NH⁴⁺ concentration in an individual droplet was determined by forming a Liesegang ring on a gelatin film containing NaB(C₆H₅ ) 4 . The NH⁴⁺ concentration (mol L ^–1 abbreviated to M) was calculated from the NH⁴⁺ amount (mol) ascertained in a droplet using pixel count measurements. The droplet volume (L) was calculated by measurement of the diameter of a droplet print on the gelatin film. For rainwater, the NH⁴⁺ concentration estimated using this method corresponded with results obtained using ion chromatography.