ISQ User Guide - Write Frame of Mind

. Configure the Pre-Injection group:
4 Creating a Method
• Pre-Injection—Use the Solvent and Cycles fields to set the number of solvent
purges that will occur before the autosampler touches your sample. You should
always have some sample rinses, either before or after injection, to make sure you
do not have sample carryover from one injection to the next. You can configure
the settings so that the syringe is purged with the same solvent that was used in
location A, B, C or D or with solvents A and B or C and D. Typically, there is 0
or 1 cycles of pre-injection purges.
• Sample—Use the Rinses pull-down menu to select the number of times the
syringe is rinsed with your sample before each injection. Rinses help ensure the
sample being injected is not diluted by the residual rinse solvents. By purging the
syringe with your sample before injection, the dilution is minimal. The standard
setting is between 1 and 3 rinses. If you have a very limited amount of sample,
however, you may want to set this field to 0 to conserve the sample.
• Post-Injection—Use the Solvent and Cycles fields to set the number of solvent
purges that will occur after the autosampler touches your sample. You should
always have some sample rinses, either before or after injection, to make sure you
do not have sample carryover from one injection to the next. You can have the
syringe purged with the same solvent that was used in location A, B, C or D or
with solvents A and B or C and D. Typically, there are 1 to 5 cycles of
post-injection purges.
c. Configure the Injection group:
• Injection Depth—Use the pull-down menu to select Standard or Minimum to
indicate how the sample is introduced into the GC. If you select Standard, the
autosampler will insert the needle all the way into the injection port. If you select
Minimum, the autosampler will barely enter the injection port.
• Pre-inj Dwell Time(s)—Use this field to enter the time (in seconds) that the
needle will be in the injection port before the plunger injects the sample.
• Post-inj Dwell Time (s)—Use this field to enter the time (in seconds) that the
needle will be in the injection port after the plunger injects the sample.
The two main forms of injection are a hot needle technique and a cold needle
technique.
In a hot needle injection, the needle is preheated before the sample is introduced,
which causes the sample to vaporize before it leaves the needle. The vapor is then
mixed with carrier gas and swept into the column.
In a cold-needle injection, the needle is kept as cold as possible so that the sample
can be introduced as a liquid stream that vaporizes in the injector. The sample
vapor is produced closer to the column inlet, which can lead to better sensitivity,
but worse reproducibility from one run to the next.
Thermo Scientific ISQ User Guide 33