Page 84 - Inorganic Mass Spectrometry : Fundamentals and Applications

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, F. Nebulizer Gas
I

1‘ . . I
Ar ,-. I

Micronebulizers: (a) Meinhad high-efficiency nebulizer (€EN). (b) Cetac
microconcentric nebulizer (MCN).

used for solutions containing hydrofluoric acid. Cross-flow nebulizers are typi-
cally made from materials that are resistive to corrosive acids and bases, and some
concentric nebulizers from inert materials have also been recently introduced.
Pneumatic, concentric micronebulizers have become available in recent
years (Fig. 3.5) with very small internal dead volume. The Meinh~~ high-
efficiency nebulizer (HEN) is a glass nebulizer with a very small gas ring area and
thin-walled, small-inner-diameter (90-pm) sample carrying capillary. Although
EN requires a higher-pressure Ar gas supply (approximately 170 psi at an
argon gas flow rate of 1.0 L/min) than the conventional concentric pneumatic
nebulizers, it produces a somewhat smaller aerosol than other, “conventional”
concentric nebulizers [12]. Also, because of the small gas ring area, the HEN pro-
at
duces sonic gas velocities and fine aerosols even nebulizer gas flow rates as low
as 0.2 L/min, The Cetac MCN-100 microconcentric nebulizer (MCN) has a gas
ring orifice that is slightly smaller than that of a conventional nebulizer. The most
unique property of the MCN is that it is made of €F-resistant materials, including
a narrow polyimide nebulizer capillary [ 1.31. Therefore, the MCN is particularly
attractive for the analysis of small volumes of HF solutions such as those used for
of
analysis of semiconductor wafers and small volumes biological samples includ-
ing metalloproteins (which may be more likely to adsorb to glass surfaces). The
main advantage of the micronebulizers is their low internal volume (9 and 0.5 p,L
for the HEN and MCN, respectively, compared to pL typical of a conventional
90
pneumatic concentric nebulizer). This makes analysis of sample volumes as low
as a few microliters possible by ICP-MS.
Spray C~a~~ers. Spray chambers [ 141 were designed mostly empirically
for use with conventional pneumatic nebulizers during the development of ICP
optical emission spectrometry. The main purpose of the spray chamber was
thought to be to remove large droplets that would not have sufficient time to be
the
in
completely vaporized during their 1- to 2-msec travel plasma, although what