Ultrasonic Nebulizers USN

The transfer efficiencies for ultrasonic nebulizers (USN) are about 20% at a sample uptake of about 1 ml/min. Almost 100% transfer efficiency can be attained at lower sample uptakes of about 5-20 pl/min. With ultrasonic nebulizers, carrier gas flows to the plasma flame can be lower than for pneumatic nebulizers because they transfer sample at a much higher rate. Furthermore, reduction in the carrier-gas flow means that the sample remains in the mass measurement system for a longer period of time which provides much better detection limits. 

In addition to concentric pneumatic nebulizers that are used most frequently for the majority of atomic spectrometric systems, a range of other nebulizers also exist. Some nebulizers that are used for plasma instrumentation, e.g. direct injection nebulizers (DIN) or ultrasonic nebulizers (USN), increase... 

In ICP-MS mostly liquids are analyzed. The aqueous solution is nebulized using an effective pneumatic nebulizer (e.g., Meinhard or MicroMist nebulizer with cyclonic spray chamber, ultrasonic nebulizer (USN), microconcentric nebulizer with desolvator (e.g., Aridus or APEX), the latter for the introduction of small volumes of solution)3 as described in Section 5.1.6. 

An ultrasonic nebulizer (USN) has been found to be amenable to CE-ICP-MS interfacing [102]. The ground path was again provided by a sheath electrolyte, and separations were superior to those obtained by using a concentric nebulizer. It should be noted that the noisy background obtained by the USN may not give better detection limits than other nebulizers. 

Fig. 2 (A) The concentric nebulizer (B) The cross-flow nebulizer (C) The ultrasonic nebulizer (USN) (D) The microconcentric...

A basic understanding of the nebulizer function and the types of nebulizers is necessary to successfully interface CE to the ICP-MS. Nebulization, as previously described, is the process to form an aerosol, i.e., to suspend a liquid sample into a gas in the form of a cloud of droplets. The quality of any nebulizer is based on many different parameters including mean droplet diameter, droplet size distribution, span of droplet size distribution, droplet number density, and droplet mean velocity. There are numerous nebulizers commercially available for the use with ICP-MS systems, and their detailed description can be found elsewhere.Pneumatic designs, both concentric and cross flow, are the most popular for CE interfaces with the occasional use of the ultrasonic nebulizer (USN). Figure 2 shows some typical nebulizers. The pneumatic nebulizer is either a concentric design (Fig. 2A), where both the gas stream and the liquid flow in... 

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 ... 

Ultrasonic nebulizers (USN) operate by having the hquid sample pumped onto an oscillating quartz plate. The frequency of oscillation of the quartz plate for a commercial USN is 1.4 MHz, for example. The rapid oscillations of the quartz plate break the liquid film into an aerosol. This aerosol is of very fine, uniform droplets, unlike the aerosol from a pneumatic nebulizer. The fine aerosol contains a significant amount of solvent that must be... 

Source Data courtesy of Teledyne CETAC Technologies, Omaha, NE, www.cetac.com. Note The ultrasonic nebulizer (USN) used in both cases was the CETAC U-5000AT+. 

Descriptions of other sample introduction systems, including ultrasonic nebulization (USN), direct injection nebulization (DIN), and electrothermal vaporization (ETV), can be found in the literature [64—66]. 

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. 

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