NEWS
Experimental
The first experiments were conducted on a Thermo ICAP 6500
Duo, operated under the conditions listed in Table 2. To avoid any
fluctuations in measurements due to temperature variations, the
IsoMist Programmable Temperature Spray Chamber was utilized
with a Twister baffled glass spray chamber held constant at 21°C.
A ceramic D-Torch was also used to avoid the deleterious effects
of salt during the high dissolved solids experiments. Under these
conditions the performance of the DuraMist was compared to the
SeaSpray and a NCPN, examining precision and sensitivity.
The second portion of this report compared the performance of
the DuraMist to the OpalMist and PolyCon. For these experiments
a PerkinElmer Optima 2100DV was utilized, operating under
the conditions listed in Table 3. As in the initial experiments, an
IsoMist and ceramic D-Torch were employed. The common ICP
figures of merit established by Poussel and Mermet were used to
compare plasma robustness, atomization/ionization, excitation,
efficiency, and stability for each of the three inert nebulizers. The
tolerance to a 20% TDS solution was also examined. As a final
test to complete the DuraMist evaluation, long-term stability was
examined in the presence of a 2.5% NaCl solution. Results
PE Optima 2100 Operating Conditions
RF power (W) 1400
Plasma gas (L/min) 15
Auxiliary gas (L/min) 0.2
Nebulizer gas(L/min) 0.65
Replicates 3
Read delay (sec) 15
Min integration time (sec) 1
Max integration time (sec) 10
Source equilibration delay (sec) 15
Plasma view Axial (Na 589 – Radial)
Table 3: PE Optima 2100 Operating Conditions
The SeaSpray is the most popular nebulizer due to its excellent
precision and sensitivity and ability to handle high TDS. In the
first set of experiments the goal was to compare the performance
of the DuraMist to the SeaSpray. We also compared its
performance to that of a non-concentric polymer nebulizer.
When comparing precision (Figure 2), the DuraMist has a
slightly smaller range of relative standard deviation (RSD) values
compared to the SeaSpray. The range in precision values of the
NCPN is larger compared to both the DuraMist and SeaSpray,
which is not unexpected due to its increased sensitivity to
peristaltic pump pulsations.
The next step was to compare the sensitivity of the SeaSpray,
DuraMist, and NCPN. In Figure 3 sensitivity measurements
of the DuraMist and NCPN are normalized to the sensitivity
measurements taken with the SeaSpray. On average the DuraMist
is within 13% of the sensitivity of the SeaSpray and is slightly
higher than the NCPN for almost all wavelengths examined.
In the second portion of this study the performance of the
DuraMist is compared to that of the other two inert concentric
nebulizers offered by Glass Expansion, the OpalMist and the
PolyCon. In Figure 4 sensitivity measurements of the OpalMist
and PolyCon are normalized to the sensitivity measurements
taken with the DuraMist. On average the DuraMist shows a 25%
higher sensitivity compared to both the OpalMist and PolyCon
for a wide range of wavelengths.
The experiments for ICP figures of merit established by Poussel
and Mermet are most commonly used to examine plasma
robustness, atomization/ionization, excitation, efficiency, and
stability (Table 4), all of which can be affected by nebulizer
performance. The ICP figures of merit for the DuraMist, PolyCon,
and OpalMist are compared in Figure 5 (a) and 5 (b). The Mg
and Cr ratios are monitored to measure the robustness and
atomization/ionization efficiency of the plasma. On the PE Optima
2100DV ICP the DuraMist shows a slightly higher robustness
and atomization/ionization efficiency compared to the other two
GE inert nebulizers.
The Zn 206/Ba 455 ratio is used to measure excitation efficiency
of the ICP, which is virtually the same with all three inert nebulizers.
As a measure of nebulizer efficiency, the RSD for Mg 285 is
monitored; with the DuraMist showing the second highest
efficiency and the OpalMist offering the highest efficiency.
Figure 1: DuraMist nebulizer, UniFit sample line, ractchet EzyLok connector, and EzyLok kit.
Thermo iCAP 6500 Operating Conditions
RF power (W) 1350
Plasma gas (L/min) 15
Auxiliary gas (L/min) 0.2
Nebulizer gas(L/min) 0.65
Replicates 3
Sample flush time (sec) 65
Plasma view Auto
Max integration time (sec) 15
Peristaltic pump rate (rpm) 37
Pump tubing Orange/white (0.64 mm i.d.)
Table 2: Thermo iCAP 6500 Operating Conditions
www.geicp.com Glass Expansion Newsletter | Issue 26 | page 2