the end of the filling process to check the concentration once
again, to account for any dilution during the degassing and
cell-loading processes.
31. In instruments where the injection is made by a screw-driven
Hamilton syringe, the volume of the first one or two injections
can be reduced due to slack in the connection between the
driving screw and the Teflon plunger [30]. This potential
artifact can be avoided by advancing the plunger of the injector
by a small fraction (a few percent) of its total travel before
inserting the injector into the calorimeter cell.
32. For an instrument with a 1.4-mL cell volume and a 300-μL
injector syringe volume, a typical injection protocol would be
1 Â 1 μL injection followed by 29 Â 10 μL injections. For an
instrument with a 200-μL cell volume and a 40-μL injector
syringe volume, a typical injection protocol would be
1 Â 0.4 μL injection followed by 19 Â 2 μL injections. The
reference power value should be set in the middle of the
dynamic range of the instrument. The time between injections
should be such that the differential power returns to and
remains in the baseline for some time after the injection. For
an instrument with a 1.4-mL cell volume, a typical delay
between injections would be 300 s; for an instrument with a
200-μL cell volume, typical delay would be 120 s. The averaging time for a single point should be set short enough to ensure
that there is sufficient data density properly to sample the shape
of the injection peaks, but not so short as to give excessive
noise. The reference power value should be set in the middle of
the dynamic range of the instrument, and the feedback in the
power compensation circuit should be set to give the fastest
response possible.
33. The differential power signal will deviate significantly from the
set value if the heat capacity of either cell is very different from
that of aqueous solution due to the presence of trapped air. A
misfilled sample cell containing air bubbles will cause the differential power to settle at a value lower than the set value. This
is explained in more detail in Chapter 5.
34. The signal-to-noise of the titration under these conditions is
such that the baseline determination and integration should be
robust and reliable with little manual intervention. We have
obtained essentially identical results using Microcal Origin for
ITC with small manual adjustments of the baseline, or using
the automated procedures in Affinimeter and NITPIC. In
general, we would prefer the automated procedures because
they are less prone to user bias and provide estimates of the
error on integrations that are important for determining the
true error on fitted parameters.
Interactions by Multiple Methods
77
again, to account for any dilution during the degassing and
cell-loading processes.
31. In instruments where the injection is made by a screw-driven
Hamilton syringe, the volume of the first one or two injections
can be reduced due to slack in the connection between the
driving screw and the Teflon plunger [30]. This potential
artifact can be avoided by advancing the plunger of the injector
by a small fraction (a few percent) of its total travel before
inserting the injector into the calorimeter cell.
32. For an instrument with a 1.4-mL cell volume and a 300-μL
injector syringe volume, a typical injection protocol would be
1 Â 1 μL injection followed by 29 Â 10 μL injections. For an
instrument with a 200-μL cell volume and a 40-μL injector
syringe volume, a typical injection protocol would be
1 Â 0.4 μL injection followed by 19 Â 2 μL injections. The
reference power value should be set in the middle of the
dynamic range of the instrument. The time between injections
should be such that the differential power returns to and
remains in the baseline for some time after the injection. For
an instrument with a 1.4-mL cell volume, a typical delay
between injections would be 300 s; for an instrument with a
200-μL cell volume, typical delay would be 120 s. The averaging time for a single point should be set short enough to ensure
that there is sufficient data density properly to sample the shape
of the injection peaks, but not so short as to give excessive
noise. The reference power value should be set in the middle of
the dynamic range of the instrument, and the feedback in the
power compensation circuit should be set to give the fastest
response possible.
33. The differential power signal will deviate significantly from the
set value if the heat capacity of either cell is very different from
that of aqueous solution due to the presence of trapped air. A
misfilled sample cell containing air bubbles will cause the differential power to settle at a value lower than the set value. This
is explained in more detail in Chapter 5.
34. The signal-to-noise of the titration under these conditions is
such that the baseline determination and integration should be
robust and reliable with little manual intervention. We have
obtained essentially identical results using Microcal Origin for
ITC with small manual adjustments of the baseline, or using
the automated procedures in Affinimeter and NITPIC. In
general, we would prefer the automated procedures because
they are less prone to user bias and provide estimates of the
error on integrations that are important for determining the
true error on fitted parameters.
Interactions by Multiple Methods
77