Minimizing Liquid Delivery Risk: Operators as Sources of Error

This is the third in a series of articles entitled “Minimizing Liquid Delivery Risk,” addressing the most common causes of liquid delivery error and providing guidance on how to address and overcome these errors.

For laboratory quality assurance, all critical tasks must be standardized, including liquid handling. Laboratory liquid handling quality assurance programs commonly focus on pipet calibration, repair, and maintenance, but rarely include protocols on verifying operator technique. Yet just as malfunctioning pipets and automated liquid handlers can result in inaccurate delivery volumes and alter laboratory results, so too can poor pipetting skills.

The urgent need for operator training is discussed in a recently distributed letter from the Centers for Medicare and Medicaid Services, which cited “poor pipetting technique” as one of the causes of “questionable test results” generated with an HIV test kit. After the erroneous results were reported, a root cause analysis determined that the operator incorrectly used the pipetting system during the test protocol, which required the addition of a microspecimen of sample. Following this incident, the Center’s Department of Health and Human Services formally recommended that laboratories institute staff training, competency assessments, and the evaluation of quality assurance protocols to prevent similar error.1

Like baseball players being coached on swinging a bat and new drivers taking lessons before being able to legally operate a car, laboratory technicians must be trained on proper pipetting skills. Technique must be standardized within and across laboratories to minimize error and facilitate data comparability. Otherwise data integrity may be at risk.

This article discusses common pipetting technique errors, their impact on pipetting accuracy and precision, and how effective training programs can minimize the risk of error.

How operator technique contributes to error

Laboratorians pipet on a daily basis. Yet many have never received formal training on pipetting, and like most repetitive, common tasks, pipetting is often taken for granted. It is important to understand the steps that laboratorians can take to improve pipetting skills. First, however, it is helpful to evaluate common pipetting errors that can contribute to volume variation, all of which can be avoided with proper training. Common pipetting errors include: 

  • Failure to prewet pipet tip: If pipet operators do not prewet the pipet tip prior to initial delivery, sample volume can be lost due to evaporation within the tip. Aspirating and expelling sample liquid at least three times before delivery can mitigate this risk, and is especially important when handling volatile solutions such as organic solvents.
  • Disregarding temperature: Sample volume can be altered if the pipet and the liquid being dispensed are not temperature equilibrated. This is because air displacement pipets are affected by air pressure, relative humidity, and vapor pressure of the liquid, all of which are temperature dependent. Human body heat can also be transferred from the user to the pipet if handled for too long, also causing volume variation.
  • Tip wiping: Unnecessary tip wiping can lead to sample loss, especially if wiping with absorbent materials, which can carry sample from the pipet tip.
  • Choosing the wrong pipetting mode: The choice of reverse or forward mode during pipetting is often arbitrary or based on operator preference. Yet reverse mode should only be used for viscous samples. During reverse mode, the plunger is depressed completely (past the first stop) to aspirate the sample and then depressed only to the first stop to deliver it. Therefore, using reverse mode with aqueous solutions leads to overdelivery, while using forward mode with viscous solutions results in underdelivery.
  • Working too quickly: After aspirating, failure to pause with the pipet tip in the liquid can lead to underdelivery. This is because the liquid is not still at first insertion and requires about one second to settle.
  • Pipetting at an angle: Touching the pipet tip to the container sides during aspiration results in loss of sample. In addition, removing the pipet at an angle can cause volume variation due to surface tension effects, especially when pipetting small volumes. Pulling the pipet straight out of the container can minimize error.
  • Using the wrong pipet tips: Failure to choose the proper tips for a given type of pipet can lead to an inadequate seal between the pipet and tip, causing leakage and sample loss.

Trends highlighting the need for training

The need to include pipetting technique training in laboratory quality assurance programs is growing due to several trends in today’s life sciences industry. First, laboratories across markets are working with smaller liquid volumes and more complex multipart tests, including serial dilution protocols and PCR assays, where inaccuracies of just one microliter can be detrimental. Because microliter quantities are more sensitive to volume variation, operator variability can significantly alter research results.

Another trend, as evident in the letter distributed by the Centers for Medicare and Medicaid Services referenced above, is a shortage of trained laboratory professionals, and a corresponding increased focus by regulatory bodies on ensuring operator competency. International standards such as ISO 17025, “General Requirements for the Competence of Testing and Calibration Laboratories,” and ISO 15189, “Medical Laboratories—Particular Requirements for Quality and Competence,” place a strong and appropriate emphasis on assessment of operator competency.

Solution: Pipetting technique training

By providing technicians with proper training from expert professionals in liquid handling, laboratories can minimize the risk of volume variability caused by operators (Figure 1). Yet to reduce the risk of laboratory error, a comprehensive and standardized method of pipetting technique training is essential.

Figure 1 - Bjoern Carle, Laboratory Applications Scientist, ARTEL, helps a student improve her multichannel pipetting technique using the ARTEL Method™ of training which provides hands-on technique coaching with immediate feedback, and pre- and post-training skills assessments.

The first step in improving operator technique is educating users about the pipet itself. Topics should include the mechanical function of modern pipets, which work through air displacement, and the variables that can affect accuracy and precision. This portion of the training should also include an overview of the various types and brands of pipets and when best to use each, as well as how to select the proper tips. It is also important to review existing regulations and quality standards to ensure compliance, and illustrate how technique can alter laboratory data.

After providing a foundation of knowledge about pipets, demonstration of proper technique and hands-on coaching follow (Figure 2). This stage of the training is most effective when coupled with measurement technologies that can provide immediate feedback. Operators can instantly verify how various physical actions alter final volume and change their technique accordingly.

Figure 2 - ARTEL’s Pipetting Technique Training and Certification Program helps laboratories standardize pipetting technique and reduce operator error.

Like any class or seminar, the ability to measure learning and proficiency is essential. With pipetting technique training programs, pre- and post-training skills assessments are necessary to gauge improvement in pipetting accuracy and precision.

Standardized measurement tools that document the effectiveness of a training program coupled with standardized training can be used to facilitate certification. This certification can provide laboratory managers with objective evidence and documentation to support the pipetting competency and consistency of their technicians, and this will prove useful as regulations continue to advance.

It is not enough to only train pipet operators. Training is important for laboratorians at all levels, whether they are on-the-bench scientists and technicians or laboratory managers. Process control-focused training can be beneficial for quality and laboratory managers and supervisors. This level of training can include information about pipet repair and maintenance, detailed information about relevant regulations and quality standards, and calibration technologies. Best practices for the development and implementation of liquid handling quality assurance programs must also be addressed.

Lastly, pipetting technique training should not be a one-time event. Annual or semiannual training is optimal to ensure that operators pipet consistently on an ongoing basis.


It is evident that operators contribute to laboratory error through inconsistent pipetting technique. For this reason, instrumentation is not the only thing that needs frequent calibration or checks. Laboratory technicians also need ongoing training. To minimize risk of liquid handling inaccuracy and enhance data integrity, pipetting technique training programs are essential.

See for how environmental conditions can contribute to laboratory error.



Ms. Vaccaro is Technical Services Manager, ARTEL, 25 Bradley Dr., Westbrook, ME 04092, U.S.A.; tel.: 207-854- 0860; fax: 207-854-0867; e-mail: