Abstract: Flow injection gas diffusion-ion chromatography (FIGD-IC), is a new hyphenated technique for the simultaneous analysis of nanomolar levels of ammonia (NH3) and methylamines (MAs) in < 50 mi of marine, estuarine and freshwaters. Alkaline EDTA is added online to flowing sample to achieve a sufficiently high pH (> 12.0) needed to deprotonate > 95% of the amines to their uncharged volatile forms. In addition the reagent chelates Mg2+ and Ca2+ to prevent their precipitation as Ca(OH)(2) and Mg(OH)(2). The amines diffuse selectively across a gas-permeable microporous PTFE Goretex(R) membrane into a recirculating flow of acidic 'acceptor' in which they are reprotonated and pre-concentrated. The acceptor solution is then injected onto an ion chromatograph (IC) where NH4+ and MA cations are separated within 15 min and detected by chemically suppressed conductimetry using cyclopropylamine as an internal standard for quantification. The response of the coupled FIGD-IC system was sensitive (ca. 3-5 nM for MAs, 20-40 nM for NH3), linear (r2 = 0.99, 0-2000 nM in seawater) and precise (RSD = 1-6% at 1 µM) for all analytes. The applicability of FIGD-IC is demonstrated through laboratory analysis of NH3 and MAs in a range of natural water samples, on-board a research vessel, and through inter-comparisons with fluorimetric assay of NH3. (40 References)

Abstract: The automation and improved design and performance of Flow Injection Gas Diffusion-lon Chromatography (FIGD-IC), a novel technique for the simultaneous analysis of trace ammonia (NH3) and methylamines (MAs) in aqueous media, is presented. Automated Flow Injection Gas Diffusion (FIGD) promotes the selective transmembrane diffusion of MAs and NH3 from aqueous sample under strongly alkaline (pH > 12, NaOH), chelated (EDTA) conditions into a recycled acidic acceptor stream. The acceptor is then injected onto an ion chromatograph where NH3 and the MAs are fully resolved as their cations and detected conductimetrically. A versatile PC interfaced control unit and data capture unit (DCU) are employed in series to direct the selonoid valve switching sequence, IC operation and collection of data. Automation, together with other modifications improved both linearity (r2 > 0.99 MAs 0-100 nM, NH3 0-1000 nM) and precision (< 8%) of FIGD-IC at nanomolar concentrations, compared with the manual procedure. The system was successfully applied to the determination of MAs and NH3 in seawater and in trapped particulate and gaseous atmospheric samples during an oceanographic research cruise. (33 References)