MICROPIPETTES ARE DEVICES THAT ARE USED TO DELIVER SMALL VOLUMES OF LIQUID;
USUALLY IN THE RANGE OF 0.5 TO 1,000 MICROLITERS.
AND LIKE OTHER FORMS OF LABORATORY INSTRUMENTATION,
THE MICROPIPETTE MUST BE OPERATED WITH PRECISION SO THAT YOUR MEASUREMENTS CAN BE REPRODUCED
CONSISTENTLY.
THE FIRST STEP IS TO SET THE MICROPIPETTE TO THE CORRECT VOLUME YOU WANT TO TRANSFER.
FOR THIS EXAMPLE, WE’LL USE 750 MICROLITERS.
THE MICROPIPETTE REQUIRES A DISPOSABLE TIP.
TIPS ARE OFTEN STORED IN AUTOCLAVED PLASTIC RACKS.
DON’T TOUCH THE TIP WITH YOUR HANDS BECAUSE THIS COULD INTRODUCE CONTAMINATION.
ATTACH A TIP BY PRESSING THE MICROPIPETTE FIRMLY DOWN ONTO THE TIP.
THE TUBE WITH RED LIQUID IS OUR SAMPLE SOLUTION.
LET’S USE THE MICROPIPETTE TO TRANSFER 750 MICROLITERS TO THE EMPTY MICRO-CENTRIFUGE
TUBES.
PRESS THE PLUNGER TO THE FIRST STOP,
AND INSERT THE TIP INTO THE LIQUID, JUST BELOW THE MENISCUS.
A GOOD RULE OF THUMB IS TO PLACE ABOUT HALF OF THE TIP INTO THE SOLUTION.
ALLOW THE PLUNGER TO SLOWLY RETURN TO ITS UN-DEPRESSED POSITION
AS THE SAMPLE SOLUTION IS DRAWN INTO THE TIP.
PAUSE FOR ONE SECOND.
NOW PULL THE MICROPIPETTE STRAIGHT UP.
PLACE THE TIP INTO THE FIRST MICROCENTRIFUGE TUBE.
PRESS THE PLUNGER ALL THE WAY TO THE SECOND STOP.
THE SAMPLE IS EXPELLED INTO THE CONTAINER.
HOLD THE PLUNGER DOWN AND PAUSE FOR ABOUT 2 SECONDS.
DON’T WORK TOO QUICKLY.
WITH THE PLUNGER STILL FULLY DEPRESSED, SLOWLY REMOVE THE MICROPIPETTE.
NOW YOU CAN RELEASE THE PLUNGER AND EJECT THE TIP INTO A WASTE CONTAINER.
NOW WE’VE SUCCESSFULLY USED A MICROPIPETTE.
IT’S NOT HARD; SO DON’T BE INTIMIDATED BY IT.
BUT IT DOES TAKE PRACTICE.
YOUR TECHNIQUE IS VERY IMPORTANT.
AND SINCE A MICROPIPETTE DELIVERS SUCH SMALL VOLUMES,
A MINOR OPERATIONAL FLAW COULD MAKE A HUGE NEGATIVE IMPACT ON THE ACCURACY OF YOUR MEASUREMENTS.
LET’S LOOK AT SOME EXAMPLES OF COMMON MISTAKES.
SEE IF YOU CAN IDENTIFY WHAT THE TECHNICIAN IS DOING INCORRECTLY.
WHAT’S WRONG WITH THIS TECHNIQUE?
IN THIS EXAMPLE, THE TECHNICIAN IS PRESSING THE PLUNGER AFTER THE TIP HAS BEEN PLACED
IN THE SOLUTION, FORCING AIR BUBBLES INTO THE SOLUTION.
THE CORRECT PROCEDURE IS TO PRESS THE PLUNGER TO THE FIRST STOP, THEN INSERT THE MICROPIPETTE
INTO THE SOLUTION.
WHAT’S THE MISTAKE IN THIS EXAMPLE?
HERE THE TECHNICIAN PRESSES THE PLUNGER TO THE SECOND STOP BEFORE PLACING THE TIP INTO
THE LIQUID.
THIS CAUSES EXTRA LIQUID TO BE DRAWN INTO THE TIP.
YOU CAN SEE THE DIFFERENCE.
THE MICROPIPETTE ON THE RIGHT WAS USED PROPERLY AND HOLDS THE CORRECT VOLUME.
THE CORRECT PROCEDURE IS TO PRESS THE PLUNGER TO THE FIRST STOP AS SEEN HERE.
WHAT’S WRONG THIS TIME?
HERE THE TECHNICIAN IS WORKING TOO QUICKLY AND HE’S ALLOWING THE PLUNGER TO SNAP UP
WITHOUT ANY RESISTANCE.
THIS WILL LEAD TO INCORRECT MEASUREMENTS AND MAY EVEN DAMAGE THE MICROPIPETTE.
REMEMBER TO PIPETTE SLOWLY AND METHODICALLY.
USE CONSISTENT SPEED AND PRESSURE TO RELEASE THE PLUNGER IN A STEADY MANNER.
NOW LET’S EXAMINE A COMMON MISTAKE WHEN DELIVERING AN ALIQUOT TO A NEW VESSEL.
WATCH THE TECHNICIAN CAREFULLY AND IDENTIFY HIS MISTAKE.
HERE THE TECHNICIAN PRESSED ONLY TO THE FIRST STOP TO DELIVER THE SAMPLE.
YOU CAN SEE THAT THERE IS STILL SOME LIQUID IN THE PIPETTE TIP.
THE CORRECT TECHNIQUE IS TO PRESS THE PLUNGER DOWN TO THE SECOND STOP,
WAIT ABOUT 2 SECONDS, AND REMOVE THE TIP FROM THE VESSEL WITH THE PLUNGER STILL FULLY DEPRESSED.
SO NOW WE’VE SEEN SOME OF THE MOST COMMON MICROPIPETTING MISTAKES.
LET’S REVIEW THE CORRECT TECHNIQUE ONE MORE TIME.
SELECT THE VOLUME.
SET THE TIP.
PRESS AND HOLD THE PLUNGER AT THE FIRST STOP.
PLACE THE TIP INTO THE LIQUID.
SLOWLY RELEASE THE PLUNGER.
PAUSE FOR A SECOND AND THEN REMOVE THE TIP.
INSERT THE TIP INTO THE DELIVERY VESSEL.
PRESS THE PLUNGER TO THE SECOND STOP
PAUSE FOR 2 SECONDS.
REMOVE THE TIP
RELEASE THE PLUNGER
AND EJECT THE TIP INTO THE WASTE CONTAINER.
THAT’S IT.
NOW YOU’RE READY TO PRACTICE USING A MICROPIPETTE.