Application Spotlight
Introduction
The IsoMist, first introduced by Glass Expansion in 2007,1 provided
ICP laboratories with a convenient self-contained alternative to a
jacketed spray chamber by eliminating the need for a bulky chiller,
liquid coolant, complex coolant tubing and the icing-up of the spray
chamber. In contrast to the limited temperature range of a jacketed
spray chamber, the IsoMist provided a programmable range of -10°C
to +60°C in increments of 1°C. This temperature flexibility addressed
the challenges associated with several ICP applications.1-12
The IsoMist XR incorporates an improved thermodynamic design,
providing an extended temperature range and faster equilibration
so that your target temperature is attained more quickly. The spray
chamber temperature of the IsoMist XR is accurately controlled
using a multi-stage Peltier device, with a range of -25°C to +80°C
in increments of 1°C. The proprietary software of the IsoMist XR is
connected via a USB port or wireless Bluetooth® technology.
A cyclonic spray chamber encapsulated with a temperature
conductive resin provides the IsoMist XR with a uniform spray
chamber temperature from top to bottom and an air tight fit within
the module.5,6 These features allow for a stable temperature to be
maintained with an unmatched accuracy of +/- 0.1°C and prevent
condensation build-up and freezing. The combination of the
encapsulated spray chamber and dual-stage Peltier allows the
IsoMist XR to reach -25°C in less than 15 minutes (from ambient
temperature).
The IsoMist XR is compatible with interchangeable glass, quartz
and PFA cyclonic spray chambers, offering the analyst the utmost
flexibility and optimum setup for any matrix. Glass Expansion’s
proprietary HelixTM o-ring free nebulizer interface eliminates sample
contamination and ensures easy nebulizer removal. This zero dead
volume nebulizer interface reduces carry-over, improves washout
between samples5 and a built-in positive stop ensures optimum
and reproducible nebulizer insertion depth for consistent nebulizer
performance.
Results
In order to achieve optimum ICP performance in each of the
applications described, it is important to note that in addition to
using the IsoMist XR, a proper nebulizer and optimum ICP operating
conditions were selected to best handle the particular sample matrix
studied. This is essential when dealing with a challenging sample
matrix.
Improved Stability
Fluctuations in laboratory temperature affect sample viscosity and
nebulization efficiency. Previous investigations showed a change of
1°C in spray chamber temperature can result in a sensitivity change
of 3%6 Figure 2 compares the long term signal intensity achieved
with the IsoMist XR held at a constant temperature compared to
a conventional cyclonic spray chamber. The results show that
maintaining a constant temperature with the IsoMist XR significantly
enhances long term stability of the ICP signal intensity, resulting in
improved analytical reproducibility and accuracy. Maintaining a stable
ICP signal with the IsoMist XR also enhances throughput and lowers
operating costs by reducing the need to re-run samples should a QC
check drift outside the acceptable range.
Figure 2. Effect of IsoMist XR on signal stability at ambient temperature
With IsoMist XR at constant 21oC
Standard System
Normalised Counts
0
1.04
1.02
1.00
0.98
0.96
0.94
0.92
Al
Cr
Cu
Mn
Ni
Zn
50 100 150 200
Time (minutes)
Reduced Oxide Interferences
Using the IsoMist XR spray chamber at sub-ambient temperatures
on an ICP-MS reduces the water vapor transferred to the plasma
resulting in lower oxide formation and reduced polyatomic (ArO,
ArOH) interferences. Figure 3 shows the effect of IsoMist XR
temperature on the ICP-MS oxide ratio obtained on a PerkinElmer
Elan ICP-MS. A reduced temperature between 1 and 4°C provides
the optimum oxide ratio. Lowering oxide formation in the plasma
translates to fewer interferences, improving accuracy and detection
limits.1
Figure 3. Effect of IsoMist XR Temperature on ICP-MS Oxide Ratio
CeO/Ce %
-5
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0 5 10 15 20 25
Volatile Solvents
Temperature ºC
Volatile organic solvents are a challenge due to high transport
efficiency to the plasma, creating an excessive load resulting in
plasma instability or, in the worst case, cessation. One of the most
difficult and commonly analyzed solvents is light naphtha. Due to its
high volatility, naphtha is usually diluted with a less volatile solvent,
like kerosene. However, a dilution restricts lower detection limits
from being achieved. The IsoMist XR was used in combination with a
Thermo iCAP 6500 Duo ICP-OES for the direct analysis of naphtha,
without dilution12 Setting an IsoMist XR temperature of -25°C,
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