Unravelling the avenue to reliable pipetting

Unravelling the avenue to reliable pipetting


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  • Source: Eppendorf

  • Date: 28 Mar,2024

Ever since the invention of mechanical micropipettes 60 years ago by Eppendorf, this small tool has become a vital part of laboratories worldwide until today to handle micro volumes of liquids, from analytical, clinical or life science labs up to highly sophisticated genomic labs. Early users were the ones who were concerned about the volumetric accuracy in their work got rid of their glass pipettes assisted with rubber bulb to aspirate and dispense liquids. The adaptation to micropipette was a revolution in laboratories requiring low volume liquids to process their samples and to execute their experiments using analytical devices, which in-turn reduced the experiment volume of samples and paved way for high throughput analysis resulting in a drastic reduction in cost per experiment. These micropipettes over the time have evolved in their size, shape, weight, material of construction, ease of use, finesse etc.

Micropipettes are broadly classified in to 2 major types, Air cushion and positive displacement pipettes. In the air cushion pipettes, the piston operates inside an airtight cylinder creating vacuum, and helping the liquid sample to enter inside the tip attached when released for aspiration. The amount of sample aspirated is directly proportional to the displacement of the piston inside the cylinder and the displacement can be defined by adjusting the mechanical gear assembly for specific volumes (a stepper motor in case of electronic pipettes). The precision design of this gear (rachet mechanism) assembly has direct influence on the overall workable volume range of the pipette and its accuracy.

Volume accuracy is a key deciding factors in selecting the right pipette, however maintaining the pipetting accuracy while in use is critical and several factors can impact this. A clear understanding of these factors can help the labs in maintain highest level of accuracy.

Few factors that need attention are listed below.

  1. Number of User handling the pipette
  2. Characteristics of samples – physical & chemical properties
  3. Environmental conditions of the laboratory
  4. Individual users pipette handling practice

User is expected to understand these parameters to decide the frequency of calibration and preventive maintenance. Calibration of the pipette ensures that the pipette delivers the results as accurate as the manufacturer’s specification and preventive maintenance take care of the wearing components of the mechanical assembly that might impact the performance.

As we know, over prolonged usage, pipettes experiences systematic (inaccuracy) and random (precision) errors. Quality Assurance department of the laboratories may want to know the performance deterioration of the pipettes used in their laboratory to decide the frequency of maintenance and calibration. This method of finding the performance status by a calibrating laboratory before attempting any maintenance and calibration is called “as-found” Calibration. Similarly, a calibration performed after complete maintenance of a pipette is called “as-left” calibration. “As-found” and “As-left” measurements shall be performed to do trend analysis of the calibration results.

Preventive care of pipettes is crucial to ensure accurate and reliable measurements, reduces unexpected faults during usage, gives complete peace of mind to the user. Pipette is built with several moving parts and few internal parts like O rings, seals and springs shall be replaced at regular intervals. This wear and tear part replacement should be a part of every preventive maintenance and calibration.

How to choose calibration agency!

Calibration lab (agency) that is accredited by reputable organizations such as ISO/IEC 17025/NABL, who ascertains the measurement error of each pipette is recommended. Accreditation ensures that the lab meets internationally recognized standards for competence and impartiality. Academic institutions and other non- regulated laboratories, who uses pipettes mainly for research activities must still do the Non-Accredited calibration.

While many service providers and laboratories claim that they have the accreditation as per ISO 17025, the user must evaluate the laboratory’s competency before choosing to award the contract.

The approach towards selecting the calibration partner should be based on the value additions that they can offer from the below list.

  1. Laboratory scope covering Measurement Uncertainty and volume range
  2. Qualification and competency of calibration engineers
  3. Proof of NABL certification
  4. CMC (Calibration measurement capability) – as per the scope certificate – lower the CMC values, better the laboratory’s competency.
  5. Traceability information, training records, documental evidence related to lab operation as per ISO 17025, ISO 8655, ISO 20461 and associated NABL documents
  6. Calibration raw data to be shared for statistical evaluation and verification
  7. Usage of a validated software and system that fetches raw data from weighing balance and provide end results without any human intervention
  8. Calculated systematic and random error components along with nominal limits and the status of calibration shall be reported in the calibration certificate.
  9. 4 eye principle to be followed while releasing of calibration certificates.
  10. Digital Calibration certificates are preferred as a part of sustainability measures and also to support LIMS (Laboratory Information Management system).

Vendor audit must be executed as a part of vendor selection and approval which will reduce any possible discrepancy.

Pay larger attention towards maintaining the micro pipettes at your laboratory and keep delivering the most accurate volumes and the best results every time.

For any further support, please do contact Eppendorf at calibration@eppendorf.co.in or info@eppendorf.co.in

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