FID: Flame Ionisation detector



Level

The flame ionization detector (FID) is an almost universal, highly sensitive detector for all organic compounds with a C-H bond.

 

 

The FID measures the conductivity of a flame. With only the usual carrier gases and the detector gases hydrogen (as fuel) and air (as oxygen supplier) present, the conductivity is almost zero. When an organic component enters the flame plasma, the flame breaks these compounds into ions and electrons and the conductivity of the flame increases.

This change in conductivity is measured using two electrodes: the flame tip is the cathode and a cylindrical collector surrounding the flame is used as the anode. After amplification, the resulting current is fed to a recorder or a data system.

The flame tip is positioned in the detector block. This block should be heated to avoid any condensation of sample components. In practice it is advised to use a temperature some 20oC above the maximum temperature of the temperature program. Temperatures below 150oC should not be used to avoid condensation of the water vapour formed in the flame.

 

 

The response of the FID depends on the number of ionizable carbon atoms in the sample components: carbon atoms bonded to hydrogen.

 

The FID responds to almost all  organic compounds with a C-H bond, and is therefore called a universal detector.

 

The FID is not sensitive towards compounds that do not contain C-H bonds. The response is more or less directly related to the number of carbon atoms. The presence of the so called hetero atoms (O, S, N, P) in an organic compound reduces the sensitivity of the FID considerably. On the other hand, if a compound contains a large number of C-atoms, the influence of a few hetero-atoms will only have a marginal effect.

 

You really understand separation?


Did you ever try to explain separation to your employees or students? Well, try no more: Lee Polite did it for you in a way which is hard to beat. We will open up one example of his whiteboard class. Click this link to watch the video. To see more, you can register here. Students can access free for one month.

Discover Chromedia

The links in the table of contents on the right lead to a vast number of educationally focused articles with videos, visualisations and animations. The first click leads you from the home page to the basics, more than enough for laboratory schools and universities, all further clicks lead you to more advanced knowledge on analytical techniques with all the details for in-depth understanding.
Chromedia is used globally by numerous universities and industries, our authors are ranked as the finest teachers in the world. So go ahead and discover Chromedia by getting a 30 days subscription, which is free for students.

Chromedia partners:

- Our expert team
- The Analytical Scientist
- American Chemical Society
- Wiley:
- separationsNOW 
- spectroscopyNOW

Register to get full access

For full access to Chromedia: click here for a paid subscription.

Click here to go to the Home-page
Home ->