Evaluation of atomizer conditioning and pyrolysis and atomization temperature control to improve procedures based on tungsten coil atomic emission spectrometry

Abstract

Tungsten coil atomic emission spectrometry (WCAES) allows for simultaneous sensitive multielement determinations, but is limited by the lack of isothermality around the atomizer and by matrix effects. A better control of temperatures during the heating cycle, and atomizer surface modification can minimize these limitations and improve precision and accuracy. In this work, a simple, fast and effective voltamperometric method is used to determine atomizer surface temperatures in real time during all steps of a WCAES heating cycle. An optical microscope and an analytical balance are used to determine length-to-area ratios (L/A) of brand new and conditioned coils. The calculated L/A values are then used to determine atomizer surface temperatures simply by monitoring the potential across the coil with a digital multimeter. Tungsten filaments extracted from 150W, 15V microscope light bulbs are used as atomizers. Conditioned coils reach higher surface and gas phase temperatures when compared with brand new ones. Aluminum, Ca, Cr, Mn and V were used as test elements. The combination of atomizer conditioning, temperature control and optimization of pyrolysis and atomization steps resulted in higher sensitivities and better precision in most cases. Different matrices were evaluated, and less intense effects were observed in V determinations. A systematic optimization of pyrolysis temperature and time for specific matrices may improve WCAES performance for different elements. Adopting temperature-based heating programs rather than current- or voltage-based ones facilitates transferability of procedures and allows for a broader and simpler application of tungsten coil-based methods.