10 julio, 2024

Graduated pipette: characteristics and uses

The graduated pipette It is a straight glass or plastic tube that has a narrowing at one end, called a conical tip, and a mouthpiece at the other end. They are calibrated in small divisions, so that different amounts of liquid can be measured in units between 0.1 and 25 ml.

It has a wide neck, which makes it less precise than the volumetric pipet. Consequently, they are used when taking a volume of solutions in which the precision does not have to be very high. They are used in laboratories to measure volume or transfer a quantity of liquid from one container to another.

Graduated pipettes are divided into two types: Mohr or subterminal pipette and serological or terminal pipette. The difference between the two is that, while in the Mohr pipette the graduation is along the length of the tube, ending before the tip, in the serological one it reaches the tip.

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Features of the graduated pipette

Among the most relevant characteristics of graduated pipettes are the following:

– They are made of plastic or borosilicate glass (pyrex).

– Along the body of the tube there are lines indicating the total volume. These have numbers that indicate the volume of liquid in the line.

– Although the units of the graduated pipette range from 0.1 to 25 ml, the most frequent volumes in laboratories are: 0.5 ml, 1.5 ml, 5 ml and 10 ml.

– On the neck of the pipette are printed the specifications that indicate: its maximum volume; the size of its divisions, represented as 1/10, 1/100; the calibration temperature; and a legend identified as TD or TC, for the acronym in English of To delivery (former) or To contain (in), which mean to pour or empty, respectively.

– Very small volume pipettors allow for fairly accurate measurement of fluids, while larger volume measurement pipettors allow for less critical measurement.

Applications

Graduated pipettes are generally used in chemistry, biology, or medicine laboratories. Thanks to the fact that it has a graduated scale, this pipette is used to measure different volumes of liquids.

The proper use of these corresponds to the knowledge that one has of the instrument and of daily practice. There are some general considerations to take into account:

– The correct way to hold the pipette must be known. The proper way is to take it by the upper third, between the thumb and the middle finger.

– They have a graduation to determine the volume but it must be considered that, for an effective measurement, the final measurement (or total capacity of the graduated pipette) is more precise than the intermediate measurements. Therefore, the recommendation is to choose the pipette according to the exact volume to be measured.

– The pipette must be placed approximately 6 mm from the bottom of the container, in order to collect the liquid to be measured.

– It is not recommended to suck the liquid with the mouth to avoid risks. For this purpose, the propipette or pump is used, closing the nozzle with the tip of the index finger when reaching the required measure.

– The filling can be done by other means, such as ascension or injection.

– Once the liquid is in the pipette, it should be placed at an angle of 10 to 20°.

– To release the liquid, you only need to lift your index finger.

Understanding the specifications of the pipettor is of great importance, since these indicate the calibration. For example: the inscription «1ml in 1/100 TD 20° C» on a pipette indicates that it is calibrated in divisions of 1/100, pouring up to 1 ml with liquids no higher than 20° C.

Additionally, it is common for graduated pipettes to also contain the acronym “AS” inscribed on the tube along with the specifications. This acronym is usually found below the pipette volume and indicates grading accuracy: “A” stands for Highest Level Accuracy and “S” stands for Fast Delivery.

Differences between graduated pipette and volumetric pipette

– The graduated pipette has a graduated scale, while the volumetric pipette has a gauge.

– The use of the graduated pipette allows to measure the volume of different liquids according to the range that it has carved in the body of the same. In the case of the volumetric pipet, only a single value can be measured.

– The precision of a volumetric pipet is higher than that of a graduated pipet.

Differences between graduated pipette and buret

The burette is a measuring instrument for volume of liquids. It is composed of a long glass cylinder open at the top with a stopcock at the bottom, to prevent the liquid from escaping.

It has a series of volumetric markings that allow the user to take only the amount of liquid or gas that is desired in a particular laboratory process.

The differences between the graduated pipette and the burette lie in the following main aspects:

– Graduated pipettes are only used to measure liquids, while burettes measure liquids or gases.

– By having a stopcock, the structure of the burette is different from that of the graduated pipette. This key allows a less precise release than that generated by the volumetric pipet.

– Burettes can contain liquids from 10 to 40 ml. On the other hand, graduated pipettes admit smaller quantities.

– In the case of the burette, measurements are made from top to bottom. Consequently, the difference between the initial and final volume is equal to the total amount of the liquid or solution.

Other topics of interest

Serological pipette.

Beral pipette.

Volumetric pipette.

References

Biology online dictionary._ Graduated pipette._ Taken from biology-online.org.
Generalic, Eni. “Graduated pipette.” Croatian-English Chemistry Dictionary & Glossary._ Taken from: periodni.com
Marienfeld-Superior._ Graduated pipettes, glass._ Taken from marienfeld-superior.com
What is the difference between TD and TC Pipettes? Taken from westlabblog.wordpress.com
Wikipedia contributors._ Graduated pipette. In Wikipedia, The Free Encyclopedia. Taken from wikipedia.org

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