PerkinElmer OilExpress 4, User Manual

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148 . OilExpress 4 System User's Guide
Appendix 3: Liquid Handling
The autosampler uses a method of sampling referred to as “aspirate and dispense”. System
liquid is used as hydraulic fluid in the instrument. Before the sampling tips can aspirate liquid,
the system must be primed with the system liquid.
The system liquid, once primed through the tubing and sampling tips, acts like
non-compressible hydraulic fluid in a braking system. The syringe pump moves the syringe
plunger up and down in the syringe barrel like a piston. The movement of the syringe
plunger moves the system liquid. The motion of the system liquid pulls and pushes sample
liquids, and other fluids, into and out of the sampling tip.
A small volume of air is aspirated between the system liquid (the system air gap) and the
sample to minimize contamination/dilution of sample with the system liquid. The sample is
then aspirated. A small volume of sample (100 µL) is aspirated as “waste volume”. The first
sample aspirated may come into contact with tiny droplets of system liquid inside the
VersaTip and tubing, and so the leading part of the sample may pick up these droplets,
becoming diluted. A small amount of air known as a transport gap is aspirated to prevent the
sample from dripping from the tip. The sample volume is dispensed into the fill cup. The
waste volume and the system air gap are then dispensed into the waste trough.
NOTE: Dripping from the tip could indicate a leak in the system.
The aspirate and dispense volumes, aspirate and dispense rates, and air gaps have been
optimized and pre-defined for OilExpress 4 FT-IR analysis, and cannot be adjusted by the
user. However, if you would like to read a more detailed account of the principles behind this,
you can refer to the
JANUS® Automated Liquid Handling System User Manual
(Document
Number 1694282H). If you have purchased an OilPrep 4 system, you can also refer to the
OilPrep Oil Dilution System Operation Manual
(Document Number 8860042).