Pipette Service and Calibration FAQs

1. What does UKAS Accreditation mean to me?

Based on rigorous documentation, extensive training, and long-term proficiency testing, METTLER TOLEDO’s Pipette Service division has achieved the highest level of calibration competency and data integrity when using the gravimetric method. It has held UKAS accreditation since 1998 and now provides a single point for servicing of all major brands of pipettes to this level.

When you choose UKAS calibration you will receive additional information on your Calibration Certificate including statement of measurement uncertainty per volume setting. Whether or not you choose this option, METTLER TOLEDO’s Pipette Service complies with all quality standards as set forth by ISO guidelines and UKAS interpretation, assuring you of the highest level of calibration competency and traceability.

Isn’t it comforting to know that UKAS auditors have ensured the highest calibration standards are being met, so you can trust your service provider.

2. What is ISO 8655?

ISO 8655 is an international standard for the volumetric calibration of Piston Operated Volumetric Apparatus (POVA).

Calibration methods are detailed in the standard and the gravimetric test is the reference method. Maximum errors for trueness (Inaccuracy) and precision (CV%) are listed for all types of POVA device.

ISO 8655 defines the useful volume range of a pipette as being from 10% of nominal to 100% of nominal. The most commonly used volume settings take after the ISO standard; the nominal volume (100%), 50% of nominal and the lower limit or 10% of nominal volume (ISO 8655-6:2002 section 7.1.1).
Volume settings can sometimes vary depending on the calibration standard applied.

The standard states "Apparatus shall be calibrated with noted tips. (A pipette calibrated with a specific tip shall only be deemed within calibration with that tip)".

ISO 8655 recognises pipettes, tips and service as a complete system.

1. How long is the METTLER TOLEDO pipette performance warranty following service?

METTLER TOLEDO guarantees that parts are replaced with new, high quality spares. This commitment to quality allows us to warranty our service for 3 months.

2. How often should I return my pipettes for service and 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 pipetted 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.

As a population, pipettes checked annually without any preventative maintenance or regular servicing procedures in place, will have a 20% or more failure rate.

Approximately 95% of pipette failures are attributable to sealing system defects. This is predictable but preventable. Under normal use and based on manufacturer’s recommendations seals should be replaced at least once per year, while tip holders and pistons should be replaced every three to five years. Seals, o-rings, tip holders, tip ejectors and the volume adjustment knobs can easily be changed in your own laboratory without affecting the calibration of your pipettes There are however a number of parts that when changed can alter the pipettes calibration. These parts include the piston and piston assembly, friction o-ring, operating rod and volumeter. When these need changing it is best to return your pipettes to your service provider for replacement and pipette re-calibration.

3. What can I do in my laboratory to maintain my own pipettes?

Prevention is better than cure. It is recommended that you check your pipettes daily before use and establish a routine for basic servicing. There are a number of basic care checks for your pipettes that can be performed in your own laboratory to maintain correct functionality in between full servicing. These include a simple functionality check and a visual leak test.

1. 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 is the weight as read on the balance, e is 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.

2. Why do METTLER TOLEDO change the seal and O-ring on every service and calibration?

Other service agencies who wish to reduce costs, may use grease to obtain an air-tight seal rather than replacing parts. Many commonly used pipettes 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.

3. 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.

Even with METTLER TOLEDO’s most basic level of service, volumes are checked at both extremes of a pipettes range. Our standard service level is 2.2, meaning two volumes are checked with two weighings to ensure both accuracy and linearity.

To increase their throughput some other service agents only perform checks at a single mid-point volume with three or five weighings, 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 it’s specification range by testing only one volume? Always ask what level of service you are getting for your money.

4. Why should dry-seal pipettes 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.

Dry-seal pipettes maintained in the correct way, should never require grease to be applied. They can be cleaned and seals and O-rings replaced without altering the calibration.

METTLER TOLEDO always replaces these critical dry-seal parts during servicing to maintain high levels of accuracy and precision. Other service agencies who do not use quality spare parts or 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. For pipettes that are not designed as a greased system this quick fix will have a long term detrimental effect on the pipette with a loss of calibration over time.

 1. Can METTLER TOLEDO test all brands of thermal cyclers?

Yes. CYCLERtest is a completely independent calibration system and as long as your thermal cycler has a regular 0.2ml, 0.5ml or 384 well block METTLER TOLEDO can carry out the calibration. We can also test gradient cyclers with our special gradient protocol, and multiple and/or exchangeable blocks.

2. Can CYCLERtest be used to calibrate my Real Time PCR machine?

Yes, there is a new wireless version of CYCLERtest which has been specifically designed to measure the closed (q)PCR/RT-PCR system. It works by sending the results to the hardware box via radio waves. This system is compatiable with the ABI 7500, ABI 7300, ABI 7900HT with standard 96 well format and Stratagene MX3000 and MX3005P systems. Roche light cyclers can also be calibrated.

3. Can temperature deviations really influence my PCR results?

Yes, when the denaturation temperature is too high, the DNA polymerase will soon loose activity during the PCR process, resulting in low or no yields. Annealing temperatures are very specifically determind. Changes will result in specific bands or no annealing at all./p>

4. How can I change the standard 8 step protocol of my Driftcon system?

By registering on the Driftcon web site www.driftcon.com you can obtain up to 8 different protocols free of charge.

5. How does the heated lid affect the CYCLERtest calibration?

The CYCLERtest calibration can be carried out with either the heated lid being open or closed. Measuring with the heated lid closed can lead to differences, depensing on how the thermocycler reacts on closing the lid. We typically see improvements in uniformity as the thermocycler does not loose heat to the environment and 0.2-0.4C higher accuracies, but for some thermocyclers there is no difference at all. For the Mx3000/3005 you see a deterioration if the uniformity.

6. How often do METTLER TOLEDO advise a thermal cycler should be calibrated?

We advise to have a calibration test at least every year, or every 250 runs, whatever comes first. Some laboratory, national or international regulations might require you to do this more often. We would therefore suggest you take advice from your accredited authority.

7. Isn’t it possible to do a temperature measurement myself?

It will be very difficult. CYCLERtest uses the MTAS (Mobile Temperarure Acquisition System) that was developed by GENOtronics. It uses very sophisticated temperature sensors (thermistors), electronics and software algorithms, to correct for possible deviations. The overall accuracy of this system is better than 0.1ºC. It also makes dynamic multichannel measurements.

8. What does thermal cycler calibration mean and what benefit is it to me?

We test your thermal cycler against internationally accepted standards, and the measurement system itself is complying with the offical temperature measurements regulations. This means that if you have your thermal cycler performance tested with our system, it is also calibrated according to these regulations.

9. What if I buy a new model thermal cycler - how can I obtain the specification sets for my Driftcon system?

You can purchase these from METTLER TOLEDO. The specifications will be loaded onto your computer when you synchronise with CYCLERtest via the Driftcon software. 

10. What if I want to check my cyclers’ performance more often?

We have also developed the Driftcon system for checking the performance of your cycler on a monthly, weekly or daily basis. It is an end user temperature measurement fixture that will show the drift of the accuracy and the spread of your thermal cycler in time, and in relation with the global field specifications of that brand and type of cycler.

11. What if my machine fails after a CYCLERtest calibration?

If your machine fails, the generated report will allow you to make an informed decision based upon the errors found. If the errors are small you may decide they are acceptable. If the errors are found in a specific area then this would suggest a mechanical fault and therefore repairs would be needed. You would then need to return your thermal cycler to the manufacturer.

12. What is an overshoot and an undershoot?

Due to the lack of control, cyclers often are not able to reach a target temperature in a stable way. This means that a denaturation temperature can go much higher that the set temperature, before reaching a plateau. For the annealing temperature plateau, undershoots of up to several degrees are not uncommon.

13. What is the definition of accuracy and spread?

Accuracy is defined as the difference in display and the actual block temperature. Spread (or non-uniformity) is the difference in the temperature between the wells of a cycler block.

14. What is the difference between sending my thermal cycler away to the manufacturer for servicing and METTLER TOLEDO performing the CYCLERtest calibration?

The CYCLERtest (MTAS) calibration is a far more detailed and dynamic calibration check compared to that carried out when your machine is serviced by the manufacturer.

METTLER TOLEDO, by using CYCLERtest, will provide you with a comprehensive report on how your machine is performing. We will not service the machine and repair problems which are found during the test.

15. What kind of report/documentation do I receive with a CYCLERtest calibration?

The test report is encrypted and so can not be modified by an external source. A certificate of Thermal Calibration accompanies every test report, this certificate represents the results of the measured and calculated parameters of the tested instrument.

16. What’s the warranty on your calibration and performance test?

There is no ’warranty’ on the test. We show the output performance of your cycler at the time of measurement. The performance measurement cannot predict what will happen with the accuracy and spread of your cycler in time, nor will it predict if your cycler breaks down the next day. Thermal cyclers wear in time and so will their performance.

17. Which thermal cycler is the best?

Despite all the data that has been collated, CYCLERtest and METTLER TOLEDO will refrain from making any statements on this issue. First of all, we want to be completely independent. Secondly, it is very difficult to make general statements about certain brands or types, because there are already hugh differences between machines of the same type or brand, and also the age of the cycler is of influence.

18. Why are the probes placed in specific well positions?

The positioning of the probes has been devised by using empirical and mathematical data in order to place the probes in the optimum positions for accurate and precise temperature measurements.

19. Why do METTLER TOLEDO not test all 96 wells of the block?

Each well is not individually controlled by the heating and cooling system therefore the positions selected allow an overview of the block to be ascertained, however if you specifically require all wells to be tested this can be carried out. Please contact METTLER TOLEDO to discuss this further.

20. Why should I test my thermal cycler? My results are always OK...

It is very important to know how your thermal cycler behaves. Negative results could be caused by temperature differences in the block, and could be positive in reality. Biological controls are not sufficient to compensate for these differences as variances can occur between wells.