Slurry atomization

Because of the difficulty and inconvenience of sample dissolution for soil and geological samples prior to analysis by atomic spectrometry, a number of authors have investigated the possibility of direct nebulization of slurry samples into flames or plasmas.20,21 However Ebdon et al.22 reported problems 

Cresser, in Atomic Absorption Spectrometry Theory, Design, and Applications , ed. S.J. Haswell, Elsevier, Amsterdam, 1991, p. 515. 

Pio and A. Hall, in Instrumental Analysis of Pollutants , ed. C.N. Hewitt, Elsevier Applied Science, London, 1991, p. 1. 

Spurny, in Physical and Chemical Characterization of Individual Airborne Particles , ed. K.R. Spurny, Ellis Horwood, Chichester, 1986, p. 40. 

To date, slurry nebulization has not found widespread or routine application in environmental analysis by flame spectrometry. In the author s experience the time saving is small or even non-existent, because the use of standard additions procedures is time consuming, and samples often have to be processed one at a time when slurry atomization is to be used. 

With powders, stable slurries can often be formed by using suitable dispersing fluids. These fluids should be able to wet the powder and form stable suspensions, both of which depend on their physical properties (viscosity, density and surface tension). For example, the surface tension, which is largely also a function of the pH, is known to influence the surface charge of suspended particles and therewith the stability of the slurry (for Zr02 powders see e.g. Ref. [117]). The stability of 

After solvent removal the aerosols produced from slurries deliver solid particles, the diameters of which are those of the powder particles. In slurry nebulization used for flame work or plasma spectrometry, they are injected with a velocity that is less than or equal to the nebulizer gas atom velocities, as viscosity drag forces are responsible for their entrainment into the ICP. The velocity of the gas atoms (vG) can be calculated from the gas temperature at the location considered (TG), the injection velocity (vi) and the temperature at the point of injection (T), as vG = Vi x TG/Ti and the acceleration of particles (d2z/dt2) as a result of the viscosity drag forces is  

The particle size distribution of powders in the range 0.2-0.5 pm can be determined by automated electron probe microanalysis, as developed for particle characterization work at the University of Antwerp (see e.g. Ref. [202]). Here the exciting electron beam of a microprobe scans a deposit of the aerosol particles collected on a Nuclepore filter under computer control, and from the detection of element specific x-ray fluorescence signals, the diameters of a large number of particles are determined automatically. As shown by results for AI2O3, the particle size distributions determined by automated electron probe microanalysis agree to a first approximation with those of stray laser radiation (Fig. 62) [203], Deviations, however, 

In any case it is often necessary to apply ultrasonic stirring to destroy agglomerates and to disperse powders optimally prior to and even during the slurry analyses. 

This is e.g. done during slurry sampling by automated syringes into the graphite furnace. The addition of surface active substances such as glycols [207] has been proposed, however, this might introduce contamination when trace determinations are required. 

The particle size distribution of powders in the range 0.2-0.5 pm can be determined by automated electron probe microanalysis, as developed for particle charac- 

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Ebdon, L. and Lechotycki, A., The determination of lead in environmental samples by slurry atomization-graphite furnace-atomic absorption spectrophotometry using matrix modification, Micmchemical J., 34, 340-348, 1986. 

S. Lynch, D. Littlejohn, Development of a slurry atomization method for the determination od cadmium in food samples by eletrothermal atomization atomic absorption spectrometry, Talanta, 37 (1990), 825-830. 

The most feasible approach for direct powder analyses with flame and furnace AAS, however, is the work that has been done with slurries. Slurry atomization was introduced for flame AAS by Ebdon and Cave [116] in 1982. Although it has been shown to be useful for flame work, this is only for the determination of relatively volatile elements in samples of which the matrix can easily be thermally decomposed. This is, for example, the case in a number of biological samples, such as powdered plant or tissue materials. 

Vinas P, Campillo N, Garcia IL and Cordoba MH (1993b) Flow-injection flame atomic absorption spectrometry for slurry atomization. Determination of calcium, magnesium, iron and manganese in vegetables. Anal Chim Acta 283 393-400. 

P Vinas, M Pardo-Martinez, M Hernandez-Cordoba. Slurry atomization for the determination of arsenic in baby foods using electrothermal atomic absorption spectrometry and deuterium background correction. J Anal At Spectrom 14 1215-1219, 1999. 

Dowex 50" resin, in distilled water, slurry Atomic Energy L 85 125 — <0.0001 <0.0001 ... 

Ebdon, L. and GoodaU, P. (1992) Slurry atomization using hydrogen-modified inductively coupled plasmas. J. Anal. At. Spectrom., 7,1111. 

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