4

I have some questions about the sensitivity of potassium iodide starch paper.

Patients with asthma caused by allergic airway inflammation have high levels of nitric oxide ($\ce{NO}$) in exhaled breath. This is usually measured with chemiluminescence analyzers by measuring the light generated by a chemical reaction of $\ce{NO}$ with ozone. This technique has high sensitivity, and NO can be accurately measured in the parts per billion (ppb) range.

This above method requires a complicated apparatus.

I am now considering an alternative method.

When NO is exposed to oxygen, it is converted into nitrogen dioxide:

$$ \ce{NO + O2 \rightarrow 2 NO2} $$

When wet potassium iodide starch paper is exposed to an oxidizing gas, such as $\ce{NO2}$, its color changes to purple or blue. The intensity of the color depends on the concentration of the oxidizer.

My questions are:

  • If, at room temperature, 1 litre of exhaled air is enclosed in a container, inside of which a wet potassium iodide starch paper is placed, would that paper ever get a blue tint if the NO concentration in the exhaled air is only 25 ppb (parts per billion)?

  • How long would it take?

  • Would it help if the volume was bigger, for example 10 litres?

  • Could one improve the sensitivity in some simple way?

Magnus
  • 141
  • 5
  • 1
    If nitric oxide and oxygen reacted quickly there wouldn't be any nitric oxide in an exhaled breath. The body doesn't get all the oxygen. // Is just a qualitative test sufficient? I'd guess quantitative data is wanted. – MaxW Mar 05 '17 at 17:03
  • MaxW: If I understand correctly, the chemiluminescence analyzers depend on a quick flow of exhaled air so that the NO2 is freshly "produced" in the apparatus (by contact between NO and O3, ozone). Some of the freshly produced NO2 then, by changing exitation state, emitts light, which is measured. In my method though, it does not matter if the NO2 is old or not. Regarding quantitativ/qualitative: I would like it to be somewhat quantitative, but high resolution is not required. – Magnus Mar 05 '17 at 17:51
  • MaxW: I should perhaps add that my idea with the container method I describe, is that NO will eventually be converted to NO2 (by contact with the oxygen in the air), and that this NO2 then reacts with the wet paper. – Magnus Mar 05 '17 at 18:03
  • 1
    At link it says: At room temperature, NO combines with molecular oxygen to form NO2 at a rate that is dependent on the oxygen concentration and the square of the NO concentration. Therefore, oxidation is extremely slow at very low concentrations. This finding has important consequences for the pathophysiological and pharmacological relevance of NO in the respiratory tract. So my method will not work well becuase of the extremely low concentrations. That could perhaps be fixed by oxidizing with potassium permanganate. – Magnus Mar 06 '17 at 16:48
  • Correct. The point being that ozone is an extremely powerful oxidizer and will react very quickly with NO. – MaxW Mar 06 '17 at 16:51

0 Answers0