Anionic species, flow injection analysis

Simultaneous determination of both cations and anions in acid rain has been achieved using a portable conductimetric ion-exclusion cation-exchange chromatographic analyzer.14 This system utilized the poly(meth-ylmethacrylate)-based weak acid cation exchange resin TSK-Gel OA-PAK-A, (Tosoh , Tokyo, Japan) with an eluent of tartaric acid-methanol-water. All of the desired species, 3 anions and 5 cations, were separated in less than 30 minutes detection limits were on the order of 10 ppb. Simultaneous determination of nitrate, phosphate, and ammonium ions in wastewater has been reported utilizing isocratic IEC followed by sequential flow injection analysis.9 The ammonium cations were detected by colorimetry, while the anions were measured by conductivity. These determinations could be done with a single injection and the run time was under 9 minutes. 

The second part describes the application of this automated potentiostat as an electrochemical detector for various electro-inactive anionic species nitrate (NOg ), nitrite (NOg"), sulfate (SO "), chloride (CD, etc. (1,2). The electrochemical detection involves the use of a conducting poly(3-methylthiophene) (P3MT) polymer modified platinum electrode in a flow injection analysis (FIA) mode. 

One of the first reported uses of a conducting polymer moditied electrode for the detection of anions by flow ipjection analysis (FIA) utilized poly(pyrrole) 13). Low detection limits were achieved. However, poly(pyrrole) is irreversibly oxidized in the presence of oxygen at potentials of around +1.0 volts. Poly(3-methylthiophene) does not exhibit this behavior. Therefore, poly(3-methylthiophene appeared to be a good candidate as an electrochemical detector for anionic species by FIA with electrochemical detection at an poly(3-methylthiophene) modified electrode. Also P3MT does not need to be undoped (cyded between the negative and positive detection potentials) between successive injections as many other polymer systems must. 

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