NEWS
PRODUCT DESIGN FOCUS
Inert Spray Chambers
Early ICP spectrometers mostly used large volume (>100mL)
“Scott style” spray chambers. These generally provided good
stability and detection limits. However they had some limitations,
including low efficiency and long wash-out times. The availability
of the cyclonic spray chamber in the 1990’s helped overcome
these limitations.
Glass cyclonic spray chamber Sensitivity of inert spray chambers relative to glass spray chamber (relative sensitivity = 1)
With the cyclonic spray chamber, the aerosol is introduced
tangentially. The aerosol flows in a vortex about the axis of
the spray chamber and the larger droplets are eliminated by
centrifugal action. These larger droplets strike the wall of the
spray chamber and flow to the drain while the smaller droplets
are swept into the torch by the argon stream.
Compared with the Scott style spray chambers, the newer
cyclonic spray chambers are of lower volume (usually about
50mL) and provide improved efficiencies as well as faster washout
times and reduced carryover from one sample to the next. At the
same time, they are able to match the excellent precision of the
Scott style spray chambers.
Both the Scott style and cyclonic spray chamber are usually
made from borosilicate glass. Glass provides sufficient purity
and chemical resistance to make it a cost-effective material
for the majority of ICP applications. It also exhibits excellent
drainage characteristics, leading to very good precision and low
carryover. However, it does have some limitations. It is attacked by
hydrofluoric acid (HF) and is therefore not suitable for the analysis
of samples containing even low levels of HF. It is also not suitable
for the ultratrace determination of some elements (eg. silicon,
boron) by ICP-MS.
For applications where a glass spray chamber is not suitable,
it has been common to use spray chambers made from various
plastics. Again, the early plastic spray chambers were of the
Scott style but more recent models are of the cyclonic design.
A big problem with plastic is that the surface does not wet easily.
This results in the formation of large drops, erratic drainage, poor
precision and poor sensitivity. To reduce these problems, some
form of surface treatment is necessary. One option is to sandblast
the surface and this treatment was used by Glass Expansion for
several years. It improves the performance significantly but the
performance of sandblasted spray chambers is still markedly
inferior to that of glass spray chambers.
A major breakthrough in the performance of polymer based spray
chambers came with the introduction of the proprietary Stediflow
surface treatment by Glass Expansion in 2006. The Stediflow
treatment improves the wettability of the surface, ensuring efficient
drainage, and delivering sensitivity and precision almost as good
as those achieved with a glass cyclonic spray chamber. The
graph below shows the sensitivity obtained using a Teflon spray
chamber with Stediflow surface treatment and a polypropylene
spray chamber with sandblasted surface compared with a
Tracey glass cyclonic spray chamber (Intensity = 1). Whereas the
sensitivity with the polypropylene spray chamber is only about
50% of the sensitivity with the glass spray chamber, the sensitivity
with the Teflon spray chamber is almost as good as that of the
glass spray chamber.
Polypropylene
1
0
1.62
3.88
5.80
11.22
Teflon
12.07
2.69
4.35
12.25
14.27
3.07
5.42
12.93
16.51
3.79
13.07
Relative Sensitivity
E (eV)
It is important to note that the Stediflow treatment actually changes
the molecular structure of the polymer material. It is not a coating
and it does not introduce any potential contaminants. We have
standardized on PTFE (Teflon) for our inert ICP-OES spray chambers
(Tracey TFE model) and, due to its higher purity, we use PFA for
our inert ICP-MS spray chambers (Tracey PFA44 models). There
is a Tracey TFE or Tracey PFA44 spray chamber with Stediflow
treatment available for every ICP-OES and ICP-MS model.
Tracey TFE spray chamber
Tracey PFA44 spray chamber
www.geicp.com Glass Expansion Newsletter | Issue 26 | page 6