Air Displacement or Positive Displacement Pipettes: How to Choose

This article presents an original GuideGxP selection approach and matrix. It is neither a calibration protocol nor a universal pipetting procedure. Acceptance criteria must come from intended use and applicable references, rather than a percentage copied from a generic table.

1. Define the transfer before selecting the instrument

Describe the analytical decision that depends on the transferred volume. A dilution used for a quantitative result and the addition of a reagent in excess may have different needs, even when they use the same volume. GuideGxP recommends an intended-use record covering liquid, volume range, source and destination containers, sequence, users and consequences of an inadequate transfer.

Distinguish the pipette’s nominal volume, selected volume and actual delivered volume. ISO 8655-2:2022 covers air-displacement and positive-displacement pipettes, both single-channel and multichannel, considered with their selected tips and other essential components. The standard’s publicly accessible scope therefore makes clear that the pipette body alone does not constitute the entire system to assess.[1]

Also specify workload: isolated transfers, repeated series, plates, frequent volume changes or different liquids. Avoid a daily average that conceals the most demanding sequences. Establish which requirements are mandatory and which are preferences before a persuasive demonstration implicitly changes the priorities.

2. Understand the two principles without confusing them with electronics

In an air-displacement pipette, the piston acts through a volume of air separating the mechanism from the liquid in the tip. In a positive-displacement system, the piston operates in contact with the liquid in the capillary. These are transfer principles; manual and electronic describe actuation. An electronic pipette is not necessarily a positive-displacement pipette. The NIST educational publication addresses these distinctions and the performance limitations of volumetric transfer.[5]

This difference suggests which influences to investigate, rather than a universal winner. During selection, ask which combination of body, consumable and operating mode has been assessed. For positive displacement, check the availability and compatibility of the capillary-piston assembly; for air displacement, establish which tips are covered by the evidence presented. A consumable fitting onto the instrument does not, by itself, demonstrate equivalent performance.

If a solution offers electronic functions, assess how volume, mode and sequence are set and identified. GuideGxP suggests including an operator handover test: the incoming user must understand the instrument’s state without relying on the previous user’s memory. The most advanced function is useful only when it supports the actual task.

3. Assess viscosity, volatility and thermal conditions

The literature on air-displacement systems describes influences from temperature, evaporation, density, inclination, immersion and interaction between liquid and tip. A temperature difference between liquid and instrument must not be confused with the ambient temperature value alone.[3] The DKD study on air-cushion pipettes confirms the role of environmental conditions, the pipette-tip system and handling; it is used here for these principles, rather than to transfer all its experimental conditions into the laboratory.[4]

Translate properties into observations to investigate. For a viscous matrix, examine completion of aspiration and residual liquid; for a volatile matrix, assess transfer stability and evaporation management. For liquids with different wetting behaviour, observe residues and drop detachment. These are GuideGxP selection questions, rather than sufficient visual criteria for declaring a volume correct.

Do not automatically attribute every difference to the pipette. Check liquid composition and temperature, consumable, container and sequence. If the comparison involves a solvent or hazardous matrix, use only previously approved conditions and protective measures. Selecting the transfer principle does not replace chemical compatibility assessment or assessment of risks to the operator.

4. Select the range, channels and consumables

Compare stated performance at the volumes you will use, rather than only at the maximum nominal volume. Record the units, conditions and configuration to which the data apply. Do not turn a practical rule about using the upper part of the range into a universal prohibition: suitability must be demonstrated at points relevant to the activity.

The number of channels must relate to the task’s geometry. A multichannel pipette may be a candidate for a plate sequence, but requires compatibility between spacing, tips, wells and the aspiration vessel. A single-channel instrument may be more suitable for transfers between different containers. This stage selects the configuration; channel uniformity requires a specific assessment, rather than only the mean volume.

Define tips, any filters, capillaries, contact materials, packaging format and procurement arrangements. GuideGxP proposes treating a consumable substitution as a change to assess, with proportionate responsibilities and checks. Do not declare two options interchangeable simply because the same volume appears on their packaging.

5. Compare performance under intended conditions of use

ISO 8655-10:2024 addresses selection, use, competence and suitability of piston-operated volumetric apparatus. Its official scope and preview were consulted, rather than the complete text; consequently, no unverified test counts or tolerances are attributed to the standard.[2] The following plan is a GuideGxP proposal for approval within the laboratory’s system.

Prepare the comparison before receiving results: candidate configurations, representative liquids, volumes, containers, conditions, operators, measurement method and decision criteria. If you use a substitute liquid, justify which properties it represents and which it excludes. A check with water does not automatically answer every question about a different sample.

Separate the observed systematic component from transfer dispersion and consider the uncertainty of the comparison method. A balance displaying many digits does not automatically make the measurement suitable. Also provide for recording leaks, residues, interruptions and operational difficulties, without using these observations as a substitute for volumetric data.

Compare equivalent conditions and retain unfavourable results and reasons for exclusions. If you change pipette, tip, operator and technique simultaneously, you may not understand which factor explains the difference. Use interpretable comparisons. Calibration documents performance under the reported conditions; fitness for the task requires connecting that information to the intended work.

6. Original matrix: liquid and task, requirement, candidate and test

The following matrix does not prescribe a technology. It makes the choice open to discussion and verification. Add justified acceptance criteria and an owner for each test; no row represents an experimental result already obtained.

7. Consider ergonomics, maintenance and lifetime cost

GuideGxP recommends a trial with the intended users, at the actual workstation or in a representative arrangement. Observe grip, container accessibility, fitting and ejecting consumables, reading settings and necessary interruptions. Do not infer comfort solely from the weight stated in a specification. The comparison must include the sequence, rather than just a few actuations.

Include consumables, training, cleaning, maintenance, checks, service and downtime in the cost. For an electronic instrument, add relevant operational dependencies such as charging and settings management. Do not assign an economic advantage without actual consumption data. A lower purchase price may require more resources during use; the opposite must equally be demonstrated.

EU GMP requires equipment and resources appropriate to QC activities, and records of relevant activities.[6] Selection should therefore clarify who maintains use status, manages a failure and decides on return to service. Do not confuse maintenance, calibration and demonstration of fitness for use.

8. Simulated case: three liquids and a differentiated decision

A laboratory needs to transfer an aqueous solution, a viscous matrix and a volatile solvent. This is a reasoning example without invented experimental results. The initial request is to purchase one electronic model for every activity. The team immediately distinguishes electronic actuation from the transfer principle and establishes volumes, containers and sequences.

For the aqueous solution, it selects an air-displacement configuration as an initial candidate, checking the system with the intended tip. For the viscous matrix, it compares positive displacement with an air-displacement alternative only if supported by a rationale and appropriate operating mode. For the solvent, it also evaluates contact materials, evaporation and previously approved protective conditions.

Tests are designed with criteria defined before the comparison. If a solution meets performance requirements but makes the sequence awkward, the issue remains open; if it is comfortable but fails the metrological requirements, lower cost does not compensate for the gap. The laboratory may conclude that different configurations are needed, or justify a common one: the case does not anticipate the result.

The final decision should specify covered liquids and volumes, consumables, conditions, limits, evidence and necessary training. A new matrix does not automatically fall within the same scope. The responsible person assesses whether existing information is relevant or a new comparison is needed.

9. Frequent mistakes and documenting the choice

• Equating electronic with positive displacement: record principle and actuation separately.
• Reading “suitable for difficult liquids” as a guarantee: identify properties, conditions and performance to demonstrate.
• Assessing only nominal volume: check the activity’s volumes and containers.
• Ignoring the consumable: retain the exact configuration to which the data apply.
• Choosing after one favourable demonstration: use a planned comparison and retain the limitations too.

The concluding record should distinguish satisfied mandatory requirements, preferences, accepted trade-offs and unresolved questions. Do not hide a gap behind a high overall score. Assign actions before routine use and define events requiring review, such as new liquids, tip substitution or changes in sequence.

Operational conclusion

Select the system that demonstrates its ability to support the required transfer under intended conditions. Connect liquid properties, configuration, performance, users and lifecycle; retain the decision’s limits too. No pipette is universally best irrespective of its use.

Continue in the Liquid Handling and Sample Preparation HUB. For evidence management, see the Data Integrity principles for QC laboratories. The following support route concerns selection of liquid-handling equipment.

Sources and applicability limits

Sources checked on 29 September 2026. ISO standards are distinct from GMP requirements: applicability must be established in context. ISO catalogue pages and previews do not replace the complete text. The matrix, comparison approach and case are original GuideGxP contributions; they are neither a pharmacopoeial protocol nor an experimental demonstration.

1. ISO 8655-2:2022 — Piston-operated volumetric apparatus, Part 2: Pipettes. Edition 2, April 2022, published. Official scope and status consulted; no tolerance table reproduced.
2. ISO 8655-10:2024 — User guidance, and requirements for competence, training, and POVA suitability. Edition 1, February 2024, published. Official scope and preview consulted; complete text not consulted.
3. Feldmann and Lochner — Influences on volume in piston-operated air-displacement pipettes. Accreditation and Quality Assurance 21, 69–82, 2016; online publication 2015. Abstract and preview consulted; a scientific reference, not a universal operating limit. One author was affiliated with a manufacturer; no commercial link.
4. PTB/DKD — Experimental study on the calibration of piston-operated pipettes with air cushion. DKD-E 8-1, September 2013 edition, revision 1, DOI 2025. Official PDF consulted, particularly section 5.2; physical principles and study conditions distinguished from current requirements.
5. NIST, Lane C. Sander — Volumetric Transfer of Liquids. Journal of Research of NIST 122, article 2, 2017. Publication page and presentation summary consulted; no claim of a complete video review.
6. European Commission — EU GMP, Chapter 6: Quality Control. Effective 1 October 2014, listed in the current EudraLex index; framework for human medicines, subject to specific applicability assessment.