Gilson 402 User Manual page 64

Operation - Advanced Use
Measurement Screen
High precision is obtained by
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performing this action at a low flow
rate. And, because the piston
accelerates after pressing the
command button, you are advised
to start-and-stop dispensing by
repeatedly pushing the command
button with an increasing frequency
as the liquid nears the tip.
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After completely aspirating the liquid being measured,
you see (for example) the Measurement Screen.
Procedure
1) Aspirate all the liquid contained in the source
vial, plus an air cushion, to ensure that you have
aspirated all the liquid. You should press the
command button to stop aspirating when you
can see the air/liquid interface in the transfer
tubing.
2) Press the Asp key to reverse the direction of
flow; (Asp is replaced by Disp).
3) With the tip of the tubing in the vial, press the
command button to start dispensing the air
cushion.
4) While carefully watching the air/liquid inter-
face, press the command button to stop dispens-
ing at the instant the liquid arrives at the tip of
the tubing .
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5) Read the volume shown on the screen (496.7 µL
in the example).
6) With the tip of the tubing in the vial, press the
command button to dispense the liquid back into
the source vial.
7) Before repeating this procedure with other vials,
remember to reverse the direction of flow by
pressing the Disp key again (Disp is replaced by
Asp).
Conclude the current measurement by pressing
STOP or End (see Prime for details).
Titrate
The use of this direct manipulation is the same as
classical titration (using a burette) where the idea is
to run a quantity of reagent into a sample that
includes a pH indicator, up to the point where the
color changes. With 402, you may also use titrate to
fill plates, vials, or bottles.
To titrate, you aspirate a known volume of reagent,
dispense part of the volume required into the sample,
agitate the sample, dispense a small amount,
agitate again, dispense a smaller amount, agitate
again, etc., as you move in finer and finer steps
towards the point where you have added the
precise volume required to change the color.
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