CONTINUOUS-FLOW AND FLOW-INJECTION HALOGEN GENERATION FOR CHLORIDE, BROMIDE AND IODIDE DETERMINATIONS BY MICROWAVE-INDUCED PLASMA-ATOMIC EMISSION-SPECTROSCOPY

Continuous flow generation of molecular, volatile halogens (I2, Br2, Cl2), based on chemical oxidation, is a very useful sample introduction technique in microwave induced plasma atomic emission spectrometry (MIP-AES), which provides improved transport efficiency for sample to plasma, thus enhancing the sensitivity of the determinations. Optimum conditions for halogen generation/MIP detection (chemical oxidant system, type and size of gas-liquid separator, influence of halide concentration and MIP instrumental parameters) are discussed with an aim to improving both the intensity of the emission signal, and its stabilization time for I-, Br- and Cl- determinations. For continuous halogen generation, the influence on the MIP emission signal (and its stabilization time) of (i) the size and form of the gas-liquid separator, and (ii) the atomic weight and concentration of the halogen itself has been investigated in detail. Even for optimum conditions, iodine generation/transport to the plasma is rather slow (i.e. 4 min for signal stabilization). The use of flow injection analysis (FIA) however, allows an increase of the attainable sample throughput by up to 60 samples/h, but at the expense of a slight loss of sensitivity (20-30%) compared with continuous flow generation. The influence on the MIP signal that was observed with FIA parameters (such as the injected sample volume and flow rates of the different reagents) is discussed.