AUTOMATION OF FLOW-INJECTION GAS-DIFFUSION ION CHROMATOGRAPHY FOR THENANOMOLAR DETERMINATION OF METHYLAMINES AND AMMONIA IN SEAWATER AND ATMOSPHERIC SAMPLES

The automation and improved design and performance of Flow Injection G as Diffusion-lon Chromatography (FIGD-IC), a novel technique for the s imultaneous analysis of trace ammonia (NH3) and methylamines (MAs) in aqueous media, is presented. Automated Flow Injection Gas Diffusion (F IGD) promotes the selective transmembrane diffusion of MAs and NH3 fro m aqueous sample under strongly alkaline (pH > 12, NaOH), chelated (ED TA) conditions into a recycled acidic acceptor stream. The acceptor is then injected onto an ion chromatograph where NH3 and the MAs are ful ly resolved as their rations and detected conductimetrically. A versat ile PC interfaced control unit and data capture unit (DCU) are employe d in series to direct the selonoid valve switching sequence, IC operat ion and collection of data. Automation, together with other modificati ons improved both linearity (R(2) > 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 an d gaseous atmospheric samples during an oceanographic research cruise.