Metrohm 730 Sample Changer - Manuel (Page 119)

4.7 Pipetting with the Swing Head
730 Sample Changer, Detailed Description 116
Preparing the pipetting system
Before using for the first time, rinse the cylin-
der of the Dosino and the pipetting tube with
n-hexane to remove any fatty residues. Then
blow all parts dry with air or nitrogen.
Draw the pipetting tube with extended tip
through the guide shaft and cut the tip down
to approx. 1 cm with a sharp knife.
Wherever possible, use completely de-
gassed
, deionized water as the dosing liquid.
Before using the pipetting system for the first
time, or if the system has not been used for
some time, execute the "prepare" command
(<DOS> key) approx. three times to guaran-
tee the absence of air bubbles in the dosing
system.
Factors that influence the accuracy of the pipetting process
• Dosing or filling rates that are too high may cause air bubbles in
the system, and may prevent the liquid being pipetted from be-
ing completely ejected. Reduce the rates to obtain more accu-
rate results and to avoid carry-overs.
• When using a 10 mL pipetting tube (6.1562.100) with a 2 mm
diameter, the volume of the air bubble between the two liquid
systems should be approx. 50
µ L, which is equivalent to a
length of approx. 1.6 cm. If it is too large, the air is compressed
or expanded, which alters the volume during aspiration and
ejection.
• After ejecting the rinsing liquid, drops of liquid may remain on
the tip of the pipette. They should be scraped off on a
"scraper", as described on page 117 before aspirating more
sample solution.
• All sample vessels should be filled to approximately the same
level to allow an optimum lift height to be set for aspirating the
solution.
• The dosing commands 'adjust' and 'level' serve to eliminate
mechanical play between spindle and cylinder.
adjust: Eliminate play away from the direction of the last piston
movement.
level: Eliminate play in the direction of the last piston movement
after turning the cock to the fill position.
Pipetting
tip, approx.
1 cm
Guiding
shaft
Screw
plug