Ultrasonic nebulizer performance

In a previously mentioned work by Kirlew et al., electrophoretic separations of Se, Se As As, and dimethylarsinic acid were performed using various ultrasonic nebulizer (USN) interfaces. Using the optimized CE interface conditions and a borate run buffer at pH 8, a separation was accomplished within 10 min. Electrokinetic injections gave better sensitivities for the analytes as compared to hydrostatic sample injection. In the Kirlew study, arsenate and selenite ions had very similar migration times, but these analytes were easily resolved by the multielement capability of the ICP-MS detector. An electropherogram of this work is shown in Fig. 5. In an application to field samples. Van Holderbel ... 

Secondly, the thermal evaporation process can be performed with a conversion efficiency of 100%, by which the analyte introduction efficiency into the source may be increased from a few percent in pneumatic nebulization, through around 10-20% in ultrasonic nebulization to nearly 100%. 

A Woller, Z Mester, P Fodor. Determination of arsenic species by high-performance liquid chromatography-ultrasonic nebulization atomic fluorescence spectrometry. J Anal At Spectrom 10 609-613, 1997. 

Pillai and colleagues (67) evaluated the importance of differences in aerosol particle size on the observed therapeutic effect of inhaled insulin in rhesus monkeys. They compared the performance of two nebulizer systems, an ultrasonic nebulizer... 

Although not part of the standard ICP equipment, ultrasonic nebulizers are increasingly becoming a necessity for a high-performance ICP systems. This is particularly true for trace-level element analyses. 

The sample introduction from an LC column to ICP-MS is performed by a nebulizer. The usual nebulizers are pneumatic nebulizers, such as Meinhard, crossflow, or microconcentric nebulizers (MCNs). Additionally, there is the ultrasonic nebulizer (USN), the direct-injection nebulizer (DIN), and the hydraulic high-pressure nebulizer (HHPN). The nebuli-zation efficiency depends on nebulizer type and is typically low for Meinhard and crossflow nebulizers (only around 1—5 %, [23]), whereas it is high for the DIN and USN. 

There are many other nonstandard sample introduction devices such as laser ablation, ultrasonic nebulizers, desolvation devices, direct injection nebulizers, flow injection systems, and electrothermal vaporization, which are not described in this chapter. However, because they are becoming more and more important, particularly as ICP-MS users are demanding higher performance and more flexibility, they are covered in greater detail in Chapter 17. 

The sample introduction system can simply be re placed by a high-efficiency one, such as an ultrasonic nebulizer coupled to a desolvation system. Analyte transport efficiencies of 10-20% are typically achieved using such a system. Other high performance nebulization systems include direct injection nebulization, which introduces 100% of the sample directly into the plasma (i.e. no spray chamber is needed), thermospray, hydraulic high-pressure nebulization and monodisperse dried microparticulate injection. 

Chatterjee, A., Shibata, Y., Yoshinaga, J., and Morita, M. (2000) Detamination of arsenic compounds by high-performance liquid chromatography-ultrasonic nebulizer-high power... 

Thermospray nebulizers are somewhat expensive but can be used on-line to a liquid chromatographic column. About 10% of sample solution is transferred to the plasma flame. The overall performance of the thermospray device compares well with pneumatic and ultrasonic sprays. When used with microbore liquid chromatographic columns, which produce only about 100 pl/min of eluant, the need for spray and desolvation chambers is reduced, and detection sensitivities similar to those of the ultrasonic devices can be attained both are some 20 times better than the sensitivities routinely found in pneumatic nebulizers. 

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