Q. How often should I return my pipettes for service & calibration?
The frequency of both service and re-calibration is based on risk assessment. The risk assessment is likely to consider the frequency of the use of the pipette, the corrosiveness of the liquid being dispensed and the risk to the business if the pipette goes out of calibration. This would normally result in the decisions on how often being set between 3 months and a year.
Q. What is the Gravimetric Method?
The Gravimetric test is the most commonly used method for pipette calibration by pipette manufacturers and international standard organisations.
It is based on the determination of the weight of water samples delivered by the pipette. Implementation of this method requires the strict monitoring of environmental conditions and the systematic use of adequate and controlled equipment. Ambient temperature, barometric pressure and relative humidity must all be checked and regulated.
Conversion of weight to volume must take into account the density of the liquid as well as evaporation during the cycle time.
For each measurement, the corresponding volume (Vi) can be calculated as follows: Vi = (Wi + e) Z.
Wi – the weight as read on the balance;
e – the mean evaporation loss during the cycle time;
Z – expressed in µl/mg, is a conversion factor incorporating density of water buoyed in air, at test temperature and barometric pressure.
Always calibrate to ISO standards.
Q. Why should the Seal and O-ring be changed on every service & calibration?
Replacing seals & O-rings during service as recommended by the Manufacturer maintains high levels of accuracy & precision. Some service agencies, may use grease to obtain an air-tight seal rather than replacing parts. PIPETMAN® (‘G’ excluded) are not designed as a greased system and this quick fix will have long term detrimental effects on pistons and tip holders with a loss of calibration over time.
Q. Why is it important to check pipette linearity?
For mechanical reasons, pipettes can only deliver samples accurately over a limited range of volumes for each particular model.
Ideally, the volume of liquid delivered in that range follows a precise linear relationship to that selected. It is essential to check this linearity when the pipette is serviced to ensure correct functionality at both the upper and lower limits of the pipettes capacity.
With the most basic level of service, volumes are checked at both extremes of a pipettes range. We would always recommend a minimum of 2.2; meaning two volumes are checked with two weightings’ to ensure both accuracy and linearity.
To increase their throughput some service agents only perform checks at a single mid-point volume with three or five weighing, and even issue calibration certificates based on these minimal readings.
As the majority of pipettes are variable volume how can you ensure that a pipette is linear across its specification range by testing only one volume?
Always ask what level of service you are getting for your money.
Q. Why should Gilson® PIPETMAN® ('G' excluded) NOT be greased?
If you apply grease to the internal parts of a pipette, it will need to be removed with a solvent for cleaning during servicing. The amount of grease re-applied may vary and could alter the calibration of the pipette.
PIPETMAN® maintained in the correct manner, as specified by Gilson®, should never require grease to be applied. PIPETMAN® can be cleaned and seals and O-rings replaced without altering the calibration.
Delsaro always replace these critical dry-seal parts during servicing to maintain PIPETMAN®’s high levels of accuracy and precision. Service agencies who wish to reduce costs, rather than replacing parts, may use grease to obtain an air-tight seal. Grease may harbour contaminants within the pipette, introduced through aerosols or when pipetting volatile liquids. These are retained in the grease and may advance corrosion of internal pipette parts such as pistons.
Such damage may increase costs as additional parts are required more frequently than if the pipette is correctly maintained. PIPETMAN® (‘G’ excluded) is not designed as a greased system and this quick fix will have a long term detrimental effect on the pipette with a loss of calibration over time.
Don’t let anyone grease your PIPETMAN® (‘G’** excluded) !
** Manufacturer only grease required
Q. Why should I ensure that only quality spares are used by my service agent?
The pipettes manufacturers’ warranty and specification will only be honored when quality replacement spare parts are used during service and calibration.
Our pipette spares are subject to the highest levels of quality control and are checked and warranted. They ensure the use of quality materials such as PVDF for the best chemical resistance, compatibility and durability. The perfect size dimensions of pistons, tip-holders and tip ejectors guarantee maximum accuracy and precision plus trouble free ejection of tips.
Q. How old is my Gilson® pipette?
All Gilson pipettes carry a serial number which identifies the pipette and the date of manufacture (see example below).
Example of a serial number A10369H
The first letter represents the year of manufacture.
The number is the individual production number.
The last letter corresponds to the month of manufacture.
Click here for more about Gilson® Serial Numbers
Q. What are the main causes of leaks?
There are various reasons for leaks, the most common of which are;
Tip holder is scratched or damaged
Use of non-manufacturer tips
Use of non-manufacturer seals
Vapour pressure from organic solvents
Q. What causes leaks when using organic solvents?
When an organic solvent is used with an air-displacement pipette, leaks may occur. These leaks are caused by the difference between the vapour pressure of the solvent and pressure of the air cushion between the piston and the sample.
Solution:
- Use a positive-displacement pipette (Microman®), because it has no air cushion.
- If you are using an air-displacement pipette, saturate the air cushion of your pipette with solvent vapour by aspirating and distributing solvent repeatedly. The leak will stop when pressure equilibrium is reached.
Q. How can I prevent piston corrosion?
After contact with corrosive liquids, a piston should be cleaned with alcohol and a soft tissue.
Take care to avoid shocks or scratches.
Q. Why do I need a pipette holder?
To prevent corrosion, contamination or breakage, always store your pipettes vertically to prevent liquids from running inside the shaft of the pipette.
Do not leave your pipette lying on the workbench where it can come into contact with chemicals or fall off and break.
Q. How do I prevent aerosol contamination?
Use a pipette with sterilized filter tips when faced with at least two of the following situations at the same time:
– working in sterile conditions
– pipetting aqueous samples
– avoiding cross-contamination
Use a positive-displacement pipette with sterilized capillaries and pistons when faced with at least two of the following situations at the same time:
– working in sterile conditions
– pipetting viscous samples
– avoiding cross-contamination
Q. What are the best replacement parts for my Pipettes?
We recommend only manufacturer genuine replacement parts should be used for your pipettes, during the manufactureres’ warranty period, otherwise your warranty may become void. Once the Manufacturers’ warranty has lapsed, we recommend only quality spares are used.
Q. What are published specifications?
Specifications are established by the manufacturer. They guarantee, in terms of accuracy and precision, the performance of all pipettes of a given brand and a given model at a certain volume setting.
Accuracy – is the ability of a measuring instrument to give responses close to a true value. Precision – is the ability of an instrument to provide closely similar responses (measurements). Precision is also referred to as repeatability and/or reproducibility.
Q. The tips do not fit well, what should I do??
Always use manufacturer calibrated pipette tips for your pipettes.
Push upward on the tip-ejector to make sure it is positioned properly.
Clean the tip holder with alcohol. If it is worn or has been chemically attacked, order a new part.