A mobile drop based approach was utilized for the conductometric determination of aqueous
ammonium ion. A liquid drop was manipulated by gravity to remain or move out of a conductivity
measurement zone located on a hydrophobic path. A dilute sulfuric acid drop functioned as a micro gas
absorber. Gaseous NH3 was liberated from a sample containing NHþ
4 by adding NaOH and purged to flow
over the absorber drop. As Hþ in the absorber drop was converted to NHþ
4 , the conductivity decreased.
The rate of the conductivity decrease thus ultimately depended on the NHþ
4 concentration in the sample.
While the sample could be complex, the liberation of NH3 gas essentially freed the analyte of interest
from the matrix and allowed the use of an otherwise nonselective detector. The system was applied to
the determination of NHþ
4 in some natural waters without prior filtration; the results agreed well with
those from a manual indophenol blue method. The approach exhibited a limit of detection (LOD) of 5 μM
and a relative standard deviation (RSD) ofo5%. The mobile drop gave a constant volume of the gas
absorbing solution and provided a cost-effective and simple analytical platform