Spark ablated aerosol

For the majority of applications, the sample is taken into solution and introduced into the plasma as an aerosol in the argon stream. The sample solution is pumped by a peristaltic pump at a fixed rate and converted into an aerosol by a nebulizer (see atomic absorption spectrometry). Various designs of nebulizer are in use, each having strengths and weaknesses. The reader is directed to the more specialist texts for a detailed consideration of nebulizers. There is an obvious attraction in being able to handle a solid directly, and sample volatilization methods using electric spark ablation, laser ablation and electrothermal volatilization have also been developed. 

To analyze metals and alloys directly without dissolution, both spark ablation [349] and laser ablation [61,211] dry aerosol generation systems have been used to introduce samples into an ICP-MS. These approaches often require matrix-matched standards, although several active research groups are focusing on techniques to reduce that requirement. The amount of material ablated depends on the sample type. Fractionation of elements can also be a problem, depending on the sample, the laser fluence, the laser wavelength, and the number of laser pulses used to sample from a fixed location. Volatile elements that are segregated in the samples appear to be most prone to fractionation problems [61],... 

For compact solids arc and spark ablation are a viable approach for metals [100, 214]. Aerosols with particle sizes at the pm level [216] and detection limits at the pg/g level are obtained [213]. Owing to the separate ablation and excitation stages, matrix influences are particularly low, as shown for aluminum [100] and for steel samples [213], In the first case, only for supereutectic silicon concentrations were matrix effects obtained (Fig. 100). For low-alloyed samples straight calibration curves are obtained and in the case of high-alloyed steels, even samples with widely different Cr or Ni contents are on the same calibration curves, which, are in fact slightly curved. 

Methods that Convert Solid Samples into an Aerosol or Vapour. These methods include (i) electrothermal vaporization, (ii) arc and spark ablation, and (hi) laser ablation. 

Solid samples can be analyzed using a plasma torch by first ablating the solid to form an aerosol, which is swept into the plasma flame. The major ablation devices are lasers, arcs and sparks, electrothermal heating, and direct insertion into the flame. 

Various techniques have been employed to introduce solid samples directly into plasma. These techniques may be divided into two groups (1) direct insertion of samples into the plasma, and (2) methods that convert solid samples into an aerosol or a vapour, which is then transported into the plasma. The latter techniques include electrical spark and arc ablation, electrothermal vaporization, and laser ablation. 

For conventional analysis by ICP or DCP, liquid samples are used, which are either easily prepared or commercially available. Interference problems are reduced to a minimum if the cahbration solutions are matched to the samples with respect to their content of acids and easily ionisable elements (see above). Calibration curves obtained with sparks, arcs, and laser ablation systems are usually curved so that 8—15 calibration samples or more are needed to define a suitable calibration. In the case of liquid analysis by DCP and ICP, fewer cahbration samples can be used due to the better linearity and dynamic range and absence of selfabsorption effects. With the introduction of hquids, the spray chamber is the major source of flicker noise due to aerosol formation and transport. While shot noise can easily be compensated by longer integration times, the flicker noise is of multiplicative nature so that any element can be used as an internal standard provided that a true simultaneous measurement of the analyte and internal standard line intensity is possible. 

Several techniques have been proposed during the last two decades for the direct introduction of solids into atomizers, thus avoiding the need to dissolve or decompose the sitmple. These techniques include (1) direct manual insertion of the solid into the atomization device, (2) electrothermal vaporization of the sample and transfer of the vapor into the atomization region, (3) arc, spark, or laser ablation of the solid to produce a vapor that is then swept into the atomizer, (4) slurry nebulizalion in which the finely divided solid sample is carried into the atomizer as an aerosol consisting of a suspension of the solid in a liquid medium, and (5) sputtering in a glow discharge device. None of these procedures yields results as satisfactory as those... 

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