Fused-Silica-Aperture Thermospray Sample Introduction into Axially Viewed Inductively Coupled Plasma—Atomic Emission Spectrometry

Axially viewed inductively coupled plasma–atomic emission spectrometry (ICP-AES) has encountered a resurgence in popularity over the past few years. It has been demonstrated that 5- to 10-fold improvements in limits of detection (LODs) can be obtained with axial viewing compared to conventional side-on-viewed ICP-AES. In this report, the coupling of fused-silica-aperture thermospray (FSApT)-based sample introduction with axially viewed ICP-AES is reported, in order to combine the properties of increased sample transport and reduced LODs for FSApT with the improved detection power of axially viewed ICP-AES. When FSApT was used with the standard axial torch having a large-diameter (2.3-mm) injector, high signal and background relative standard deviations (RSDs) resulted, as compared to results for pneumatic nebulization, limiting the LOD improvements obtained with FSApT. Smaller injectors (0.8-mm and 1.5-mm i.d.) allowed RSDs for FSApT that were similar to pneumatic sample introduction levels, and larger LOD improvements (10×) resulted. Data for FSApT with axially viewed ICP-AES were also compared with data for FSApT with side-on-viewed ICP-AES, and axial viewing averaged an improvement of only a factor of 2. This small level of improvement suggests that the optical system for the axial system is not optimized for use with high-performance sample introduction. On the basis of improvement factors for FSApT with side-on viewing, FSApT with axially viewed ICP-AES averages LODs that are about 73 times better than those for the conventional side-on-viewed ICP-AES with pneumatic nebulization.