ELECTROTHERMAL VAPORIZATION AND ULTRASONIC NEBULIZATION FOR THE DETERMINATION OF AQUEOUS SULFUR USING A KILOWATT-PLUS HELIUM MICROWAVE-INDUCED PLASMA

A study of the determination of inorganic and organic sulfur in aqueous solutions using a kilowatt-plus helium microwave-induced plasma is presented. For sample introduction, both ultrasonic nebulization (USN) and electrothermal vaporization (ETV) were investigated. Atomic emission lines in the near-infrared spectral region were chosen rather than lines in the visible region to minimize molecular emission band interferences. Detection limits and calibration plots for organic and inorganic sulfur-containing compounds were obtained. Limits of detection ranged from 3 to 5 ppm using ETV and were a factor of 10 greater using USN. Linear responses were greater than two orders of magnitude. The matrix effects of sodium, potassium, lead, nickel and cadmium were investigated with ETV sample introduction and lead, nickel and cadmium were found to affect the sulfur signals only minimally. However, significant sulfur emission depression was caused by the easily ionizable elements, sodium and potassium. Temperature programming with the ETV allowed thermal separation and determination of inorganic and organic sulfur.