m e - - >

A b u n d a n c e

T I C : C 9 C 2 5 R A T E 8 M O D 4 S _ 1 . D \ d a t a . m s

nC25 @ 6 lt/min cold flow

0.25 sec Hot Pulse Time

7 modulations vs 2.28 theorical modulations = Modulator trapping effect

2 5 .5 02 5 .5 52 5 .6 02 5 .6 52 5 .7 02 5 .7 52 5 .8 02 5 .8 52 5 .9 02 5 .9 52 6 .0 00

2 0 0 0 0 0

4 0 0 0 0 0

6 0 0 0 0 0

8 0 0 0 0 0

1 0 0 0 0 0 0

1 2 0 0 0 0 0

1 4 0 0 0 0 0

1 6 0 0 0 0 0

1 8 0 0 0 0 0

2 0 0 0 0 0 0

2 2 0 0 0 0 0

T im e -->

A b u n d a n c e

T IC : C 9 C 2 5 R A T E 8 M O D 4 S _ 7 .D \ d a ta .m s

*Hot Jet: flash heating

to launch the trapped

compounds

nC25 @ 6 lt/min cold flow

0.50 sec Hot Pulse Time

2+ modulations vs 2.28 theorical modulations = Any Modulator contribution