Determination of the total inorganic and ammoniacal nitrogens in water by gas-phase molecular-absorption spectrometry

Based on a vapor-liquid equiribrium of ammonia, a simplified and rapid technique was developed for the determination of the total inorganic and ammoniacal nitrogens in aqueous solution. Ammonium ion was converted into gaseous ammonia by adding a sodium hydroxide solution to a sample solution. The generated ammonia was directly introduced into a quartz cell in order to measure the molecular absorption. As for the determination of the total inorganic nitrogen, the sample solution was pretreated with titanium(III) chloride solution in order to reduce nitrate and nitrite ions to ammonium ion. The ammonia was then evolved and determined in the same manner as mentioned above. The detection limit (3 S/N) of 0.01 mu g cm(-3) for both ammonia and the total inorganic nitrogen was obtained. The calibration graph was linear up to 0.8 mu gN cm(-3) for each nitrogen species. The relative standard deviations for five replicate measurements were 3.9, 4.5 and 4.7% for 0.40 mu g cm(-3) of nitrogen present in the form of ammonium, nitrate and nitrite ions, respectively. The analytical results for some environmental and industrial water samples are presented.