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What's the difference between pipettes calibrated TD, TC, Blow-out and related terms?
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Marcio Da Silva
What's the difference between pipettes calibrated TD, TC, Blow-out and related terms?
As you noted, "pipettes are either calibrated 'to deliver' (TD) or 'to contain' (TC)."
Because a bit of solution typically remains in pipettes, TC pipettes must be blown out.
Serological pipettes can be both TC and TD because they are graduated. So for a 10 ml pipette graduate to 0.1 ml, then the pipette will deliver TD from say between the 9.80 ml and 5.30 marks. That would be of course 4.50 ml. However to get all of the last 0.10 ml of liquid, then you'd have to blow out the pipette.
As you noted, "pipettes are either calibrated 'to deliver' (TD) or 'to contain' (TC)."
Because a bit of solution typically remains in pipettes, TC pipettes must be blown out.
Serological pipettes can be both TC and TD because they are graduated. So for a 10 ml pipette graduate to 0.1 ml, then the pipette will deliver TD from say between the 9.80 ml and 5.30 marks. That would be of course 4.50 ml. However to get all of the last 0.10 ml of liquid, then you'd have to blow out the pipette.
(link downloads a pdf) that source, for instance, has, in page 13, pictures of what I would consider serological pipettes and explicitly states that these should NOT be blown out.More
Ignacio - I doubt there is a IUPAC definition for a "serological pipette." To me such a pipette is simply one that is graduated rather than one have a single fill mark. Such graduations would also require a constant diameter. On the other hand a "volumetric pipette" would typical have a large bulb. Assuming a 0.1 ml graduation, then it would seem that the last 0.1 ml of a serological pipette could either be TC or TD.More
In olden days, (I was taught to both suck up and blow out a pipet by MOUTH), TD and TC about covered it. Now days, we're talking about micro-liters and automatic pipets and use for GC/MS calibration, and all sorts of more technical more SPECIALIZED uses. Wouldn't you expect that more specialized uses require more specific equipment? Temperature, gravitational field, density, surface tension, humidity, viscosity...those are the factors that can lead to variations in the amount of liquid left inside the pipet at the end of the delivery process. (I'm not saying all of them are important at sea level on Earth). FWIW, different needs will need different things. I think a good overview would be to discuss TD/TC and then explain one specific high accuracy micropipette. FWIW.
In olden days, (I was taught to both suck up and blow out a pipet by MOUTH), TD and TC about covered it. Now days, we're talking about micro-liters and automatic pipets and use for GC/MS calibration, and all sorts of more technical more SPECIALIZED uses. Wouldn't you expect that more specialized uses require more specific equipment? Temperature, gravitational field, density, surface tension, humidity, viscosity...those are the factors that can lead to variations in the amount of liquid left inside the pipet at the end of the delivery process. (I'm not saying all of them are important at sea level on Earth). FWIW, different needs will need different things. I think a good overview would be to discuss TD/TC and then explain one specific high accuracy micropipette. FWIW.
I certainly agree with you that specific, niche needs require highly specialized equipment, but I dont think that was what I was getting at with the question. Could you provide a definition of what it means for a pipette to be "TD" or "TC"? Do you know if any international or national standards organization regulates how these terms are used?More
Most commercially available laboratory glassware is in accordance with these standards. However, some nonconforming volumetric instruments are also available, for example in non-standard sizes.
Due to retention of liquid on the inner surface of the volumetric instrument, the volume of liquid delivered is not identical with the volume of liquid contained by the volumetric instrument. Volumetric instruments are either adjusted ‘to contain’ (i.e. the capacity printed on the instrument corresponds to the contained quantity of liquid) or ‘to deliver’ (i.e. the capacity printed on the instrument corresponds to the delivered quantity of liquid; the wetting residue remaining in the instrument has already been taken into account in the calibration). According to international standards, the marking ‘Ex’ is used to indicate that the volumetric instrument has been adjusted to deliver; the marking ‘In’ is used to indicate that the volumetric instrument has been adjusted to contain. Most typical graduated pipettes, bulb pipettes, and burettes are usually adjusted to deliver, whereas typical graduated cylinders, volumetric flasks, and capillary pipettes (i.e. very small measuring pipettes with a capacity of up to 0.2 ml) are usually adjusted to contain.
ISO 648 and ISO 835 specify three classes of accuracy for pipettes:
Class A (higher grade, without waiting time)
Class AS (higher grade, with a specified waiting time)
Class B (lower grade, without waiting time)
‘Waiting time’ is the period to be observed in order to ensure complete delivery after apparent completion of the liquid delivery of the pipette (i.e. after the meniscus appeared to come to rest) and before the final reading of the delivered volume is taken (i.e. before the tip of the jet is removed from the inner surface of the receiving vessel).
Furthermore, four types of graduated measuring pipettes are standardized in ISO 835:
Type 1: Partial delivery (adjusted to deliver from zero line at the top to any graduation line; nominal capacity is represented by the lowest graduation line)
Type 2: Total delivery (adjusted to deliver from any graduation line down to the jet; nominal capacity is represented by the highest graduation line)
Type 3: Total and partial delivery (adjusted to deliver from zero line at the top to any graduation line; nominal capacity is obtained by delivery down to the jet)
Type 4: Blow-out (adjusted to deliver from zero line at the top to any graduation line; nominal capacity is obtained by delivery down to the jet where the last drop of liquid in the jet is expelled by blowing. Blow-out pipettes are only adjusted to accuracy Class B.)
Typical graduated measuring pipettes with a capacity from 0.5 ml to 25 ml are commercially available in accordance with ISO 835 as Type 1, 2, or 3 and in Class A, AS, or B. Bulb pipettes with a capacity from 0.5 ml to 100 ml are available in accordance with ISO 648 in Class A, AS, or B. They are all adjusted to deliver (‘Ex’); i.e. the residual liquid still left in the tip has already been taken into account during calibration and must not be expelled into the vessel by blowing out.
Very small measuring pipettes with a capacity of up to 0.2 ml (capillary pipettes) are designed as Type 4 (blow-out) in Class B; however, most available capillary pipettes are actually adjusted to contain (‘In’), which is strictly not conforming with ISO 835. Though, the formal difference between blow-out pipettes adjusted to deliver and pipettes adjusted to contain may be small for total delivery since the last drop of retained liquid in the jet can be expelled by blowing in both cases. Nevertheless, when the greatest possible accuracy is desired, it is not sufficient to simply empty pipettes that are adjusted to contain by blowing out the liquid with a pipetting aid; such pipettes should also be rinsed two to three times with the diluting medium.
The general procedure for the use of pipettes that are adjusted to deliver (‘Ex’) is described in ISO 4787 as follows. However, when the greatest possible accuracy is desired, pipettes should be used as closely as possible to the manner in which they have been calibrated (which is also specified in ISO 4787, ISO 648, and ISO 648).
10.5.1 Pipettes adjusted to deliver (see ISO 648 and ISO 835)
After rinsing with the liquid or reagent to be used, fill the pipette by suction to a few millimetres above the selected graduation line. Remove any liquid remaining on the outside of the jet. The final setting of the meniscus shall then be made by dispensing the surplus liquid through the jet. Remove any drops of liquid adhering to the jet by bringing an inclined ground glass vessel into contact with the tip of the jet. Delivery shall then be made with the tip of the jet in contact with the inner surface of the inclined receiving vessel.
If the setting after delivery is done at a lower graduation line, the liquid flow has to be nearly stopped a few millimetres above the graduation line. After observing a waiting time, if specified, complete the final setting quickly.
A waiting time, if specified, shall be observed before making the final setting for delivery of a given volume.
The corresponding procedure for the use of pipettes that are adjusted to contain (‘In’) is described in ISO 4787 as follows. Note that, when the greatest possible accuracy is desired, it is not sufficient to simply empty the pipette by blowing out the liquid with a pipetting aid; the pipette should also be rinsed two to three times with the diluting medium.
10.5.2 Pipettes adjusted to contain
Rinse the pipette with the reagent to be used to a few millimetres below the desired graduation line. Fill the pipette by suction to as close as possible above the selected graduation line. Remove any liquid remaining on the outside of the jet. Make the final setting of the meniscus to the line by withdrawing the surplus liquid by means of filter paper. For the discharge, rinse the pipette several times with the diluting medium.
Most commercially available laboratory glassware is in accordance with these standards. However, some nonconforming volumetric instruments are also available, for example in non-standard sizes.
Due to retention of liquid on the inner surface of the volumetric instrument, the volume of liquid delivered is not identical with the volume of liquid contained by the volumetric instrument. Volumetric instruments are either adjusted ‘to contain’ (i.e. the capacity printed on the instrument corresponds to the contained quantity of liquid) or ‘to deliver’ (i.e. the capacity printed on the instrument corresponds to the delivered quantity of liquid; the wetting residue remaining in the instrument has already been taken into account in the calibration). According to international standards, the marking ‘Ex’ is used to indicate that the volumetric instrument has been adjusted to deliver; the marking ‘In’ is used to indicate that the volumetric instrument has been adjusted to contain. Most typical graduated pipettes, bulb pipettes, and burettes are usually adjusted to deliver, whereas typical graduated cylinders, volumetric flasks, and capillary pipettes (i.e. very small measuring pipettes with a capacity of up to 0.2 ml) are usually adjusted to contain.
ISO 648 and ISO 835 specify three classes of accuracy for pipettes:
Class A (higher grade, without waiting time)
Class AS (higher grade, with a specified waiting time)
Class B (lower grade, without waiting time)
‘Waiting time’ is the period to be observed in order to ensure complete delivery after apparent completion of the liquid delivery of the pipette (i.e. after the meniscus appeared to come to rest) and before the final reading of the delivered volume is taken (i.e. before the tip of the jet is removed from the inner surface of the receiving vessel).
Furthermore, four types of graduated measuring pipettes are standardized in ISO 835:
Type 1: Partial delivery (adjusted to deliver from zero line at the top to any graduation line; nominal capacity is represented by the lowest graduation line)
Type 2: Total delivery (adjusted to deliver from any graduation line down to the jet; nominal capacity is represented by the highest graduation line)
Type 3: Total and partial delivery (adjusted to deliver from zero line at the top to any graduation line; nominal capacity is obtained by delivery down to the jet)
Type 4: Blow-out (adjusted to deliver from zero line at the top to any graduation line; nominal capacity is obtained by delivery down to the jet where the last drop of liquid in the jet is expelled by blowing. Blow-out pipettes are only adjusted to accuracy Class B.)
Typical graduated measuring pipettes with a capacity from 0.5 ml to 25 ml are commercially available in accordance with ISO 835 as Type 1, 2, or 3 and in Class A, AS, or B. Bulb pipettes with a capacity from 0.5 ml to 100 ml are available in accordance with ISO 648 in Class A, AS, or B. They are all adjusted to deliver (‘Ex’); i.e. the residual liquid still left in the tip has already been taken into account during calibration and must not be expelled into the vessel by blowing out.
Very small measuring pipettes with a capacity of up to 0.2 ml (capillary pipettes) are designed as Type 4 (blow-out) in Class B; however, most available capillary pipettes are actually adjusted to contain (‘In’), which is strictly not conforming with ISO 835. Though, the formal difference between blow-out pipettes adjusted to deliver and pipettes adjusted to contain may be small for total delivery since the last drop of retained liquid in the jet can be expelled by blowing in both cases. Nevertheless, when the greatest possible accuracy is desired, it is not sufficient to simply empty pipettes that are adjusted to contain by blowing out the liquid with a pipetting aid; such pipettes should also be rinsed two to three times with the diluting medium.
The general procedure for the use of pipettes that are adjusted to deliver (‘Ex’) is described in ISO 4787 as follows. However, when the greatest possible accuracy is desired, pipettes should be used as closely as possible to the manner in which they have been calibrated (which is also specified in ISO 4787, ISO 648, and ISO 648).
10.5.1 Pipettes adjusted to deliver (see ISO 648 and ISO 835)
After rinsing with the liquid or reagent to be used, fill the pipette by suction to a few millimetres above the selected graduation line. Remove any liquid remaining on the outside of the jet. The final setting of the meniscus shall then be made by dispensing the surplus liquid through the jet. Remove any drops of liquid adhering to the jet by bringing an inclined ground glass vessel into contact with the tip of the jet. Delivery shall then be made with the tip of the jet in contact with the inner surface of the inclined receiving vessel.
If the setting after delivery is done at a lower graduation line, the liquid flow has to be nearly stopped a few millimetres above the graduation line. After observing a waiting time, if specified, complete the final setting quickly.
A waiting time, if specified, shall be observed before making the final setting for delivery of a given volume.
The corresponding procedure for the use of pipettes that are adjusted to contain (‘In’) is described in ISO 4787 as follows. Note that, when the greatest possible accuracy is desired, it is not sufficient to simply empty the pipette by blowing out the liquid with a pipetting aid; the pipette should also be rinsed two to three times with the diluting medium.
10.5.2 Pipettes adjusted to contain
Rinse the pipette with the reagent to be used to a few millimetres below the desired graduation line. Fill the pipette by suction to as close as possible above the selected graduation line. Remove any liquid remaining on the outside of the jet. Make the final setting of the meniscus to the line by withdrawing the surplus liquid by means of filter paper. For the discharge, rinse the pipette several times with the diluting medium.
As you noted, "pipettes are either calibrated 'to deliver' (TD) or 'to contain' (TC)."
Because a bit of solution typically remains in pipettes, TC pipettes must be blown out.
Serological pipettes can be both TC and TD because they are graduated. So for a 10 ml pipette graduate to 0.1 ml, then the pipette will deliver TD from say between the 9.80 ml and 5.30 marks. That would be of course 4.50 ml. However to get all of the last 0.10 ml of liquid, then you'd have to blow out the pipette.
As you noted, "pipettes are either calibrated 'to deliver' (TD) or 'to contain' (TC)."
Because a bit of solution typically remains in pipettes, TC pipettes must be blown out.
Serological pipettes can be both TC and TD because they are graduated. So for a 10 ml pipette graduate to 0.1 ml, then the pipette will deliver TD from say between the 9.80 ml and 5.30 marks. That would be of course 4.50 ml. However to get all of the last 0.10 ml of liquid, then you'd have to blow out the pipette.
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In olden days, (I was taught to both suck up and blow out a pipet by MOUTH), TD and TC about covered it. Now days, we're talking about micro-liters and automatic pipets and use for GC/MS calibration, and all sorts of more technical more SPECIALIZED uses. Wouldn't you expect that more specialized uses require more specific equipment? Temperature, gravitational field, density, surface tension, humidity, viscosity...those are the factors that can lead to variations in the amount of liquid left inside the pipet at the end of the delivery process. (I'm not saying all of them are important at sea level on Earth). FWIW, different needs will need different things. I think a good overview would be to discuss TD/TC and then explain one specific high accuracy micropipette. FWIW.
In olden days, (I was taught to both suck up and blow out a pipet by MOUTH), TD and TC about covered it. Now days, we're talking about micro-liters and automatic pipets and use for GC/MS calibration, and all sorts of more technical more SPECIALIZED uses. Wouldn't you expect that more specialized uses require more specific equipment? Temperature, gravitational field, density, surface tension, humidity, viscosity...those are the factors that can lead to variations in the amount of liquid left inside the pipet at the end of the delivery process. (I'm not saying all of them are important at sea level on Earth). FWIW, different needs will need different things. I think a good overview would be to discuss TD/TC and then explain one specific high accuracy micropipette. FWIW.
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Since you are explicitly asking for standards, you might want to start with ISO 4787 Laboratory glassware – Volumetric instruments – Methods for testing of capacity and for use. This international standard provides methods for testing as well as for use of various volumetric instruments made from glass. Further requirements for individual volumetric instruments can be found in
Most commercially available laboratory glassware is in accordance with these standards. However, some nonconforming volumetric instruments are also available, for example in non-standard sizes.
Due to retention of liquid on the inner surface of the volumetric instrument, the volume of liquid delivered is not identical with the volume of liquid contained by the volumetric instrument. Volumetric instruments are either adjusted ‘to contain’ (i.e. the capacity printed on the instrument corresponds to the contained quantity of liquid) or ‘to deliver’ (i.e. the capacity printed on the instrument corresponds to the delivered quantity of liquid; the wetting residue remaining in the instrument has already been taken into account in the calibration). According to international standards, the marking ‘Ex’ is used to indicate that the volumetric instrument has been adjusted to deliver; the marking ‘In’ is used to indicate that the volumetric instrument has been adjusted to contain. Most typical graduated pipettes, bulb pipettes, and burettes are usually adjusted to deliver, whereas typical graduated cylinders, volumetric flasks, and capillary pipettes (i.e. very small measuring pipettes with a capacity of up to 0.2 ml) are usually adjusted to contain.
ISO 648 and ISO 835 specify three classes of accuracy for pipettes:
‘Waiting time’ is the period to be observed in order to ensure complete delivery after apparent completion of the liquid delivery of the pipette (i.e. after the meniscus appeared to come to rest) and before the final reading of the delivered volume is taken (i.e. before the tip of the jet is removed from the inner surface of the receiving vessel).
Furthermore, four types of graduated measuring pipettes are standardized in ISO 835:
Typical graduated measuring pipettes with a capacity from 0.5 ml to 25 ml are commercially available in accordance with ISO 835 as Type 1, 2, or 3 and in Class A, AS, or B. Bulb pipettes with a capacity from 0.5 ml to 100 ml are available in accordance with ISO 648 in Class A, AS, or B. They are all adjusted to deliver (‘Ex’); i.e. the residual liquid still left in the tip has already been taken into account during calibration and must not be expelled into the vessel by blowing out.
Very small measuring pipettes with a capacity of up to 0.2 ml (capillary pipettes) are designed as Type 4 (blow-out) in Class B; however, most available capillary pipettes are actually adjusted to contain (‘In’), which is strictly not conforming with ISO 835. Though, the formal difference between blow-out pipettes adjusted to deliver and pipettes adjusted to contain may be small for total delivery since the last drop of retained liquid in the jet can be expelled by blowing in both cases. Nevertheless, when the greatest possible accuracy is desired, it is not sufficient to simply empty pipettes that are adjusted to contain by blowing out the liquid with a pipetting aid; such pipettes should also be rinsed two to three times with the diluting medium.
The general procedure for the use of pipettes that are adjusted to deliver (‘Ex’) is described in ISO 4787 as follows. However, when the greatest possible accuracy is desired, pipettes should be used as closely as possible to the manner in which they have been calibrated (which is also specified in ISO 4787, ISO 648, and ISO 648).
The corresponding procedure for the use of pipettes that are adjusted to contain (‘In’) is described in ISO 4787 as follows. Note that, when the greatest possible accuracy is desired, it is not sufficient to simply empty the pipette by blowing out the liquid with a pipetting aid; the pipette should also be rinsed two to three times with the diluting medium.
Since you are explicitly asking for standards, you might want to start with ISO 4787 Laboratory glassware – Volumetric instruments – Methods for testing of capacity and for use. This international standard provides methods for testing as well as for use of various volumetric instruments made from glass. Further requirements for individual volumetric instruments can be found in
Most commercially available laboratory glassware is in accordance with these standards. However, some nonconforming volumetric instruments are also available, for example in non-standard sizes.
Due to retention of liquid on the inner surface of the volumetric instrument, the volume of liquid delivered is not identical with the volume of liquid contained by the volumetric instrument. Volumetric instruments are either adjusted ‘to contain’ (i.e. the capacity printed on the instrument corresponds to the contained quantity of liquid) or ‘to deliver’ (i.e. the capacity printed on the instrument corresponds to the delivered quantity of liquid; the wetting residue remaining in the instrument has already been taken into account in the calibration). According to international standards, the marking ‘Ex’ is used to indicate that the volumetric instrument has been adjusted to deliver; the marking ‘In’ is used to indicate that the volumetric instrument has been adjusted to contain. Most typical graduated pipettes, bulb pipettes, and burettes are usually adjusted to deliver, whereas typical graduated cylinders, volumetric flasks, and capillary pipettes (i.e. very small measuring pipettes with a capacity of up to 0.2 ml) are usually adjusted to contain.
ISO 648 and ISO 835 specify three classes of accuracy for pipettes:
‘Waiting time’ is the period to be observed in order to ensure complete delivery after apparent completion of the liquid delivery of the pipette (i.e. after the meniscus appeared to come to rest) and before the final reading of the delivered volume is taken (i.e. before the tip of the jet is removed from the inner surface of the receiving vessel).
Furthermore, four types of graduated measuring pipettes are standardized in ISO 835:
Typical graduated measuring pipettes with a capacity from 0.5 ml to 25 ml are commercially available in accordance with ISO 835 as Type 1, 2, or 3 and in Class A, AS, or B. Bulb pipettes with a capacity from 0.5 ml to 100 ml are available in accordance with ISO 648 in Class A, AS, or B. They are all adjusted to deliver (‘Ex’); i.e. the residual liquid still left in the tip has already been taken into account during calibration and must not be expelled into the vessel by blowing out.
Very small measuring pipettes with a capacity of up to 0.2 ml (capillary pipettes) are designed as Type 4 (blow-out) in Class B; however, most available capillary pipettes are actually adjusted to contain (‘In’), which is strictly not conforming with ISO 835. Though, the formal difference between blow-out pipettes adjusted to deliver and pipettes adjusted to contain may be small for total delivery since the last drop of retained liquid in the jet can be expelled by blowing in both cases. Nevertheless, when the greatest possible accuracy is desired, it is not sufficient to simply empty pipettes that are adjusted to contain by blowing out the liquid with a pipetting aid; such pipettes should also be rinsed two to three times with the diluting medium.
The general procedure for the use of pipettes that are adjusted to deliver (‘Ex’) is described in ISO 4787 as follows. However, when the greatest possible accuracy is desired, pipettes should be used as closely as possible to the manner in which they have been calibrated (which is also specified in ISO 4787, ISO 648, and ISO 648).
The corresponding procedure for the use of pipettes that are adjusted to contain (‘In’) is described in ISO 4787 as follows. Note that, when the greatest possible accuracy is desired, it is not sufficient to simply empty the pipette by blowing out the liquid with a pipetting aid; the pipette should also be rinsed two to three times with the diluting medium.
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