Pneumatic nebulizer adjustment

In subsequent years (1988), the MAGIC system was commerciahzed, first by Hewlett-Packard (nowadays Agilent Technologies), and subsequently by other instrument manufacturers. Four commercial versions of the system have been available (1) the particle-beam interface, featuring an adjustable concentric pneumatic nebulizer, (2) the thermabeam interface with a combined pneumatic-TSP nebulizer, (3) the universal interface, in which TSP nebulization and an additional gas diffusion membrane is applied, and (4) the capillary-EI interface, which resulted from systematic modifications to existing PBI systems by Cappiello [83]. The first system was most widely used, and is discussed in more detail below. For some years, PBI was widely used for environmental analysis, especially in the US. 

The FBI comprises of (1) an adjustable concentric pneumatic nebulizer, (2) a heated desolvation chamber, (3) a two-stage momentum separator, and (4) a transfer line between the momentum separator and the El ion somce (Figure 4.15). 

The concentric pneumatic nebulizer, used for solvent nebulization, consists of a 100-pm-ID fused-silica capillary for liquid introduction at flow-rates in the range of 0.1-0.5 ml/min, and a circumventing high helium flow (1-3 Fmin). The relative positions of the nebulizer jacket and the liquid capillary outlet can be adjusted to optimize the spray performance. Micro-flow aerosol generators for introduction of 1-5 pFminof hquid were described by Cappiello and Bruner [83-84]. 

The optimum adjustment of the pneumatic nebulizer is to a large extent a matter of empirical trial-and-error. Relative gas and liquid flow-rates are readily optimized, although the optimization is indirect, i.e., based on the signal obtained. The gas flow appears not to be very critical, as long as it is kept between 1 and 2 1/min. 

Another unique approach is to produce a dry aerosol from a standard aqueous solution with a pneumatic nebulizer and desolvator. The aerosol produced by this apparatus is combined with the aerosol from the ablation cell using a dual gas-flow sample introduction system and a gas-mixing cell. By varying the concentration of the analyte in the standard aqueous solution, calibration curves can be created by this procedure. The composition of the standard solution can be adjusted to match the matrix composition of the bulk material of the solid sample, thereby simulating the behavior of the ablated solid in the plasma. Secondary standards can be created by this technique from selected samples. Future calibration curves can be prepared from ablating these secondary standards. 

An API-Ill triple-quadrupole mass spectrometer (or the single-quadrupole counterpart) with articulated, pneumatically assisted nebulizer atmospheric ionization is available from Perkin-Elmer Sciex Instruments. Any mass spectrometer equipped with an electrospray ionization source capable of LC/MS analysis can be substituted however, some potentials and flows may need to be adjusted for another instrument. A Harvard Apparatus 22 syringe pump is used for sample infusion with 25- 1 Hamilton blunt-tipped (SNR) syringes. 

Note These observations are equally relevant to (pneumatically assisted) ESI at standard flow rates [88]. Then, the corresponding voltages are just higher by a factor of > 2, which is mostly due to the increased gap between spray capillary and counter electrode to accommodate the larger plume. The optimization of the electrospray for temporal stability by adjustment of liquid flow, nebulizer gas pressure, and spray voltage is therefore necessary for any analytical ESI work. 

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