The application of tetramethylammonium hydroxide for generating atmospheric pressure glow discharge in contact with alkalized flowing liquid cathode solutions – evaluation of the analytical performance

Abstract

The analytical performance of atmospheric pressure glow discharge (APGD) generated in contact with the alkalized flowing liquid cathode (FLC) solutions for the determination of Zn, Cd, Ag, Pb, Ga, Ca, In, Tl, and Rb by optical emission spectrometry (OES) was studied. Tetramethylammonium hydroxide (TMAH) was applied for sample alkalization. The emission spectra of APGD generated in contact with the alkalized and acidified FLC solutions were compared and discussed. The optimization of the most crucial operating conditions, i.e., the discharge current, the solution flow rate, and the TMAH concentration, was performed. Furthermore, the analytical figures of merit were determined under the optimized conditions. Finally, the impact of the presence of selected low molecular weight organic compounds (LMWOCs) as well as commonly occurring foreign cations (i.e., Al³⁺, Ca²⁺, Cr³⁺, Cu²⁺, Fe³⁺, K⁺, Mg²⁺, Mn²⁺, Na⁺, Sn²⁺, and Zn²⁺) on the analyte signals was assessed. Although some variations between the results obtained for the alkalized and acidified solutions were found, the obtained outcomes led us to a general conclusion about the pH-independence of the excitation conditions in the discharge. Nevertheless, possible analyte reactions taking place in alkalized solutions and/or with TMAH should be taken into consideration. The detection limits (DLs) of Zn, Cd, Ag, Pb, Ga, Ca, In, Tl and Rb were similar or better, compared to the ones reported for other FLC-APGD systems, and equal to 9.7, 10, 0.81, 28, 3.0, 33, 1.0, 0.83, and 0.35 μg L⁻¹, respectively. Though the developed FLC-APGD system could not be applied for the determination of certain elements (namely K, Mg, and Na), the determined DLs for the studied elements, along with relatively wide ranges of the calibration curves linearity (up to 10 mg L⁻¹) and good precision (RSD close to 2%, on average), make the proposed FLC-APGD method a suitable alternative to both other microplasma techniques as well as conventionally applied large-scale instrumentation.