Influence of design and operating parameters of pneumatic concentric nebulizer on micro-flow aerosol characteristics and ICP-MS analytical performances

Abstract

This paper describes the development of a very simple micro-flow pneumatic ICPMS nebulizing solution based on a commercial glass concentric slurry nebulizer and a fused-silica capillary. It appears as a well-performing, low cost system able to nebulize efficiently at a low liquid flow rate (40 000 cps for a 1 ppb 238 U solution at 1 mL min À1 ). Experimentally, it provides a practical set-up for studying the influence of not only operating conditions (liquid and gas flow rates, temperature) but also nebulizer design (nozzle configuration, capillary tip shape, capillary inner diameter). More precisely it allows the study of liquid-capillary-tip to gas-exit stick-out, i.e. recessed position (e < 0), coplanar liquid and gas exits (e ¼ 0) or liquid protruding configuration (e > 0) in combination with various liquid capillary inner diameters or tip shapes. This investigation brings out several practical results even if the relation between the primary aerosol characteristics (studied by three complementary techniques (PIV, shadowgraphy and ILIDS)) and the ICPMS signal measured on a tertiary aerosol is not easy to establish precisely. These results are systematically compared to the literature data, replacing them in a more global perspective. It highlights the prime importance of the nozzle configuration i.e. stick-out and liquid capillary inner diameter. The stick-out (e) parameter is of crucial importance both for the primary spray homogeneity in terms of droplet velocity distribution and for tertiary signal intensity and stability but shows no influence on the oxide ratio or on the droplet size distribution. This last characteristic may not be the most relevant criterion for low liquid uptake nebulizers, contrary to millilitre flow-rate ones. The authors hypothesize that this may be linked to the evaporation capacity of the nebulising gas largely exceeding the liquid uptake, creating a fundamentally different situation for the two types of nebulizers. This study also displays the interest of using a flat-end capillary instead of a tapered end which is the solution most commonly employed, and it highlights the existence of an optimum nozzle configuration (e > 0) in terms of sensitivity and stability, that is dependent on the capillary inner diameter.

Application of a micro-droplet generator for an ICP-sector field mass spectrometer – optimization and analytical characterization

“…Therefore micro-concentric nebulizers are becoming more popular, because they operate at rather low sample uptake rates of below 10 mL min À1 and the transport efficiency is signicantly increased. 11 However, measurement of more than a single nanoparticle should be avoided during the integration time of the ICP-MS, which is limited to around 10 ms even for the most fast scanning commercial ICP-MS instruments based on quadrupole analysers. This problem was already discussed in the work of Franze et al who have used a pneumatic nebulizer for sample introduction of nanoparticles in ICP-MS. 12 From this point of view mDG looks more promising, because it provides just single droplets with a narrow droplet size distribution (monodisperse) and a very reproducible and user selectable generation frequency.…”

Atomic spectrometry update: review of advances in atomic spectrometry and related techniques

“…There are few new developments in this area, which is unsurprising given that the basic principles have been established for a considerable time. Geertsen et al 51 have developed a micro-flow pneumatic nebulizer which is able to operate at 1 µL min -1 and yield a sensitivity of 40,000 cps for a 1 ppb solution of U when used with ICP-MS. Using this design, based on a commercial glass concentric slurry nebulizer with an axially introduced fused silica capillary (20 μm, 50 μm, 75 μm or 100 μm i.d.…”

Atomic spectrometry update: review of advances in atomic spectrometry and related techniques

“…There are few new developments in this area, which is unsurprising given that the basic principles have been established for a considerable time. Geertsen et al 51 have developed a micro-ow pneumatic nebulizer which is able to operate at 1 mL min À1 and yield a sensitivity of 40 000 cps for a 1 ppb solution of U when used with ICP-MS. Using this design, based on a commercial glass concentric slurry nebulizer with an axially introduced fused silica capillary (20 mm, 50 mm, 75 mm or 100 mm i.d.…”