Application note on gas
chromatography optimization.
Introduction
In routine chromatographic separations, it is of crucial importance to keep the total
run time short, without jeopardizing necessary chromatographic resolution. This
application note shows an example on how this can be achieved with the MultiSimplex
software.
The application note is based on a study performed in a contract laboratory.
Problem
To reduce run time in an analytical method for determination of PCB, with HRGC/ECD.
Control variables
Four control (experimental) variables were used. The settings are specified in the
table below.
| |
Ref. value |
Step size |
| Inital temperature, °C |
190 |
10 |
| Initial time, min |
4 |
2 |
| Temperature gradient, °C/min |
6 |
2 |
| Maximum oven temp., °C |
300 |
10 |
Response variables
Three different response variables were used to characterize the outcome. The settings
are specified in the table below.
| |
Objective |
Low limit |
High limit |
Influence |
| Resolution 1 |
Maximization |
1 |
2 |
Medium |
| Resolution 2 |
Maximization |
1 |
2 |
Medium |
| Run time, min |
Minimization |
25 |
50 |
High |
The shape of the membership functions was proportional for all three
responses.
Results
The results from the 10 optimization trials are shown in the table below.
| Initial temp. |
Initial time |
Temp. gradient |
Max temp. |
Rs 1 |
Rs 2 |
Run time |
| °C |
min |
°C/min |
°C |
|
|
min |
| 185 |
5.0 |
5.0 |
295 |
1.201 |
1.959 |
45.06 |
| 195 |
5.0 |
7.0 |
295 |
1.119 |
1.811 |
39.16 |
| 195 |
5.0 |
5.0 |
305 |
1.226 |
2.020 |
39.69 |
| 185 |
3.0 |
7.0 |
305 |
1.135 |
1.870 |
34.82 |
| 195 |
3.0 |
5.0 |
295 |
1.182 |
1.992 |
41.10 |
| 200 |
3.0 |
7.0 |
305 |
1.115 |
1.820 |
32.73 |
| 208 |
2.0 |
8.0 |
310 |
1.043 |
1.725 |
28.01 |
| 197 |
1.5 |
5.5 |
313 |
1.125 |
1.880 |
32.68 |
| 198 |
2.8 |
7.8 |
322 |
1.080 |
1.735 |
27.79 |
| 199 |
2.6 |
9.1 |
335 |
1.016 |
1.698 |
24.18 |
In this study the total run time was shortened from 45 to 25 minutes, see figures
below, without any significant loss of resolution.
Click here to view run time vs. trial number
Click here to view chromatogram before optimization.
Click here to view chromatogram after optimization.
Conclusion
The MultiSimplex methods are quick and easy to apply for optimization of gas
chromatographic methods. A systematic optimization is achieved in a limited number of
trials. You proceed in the desired direction and get off when you are satisfied.
|
