Experimental
An Agilent 5100 simultaneous dual view ICP-OES was used in
combination with the SeaSpray Direct Connect (DC) nebulizer
and Twister spray chamber with Helix CT to evaluate washout
performance, in addition to highlighting the effects of nebulizer depth
and torque applied to the nebulizer seal.
Results
The Helix CT is the only nebulizer-spray chamber interface that
significantly reduces the dead volume around the nebulizer. This
unique design minimizes washout time with highly concentrated
samples, reducing sample-to-sample carryover and improving
sample throughput. Figure 3 compares the time required to washout
a 10ppm Molybdenum standard with the Helix CT interface and a
“Brand-X” spray chamber with an o-ring interface. The results show
that with the Helix CT nebulizer interface a 10ppm standard can be
washed out in as little as 4 seconds, whereas “Brand-X” takes 16
seconds. One can expect this time to significantly increase for more
troublesome or “sticky” elements that are more prone to carryover
issues.
Glass Expansion’s new Helix CT design maintains the positive stop
of the original Helix to ensure that the nebulizer is inserted to the
correct and optimum depth within the spray chamber so that both
ion and atom lines give optimum sensitivities under a wide range of
conditions.
Figure 3. 10 ppm Mo washout comparison between Helix and non-Helix spray chambers
0 2 4 6 8 10 12 14 16 18
Time (seconds)
Helix Interface Non-Helix Interface
Emission Counts
8000
6000
4000
2000
The effect of a nebulizer depth relative to the aerosol impact
zone inside a spray chamber was investigated by using radially
measured background, atom and ion line intensities as well as
the spectroscopically determined Mg ratios and Fe-excitation
temperatures. The analytes studied were As (I), Cu (I), Cu (II), Mg
(I), Mg (II), Mn (I), Mn (II), Se (I), Na (I) and K (I).
Figure 4 highlights the effect of nebulizer depth on Mn (I) and
Mn (II) sensitivities as a function of nebulizer gas flow rate for
two different height above the load coil (HALC) positions and two
different nebulizer depths (3mm: closer to the aerosol impact zone
and 9mm: away from the aerosol impact zone). For the atom line,
the highest sensitivity difference is noted at the lowest nebulizer
gas flow rate when the nebulizer is moved away from the aerosol
impact zone relative to the closest position studied. For the ion
line, increases in sensitivity difference at lower nebulizer gas
flow rate changes to decreases at higher nebulizer gas flow rate
when the nebulizer is moved away from the aerosol impact zone.
Application Spotlight
Figure 1. Helix CT ICP spray chamber
The main feature of the Helix CT spray chamber is a new Helix CT
locking screw with built-in torque control mechanism that allows for a
consistent seal of the PTFE ferrule against the nebulizer – making it
impossible to overtighten or undertighten while ensuring a gas-tight
seal each and every time. A new PressFit PTFE ferrule provides a
chemically inert seal around the nebulizer, which is immune to strong
acids and organic solvents routinely used in ICP sample preparation
(Figure 2). The new Helix CT spray chamber by Glass Expansion,
therefore, eliminates all the drawbacks of the o-ring nebulizer seal,
while improving user safety by preventing broken nebulizers.
Figure 2. Helix CT Interface with nebulizer
PressFit PTFE Helix CT seal
Helix CT locking
screw with built in
ConstantTorque
technology.
The new Helix CT nebulizer interface is also simple to use:
• Fully insert the nebulizer into the Helix CT interface, until the
nebulizer side-arm comes into contact with the moulded-in positive
stop.
• Hand-tighten the Helix CT locking screw until the ConstantTorque
mechanism clicks, indicating a secure, gas-tight seal.
www.geicp.com Glass Expansion Newsletter | Issue 45 2
/www.geicp.com