MECHANISMS OF CHLORIDE INTERFERENCES IN ATOMIC-ABSORPTION SPECTROMETRY USING A GRAPHITE-FURNACE ATOMIZER INVESTIGATED BY ELECTROTHERMAL VAPORIZATION INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY .2. EFFECT OF SODIUM-CHLORIDE MATRIX AND ASCORBIC-ACID CHEMICAL MODIFIER ON MANGANESE

The interference by sodium chloride with the atomization of manganese in electrothermal atomic absorption spectrometry (ETAAS) has been investigated using electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS). The ETV-ICP-MS technique allows direct observation of the signals of manganese along with matrix components during both the pyrolysis and the atomization step of ETAAS, and thereby allows differentiation between the manganese loss from the furnace during pyrolysis and the loss due to formation of molecular species during atomization. The mechanism of interference by sodium chloride is independent of the pyrolysis temperature. The loss of manganese does not occur during pyrolysis, but is due to vapour-phase interference caused by the formation of manganese chloride during atomization. The addition of ascorbic acid, as a chemical modifier, removes the interference by sodium chloride at all pyrolysis temperatures investigated (450-1100-degrees-C). In ETV-ICP-MS, when the sample of manganese contains only the sodium chloride matrix, the chloride appearance time coincides with that of the manganese suggesting a gas-phase interference mechanism. The addition of ascorbic acid promotes an early release of chloride during the atomization cycle. The chloride appearance temperature is approximately 250-degrees-C lower than that of the manganese (almost-equal-to 1200-degrees-C). In ETAAS this difference in the two temperatures reduces the amount of residual chloride left in the graphite furnace at the manganese appearance time, thereby eliminating the interference of sodium chloride with manganese.