Ultrasonic nebulisation

A wealth of other data can be obtained from the use of US as an analytical method. Sonoelectrochemical analysis of trace metals [220] and organic compounds [221] has been reported. Ultrasonic atomisation [222] is used in many fields where a dispersion of liquid particles is required. Ultrasonic nebulisation (USN) is used for analysis of organic solutions in conjunction with ICP-AES/MS [223,224] and MIP-AES [225],... 

As the vast majority of LC separations are carried out by means of gradient-elution RPLC, solvent-elimination RPLC-FUR interfaces suitable for the elimination of aqueous eluent contents are of considerable use. RPLC-FTTR systems based on TSP, PB and ultrasonic nebulisa-tion can handle relatively high flows of aqueous eluents (0.3-1 ml.min 1) and allow the use of conventional-size LC. However, due to diffuse spray characteristics and poor efficiency of analyte transfer to the substrate, their applicability is limited, with moderate (100 ng) to unfavourable (l-10pg) identification limits (mass injected). Better results (0.5-5 ng injected) are obtained with pneumatic and electrospray nebulisers, especially in combination with ZnSe substrates. Pneumatic LC-FI1R interfaces combine rapid solvent elimination with a relatively narrow spray. This allows deposition of analytes in narrow spots, so that FUR transmission microscopy achieves mass sensitivities in the low- or even sub-ng range. The flow-rates that can be handled directly by these systems are 2-50 pLmin-1, which means that micro- or narrow-bore LC (i.d. 0.2-1 mm) has to be applied. 

In ICP-AES and ICP-MS, sample mineralisation is the Achilles heel. Sample introduction systems for ICP-AES are numerous gas-phase introduction, pneumatic nebulisation (PN), direct-injection nebulisation (DIN), thermal spray, ultrasonic nebulisation (USN), electrothermal vaporisation (ETV) (furnace, cup, filament), hydride generation, electroerosion, laser ablation and direct sample insertion. Atomisation is an essential process in many fields where a dispersion of liquid particles in a gas is required. Pneumatic nebulisation is most commonly used in conjunction with a spray chamber that serves as a droplet separator, allowing droplets with average diameters of typically <10 xm to pass and enter the ICP. Spray chambers, which reduce solvent load and deal with coarse aerosols, should be as small as possible (micro-nebulisation [177]). Direct injection in the plasma torch is feasible [178]. Ultrasonic atomisers are designed to specifically operate from a vibrational energy source [179]. 

Berman et al. [735] and McLaren [738] attempted to determine the foregoing nine elements in seawater by a combination of ion exchange preconcentration on Chelex 100 [129,736-738], and ICP-AES using ultrasonic nebulisation. Preconcentration factors of between 25 and 100 were obtained by this technique. 

Warnken et al. [956] have reported an online preconcentration - ultrasonic nebulisation - ICP-MS method that achieved detection limits of 0.26,0.86,1.5, 10, and 0.44 ng/1 for manganese, nickel, copper, zinc, and lead in seawater. This online preconcentration method compares favourably to the state of-the-art off-line methods. 

The on-line interface of flow manifolds to continuous atomic spectrometric detectors for direct analysis of samples in liquid form typically requires a nebuliser and a spray chamber to produce a well-defined reproducible aerosol, whose small droplets are sent to the atomisation/ionisation system. A variety of nebulisers have been described for FAAS or ICP experiments, including conventional cross-flow, microconcentric or Babington-type pneumatic nebulisers, direct injection nebuliser and ultrasonic nebulisers. As expected, limits of detection have been reported to be generally poorer for the FIA mode than for the continuous mode. 

M. Grotti, E. Magi and R. Frache, Multivariate investigation of matrix effects in inductively coupled plasma atomic emission spectrometry using pneumatic or ultrasonic nebulisation, J. Anal. At. Spectrom., 15(1), 2000, 89-95. 

Wang, S.R. and Jiang, S.J. (1991) An ultrasonic nebuliser as the sample introduction device for high-performance liquid-chromatography combined with inductively coupled plasma atomic emission spectrometry./. Chinese Chem. Soc., 38, 327-332. 

While possible to obtain satisfactory products with the pneumatic nebuliser, the experimental difficulties due to clogging and the strong dependence on many interrelated variables indicated that another type of atomiser should be investigated. An ultrasonic nozzle, in which high frequency electrical energy is converted into vibratory mechanical motion at the same frequency, was therefore examined. The ultrasonic nozzle was chosen because the average droplet size was small, about 25 microns, and... 

K. L. Yang, S. J. Jiang, Determination of selenium-compounds in urine samples by liquid chromatography-inductively coupled plasma-mass spectrometry with an ultrasonic nebuliser, Anal. Chim. Acta, 307 (1995), 109-115. 

Falter, R., Wilken, R.D. Determination of carboplatinum and cisplatinum by interfacing HPLC with ICP MS using ultrasonic nebulisation. Sci. Total Environ. 225, 167-176 (1999)... 

Modern nebulisers for domestic and hospital use generate aerosols continuously for chronic therapy of respiratory disorders. A Venturi-type system is shown in Fig. 9.48(a) and an ultrasonic device in Fig. 9.48(b). The particle size distribution and hence efficiency of such... 

Figure 9.48 Schematic diagrams of (a) a Venturi-type nebuliser and (b) an ultrasonic nebuliser.

Varner A, Busse W 1996 Are you undertreating inflammation in asthma Journal of Respiratory Disease 17 656-668 Viel L 1999 Therapeutic efficacy of inhaled fluticasone propionate in horses with chronic obstructive pulmonary disease. In Proceedings of the 45th American Association of Equine Practitioners Annual Convention, Albuquerque, NM, pp. 306-307 Votion D, Ghafir Y, Munsters K et al 1997 Aerosol deposition in equine lungs following ultrasonic nebulisation versus jet aerosol delivery system. 

There are several different types of nebulisers available from local instrument suppliers (Figure 2.9). They are expensive due to the inert material used and precise engineering required to make them. The size of the hole for the gas outlet must be big enough to sustain the very high pressure required to force the sample solution to move violently and rapidly throughout the spray chamber and small enough to create a very high pressure. The two most commonly used nebulisers are pneumatic and ultrasonic. 

Figure 2.9 Overview of sample introduction methods and hyphenated techniques used in ICP-AES. (A) Pneumatic concentric (sometimes called the Meinhard nebuliser) (B) Babington (C) fritted disc (D) Hildebrand nebuliser (E) cross flow (G) standard ultrasonic nebuliser for aqueous and non-aqueous solvents (H) electro-thermal graphite ( ) electro-thermal carbon cup (K) graphite tip filament (L) laser ablation (M) hydride generation (P) flow injection...

The membrane desolvator is very effective in reducing the solvent loading further when used in conjunction with the ultrasonic nebuliser. This will allow a range of solvents to be used for ICP-AES that would otherwise quench the plasma by almost totally removing the solvent from the sample and only allowing the dried particles containing the elements of interest to enter the source. 

Figure 2.19 Schematic diagram of the percentage of droplet mist successfully going to the plasma source. Line (a) is 2% for standard nebulisers and line (b) is 20% for ultrasonic nebulisers...

CETAC Technologies. Ultrasonic Nebulisation of Liquid Samples for Analytical ICP Atomic Spectroscopy, South Shields CETAC. 

Slurry solutions can be nebulised and introduced as an aerosol to the plasma source similar to that for clear solutions and the solvent containing the particles also assists in transporting them for elemental analysis. Care must be taken in avoiding the tendency to form agglomerates and samples must be kept stirred or shaken using an ultrasonic bath prior to nebulisation. Samples of products containing very small particles, e.g. fillers in... 

Typical plastics used in electronic and electrical appliances are polyethylene, polypropylene or polyethene terphthalate, and these are studied here as part of the RoHS requirement for the presence of toxic metals. This method is to show that analysis of these plastics used in electrical and electronic equipment is essential, especially if the origin of the plastic is unknown and the supplier is unable to state whether or not they are free of these metals. The metals are measured against calibration standards curves for each metal and may also include additional attachments for improving limits of detection such as ultrasonic nebulisers for Cd, Pb and Cr and the cold trap method for Hg. 

All samples are analysed for Cd, Pb, Cr against standard calibration curves prepared from 0.0, 0.5, 2.5, 5.0 and lO.Oppm of each metal in 0.25 M HNO3. The ultrasonic nebuliser is used for the determination of Cd, Pb and Cr while the continuous cold vapour trap method is used for the determination of Hg. The recovery of each metal is determined for each metal. The Hg forms the vapour ion of the metal in solution after reduction with SnCl2(Sn2+ + Hg2+ > Sn4+ + Hg°) and the metallic mercury is swept to the plasma torch by the argon gas. This method is sensitive for Hg and has the advantage that it removes the analyte from the main solution and has very low limits of detection. 

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