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Quick links to Longreen products

• Pasteur pipettes with Silicone bulbs
• Volumetric (one-mark) pipettes
• Transfer pipettes
• Serological pipettes
• Graduated pipettes
• Motorized pipette controllers
• Micropipettes
• Multichannel pipettes
• Micropipette tips
• Micropipette rack option 1, option 2, option 3
• Pipette rack

Few laboratory tools are as common—or as easily confused—as pipettes. The term pipette covers everything from a simple glass Pasteur pipette used to transfer a few drops to a calibrated one-mark volumetric pipette, a sterile 50 mL serological pipette, or an adjustable piston micropipette capable of accurately dispensing microlitre volumes.

These devices differ not only in size and material but also in whether they actually measure volume, how they are calibrated, how liquid should be discharged, which liquids they can handle, and the level of accuracy they provide.

Before selecting a pipette, it is therefore useful to understand the entire pipette family.

Laboratory Pipettes at a Glance

Pipette type	Typical volume range	Main purpose	Quantitative measurement?	Common construction
Pasteur pipette	Drops to a few mL	Simple liquid transfer	No	Glass + separate bulb
Plastic transfer pipette	~0.5–10+ mL	Simple liquid transfer	Usually no	LDPE or similar polymer
Graduated/Mohr pipette	0.1–25 mL (ISO 835 series)	Variable-volume delivery	Yes	Usually glass
Serological pipette	~1–50 mL	Variable-volume delivery	Yes	Glass or disposable plastic
One-mark volumetric pipette	~1–100 mL	Accurate fixed-volume delivery	Yes, high accuracy	Usually glass
Disposable capillary/micropipette	µL range	Microvolume transfer	Design-dependent	Glass capillary
Piston micropipette	~0.1 µL to several mL	Precision small-volume delivery	Yes, high accuracy	Instrument + disposable tip
Multichannel micropipette	µL per channel (commonly ≤1,200 µL)	Parallel liquid handling	Yes	Instrument + multiple tips
Repeating pipette	µL to mL	Repeated dispensing	Yes	Piston/displacement system

The categories overlap somewhat because laboratory terminology developed over many decades. In particular, “transfer pipette” can mean very different things depending on context, an issue discussed below.

Pasteur Pipettes

A Pasteur pipette is one of the simplest liquid-transfer devices in the laboratory. It consists of a narrow glass tube drawn to a tapered tip and is normally operated using a separate rubber or silicone bulb.

Figure 1. Glass Pasteur pipette with separate rubber bulb.

Pasteur pipettes are primarily designed to move liquid rather than measure it. They are widely used for dropwise addition, transferring reaction mixtures, removing supernatants, spotting samples, and general sample preparation.

Traditional laboratory Pasteur pipettes are available in different lengths, commonly around 150 mm and 230 mm; ISO 7712:1983 covers disposable glass Pasteur pipettes and treats them explicitly as uncalibrated devices. Some contain a cotton plug near the upper end, which can help limit aerosols and particulates entering the aspiration system.

The critical point is that a standard Pasteur pipette is not a volumetric instrument. Even if the user learns that a particular pipette produces approximately a certain number of drops per millilitre, drop size varies with liquid properties, pipette geometry, orientation, and dispensing technique.

A Pasteur pipette should therefore not be used when the method requires an accurately measured volume.

Why Glass Pasteur Pipettes Remain Common

Glass remains particularly useful in chemistry laboratories because borosilicate glass is compatible with many organic solvents that attack common disposable polymers.

Glass also provides a rigid, narrow tip that can be useful for controlled dropwise transfer.

Its disadvantages are equally familiar: glass breaks, requires a separate bulb, and creates a sharps hazard when damaged.

Disposable Plastic Transfer Pipettes

Plastic transfer pipettes are the familiar one-piece disposable droppers with an integrated squeeze bulb.

Figure 2. One-piece disposable LDPE transfer pipette.

They are commonly moulded from flexible polymers such as low-density polyethylene (LDPE) and are widely used for aqueous reagents, staining, sample transfer, teaching laboratories, and other procedures where convenience is more important than precise volumetric measurement.

Some have moulded graduations. These markings should generally be regarded as approximate unless the manufacturer explicitly specifies volumetric accuracy and calibration.

The integrated bulb makes plastic transfer pipettes exceptionally convenient:

·      no separate pipette bulb is required;

·      breakage risk is very low;

·      they are inexpensive;

·      they can be discarded after contaminated samples;

·      they are suitable for rapid routine transfer.

Their major limitation is chemical compatibility. “Plastic” is not a chemical specification. LDPE, polypropylene, polystyrene, and other polymers behave very differently in contact with organic solvents, acids, bases, and oils.

Pasteur Pipette or Transfer Pipette?

The terminology can be confusing.

In everyday laboratory supply catalogues, plastic transfer pipette usually refers to the disposable one-piece plastic dropper. Similar products are sometimes marketed as plastic Pasteur pipettes because they perform essentially the same transfer function as a traditional glass Pasteur pipette.

In analytical glassware terminology, however, transfer pipette has historically also been used for a volumetric pipette designed to transfer one accurately measured volume.

For clear purchasing specifications, terms such as:

·      glass Pasteur pipette

·      disposable plastic transfer pipette

·      one-mark volumetric pipette

are much less ambiguous.

Graduated Pipettes

Graduated pipettes contain a scale along the stem and can therefore deliver different measured volumes from the same pipette.

Figure 3. Graduated pipette scale.

Unlike Pasteur pipettes and ordinary plastic transfer pipettes, properly manufactured graduated pipettes are volumetric measuring instruments.

ISO 835:2007 specifies metrological and constructional requirements for graduated glass pipettes and remains current following its 2023 confirmation. Its tabulated series of capacities runs from 0.1 mL to 25 mL; larger graduated pipettes are widely supplied, but fall outside that tabulated series.

Two names frequently encountered within this family are Mohr pipettes and serological pipettes. It is worth being explicit about the hierarchy, because the terms are often used as though they were alternatives: “graduated pipette” is the category, and Mohr and serological pipettes are two subtypes within it. Asking whether to use a graduated pipette or a Mohr pipette is therefore a category error — a Mohr pipette is a graduated pipette. What distinguishes the subtypes is where the graduation scale ends and how the final drop is handled. ISO 835 itself does not classify pipettes under the names "Mohr" and "serological"; it uses a formal classification based on delivery mode, Types 1 to 4 — partial delivery between graduation lines, delivery from a graduation line down to the jet, total delivery from the zero line to the jet, and blow-out designs, the last of which must be adjusted to Class B.

Mohr Pipettes

A Mohr pipette is a graduated pipette traditionally designed so that its graduation scale terminates before the tip.

Figure 4. Mohr pipette — graduation scale terminating above the tip.

Liquid is delivered between graduation marks rather than by draining the entire pipette through the tip. This makes the operating technique important. The user reads the initial meniscus, allows liquid to drain until the desired final graduation is reached, and determines the delivered volume from the difference. A Mohr pipette is useful when several different measured volumes must be delivered using the same pipette. It should not be confused with a one-mark volumetric pipette, which is optimized to deliver one specified volume with higher accuracy.

Serological Pipettes

Serological pipettes are graduated pipettes designed for measured millilitre-scale liquid handling. Modern disposable versions are ubiquitous in cell culture, microbiology, biotechnology, and pharmaceutical laboratories.

Figure 5. Sterile disposable polystyrene serological pipette.

Common nominal capacities include:

1 mL · 2 mL · 5 mL · 10 mL · 25 mL · 50 mL

Modern disposable serological pipettes are often manufactured from transparent polystyrene and supplied sterile and individually wrapped. They are typically used with a manual or electronic pipette controller rather than a small rubber bulb. Unlike ordinary plastic transfer pipettes, serological pipettes are genuine volumetric instruments when manufactured to an appropriate specification. Disposable plastic serological pipettes are covered by ISO 12771:1997 (confirmed 2024) and, in North America, by ASTM E934-94(2021), which specifies crystal-grade polystyrene construction and calibration to deliver.

Many modern serological pipettes are blow-out pipettes. After gravity drainage, the remaining liquid at the tip is expelled to complete delivery according to the pipette's calibration.

This is important because blow-out technique should never simply be assumed from appearance.

Read the pipette marking.

Mohr vs. Serological Pipettes

The two are both graduated pipettes, but their traditional designs differ.

Figure 6. Mohr and serological graduations compared.

Feature	Mohr Pipette	Serological Pipette
Graduations	Traditionally stop before tip	Typically extend toward/to tip
Variable-volume delivery	Yes	Yes
Complete drainage commonly used	Generally no	Often yes
Blow-out	Generally no	Common in modern serological designs
Common material	Glass	Glass or disposable plastic
Typical modern application	General analytical chemistry	Biology, cell culture, microbiology

The exact delivery procedure should always follow the markings and manufacturer's specification rather than the name alone.

One-Mark Volumetric Pipettes

The one-mark volumetric pipette is the classic high-accuracy glass pipette used in quantitative analytical chemistry. Its shape is distinctive: a narrow upper stem, a large central bulb, and a narrow lower delivery stem. A single calibration line on the upper stem defines the specified volume.

Figure 7. One-mark volumetric pipette.

Rather than measuring many possible volumes, the instrument is optimized to deliver one volume accurately. ISO 648:2008 specifies requirements for single-volume laboratory glass pipettes, including one-mark total-delivery and two-mark designs. The standard was confirmed in 2022 and remains current.

Typical capacities include:

1 · 2 · 5 · 10 · 20 · 25 · 50 · 100 mL

Class A or Class AS products are commonly used for preparing analytical standards, quantitative dilutions, titrimetric procedures, and other measurements where volumetric uncertainty matters.

Why the Bulb?

The enlarged bulb is functional rather than decorative. Most of the liquid is contained in the wide bulb, while the calibration mark lies on a narrow stem. Because the stem is narrow, a given increment of volume corresponds to a large vertical movement of the meniscus—so the small setting error inherent in aligning a meniscus by eye translates into a very small volume error. In a wide tube the same setting error would correspond to a much larger volume error.

Figure 8. Meniscus aligned to the calibration line.

This is one reason a one-mark volumetric pipette can achieve substantially better volumetric accuracy than a general graduated pipette.

TD, EX, TC and IN: What Do the Markings Mean?

Volumetric glassware can be calibrated either by the amount it contains or by the amount it delivers.

TD (to deliver) and EX (the equivalent marking used on ISO and DIN glassware) indicate that the instrument is calibrated according to the volume delivered under specified conditions. TC (to contain) and IN indicate calibration according to the volume contained.

Pipettes used for liquid transfer are normally delivery instruments.

This distinction matters because a thin film of liquid remains on the internal surface after drainage. A TD/EX pipette is calibrated with its prescribed drainage behaviour already taken into account. Calibration is also referenced to a temperature: ISO volumetric glassware is adjusted for delivery at a standard reference temperature of 20 °C—or 27 °C in countries that have adopted the tropical alternative—and that temperature is marked on the instrument.

ISO 4787:2021 provides methods for testing and use of volumetric instruments made from glass and plastic, including single-volume and graduated pipettes. Its scope covers nominal capacities from 100 µL to 10 000 mL and expressly excludes smaller micro-glassware.

Should You Blow Out the Last Drop?

Only if the pipette is designed for it. This is one of the most common pipetting errors.

With many traditional volumetric pipettes, a small amount of liquid remains in the tip after free drainage. Do not blow this liquid out. The residual amount has already been accounted for in the calibration.

A blow-out pipette is different. Its specified delivery requires the remaining liquid to be expelled.

Marking conventions are defined by the applicable standard. ISO 835 requires a blow-out glass graduated pipette to carry a narrow white band below any colour coding, and permits an explicit inscription such as "blow-out". The same standard requires blow-out pipettes to be adjusted to accuracy Class B, so blow-out delivery and the tightest tolerance class do not coincide. Because conventions vary between standards and manufacturers, rely on the markings and instructions supplied with the pipette rather than assuming that all pipettes operate identically.

Figure 9. Blow-out identification band (credit to https://chemistry.stackexchange.com/questions/144155/how-to-identify-a-blow-out-pipette)

Class A, Class AS and Class B

Volumetric pipettes may be supplied in different accuracy classes.

Class A instruments have tighter permissible volumetric errors than Class B instruments of equivalent nominal capacity.

Class AS combines Class A tolerances with a faster specified delivery time and a defined waiting period after the meniscus comes to rest in the jet—5 s for single-volume pipettes under ISO 648.

Class B pipettes can be entirely appropriate for routine work where the tighter tolerance of Class A is unnecessary.

For regulated or high-precision work, individually identified pipettes may also be supplied with batch or individual calibration documentation.

The important purchasing distinction is therefore not simply glass versus plastic. It is:

What accuracy class and calibration does the method require?

Capillary and Disposable Micropipettes

Long before the modern adjustable micropipette became ubiquitous, small glass capillaries were used to transfer microlitre volumes.

Disposable glass micropipettes and capillary pipettes remain useful for specialized applications, including clinical, hematological, microchemical, and analytical procedures.

Figure 10. Disposable glass capillary micropipettes.

Some are calibrated to contain or deliver a defined microvolume; others function primarily as capillary transfer devices. ISO 7550:1985 covers disposable laboratory glass micropipettes. It specifies two types: Type I, which carries a graduation line and a colour code, and Type II, which is unmarked and filled completely. Both are defined by the volume they contain rather than the volume they deliver.

These products should not be confused with modern piston-operated micropipettes.

Piston-Operated Micropipettes

The adjustable micropipette is one of the most important precision liquid-handling instruments in the modern laboratory. Rather than using a calibrated glass tube to define volume, a micropipette uses piston displacement.

“Piston-operated” is the family name rather than a competing principle. ISO 8655 applies it to the whole class of piston-driven volumetric apparatus and divides that class by how the piston couples to the liquid: air-displacement (Type A) instruments, in which a cushion of air separates the piston from the sample, and positive-displacement (Type D) instruments, in which the piston contacts the liquid directly. Every air-displacement micropipette is therefore a piston pipette, and the meaningful comparison is between the two displacement principles, which the next two subsections take in turn. The subsections that follow them — volume setting, channel count and decontamination — apply to both principles.

Common instrument ranges include approximately:

·      0.1–2.5 µL

·      0.5–10 µL

·      2–20 µL

·      10–100 µL

·      20–200 µL

·      100–1,000 µL

·      0.5–5 mL

·      1–10 mL

Exact ranges vary by manufacturer. Modern piston pipettes are covered by ISO 8655. ISO 8655-2:2022 specifies requirements for air-displacement and positive-displacement single- and multichannel pipettes together with their selected tips and other essential consumable components.

This last point is important: The pipette and tip form a measuring system.

A high-quality pipette fitted with a poorly matched tip may not achieve its intended performance.

Air-Displacement Micropipettes

Most familiar adjustable micropipettes are air-displacement pipettes.

The piston does not directly contact the liquid. Instead, an air cushion separates the piston from the sample in the disposable tip.

Figure 11. Piston-displacement and positive displacement principle (credit to https://www.knauer.net/blog/blog-9/pipetting-made-easy-part-3-pipette-selection-140).

When the piston moves upward, reduced pressure draws liquid into the tip. Depressing the piston displaces the air and dispenses the sample. Air displacement works extremely well for routine aqueous solutions but becomes more sensitive to physical properties such as:

·      viscosity;

·      vapour pressure;

·      density;

·      temperature.

Volatile solvents can evaporate into the air cushion and affect delivery. Highly viscous liquids may aspirate and dispense incompletely.

Technique therefore matters. Reverse pipetting—aspirating a small excess of liquid and dispensing only the selected volume, leaving the excess in the tip—is the standard technique-level remedy for volatile and viscous samples, and is usually worth trying before moving to a positive-displacement instrument.

Positive-Displacement Pipettes

Positive-displacement pipettes reduce or eliminate the intervening air cushion by using a piston/capillary system in which the moving piston acts much more directly on the liquid.

They are particularly useful for:

·      volatile liquids;

·      viscous samples;

·      dense liquids;

·      foaming samples;

·      liquids whose physical properties make air-displacement pipetting difficult.

ISO 8655-2:2022 covers both air-displacement (Type A) and positive-displacement (Type D) pipettes, and subdivides Type D according to whether the plunger and capillary are reusable (Type D1) or disposable (Type D2).

Positive displacement is therefore not inherently “more accurate” for every liquid. Its advantage appears particularly when sample properties make an air cushion problematic.

Fixed-Volume vs. Adjustable Micropipettes

A fixed-volume micropipette delivers one nominal volume.

An adjustable micropipette allows the user to select a volume within a specified operating range.

Adjustable models provide greater flexibility and dominate general laboratory work. Fixed-volume models can be useful in repetitive procedures where the same volume is dispensed continuously and accidental volume adjustment is undesirable.

Accuracy and precision generally deteriorate as an adjustable pipette is used near the extreme lower end of its range. A 100–1,000 µL pipette should therefore not be chosen merely because it can nominally reach a small volume if a smaller-range pipette is available and better suited to the task.

Single-Channel and Multichannel Pipettes

A single-channel pipette operates one tip at a time.

A multichannel pipette operates several tips simultaneously—commonly 8 or 12 channels, although other configurations are available.

Figure 12. Multichannel pipetting into a multi-well plate.

Multichannel pipettes are particularly useful for:

·      96-well plates;

·      ELISA;

·      PCR preparation;

·      cell-based assays;

·      repetitive analytical workflows.

ISO 8655-2 covers both single-channel and multichannel piston pipettes. For plate work, multichannel pipetting can greatly improve throughput and reduce repetitive hand movements.

Autoclaving and Decontamination

Because piston pipettes are reusable, they raise a question that disposable pipettes do not: can the instrument itself be sterilized? The answer is model-specific, and it is one of the details ISO 8655-1 expects the manufacturer to supply with the instrument, alongside chemical-resistance information.

Three cases are common:

·      fully autoclavable pipettes, which can be sterilized assembled, typically at 121 °C for 15–20 minutes;

·      partially autoclavable pipettes, in which only the lower assembly—tip cone, shaft, piston and seals—may be autoclaved, while the handle and volume-setting mechanism may not;

·      non-autoclavable pipettes, including most electronic models, where the battery and electronics rule out steam sterilization and only surface disinfection or UV treatment is appropriate.

Autoclaving is not a cost-free operation. Steam cycles stress seals, O-rings and piston lubrication, and they can shift the delivered volume. Two practical rules follow. First, let the pipette cool and dry completely before reassembly and use—residual moisture in the shaft alters the air cushion and therefore the delivered volume. Second, treat every autoclave cycle as a trigger for verification: check the volume afterwards, and re-lubricate the piston at the interval the manufacturer specifies. Laboratories that autoclave routinely generally shorten their calibration interval to match.

Tips and positive-displacement consumables follow their own rules. Tips supplied sterile are normally radiation-sterilized and intended for single use. Bulk polypropylene tips racked and autoclaved in-house usually tolerate a 121°C cycle but must be dried thoroughly, and filter or barrier tips should not be autoclaved unless the manufacturer confirms that the filter survives it. For positive-displacement systems, reusable Type D1 plungers and capillaries may be autoclavable where disposable Type D2 consumables are not.

Glassware is the straightforward case: borosilicate pipettes tolerate both dry-heat and saturated-steam sterilization, and ISO 7712 specifies resistance to both for disposable glass Pasteur pipettes. Even so, repeated cycles remain a reason to re-verify Class A volumetric ware rather than assume its calibration is unchanged.

Repeating and Electronic Pipettes

Repeating pipettes are designed to aspirate a larger volume and dispense multiple smaller aliquots sequentially. They are useful when the same volume must be delivered repeatedly into tubes, wells, or vessels.

Figure 13. Repeating and electronic pipettes.

Electronic pipettes automate some or all piston movement and may provide functions such as repeated dispensing, mixing, programmable aspiration/dispensing sequences, and controlled pipetting speeds.

These instruments belong to the broader family of piston-operated liquid-handling systems rather than traditional glass pipettes.

So What Does “Glass vs. Plastic Pipettes” Actually Mean?

Once the pipette family is understood, the common question “Should I use glass or plastic?” becomes easier to answer. There is no meaningful universal comparison between all glass pipettes and all plastic pipettes because material and pipette function are separate variables. Three comparisons are particularly useful.

Glass Pasteur Pipette vs. Plastic Transfer Pipette

For simple transfer, glass offers better compatibility with many organic solvents and a rigid fine tip. Plastic offers an integrated bulb, low cost, low breakage risk, and convenient disposal. For aqueous routine transfer, plastic is often more convenient. For varied organic solvent work, borosilicate glass is frequently the safer material choice.

Glass Volumetric Pipette vs. Plastic Serological Pipette

These instruments should not be compared solely by material because they perform different jobs.

A Class A/AS one-mark volumetric pipette is designed for high-accuracy delivery of one volume.

A disposable serological pipette is designed for flexible, graduated millilitre-scale delivery and is particularly convenient for sterile biological workflows.

If the objective is preparation of a quantitative analytical standard, the volumetric pipette usually has the advantage.

If the objective is sterile transfer of 17 mL of cell-culture medium, a disposable serological pipette is usually far more practical.

Micropipette + Plastic Tip

Modern micropipetting complicates the glass-versus-plastic distinction further.

The precision instrument itself contains mechanical components, while the liquid normally contacts a disposable polymer tip. Performance therefore depends on the complete pipette-tip-liquid system, not simply the material of one component. ISO 8655 likewise treats the selected tip and essential consumables as part of the pipetting system.

Chemical Compatibility

Chemical compatibility should always be evaluated against the specific material.

Glass

Borosilicate glass provides broad resistance to water, dilute acids, salts, and many organic solvents.

It is not universal. Hydrofluoric acid attacks silica-based glass, and strong hot alkalis can also damage glass.

Glass composition matters as well: borosilicate and soda-lime/flint glass do not have identical chemical properties.

Plastic

“Plastic” is not a material specification.

Common pipette and tip polymers include:

·      LDPE;

·      polypropylene;

·      polystyrene;

·      specialized proprietary polymers.

Their chemical resistance differs substantially.

Polystyrene serological pipettes, for example, should not automatically be assumed compatible with an organic solvent merely because the pipette remains physically intact during brief contact.

Possible effects of incompatible solvents include swelling, softening, crazing, dimensional change, and extraction of polymer constituents.

Always check the chemical compatibility of the actual polymer.

Sterility and Biological Applications

Disposable plastic pipettes have a major workflow advantage in biological laboratories.

Serological pipettes and micropipette tips may be available with specifications such as:

·      sterile;

·      individually wrapped;

·      DNase-free;

·      RNase-free;

·      non-pyrogenic;

·      low-retention;

·      filtered/barrier configuration.

These claims are not interchangeable. A product being sterile does not automatically mean it is certified RNase-free, DNase-free, or pyrogen-free.

Likewise, a filtered micropipette tip primarily provides an aerosol barrier; it should not automatically be interpreted as a sterile filter unless the product is specifically supplied and certified that way.

Adsorption, Extractables and Trace Analysis

Neither glass nor plastic is universally inert.

Proteins, peptides, hydrophobic organic compounds, nanoparticles, and other analytes can adsorb to laboratory surfaces. The magnitude depends on sample composition, concentration, contact time, and surface chemistry.

Specialized low-binding polymer tips and treated glass products are available where adsorption is important.

Plastic consumables can also introduce extractables or leachables from polymers and manufacturing processes. For routine work these may be insignificant, but they can matter in ultra-trace organic analysis, mass spectrometry, toxicology, and contamination-sensitive environmental analysis.

Glass can contribute inorganic species under certain conditions as well.

For trace analysis, consumables should therefore be evaluated as part of the analytical blank rather than assumed to be contamination-free.

Accuracy, Precision and Pipetting Technique

Accuracy describes how closely the delivered volume approaches the intended value.

Precision describes how reproducibly the same volume can be delivered repeatedly.

A pipette can be precise but inaccurate—for example, repeatedly delivering 98 µL when set to 100 µL. ISO 8655 expresses the same two ideas as systematic error (the mean deviation of the delivered volume from the selected volume) and random error (the scatter of repeated deliveries); manufacturers' specifications and calibration certificates are written in those terms.

Performance depends not only on instrument quality but also on technique.

Important factors include:

·      correct pipette size;

·      compatible tip;

·      proper tip attachment;

·      immersion depth;

·      aspiration angle;

·      aspiration and dispensing speed;

·      pre-wetting where appropriate;

·      liquid temperature;

·      complete dispensing;

·      appropriate blow-out technique;

·      regular calibration and maintenance.

For piston-operated systems, current ISO guidance extends beyond instrument specifications to testing, user competence, training, and fitness for intended use.

Never Pipette by Mouth

Laboratory liquids should never be aspirated by mouth.

Glass and graduated pipettes should be operated using an appropriate pipette bulb, pump, or controller. Modern serological pipettes are normally used with manual or electronic controllers.

This applies even to apparently harmless solutions. Mouth pipetting creates unnecessary risks of ingestion, aspiration, contamination, and exposure.

Pipette Bulbs, Pumps and Controllers

Every pipette that is not a self-contained piston instrument needs a separate filling device, and that device is part of the measurement chain rather than an accessory to it. It governs how steadily the meniscus can be set, how the liquid drains, and whether the last drop is expelled—so a well-made Class A pipette used with an unsuitable filler will not deliver its stated accuracy.

Four families are in common use, in ascending order of control:

·      Simple rubber or silicone bulbs—the teat used on a Pasteur pipette. There is no valve and no fine control, which is appropriate for uncalibrated dropwise transfer and unsuitable for setting a meniscus to a calibration line.

·      Three-valve safety fillers (the classic "Peleus" type). Squeezing the bulb with the upper valve open evacuates it; the suction valve then draws liquid up under fine control, and the delivery valve releases it. This is the traditional partner for glass volumetric and graduated pipettes.

·      Mechanical pipette pumps, in which a thumbwheel drives a small plunger. The wheel gives the finest meniscus control of any manual device and holds the volume without hand pressure; pumps are sized to the pipette (commonly 2 mL, 10 mL and 25 mL) and should be matched to nominal capacity.

·      Motorised pipette controllers, used with serological pipettes from roughly 1 mL to 100 mL. They offer adjustable aspiration and dispensing speeds, a dedicated blow-out function, rechargeable operation and a replaceable membrane filter protecting the pump.

Figure 14 Manual filling devices for pipettes

Figure 20. Motorised pipette controller.

Two points deserve emphasis because they are where filling devices quietly cause volumetric error.

First, a delivery pipette is calibrated on the assumption that it drains freely. ISO 648 requires single-volume pipettes to be adjusted so that delivery is under gravity and unrestricted, so a filler that pushes liquid out under pressure—or a controller left in a dispensing mode that forces the stream—delivers something other than the calibrated volume. Set the meniscus with the device, then let gravity do the delivery.

Second, the blow-out function on a motorised controller is a feature, not a habit. Use it where the pipette is a blow-out design and the calibration expects the residual liquid to be expelled; using it on an ordinary to-deliver pipette causes systematic over-delivery, which is simply the classic blow-out error committed with a motor.

Practical selection points: match the device capacity to the pipette so the volume can be held comfortably; check that bulb and seal materials tolerate your solvents, since natural rubber degrades in organic vapour where silicone or a PTFE-lined path holds up better; keep liquid out of the device by using the membrane filter and, where appropriate, cotton-plugged pipettes; and prefer a motorised controller for repetitive 25 mL or 50 mL work, where the hand fatigue of a manual filler becomes an error source in its own right.

How to Choose the Right Pipette

The most useful starting point is what the experiment requires the pipette to do.

Application	Appropriate starting choice
Add several drops of an organic solvent	Glass Pasteur pipette
Transfer a few mL of aqueous reagent approximately	Disposable plastic transfer pipette
Transfer variable measured volumes in general chemistry	Graduated/Mohr pipette
Transfer sterile cell-culture media	Disposable serological pipette
Prepare an analytical standard accurately	Class A/AS one-mark volumetric pipette
Dispense 100 µL repeatedly	Suitable piston micropipette
Pipette volatile or highly viscous microvolumes	Consider positive displacement
Fill a 96-well plate	Multichannel pipette
Dispense the same aliquot many times	Repeating/electronic pipette
Handle ultra-trace samples	Select and validate the complete pipette/tip/material system

A useful decision sequence is:

required volume → required accuracy → fixed or variable volume → sample chemistry → sterility → contamination tolerance → throughput → appropriate pipette type → material

Material comes relatively late in the decision process because choosing the correct type of pipette is usually more fundamental than choosing glass or plastic.

Common Pipette Selection and Use Errors

Using a Pasteur pipette as a measuring instrument. It is primarily a transfer device.

Assuming graduations on a disposable transfer pipette are analytical measurements. Unless accuracy is specified, treat them as approximate.

Assuming glass automatically means greater accuracy. A glass Pasteur pipette is much less suitable for quantitative measurement than a properly calibrated plastic serological pipette.

Using a serological pipette like a one-mark volumetric pipette. They have different designs, purposes, and delivery procedures.

Blowing out a pipette that is not designed for blow-out. Residual liquid may already be included in its calibration.

Failing to blow out a blow-out pipette. This can cause systematic under-delivery.

Treating all plastics as chemically equivalent. Always identify the polymer.

Using the wrong micropipette range. Avoid working unnecessarily close to the lower limit of a large-volume pipette.

Assuming any tip that physically fits is analytically equivalent. Pipette and tip function as a measuring system.

Autoclaving a pipette that is not designed for it, or skipping verification afterwards. Check what the manual permits, and re-check the delivered volume after the cycle.

Ignoring volatile or viscous liquid behaviour. Air-displacement pipettes may require modified technique or a positive-displacement system.

Assuming sterile means RNase-free, DNase-free, pyrogen-free, or filtered. These are separate specifications.

A Simple Way to Remember the Pipette Family

For basic laboratory work:

•        Pasteur / plastic transfer pipette → move liquid
•        Graduated / Mohr / serological pipette → measure and move variable millilitre volumes
•        One-mark volumetric pipette → deliver one millilitre-scale volume with high accuracy
•        Micropipette → precisely measure and deliver small volumes
•        Multichannel / repeating / electronic pipette → increase throughput

Once these distinctions are understood, selecting between glass, plastic, sterile, reusable, graduated, volumetric, air-displacement, and positive-displacement products becomes much more straightforward.

Laboratory Pipettes from Longreen Lab

Longreen Lab supplies liquid-handling products for chemistry, biology, environmental, healthcare, educational, and industrial laboratories, including Pasteur pipettes, disposable transfer pipettes, serological pipettes, volumetric and graduated pipettes, micropipettes, multichannel pipettes, pipette tips, bulbs, and related accessories. The best pipette is not simply the most accurate or most expensive option. It is the instrument whose volume range, calibration, delivery mechanism, material, chemical compatibility, sterility, and accuracy match the actual laboratory procedure. For formal quantitative methods, always follow the applicable method, product calibration specification, and laboratory quality system rather than substituting one pipette type for another solely because the nominal volume is the same.

Technical Standards Referenced

The principal standards underlying the terminology in this guide are ISO 648:2008 for single-volume glass pipettes (1–100 mL, confirmed 2022), ISO 835:2007 for graduated glass pipettes (confirmed 2023), ISO 4787:2021 for testing and use of glass and plastic volumetric instruments, ISO 8655-1:2022 and ISO 8655-2:2022 for piston-operated pipettes, ISO 7550:1985 for disposable glass micropipettes, ISO 7712:1983 for disposable glass Pasteur pipettes, and ISO 12771:1997 (confirmed 2024) together with ASTM E934-94(2021) for disposable plastic serological pipettes. These standards confirm an important theme of this guide: “pipette” describes a family of substantially different liquid-handling devices, not a single instrument.

Karen Guzman, "Pipetting: A Practical Guide," The American Biology Teacher 2001, 63(2), 128-131.

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