MODULATED GLOW-DISCHARGE SOURCE WITH SUPPLEMENTARY MICROWAVE EXCITATION

Spectral interferences occurring in a microwave-boosted glow discharge source due to emission lines of the carrier gas and to band systems o f molecular species were investigated. A method is described which gre atly reduces such interferences, It is shown that analytical lines are strongly dependent on the current in the de discharge whereas Ar I li nes are scarcely influenced and OH bands are influenced to only a smal l extent, By modulating the de current with the microwave discharge ru nning continuously and using a lock-in amplifier, selective amplificat ion of analyte atomic lines is achieved. In this way, spectral interfe rences by Ar I lines on Fe I lines and interferences by lines in OH ba nds an the Bi I 306.771 nm and AI I 308.216 and 309.271 nm analytical lines, which occur even when using a high resolution monochromator, ar e greatly reduced.