Straightforward way to enhance robustness in ultrasonic nebulization-axial view inductively coupled plasma optical emission spectrometry via an additional N2 gas stream

Abstract

In the present study a low flow of N2 is mixed with the aerosol produced by ultrasonic nebulization (USN) prior analysis using inductively coupled plasma optical emission spectrometry (ICP OES). The foreign gas is added for improving plasma characteristics in axially-viewed ICP. By computing the Mg ionic to atomic ratio (plasma robustness) it was concluded that N2 dissociates closer to the load coil when USN is used as sample introduction system. The maximum emission intensity of Mg(II) for pneumatic nebulization (PN) was observed at 11mm from the load coil while it was 8mm for USN, indicating earlier aerosol desolvation, atomization and excitation processes in the ICP. Emission profiles of Ar(I) 415.861nm, Ba(II) 486.601nm and Ba(II) 233.527nm indicated that metastable Ar species are overpopulated in the ICP under the N2 flow. Copper and manganese ionic lines with energy close to 16eV (Ar ionization) were monitored to evaluate spatially dependent charge-transfer reaction along the ICP axis in the presence and absence of the N2 flow. The Cu(II) signal profiles indicated abundance of Ar+ species at low distances from the load coil when N2 was added. On the other hand, differences were not observed at longer distances from the load coil for both plasmas (mixed-gas and pure Ar-ICP). The calculated limits of detection (LODs) for both plasmas had the same order of magnitude. Analysis of certified reference samples demonstrated that the accuracy was preserved by adding the low flow of N2. It was concluded that adding a low flow of N2 to the aerosol produced by USN is a simple way to increase plasma robustness, which is usually lower than that achieved using conventional PN.