Dear Vasu Babu ,

In order to setup gas sensing experiment you need to first check how you can control the gas concentration, in this context there are two ways you can adjust the concentration of the desire gas; static sensing setup and dynamic sensing setup.

Generally, the dynamic mode of gas sensing is preferred. You can read the following papers for setting your experiment with ammonia gas:

see these papers:

1. Facile one-step synthesis of TiO2 microrods surface modified with Cr2 O3 nanoparticles for acetone sensor applications

2. Effect of Pt/TiO2 interface on room temperature hydrogen sensing performance of memristor type Pt/TiO2/Pt structure

3. Strongly coupled Ag/TiO2 heterojunction: from one-step facile synthesis to effective and stable ethanol sensing performances

4. Fast highly-sensitive room-temperature semiconductor gas sensor based on the nanoscale Pt-TiO2 -Pt sandwich

You can find the information about 4-point probe gas sensor based on polyaniline here: Article Investigation of contact and bulk resistance of conducting p...

In this review, you can find the references to the sensing the ammonia gas using polyaniline thin film

:Article Conducting polymers in chemical sensors and arrays