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Injection Principle
A six-port high pressure switching valve can perform the
injections based on the
flushed loop
principle. Loopfilling can
be done on a volume basis, controlled by the digital dispenser
system, or on a time basis by headspace pressure on the
sample to shorten filling time for larger loop volumes. See
Operation
on page 17. The switching patterns of the valve in
“LOAD” and “INJECT” positions are shown in Figure 4. An
injection is performed as described in the following paragraphs.
Dispenser-controlled Injection
1. Dispenser aspirates an approximately 10 µL air bubble in the
sample needle for more efficient removal of the previous
sample.
2. With the injection valve in inject position, the coaxial needle
pair is inserted into the sample. Air pressure, applied to the
sample through the outer air needle, ensures that no air or
vapor bubbles are formed during sample withdrawal.
3. Dispenser withdraws “preflush volume” from sample vial to
fill the sample line with sample and to remove previous
sample (30 - 999 µL, programmable).
4. Injection valve switches into load position with flushed-loop
injections; dispenser transports 2 or 3 X loopvolume through
the loop to fill the loop quantitatively.
2 X loopvolume for loops equal to or larger than 100 µL
3 X loopvolume for loops smaller than 100 µL
5. Injection valve switches into inject position. The sample loop
is now part of the HPLC mobile phase flow path. The
sample is transported to the column, and the analysis time
starts.
If one injection is to be made out of each sample vial, the needle
pair withdraws after analysis time and sequence 1-5 is repeated
for the next vial. If more than one injection is to be made out of
the same sample vial, the needles remain in the vial and after
Summary of Contents for ProStar 400
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