What is best detector for free chlorine/ammonia analysis?

[jerry_76]

I have a Varian GC 3800 with FID, but should start working on analysing the free chlorine and free ammonia concentration in air. Since I can't afford a new system right now, I'm thinking about upgrading the one I have by installing another detector in this GC. I checked the forum and it seems PID and TCD detectors should work. The concentrations aren't that high, less than 1% vol. Anyone who has been working with such analysis and can recommend anything?

[chromatographer1]

TCD should work for either analyte. But talk about separate ends of the pH meter !

Chlorine can damage metal surfaces of the detector. Often these parts are gold plated for durability. Something to think about.

For trace amounts, an ECD for chlorine and a PID for ammonia work well.

Good luck with your work,

Rod

[jerry_76]

Thank you. Would this mean TCD is equally sensitive to both gases? For some reasons most of people I have asked so far recommend PID. Plus, I've just found out this particular model can't have two detectors installed at the same time so it looks like I will have to look for another system - this time with the suitable pair of detectors...

[chromatographer1]

I have no experimental data to make any claims.

If you can determine the thermal conductivity of each gas you can calculate the response of each.

OR

You could simply buy one detector to measure both gases.

Ask AIC and talk with Matthew, or talk to Valco about installing their pHID. Then you could visit GOW-MAC and compare their HID.

The good news is the detectors mentioned should have a similar sensitivity for both gases and a sensitivity to both which compares to an FID's response to hydrocarbons.

best wishes,

Rod

[AICMM]

jerry_76,

Posting my standard disclaimer that I make an HID/AID detector, I would say that you could measure both of these with an HID and you can certainly measure the ammonia with the AID. You can do ammonia (IP = 10.1) with PID as well but it will want to interact with the window. Advantage of AID is that there is no window to get fogged since it is a flow through detector. I work with a company that builds this application for process analysis.

Chlorine (IP = 11.5) cannot be done by AID so you would have to revert to either HID or ECD. I have seen a reference or two about chlorine by ECD (very interested in this topic - especially at low levels) but I have not tried it yet. Certainly it will be detected by HID since this will do almost all GC' able compounds. The issue here will be getting sufficient separation of the chlorine from other constituents since the HID will see the air, water, etc... that you inject. Not to mention Rod's comments about sticky compounds....

Finally, the 3800 should support multiple detectors so you comment there is a bit puzzling. The good news is, switching between AID and HID with my detector is relatively easy and you can use your current FID electronics to boot.

Sorry for the long winded reply. You can contact me at aicmm at flash.net for more discussion if you would like.

Best regards,

AICMM

[jerry_76]

Thank you guys very much for all the info and recommendations. Now I need to check the prices for different detectors - unfortunately money is often the most limiting factor in analysis

AlCMM, you are correct, and I wrote wrong number - it is 3900 model. The info I got was from different GC suppliers, things got a bit complicated after Agilent bought Varian - I was also told even though Varian is a part of Agilent, it is Bruker which got the GC servicing (?). As for Cl2 levels, I found this paper:
http://pubs.rsc.org/en/content/articlel ... 9963300061

seems like something I want to do; the lowest detection limit was 3ppm, the range I'm interested in. This is done by TCD though; separation with PoraPLOT. I found also some info on gold-plated TCD, probably would do against corrosion.
What may be extra challenging is that the air stream with the gases to be analysed should be wetted, so this I guess would kill PID (?). Would water be the problem for HID? I'm wondering now about some water trap which would not interact with gases, but this may not be easy to find.