Use of ultrasonic nebulizers with atomic spectrometers

As noted earlier, USNs have been employed for sample insertion into atomic spectrometers suoh as flame atomio absorption spectrometry (FAAS) [9,10], electrothermal atomic absorption speotrometry (ETAAS) [11], atomic fluorescence spectrometry (AFS) [12,13], induotively ooupled plasma-atomic emission spectrometry (ICP-AES) [14,15], inductively coupled plasma-mass spectrometry (ICP-MS) [16,17] and microwave induced plasma-atomic emission spectrometry (MIP-AES) [18,19]. Most of the applications of ultrasonic nebulization (USNn) involve plasma-based detectors, the high sensitivity, selectivity, precision, resolution and throughput have fostered their implementation in routine laboratories despite their high cost [4]. 

Except for a few laboratory-made units and some devices marketed by other firms, most applications of ultrasonic nebulization (USNn) in atomic spectrometry have been developed with two commeroial devioes from CETAC Technologies viz. the U-5000AT+ and U-6000AT+). It should be noted that these two commercial ultrasonic devices were originally designed for ICP instruments but have been used with other types of detectors [20]. 

Liquid sampies are inserted into the two commerciai USNs through the inlet tubing by pumping with, for exampie, a peristaitic pump. For this reason, these nebulizers are frequently said to operate in the continuous mode [23]. The inlet tube also allows the USN to be used as an interface between a flow system, where other steps of the analytical process can be developed, and the detector. CETAC USNs have been used in official methods of analysis such as US-EPA Method 200.15 for the determination of metals and trace elements in water by USN-ICP-AES [24]. 

The relatively high cost of commercial USNs has promoted the development of custom-made prototypes. Thus, some authors have modified commercial humidifiers to obtain batch USNs for use with atomic spectrometers. However, these custom-made nebulizers are impractical and feature a severely limited throughput. Thus, Yeon et al. used a humidifier to make a continuous USN for ICP-AES with a configuration similar to that of the CETAC units [23]. The prototype exhibited improved sensitivity relative to a pneumatic nebulizer, but also impaired precision owing to signal instability. 

The solvent where the sample is diluted is another significant variable to be optimized (in terms of the detection system, sample stability, etc.) in order to ensure the best possible operating conditions. 

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