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Figure 4: The Multimode Inlets (MMIs) we measured experienced almost twice the tem-
perature drop (190 °C) of a standard split/splitless inlet between the inlet setpoint to the
top of the liner.
Figure 2: A temperature gradient exists within a GC inlet, and temperature profiles can vary
between similar inlets. These variations increase dramatically with the absence of insulation.
When insulation is missing at the top of the
inlet, the inlet loses heat to the open air; how-
ever, when insulation is missing at the bottom,
the GC oven influences the temperature in
both directions (Figure 3). Because column
installation can be more challenging with the
insulated nut warmer cup installed, analysts
may be tempted to leave it in a drawer, but
the effect on your inlet temperature can be
significant.
Temperature Can Vary Drastically
Between Dissimilar Inlets
The newly introduced Agilent Multimode Inlet
(MMI) is said to be capable of performing both
hot split and hot splitless injections like a nor-
mal split/splitless inlet. But, when we measured
the thermal profiles for two MMI inlets, it was
interesting to note how different the MMI ther-
mal profiles were from a split/splitless inlet—a
drop of over 190 °C from the setpoint to the
top of the inlet as opposed to around 100 °C
for the split/splitless inlets (Figure 4). This varia-
tion shows that changing equipment may also
change your results, even if the equipment is
nominally able to do the same analysis.
The Effects of Inlet Temperature
Variations on Chromatography
As demonstrated here, thermal gradients
exist within a single GC inlet, and temperature
profiles can vary between similar, as well as
between dissimilar, inlets. How do these varia-
tions affect the vaporization of a liquid sample
(and, thus, the overall success of the analysis)?
We answer these questions and offer details on
our temperature data collection at
Figure 3: Installing the nut warmer cup can help minimize the effects of oven temperature
on the actual temperature of the inlet. (Inlet shown belowwas set to a constant 250 °C.)
NOTE: To ensure relative accuracy between inlets, all split/splitless temperature readings were taken
in the same manner.
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