In a 2014 application spotlight,2 Glass Expansion highlighted
the advantages of a cyclonic spray chamber versus a Scott-type.
A combination of the cyclonic design and Stediflow treatment
provides the ICP analyst with sensitivity gains and reduced washout
times that are not possible with inert Scott-type spray chamber
designs. Furthermore, the baffled Twister spray chamber provides a
smaller particle size and narrower distribution compared to a single
pass cyclonic (Tracey). Smaller droplet sizes reduce matrix effects
and improve short-term precision, making the PTFE Twister the most
suitable choice for high matrix samples containing HF.
Figure 3. Sensitivity of inert spray chambers relative to glass spray chamber (relative sensitivity = 1)
TraTF 50
Polypropylene Teflon
3.07 3.88 5.42 11.22 12.25 13.07 16.51
E (ev)
TraPP 50
I rel (I (Spray Chamber) / I (Tra St 50))
1.62
1.0
0.5
0
Inert Nebulizer Design
Choosing an inert nebulizer is just as important as the type of spray
chamber selected. Key categories to review when choosing an inert
nebulizer are: chemical resistance to HF, purity of the raw material,
tolerance to particulates and overall performance (sensitivity and
precision). This way the best nebulizer is chosen for the application
and sample matrix.
Glass Expansion currently offers two inert concentric nebulizer
designs, the OpalMist and DuraMist. Other popular inert nebulizer
models include the cross-flow and a polymeric, parallel path,
"v-groove" nebulizer referred to as NPCN throughout the remainder
of the discussion. The CrossFlow and NCPN provide tolerance to
HF and particulates, but suffer from poorer analytical precision,
reduced sensitivity and enhanced matrix effects compared to the
concentric nebulizer design. These nebulizers typically produce
an aerosol that has larger droplets with a wider droplet size
distribution. Larger droplets can pass through the plasma without
desolvating and incomplete evaporation, which results in poor
precision, reduced nebulization efficiency, increased matrix effects
and reduced plasma robustness. Smaller droplet size provides higher
transport efficiency (sensitivity) and improved precision (RSD).
Application Spotlight
Introduction
For ICP sample digestions that require hydrofluoric acid (HF) and/
or if the final sample matrix contains trace amounts of HF, a glass or
quartz ICP sample introduction system is unsuitable. Glass or quartz
is also unsuitable for the ultra-trace determination of some elements
by ICP-MS (e.g. silicon or boron). For these types of ICP analyses,
an inert sample introduction system, consisting of a spray chamber
and nebulizer made from various plastic materials, are used.
Common polymers used in the manufacture of inert spray chambers
and nebulizers include:
• Polytetrafluoroethylene (PTFE)
• Perfluoroalkoxy alkane (PFA)
• Polyphenylene sulfide (PPS)
• Polypropylene (PP)
• Polyether ether ketone (PEEK)
• Polyimide (PI)
A common problem with these materials is they do not wet completely
and large droplets collect on the inside walls. The formation and
collection of droplets degrades ICP performance, leading to erratic
drainage, poor precision (RSD), and poor signal stability.
Inert Spray Chamber Design
A major breakthrough in the performance of inert spray chambers
came with the introduction of the proprietary Stediflow surface
treatment by Glass Expansion in 2006.1 The Stediflow treatment
(shown in Figure 2) improves the wettability of the surface, ensuring
efficient drainage, and delivering sensitivity and precision comparable
to those achieved with a glass cyclonic spray chamber.
Figure 2. Glass Expansion’s proprietary Stediflow surface treatment
In previous work,1 the sensitivity of the a Glass Expansion PTFE
Tracey cyclonic spray chamber with Stediflow surface treatment
and a PP cyclonic spray chamber with a sandblasted surface were
both compared to a Tracey glass cyclonic spray chamber (Figure 3).
Sandblasting of the plastic is a common surface treatment technique
used to improve performance. However, that improvement still only
provides about 50% of the sensitivity of the glass spray chamber,
whereas the sensitivity of the Stediflow treated PTFE spray chamber
was nearly equivalent to the glass spray chamber.1
www.geicp.com Glass Expansion Newsletter | Issue 46 2
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