Pipette Tip Bend Test
A pipette (also spelled pipet or pipettor) is used to aspirate and dispense fluids in wells for analysis and further testing. There are many types of piston pipettes, but all work on essentially the same principle; hand or mechanical pressure on a piston or plunger working over a fixed length in a cylinder forces a pre-determined volume of liquid out of the orifice of the pipette. Pipettes are used to hold body fluids, oily fluids, concentrated acids, nucleic acids, and volatile compounds.
An ADMET customer presented us with a problem. Their plastic disposable pipette tips lacked sufficient stiffness to ensure the customer’s success in dispensing fluids. The objective was to find a testing machine with servo control and constant rate of crosshead movement to apply a constant bending force to the end of the pipette tip. By acquiring the flexural strength of the pipette tip, it was possible to determine whether the stiffness was at an acceptable level or if the manufacturing process needed review.
ADMET designed the fixture pictured below to hold the pipette tip by the connection end. By loosening the hex screw on the slide base, this fixture is adjustable for different length tips.
Although the system, ADMET’s eXpert 5601, is capable of up to 25 in/min, the compression bending test profile stated 2 in/min until a load limit of 6 lbs was achieved. The customer felt that if the tip bend at 6 lbs was 45 degrees or less, the tip was stiff enough and production could continue. Each tip was put through a variety of test profiles before determining the max load that would ensure that the stiffness and angle to meet the production requirements as well as being able to compare with competitor’s similar product characteristics. ADMET’s MTESTQuattro software enabled the Quality Manger to easily set up testing profiles, define operator and user designations, and analyze individual and group test results. By obtaining the data from the testing, management can make decisions to avoid significant revenue loss.