1.1. Instruments and accessories

The instrumentation consisted of an atomic absorption spectrometer fitted with a flame atomizer (Perkin-Elmer, model AAnalyst 100), a hollow cathode Cu lamp (Л = 324.8 nm, slit width = 0.7 nm, i = 15 mA), with an air/acetylene (4:2 ratio) flame gas mixture, and back­ground correction using a deuterium lamp. Other equipment comprised an analytical bal­ance (Sartorius BL 2105) and a peristaltic pump (Ismatec, model ICP 8).

The TS-FF-AAS assembly employed a Rheodyne RE9725 injection valve, PEEK tubing, and a ceramic thermocouple insulator capillary (OMEGATITE450, OMEGA, USA). The capillary wascomposed of Al2O3(>99.8%), resistant to temperatures up to 1900 °C, with 0ext= 1.6 mm and two orifices with 0int = 0.4 mm (this capillary provided better results than a stainless steel HPLC capillary, with less noise in the absorbance signal). The atomization tubes were a metal tube composed of Ni-Cr super-alloy (Inconel, length 100 mm, 0int = 10.0 mm, 0ext = 12.0 mm, 6 orifices with 0 = 2.5 mm, perpendicular to an orifice with 0 = 2.0 mm), and a ceramic tube (99.9% Al2O3, length 100 mm, 0int = 10.0 mm, 0ext = 12.0 mm, 6 orifices with 0 = 2.5 mm, perpendicular to an orifice with 0 = 2.0 mm).

Data acquisition employed the software MQDOS (Microqrnmica), and the absorbance val­ues were proportional to the height of the transient signals.

The temperature in the interior of the atomization tube was measured in two ways. The first method employed a thermocouple with an earthed connection, positioned adjacent to the metal tube, oriented towards the orifice where the ceramic capillary used to introduce the sample into the atomizer was located. The temperature measured for the metal tube was 983 ± 1°C. Secondly, the thermocouple with connection exposed was positioned adjacent to the ceramic capillary within the tube, where a temperature of between 1030 °C and 1060°C was measured, at which the tube glowed ruby-red above the flame [16,40,45,54].

When 50 |jL of HNO3 (~0.1 mol L-1) was injected at a rate of approximately 1.5 mL min-1,there was a temperature reduction of around 50°C, due to cooling of the tube by the solution, followed by a rapid return to the maximum temperature range.