What is the Difference Between TD & TC Pipettes?

Do you ever get confused with TD or TC Pipettes? A pipette is either calibrated to "TC" or "TD," and abbreviations are normally printed on the side or bulb of the pipette.

What Are the Key Differences Between TC and TD Pipettes?

TC or TD is abbreviated for "to contain" and "to deliver," respectively. In a 'TC' marked pipette, the contained quantity of the liquid corresponds to the capacity printed on the pipette.

While in the 'TD' marked pipette, the delivered quantity of liquid corresponds to the capacity printed on the pipette. The drainage holdback error (i.e., the amount of liquid required to wet the inner surface of the pipette and the remaining liquid left at the tip of the pipette after it has been used) has already been taken into account during calibration at a standard temperature (which is generally 20°C). We can understand this in the following simple equation:

“The volume of TD pipette = Volume of TC pipette + drainage holdback error”

The double rings on the upper end of the pipette indicate that the pipette is a "blow out" type/TC pipette and should be blown using a rubber bulb. The absence of the ring indicates that the pipette is a TD pipette which means the still left liquid in the pipette has already been taken into account during calibration and shall not be expelled by blowing out.

Blow out Pipettes and Pipettes

The formal difference between the blow-out pipettes "adjusted to deliver" and pipettes "adjusted to contain" may be small (since blowing out the remaining liquid is possible in both cases), but it does make a difference when it comes to achieving the accurate result of an experiment.

According to the International Standards Organization, "ex" is used to indicate that the pipette has been adjusted "to deliver," and the marking "in" is used to indicate that the pipette has been adjusted "to contain."

TD pipettes are much more common than TC pipettes. Most typical graduated pipettes or bulb pipettes are usually calibrated to deliver (TD), whereas capillary pipettes are adjusted to contain (TC).

Defining Volumetric Container Roles

Volumetric glassware is used in laboratories to either deliver or contain a specific volume of a substance. Glassware that is calibrated to deliver a certain volume is called "to deliver" (TD) glassware, while glassware calibrated to contain a certain volume is called "to contain" (TC) glassware. TD glassware can deliver slightly more volume than the calibrated amount, while TC glassware may deliver slightly less volume than the calibrated amount if poured out. These small differences in volume can significantly affect precise measurements, which is why it is essential to use the appropriate glassware for each purpose.

Types of Graduated Pipettes

There are two kinds of graduated pipettes: 

• Serological Pipette

Serological pipettes are designed to measure and transfer solutions accurately in various laboratory settings. They have a long, thin shape with graduation markings, allowing for precise measurement of liquids. Serological pipettes are commonly made from clear polystyrene or polypropylene and are disposable after a single use to prevent contamination. They come in a range of volumes, from 1 ml to 50 ml or more, and may be sterile or non-sterile. Serological pipettes are widely used in medical, biological, and chemical laboratories for various applications such as cell culture, protein assays, and drug discovery.

• Mohr Pipette

It has a graduated scale etched on the stem, which allows for the measurement of specific volumes. Mohr measuring pipettes are designed to measure and deliver an exact volume of liquid, and they typically come in a variety of sizes, ranging from 1 ml to 50 ml. They are commonly used in titrations, sample preparation, and in the production of reagents. However, Mohr measuring pipettes are not suitable for the measurement of viscous liquids or for liquids with high surface tension.

Use of TD & TC Pipettes

TD pipettes are commonly used in quantitative analysis when precise volumes of liquid are required, as they ensure the accurate delivery of a specific volume. TC pipettes are useful when it is important to dispense the exact same volume each time, such as in serial dilutions or when preparing solutions with specific concentrations.

It is important to note that TD and TC pipettes should be used in a variety of ways, as doing so can result in inaccurate measurements and affect the results of experiments. Properly calibrating and maintaining pipettes is also important to ensure accurate measurements.

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Further information can be found in ISO 648 Laboratory glassware – Single-volume pipettes and ISO 835 Laboratory glassware – Graduated pipettes.

FAQs

Is serological pipette TC or TD?

Serological pipettes can be either TC or TD, depending on the manufacturer and intended use. It is important to check the specifications of the particular serological pipette being used to determine whether it is TC or TD.

Is Mohr Pipette TC or TD?

A Mohr pipette is a type of volumetric pipette that is usually calibrated to deliver a specific volume of liquid (TD).

How do you identify a serological pipette?

Serological pipettes are typically made of transparent or translucent plastic, such as polystyrene, and have graduations marked along their length. They also have a tapered end for attaching a pipette pump or bulb, and a narrow tip for precise dispensing of small volumes. The packaging of the pipette will often indicate its volume capacity and other specifications.