Patent claim: Pipetting system 100 200 300 400 for pipetting a test liquid 10 the system 100 200 300 400 comprising a pipetting head 20 mounted on a head translation mechanism 21 the system 100 200 300 400 further comprising an aspirationdispensing nozzle 30 attached to the pipetting head 20 and a nozzle line 31 a pump 40 and a pump line 41 a fluid supplier 50 comprising a fluid 52 and a fluid supplier line 51 and at least one valve 60 70 71 72 connected to any of the nozzle line 31 the pump line 41 and the fluid supplier line 51 the system 100 200 300 400 further comprising a controller 90 90 90 90 configured to control the at least one valve 60 70 71 72 such thatwhen the aspirationdispensing nozzle 30 is in an aspiration position 1 to aspirate a predefined volume of test liquid 10 the nozzle line 31 is fluidically connected to the pump line 41 and fluidically disconnected from the fluid supplier line 51when moving the aspirationdispensing nozzle 30 to a dispensing position 2 the nozzle line 31 is fluidically disconnected from the pump line 41before an aspirated volume of test liquid 10 is dispensed in the dispensing position 2 the nozzle line 31 is fluidically connected to the pump line 41.

Related passage: After the supply of the pressure transmission medium an operation of sucking the discharge liquid 30 in a necessary amount which is actually dispensed is performed.First the tip portion of the nozzle 12 is moved by the XYZ moving mechanism to a position above the container 41 in which the discharge liquid 30 to be dispensed is stored.Next before starting to suck the discharge liquid 30 the piston 29 of the pump 9 is slightly retracted with the tip end portion of the nozzle 12 held in air thereby sucking a very small amount of air into the tip portion of the nozzle 12 to form a gap 31.The gap 31 serves to prevent mixing of the pressure transmission medium 2 and the discharge liquid 30.If the amount of sucked air is too large the discharge amount of the discharge liquid 30 would be instable.Conversely if the amount of sucked air is too small mixing of the pressure transmission medium 2 and the discharge liquid 30 would occur.Therefore the amount of sucked air is properly selected.In the embodiment as one practical example air is sucked in an amount corresponding to about 10 of the amount of one droplet of the discharge liquid 30.Then the tip portion of the nozzle 12 is dipped in the discharge liquid 30 to be discharged and the discharge liquid 30 is sucked by retracting the piston 29 of the pump 9.The amount of thesucked discharge liquid 30 is adjusted in accordance with the stroke through which the piston 29 of the pump 9 is retracted.Here the amount of the sucked discharge liquid 30 is preferably set to be slightly larger than a total amount of the discharge liquid 30 to be dispensed.This is because if the amount of the sucked discharge liquid and the amount of the dispensed discharge liquid are equal to each other there is a risk that as approaching the end of the dispensing the discharge amount becomes instable due to an influence of the air 31 having been sucked before starting to suck the discharge liquid 30 or that the discharge liquid 30 may be discharged in a randomly scattering way upon reaching a region containing the air 31 at an end of the discharge.Here the tip portion of the nozzle 12 is preferably set to have a length enough to store an amount of the discharge liquid 30 to be dispensed at a time e.g.a total amount of the discharge liquid 30 to be dispensed when a plate including a plurality of recesses formed therein as an array is used and the discharge liquid 30 is dispensed into all the recesses.Furthermore the diameter of the nozzle 12 is appropriately selected depending on the amount of one droplet to be discharged.For example a tapered conical nozzle having a tip portion with an inner diameter of about 0.1 mm and a length of 5 to 10 mm is used in the embodiment.