NEWS
The ceramic outer tube of the D-Torch is made from sialon, which
is a ceramic material derived from silicon nitride. Sialon is one
of the most durable and robust ceramic materials known and
maintains its properties at high temperatures. A combination
of high temperature and salt deposit causes a quartz torch to
devitrify. Higher concentrations of salt in the samples lead to more
rapid devitrification. By contrast, the ceramic outer tube of the
D-Torch does not devitrify and is not affected by salt deposits. The
quartz torch in Figure 2a, was run for only 6 hours with samples
containing 10% NaCl and is already badly degraded. The ceramic
D-Torch in Figure 2b was run for the same period and with the
same samples as the quartz torch, but shows no degradation at
all. In general, the ceramic outer tube has a much longer lifetime,
greatly reducing interruptions and downtime due to torch failure.
Sialon is also beneficial for low level Si determinations, where
quartz outer tubes can produce high background signals.
a.
b.
Figure 2: Quartz torch (a) and ceramic torch (b) exposed to 10% NaCl for 6 hours.
The analytical performance of the Thermo Radial EMT quartz torch
was compared to the Radial ceramic D-Torch for the analysis of
aqueous and high salt samples.i The geometry of the two torches
is identical, the key differences are the materials used for the
outer tube and intermediate tube and that the ceramic D-Torch
is demountable. The detection limits in an aqueous matrix for
selected elements obtained with the EMT torch and the ceramic
D-Torch are compared in Table 1. The results show little difference
between the detection limits obtained with the two torches. A key
indicator of ICP torch performance is stability. Figure 3 shows a
plot of selected elements at 0.5 mg/L in a 3% NaCl matrix. The
stability exhibited by the ceramic D-Torch over a period of 5.5
hours in this high matrix sample is excellent. The ceramic D-Torch
provides equivalent analytical performance to the standard EMT
torch with the added advantage of resistance to devitrification
and premature failures with specific sample matrices, including
organics and high dissolved solids samples such as fusions.
Figure 3: Stability of elements in 3% NaCl solution using ceramic D-Torch.i
ARGON CONSERVATION
A stream of argon gas between the outer and intermediate tubes
of the ICP torch is required to provide a cooling sheath to prevent
the torch from melting in the 6000°C plasma. Quartz can require
flow rates as high as 20 L/min in order to provide an adequate
cooling sheath. This high consumption of argon can constitute
a significant cost of up to several thousand dollars per year. In
contrast to quartz which has a lower melting point, sialon has
a melting point above 2100°C and therefore needs much less
cooling. To examine the performance of the D-Torch at a reduced
plasma (coolant) gas flow, detection limits were compared at 16L/
min and 10L/min in matrices consisting of 2% HF and 2% HNO3.
The operating conditions are listed in Table 2.
Detection Limit μg/L
Element (λ) Radial EMT Torch Radial Ceramic D-Torch
Al 167 1.6 1.1
Ba 455 0.07 0.12
Cu 324 0.88 0.62
K 766 25.5 11.7
Mg 279 0.05 0.05
Mn 257 0.36 0.25
Ni 221 1.6 1.3
P 177 5.1 5.0
Zn 213 0.23 0.28
Table 1: Comparison of detection limits for EMT Torch and Ceramic D-Torch.i
ICP Parameter 2% HF 2% HNO3
Standard Low Flow Standard Low Flow
RF Power (W) 750 750 750 750
Auxiliary gas flow
(L/min)
0.50 0.50 0.50 0.50
Nebulizer gas flow
(L/min)
0.75 0.70 0.65 0.65
Plasma gas flow
(L/min)
16 10 16 10
Sapphire injector ID
(mm)
2.0 2.0 2.0 2.0
Solution flow rate
(mL/min)
2.0 2.0 2.0 2.0
Table 2: iCAP operating conditions for 2% HF and 2% HNO3 work
The detection limits for both matrices listed in Table 3 were
calculated using the standard deviation of 7 replicates and the
student T value for a 98% confidence level. The wavelengths
examined show little difference in the detection limits obtained
between a plasma gas flow rate of 16 and 10L/min. The HF
stability data shown in Figure 4 also shows there is no sacrifice
in plasma stability running the plasma gas flow rate at 10L/min.
The average RSD for a number of wavelengths collected over 3
hours was less than 1.5%. The results show that an analyst who is
not dealing with a difficult matrix such as high dissolved solids, can
also benefit from utilizing a fully ceramic D-Torch by greatly reducing
argon consumption and costs.
www.geicp.com Glass Expansion Newsletter | Issue 28 | page 2