Application of methane as a gaseous modifier for the determination of silicon using electrothermal atomic absorption spectrometry

For determination of silicon in aqueous solutions by electrothermal atomic absorption spectrometry methane/argon mixtures as a gaseous modifier were applied during the pyrolysis step to improve the analytical performance. The beneficial effects observed on thermal stabilization, signal enhancement and shape of absorbance signals were attributed to the thermal decomposition products of methane, which were hydrogen and carbon black (soot). Using a 5% CH4 mixture with argon, the optimized pyrolysis and atomization temperatures were 1350 °C and 2450 °C, respectively. A flushing step following the pyrolysis was mandatory to avoid background absorption and accelerated deposition of pyrolytic graphite. Characteristic masses of 50 and 30 pg were obtained for standard transversely heated graphite atomizer (THGA) tubes and end-capped THGA tubes, respectively, which were lower than with other previously applied modifiers. A limit of detection of 0.2 μg L− 1 (3 s, n = 10) has been obtained. In addition, this gaseous modifier did not contribute to contamination which often was significant when a liquid modifier solution was co-injected. The proposed method has been applied to the determination of silicon in ultrapure water, nitric and hydrochloric acids.

► CH4/Ar gas mixtures act as new modifier in the determination of Si using ET AAS. ► CH4 improved thermal stabilization, atomization efficiency and signal shape of Si. ► Optimum performance by addition of 5% CH4 during pyrolysis at 1350 °C. ► Gaseous modifier does not contribute to blank values. ► Optimized method suitable for determination of Si in ultrapure reagents.