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Solvent
Considerations
When the TSD is used for trace level analysis, only solvents free of
nitrogen, phosphorus, sulfur, or halogenated compounds should be used.
Depending on the volatility of the impurity in a solvent, it can produce
excessive solvent tailing or extraneous chromatographic peaks.
Chlorinated
Solvents
Chlorinated solvents can be used with the TSD. However, these solvents
generally cause an abrupt increase in both detector background signal
and sample response. These effects appear to be associated with a
temporary adsorption of chlorinated species onto the surface of the hot
alkali-ceramic bead. Repetitive injections of samples in chlorinated
solvents yield constant responses. However, once the injection of
chlorinated solvents is stopped, the background and sample response will
decay back to the response levels that existed before the initial injection
of the chlorinated solvent. Therefore, when chlorinated solvents are used,
calibration standards should be run frequently.
Bead Power
Interruption
You can minimize the effect of chlorinated solvents on the bead by
turning off bead current during the time that the solvent elutes, using the
time programming table of the detector method. The total time that the
bead is turned off should be less than 2 minutes in order to minimize
thermal re-equilibration times of the detector. (Any peaks eluting during
this off time will not be measured.)
Effect of
Silylation
Reagents
Silylation reagents affect the TSD in two ways. First, such reagents
sometimes contain nitrogen which will cause tailing of the solvent peaks.
Second, decomposition of the reagent on the hot bead produces SiO
2
which deposits on the bead surface causing loss of response. Generally,
SiO
2
deposits can be removed by cleaning the bead and usually produce
no permanent damage to the bead.
Table 24 TSD Gases, Pressures, Purity, and Flow Rates
Gas
Inlet Pressure at
Gas Cylinders
Recommended
Purity
Flow Rate (mL/min)
Carrier (packed columns):
He or N
2
80 psig
99.999%
30 mL/min
Detector Make-Up
(capillary columns):
He or N
2
80 psig
99.999%
25 ±1 mL/min
Detector Gases:
Air
60 psig
CGA Grade E
175 ±5 mL/min
H
2
40 psig
99.999%
4.0 ±0.2 mL/min
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