Talanta 64 (2004) 688–694 Sequential ﬂow injection analysis of ammonium and nitrate using gas phase molecular absorption spectrometry B. Haghighi ∗ , S. Farrokhi Kurd Department of Chemistry, Institute for Advanced Studies in Basic Sciences, P.O. Box 45195-159, Gava Zang, Zanjan, Iran Received 6 December 2003; received in revised form 15 March 2004; accepted 23 March 2004 Available online 11 May 2004 Abstract A ﬂow injection method on the basis of gas phase molecular absorption is described for the sequential determination of ammonium and nitrate. Two hundred microliters of sample solution is injected into the ﬂow line. For ammonium determination, the sample zone is directed to a line in which reacts with NaOH (13 M) and produces ammonia. But for nitrate determination, the sample zone is passed through the on-line copperized zinc (Zn/Cu) reduction column and produces ammonium ion and in the follows ammonia. The produced ammonia in both cases is purged into the stream of N 2 carrier gas. The gaseous phase is separated from the liquid phase using a gas–liquid separator and then is swept into a ﬂow through cell, which has been positioned in the cell compartment of an UV-Vis spectrophotometer. The absorbance of the gaseous phase is measured at 194 nm. Under selected conditions for sequential analysis of ammonium and nitrate, linear relations were found between the peak heights of absorption signals and concentrations of ammonium (10–650 g ml -1 ) and nitrate (20–800 g ml -1 ). The limit of detections for ammonium and nitrate analysis were 8 and 10 g ml -1 , respectively. The relative standard deviations of repeated measurements of 50 g ml -1 of ammonium and nitrate were 2.0, 2.9%, respectively. Maximum sampling rate was about 40 samples/h. The method was applied to the determination of ammonium in pharmaceutical products and the sequential determination of ammonium and nitrate in spiked water samples. © 2004 Elsevier B.V. All rights reserved. Keywords: FIA; GPMAS; Ammonium; Nitrate 1. Introduction Ammonia is a signiﬁcant alkaline pollutant in the atmo- sphere. Ammonia is released to the atmosphere from two main sources: soil and water. Ammonia reaches soil and water usually from industrial processes, natural or synthetic fertilizer application, animal excreta, decaying organic mat- ter, or natural ﬁxation from the atmosphere. Ammonia in soil and water can volatilize to the atmosphere or undergo micro- bial transformation to nitrate or nitrite anions, or be taken up by plants. Ammonia emitted into the troposphere is readily trapped by acidic cloud droplets and neutralizes the acidity of the droplets to form ammonium salt or reacts with acidic gases to form aerosol [1]. Therefore, the determination of ∗ Corresponding author. Tel.: +98-241-4242239; fax: +98-241-4249023. E-mail address: haghighi@iasbs.ac.ir (B. Haghighi). ammonium ion in wet deposition is important in atmospheric chemistry. Nitrate is naturally present in plants and its concentra- tion varies enormously. The nitrate content in vegetable may be inﬂuenced by factors related to the plant and the environment. Furthermore, nitrate, as well as nitrite, have been added intentionally at the curing process of certain meat products, due to their ability to inhibit the outgrowth spores of Clostridium botulinum and to impart charac- teristics color and ﬂavor to this kind of foodstuffs. The signiﬁcance of nitrate to human health is related to the fact that nitrate, after being metabolized or reduced to ni- trite, can react with secondary or tertiary amines to form N-nitroso compounds, which are potent carcinogens. Nitrite can also interact with hemoglobin inﬂuencing the oxygen transport mechanism, giving rise to methemoglobinemia [2]. The frequent presence of ammonium (or ammonia), ni- trate and nitrite in a wide variety of environmental, clinical 0039-9140/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2004.03.037