Dilute it with nitrogen. Connect a commercial purity nitrogen gas cylinder with a flow meter to the test chamber so that you can measure the flow rate of the nitrogen. Ammonia gas also requires a flow meter. You can premix these two gases with different ratios before sending them to the test chamber. I assume that nitrogen will not interfere with the ammonia detection. Otherwise use argon.

First ammonia absorption water depends upon following

1. Ammonia absorption favors with low temperature

2. Ammonia absorption favor at high low pressure.

Following apparatus required

1. Ammonia flow meter either mass flow OR volumetric

2. Ammonia cylinder

3. Absorption chamber

4. Piping tubes with high pressure grading

5. Ammonia mask and PPE etc.

6. DM water for absorption

The Pressurized ammonia cylinder connect with Flow meter as mentioned above with high pressure grading pipe because ammonia cylinder having high pressure and outlet of flow meter connected to absorption chamber containing DM water. So Ammonia solution can be prepared as desired.

Ammonia absorption is exothermic reaction so you may remove reaction of heat by Ice box.

Thank you Krishnan Raja and Prem Baboo