HIGH-CURRENT PULSING OF A XENON ARC LAMP FOR ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY USING A LINEAR PHOTODIODE-ARRAY

A series of 300 and 500 W xenon arc lamps, normally operated at 20 and 35 A, respectively, have been pulsed as high as 300 A to achieve high er intensities in combination with a linear photodiode array detector. Initial tests without pulsing showed that the 500 W lamps are general ly more intense, but the 300 W lamps were more intense at 200 nm. With 300 A pulses, both lamps showed a factor of 500 increase in the pulse intensity over the simmer intensity. With a 0.5 ms pulse and a 3.75% duty cycle, pulsing at 300 A provided a factor of 18 increase in the i ntegrated intensity over normal d.c. operation. The increase in integr ated intensity can result in a comparable improvement in detection lim its since the instrument is detector noise limited. Both the 300 and 5 00 W lamps exhibited failure after the equivalent of 200 atomizations at 200 A. With 100 A pulses, the 300 W lamp was still operating after the equivalent of 800 atomizations. At both pulse levels, the decrease in intensity with time was accelerated as compared with d.c. operatio n. It was concluded that an improved lamp design is necessary to make pulsed operation economically attractive.