In pharmaceutical labs, having an accurate measurement is one of the key requirements to ensure that the different tasks required to correctly execute these pharmaceuticals are performed correctly, irrespective of whether it is preparing a buffer solution, diluting a sample, or conducting an Assay test; so much so that any slight mistakes made when measuring the volumetric quantity of some substance will have an impact on all outcomes. This is the reason why laboratory glassware should be accurate, reliable and appropriately calibrated.
Laboratory glassware is usually categorized as either Class A or Class B depending upon their accuracy. While both classes are commonly used, the calibration of class A and class B glassware and their applications are largely different from each other. Correct calibration also provides pharmaceutical laboratories with assurance they are complying with good manufacturing practices and producing valid analytical results.
Simply, calibration validates whether or not the glassware to be used is giving the correct measurements of volumes.
Glassware calibration is utilizing water and weighing it (using weight to then convert to volume by using a density value) can help in determining the volume of water.
Examples of Class A laboratory glassware would include the following:
Examples of Class B laboratory glassware includes:
Because of these differences, Class A glassware has more stringent requirements for calibrating glassware used for metrology purposes.
The relationship between mass, density and volume is used to determine the volume of water in the glassware.
Volume = Mass ÷ Density
The density of water will change with temperature; therefore, a temperature correction will be applied to the measurement determination. By applying the temperature correction, accurate volume determinations of water in glassware will be made.
Examples of TC: Volumetric flasks
All of the liquid must be carefully transferred from the flask to achieve an accurate volume.
Examples of TD:
Determine the volume in ml by the formula;
Volume (in ml) = (Weight in g / 0.99602)
Where 0.99602 g is the weight of 1 ml water determined at temperature 25°C.
- Class A glassware is required to have tolerance limits that fit within narrower ranges.
- Class B glassware can have tolerances that fit within wider ranges.
Any glassware that falls within the specified tolerances can be considered calibrated, while any glassware that falls outside of these limits will not be considered calibrated, and will have to be adjusted or rejected.
Normal methods include:
1. Initial calibration before first use
2. Periodic calibration — normally each year
3. After physical damage or after repair work completed
4. When the accuracy of the glassware is questionable
Class A glassware utilized in strict conditions may need to have a higher level of verification than other glassware.
All records for glassware calibration will contain the following:
- the identification of the glassware
- the date the glassware was calibrated
- the method used for the calibration
- the values observed/calculated during calibration
- the acceptance criteria for the calibration
- the approval of whoever is authorized to approve
Recording sufficient information will allow a facility to meet traceability and audit requirements that fall under Good Manufacturing Practices.
- accurate analytical results
- consistency of testing
- compliance with regulatory agencies
- correct data
Calibration of glassware is imperative to deliver reliable results; whereas, if the calibration of glassware is invalid or inaccurate, then the results will also be invalid or inaccurate, leading to poor quality products and incorrect regulatory determinations.
The following are common errors associated with the calibration of glassware:
- Routine glassware is not calibrated
- Using dirty or damaged glassware
- Not making temperature corrections
- Poor documentation
- Using Class B glassware for critical analyses
By avoiding these types of errors, the accuracy and compliance of the laboratory can be improved.
- Calibration of analytical balances must be performed regularly.
- Calibration should take place under controlled environmental temperature conditions.
- Handle glassware to eliminate the potential for damage, which will ultimately affect the ability to conduct proper calibration.
- Train all personnel in the proper calibration methods and procedures for glassware.
- Perform calibration according to established schedule.
Adhere to sound practices for calibration; therefore, laboratories will produce accurate and consistent results.
Calibration of glassware plays a key role in pharmaceutical quality assurance. Accurate measurement of liquid volumes is imperative to achieve reliable analytical results, regardless of whether or not one uses Class A or Class B glassware.
Class A glassware will be the preferred choice of glassware for critical applications because of its accuracy, while Class B glassware is appropriate for general use. Calibration must be performed properly and documented per Good Manufacturing Practices (GMP) compliance to ensure both compliance and data integrity.
There are very strict regulations applied to this industry, and as such, even the most minor of measurement errors can have dramatic consequences; therefore, maintaining a properly calibrated glassware is not only considered a best practice but is essential to quality results.
What is Glassware Calibration?
The calibration of laboratory glassware is the measurement of the volume of glassware both that it dispenses and that it contains and ensuring that the dispensed and contained volumes match the nominal reason limits.Simply, calibration validates whether or not the glassware to be used is giving the correct measurements of volumes.
Glassware calibration is utilizing water and weighing it (using weight to then convert to volume by using a density value) can help in determining the volume of water.
Classification of Glassware
Laboratory glassware is classified based on their tolerances (the degree of allowable error in measurements). Laboratory glassware may be placed into two main categories:1. Class A
Class A laboratory glassware is produced with higher precision and tighter tolerances. Every piece of Class A glassware is calibrated individually and is certified for it’s accuracy.Examples of Class A laboratory glassware would include the following:
- Volumetric Flasks
- Pipettes
- Burettes
- Quantitative analysis
- Analytical testing
- Assay preparation
2. Class B
Class B laboratory glassware is produced with wider tolerances than Class A glassware and thus is less accurate and therefore are not collectively certified.Examples of Class B laboratory glassware includes:
- Measuring Cylinders
- Beakers
- Pipettes (general/purpose)
- Preliminary measurements
- Routine laboratory work
- Non-critical measurements
Difference Between Class A and Class B Glassware
Accuracy/tolerance amounts are the main difference between glassware classification. Class A has a higher level of accuracy, therefore making it appropriate for critical measurements. Meanwhile, Class B has a lower level of accuracy, meaning it can be used for general purpose measurements. The tolerances of Class B glassware are about double that of Class A. Additionally, Class A glassware is generally marked as having been certified, versus Class B which is not certified.Because of these differences, Class A glassware has more stringent requirements for calibrating glassware used for metrology purposes.
Principle of Glassware Calibration
The calibration of glassware is based upon the gravimetric principle. In this method, the amount of mass of water contained in or delivered by the glassware is measured.The relationship between mass, density and volume is used to determine the volume of water in the glassware.
Volume = Mass ÷ Density
The density of water will change with temperature; therefore, a temperature correction will be applied to the measurement determination. By applying the temperature correction, accurate volume determinations of water in glassware will be made.
Types of Calibration
There are two generally accepted types of calibration of glassware based on its intended use.1. Calibration to Contain (TC)
The glassware is calibrated to contain a known volume of liquid.Examples of TC: Volumetric flasks
All of the liquid must be carefully transferred from the flask to achieve an accurate volume.
2. Calibration to Deliver (TD)
The glassware is calibrated to deliver a known volume of liquid.Examples of TD:
- Pipets
- Burets
Calibration Procedure
In order to maintain accurate measurements, glassware must go through a standardized system of calibrating.1. Cleaning and Preparing the Glassware
All glassware must be cleaned completely and have no foreign contaminants on/in/around it, as any residue can alter the volume of the object you are measuring.2. Weighing the Empty Vessel
The empty container that is receiving the object being measured is weighed using a properly-adjusted (calibrated) scale.3. Filling the Glassware with Water
The glassware is filled to the line where it is calibrated with temperature-controlled distilled water.4. Weighing the Full Vessel
Once the glassware is filled with water to the correct calibration line, the weight of the filled glassware is recorded, and the difference in weight from the weight of the container gives the mass of the water.5. Calculating the Volume of the Water
Using the density of the water at the temperature at which you measured it, you can now calculate the actual volume of the water in the glassware by mathematical equations using a density reference chart.Determine the volume in ml by the formula;
Volume (in ml) = (Weight in g / 0.99602)
Where 0.99602 g is the weight of 1 ml water determined at temperature 25°C.
Tolerance Limit
|
Volumetric Flasks |
||||||||||||||
Capacity in ml
|
5
|
10
|
25
|
50
|
100
|
200
|
250
|
500
|
1000
|
|||||
Tolerance
(±ml)
|
Class A
|
0.02
|
0.02
|
0.03
|
0.04
|
0.06
|
0.08
|
0.1
|
0.15
|
0.2
|
||||
Class B
|
0.04
|
0.04
|
0.06
|
0.08
|
0.15
|
0.2
|
0.2
|
0.3
|
0.8
|
|||||
One Mark Pipette
|
||||||||||||||
Capacity in ml
|
1
|
2
|
5
|
10
|
15
|
20
|
25
|
50
|
100
|
|||||
Tolerance
(±ml)
|
Class A
|
0.006
|
0.006
|
0.01
|
0.02
|
0.02
|
0.03
|
0.03
|
0.04
|
0.06
|
||||
Class B
|
0.02
|
0.02
|
0.03
|
0.04
|
0.04
|
0.05
|
0.06
|
0.08
|
0.12
|
|||||
Burettes
|
||||||||||||||
Capacity in ml
|
10
|
25
|
50
|
100
|
||||||||||
Subdivision in ml
|
0.05
|
0.05
|
0.1
|
0.1
|
||||||||||
Tolerance
(±ml)
|
Class A
|
0.01
|
0.03
|
0.05
|
0.1
|
|||||||||
Class B
|
0.02
|
0.06
|
0.1
|
0.2
|
||||||||||
Frequency : Initially when volumetric glassware is purchased.
Note: When the volumetric glassware does not comply with the requirement as specified above, the volumetric glassware should be returned back to the party.6. Comparing the Volume to the Nominal Volume
Finally, you will compare the actual volume that you calculated to the volume that the manufacturer stamped onto the glassware when it was made. If there is a difference between the two volumes that is within the allowable tolerance zone for the class of glassware in which the glassware has been identified, then the glassware will be considered to be accurately calibrated. If the difference exists but lies outside the allowable tolerance zone, the glassware will be rejected as uncalibrated, or adjusted to fall within the allowable tolerance zone.Acceptance Criteria
Acceptance criteria are dependent on the class of glassware. For instance,- Class A glassware is required to have tolerance limits that fit within narrower ranges.
- Class B glassware can have tolerances that fit within wider ranges.
Any glassware that falls within the specified tolerances can be considered calibrated, while any glassware that falls outside of these limits will not be considered calibrated, and will have to be adjusted or rejected.
Factors Affecting Calibration Accuracy
Calibration results are impacted by multiple variables.1. Temperature
Variations in water density due to changes in temperature necessitate temperature regulation while calibrating.2. Cleanliness
Pollutants or contaminants may change the flow of liquid or the precision of your measurement.3. Meniscus Reading
An error in reading the meniscus could cause an inaccurate measurement.4. Evaporation Loss
The time that passes between weighing can contribute to evaporation loss, which may also impact your measurement.5. Balance Accuracy
Accurately weighing items affects the accuracy of the calibration; thus, the balance used for the calibration must be calibrated properly.Frequency of Calibration
Calibration of glassware should be completed at pre-established periods according to how often and how critical the glassware will be used.Normal methods include:
1. Initial calibration before first use
2. Periodic calibration — normally each year
3. After physical damage or after repair work completed
4. When the accuracy of the glassware is questionable
Class A glassware utilized in strict conditions may need to have a higher level of verification than other glassware.
Documentation Requirements
Adequate documentation is required to support compliance.All records for glassware calibration will contain the following:
- the identification of the glassware
- the date the glassware was calibrated
- the method used for the calibration
- the values observed/calculated during calibration
- the acceptance criteria for the calibration
- the approval of whoever is authorized to approve
Recording sufficient information will allow a facility to meet traceability and audit requirements that fall under Good Manufacturing Practices.
Importance of Calibration of Glassware Used in Pharmaceuticals
Quality and compliance are both dependent on the calibration of glassware. The result is:- accurate analytical results
- consistency of testing
- compliance with regulatory agencies
- correct data
Calibration of glassware is imperative to deliver reliable results; whereas, if the calibration of glassware is invalid or inaccurate, then the results will also be invalid or inaccurate, leading to poor quality products and incorrect regulatory determinations.
Common Mistakes in Glassware Calibration
Many laboratories encounter problems as a result of incorrect practices.The following are common errors associated with the calibration of glassware:
- Routine glassware is not calibrated
- Using dirty or damaged glassware
- Not making temperature corrections
- Poor documentation
- Using Class B glassware for critical analyses
By avoiding these types of errors, the accuracy and compliance of the laboratory can be improved.
Best Practices in Calibration
To ensure the reliability of calibration, laboratories will want to implement good calibration practices.- Calibration of analytical balances must be performed regularly.
- Calibration should take place under controlled environmental temperature conditions.
- Handle glassware to eliminate the potential for damage, which will ultimately affect the ability to conduct proper calibration.
- Train all personnel in the proper calibration methods and procedures for glassware.
- Perform calibration according to established schedule.
Adhere to sound practices for calibration; therefore, laboratories will produce accurate and consistent results.
Calibration of glassware plays a key role in pharmaceutical quality assurance. Accurate measurement of liquid volumes is imperative to achieve reliable analytical results, regardless of whether or not one uses Class A or Class B glassware.
Class A glassware will be the preferred choice of glassware for critical applications because of its accuracy, while Class B glassware is appropriate for general use. Calibration must be performed properly and documented per Good Manufacturing Practices (GMP) compliance to ensure both compliance and data integrity.
There are very strict regulations applied to this industry, and as such, even the most minor of measurement errors can have dramatic consequences; therefore, maintaining a properly calibrated glassware is not only considered a best practice but is essential to quality results.
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