Description of the Thermospray Formed at Low Flow Rate in Thermospray Flame Furnace Atomic Absorption Spectrometry Based on High-Speed Images

Abstract

The mechanism of the thermospray formed at low flow rates using a peristaltic pump in thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) is described here for the first time. The study was based on magnified images of the thermospray formed inside the hot tube furnace by using a high-speed CMOS camera. For this purpose different image acquisition speeds were used (from 1000 to 18,000 frames/s), revealing that the thermospray obtained under such conditions is quite different from those already reported. The frames of the thermospray evolution indicate that the Leindenfrost effect plays an important role and allow us to propose a mechanism for its formation. The analysis of the images contributed to calculation of parameters related to thermospray formation, such as pulse incidence average (110 +/- 10, 320 +/- 50, and 1200 +/- 150 pulses per second) and pulse speed (6 +/- 1, 10 +/- 1, and 14 +/- 2 m s(-1)) for 0.1, 0.4, and 1.0 mL min(-1) flow rate, respectively, for both parameters. Additionally, the evaporation constant (lambda) of 10(-4) m2 s(-1) was estimated, and the present thermospray was correlated to the conventional sprays using the Sauter mean diameter (SMD) parameter, which ranged from ca. 2 to 44 microm. In order to correlate the information obtained through images with analytical parameters employing the thermospray, the sensitivities for cadmium determination at each condition (0.12, 0.11, and 0.069 s L microg(-1) for 0.1, 0.4, and 1.0 mL min(-1) flow rate, respectively) were taken into account.