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The most frequent cause of inaccuracy in piston-operated pipettes is leakage. This arises from damage either to the seals, pistons, or tip cones.Often not detectable by the naked eye, leaks lead to significant volume errors. The BRAND pipette leak tester (PLT unit) for air displacement pipettes finds even the smallest leaks within seconds.

Air-displacement pipettes must be checked at regular intervals and the results must be compared with the ISO 8655-2 error limits. However, a calibration certificate only reflects the results at the time of testing. The time between these calibrations is crucial, since leaks can occur at any time. Well over 80% of pipettes sent in for repair have leaks and are outside their volume tolerances, even if they don’t drip.

While the PLT unit cannot replace regular gravimetric testing, daily pipette checks can provide a safeguard during the periods between calibrations. Even the smallest leaks are detected! Process reliability for the pipettes is thus significantly improved.

Leak rates, their detection and quantification
The leak rate is a measure of the quantity of material that flows through a leak per unit time. For air-displacement pipettes the PLT unit determines the rate through a differential pressure measurement, i.e., after creating a negative pressure, the pressure rise over a given time is measured.

·     The leak rate is determined by considering complex physical relationships. Calculation of the limit values resident in the PLT must include factors such as the dead volume of the pipette/tip system, flow cross section of the pipette tip, pressure rise per unit time, pipette volume and type, etc.

·     The pV value is the product of the pressure and the volume of a certain quantity of a gas at the prevailing temperature. This is a measure of the quantity of material or the mass of the gas.

·     The leak rate Q_Lis the ratio of the pV value and the period of time during which the gas flows through a path
cross-section.

·     For the pipette test, hPa ml/s is a suitable unit for the leak rate. A leak rate of e.g., 1 hPa ml/s at an air pressure of 1000 hPa (approx.atmospheric pressure) means a volume loss of about 1 μl/s.

Easy To Use
Menu-driven software, combined with a jog wheel and affirmative/negative buttons make it easy to select the correct test parameters, pressure units or language (English, Spanish or German)

A Diagnostic Tool
To check the overall pipette system, the test is conducted with mounted, unused tip. When a leak has been identified, the test can be repeated without a tip to determine whether the leak arises from the tip cone/tip coupling region. Additionally static or dynamic (piston operated during test procedure) testing can also help localize source of leaks when detected. The ability to test multichannel pipettes four channels at a time, or individually increases the throughput of testing, and assisting in the diagnosis of faulty channels.

Pass/Fail Determination
The limit values referenced during testing represent a warning limit, from which significantly lower volume values can also be determined gravimetrically. This is one quarter of the volume tolerances, according to ISO 8655-2.
The limit value for the leak volume of a given pipette allows the leak rate to be calculated. These calculations, which are based on over 35 years of experience in the development and production of pipettes, include the dead volume and the intake characteristics, among other things. If the pipette is mechanically defect-free, clean, and the test is carried out properly with the BRAND PLT unit, then the instrument is within the ISO 8655-2 tolerances.

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