Which volumetric glassware is going to deliver the required level of accuracy?
Different levels of volumetric glassware accuracy are required across a broad scope of applications. The ability to precisely measure the volume of a solution can be critical to the outcome of many experiments and analytical testing procedures. It is therefore essential to ensure that the glassware selected to make these important measurements has the requisite accuracy and precision.
Which brand of volumetric glassware should I use, Pyrex and MBL?
SciLabware manufactures two brands containing volumetric glassware products, Pyrex and MBL. As the name indicates Pyrex volumetrics are manufactured exclusively from Pyrex borosilicate glass. MBL volumetric products are manufactured either from borosilicate and soda-lime glass. Soda-lime glass is generally used for products where long-term exposure to chemicals is unlikely, e.g. one mark and graduated pipettes.
Pyrex volumetric glassware has superior thermal and chemical resistance and is better suited to glassware for storage of solutions, e.g. volumetric flasks. The use of Pyrex borosilicate glass for volumetric glassware means accuracy is retained over a longer working life than their soda-lime glass equivalents.
With everyday use, volumetric glassware requires recalibration. Soda-lime glass items will generally necessitate twice as many recalibrations as items constructed from borosilicate glass. ASTM 542 and ISO 4787 international standards for calibration of laboratory volumetric glassware recommend that volumetric flasks are recalibrated at the following intervals (or sooner if chemical corrosion is observed): Borosilicate – 10 years; Soda-lime – 5 years.
Graduated products are accurate, right?
Volumetric glassware is a class of glass vessels that are calibrated to contain or deliver specific volumes of substances. Although many glassware items are graduated i.e. beakers, flasks, bottles, etc. these graduations are approximate and only calibrated products should be used where accurate volumetric measurement is required.
Borosilicate vs Soda-lime?
Volumetric glassware can be made from both 3.3 borosilicate glass (such as Pyrex) and soda-lime glass. Borosilicate glass is much more chemically resistant than soda-lime glass. As a result, borosilicate should be used where the longer-term exposure to chemicals is more likely, such as the storage of solutions in volumetric flasks. Soda-lime glass can be used with less aggressive chemicals, or where long term exposure to chemicals is unlikely, such as pipettes. 3.3 borosilicate volumetric glassware will retain its accuracy over a longer working lifetime than a soda-lime glass equivalent
Glass which Class? - Class A/AS and Class B
- Most volumetric glassware is available in two accuracy classes – Class A/AS and Class B.
- Class A/AS is the highest volumetric accuracy and is suitable for analytical applications where precision volumetric measurement is essential.
- Class B products are calibrated to accuracy tolerances twice those of Class A/AS tolerances and are suitable for general volumetric applications.
- Class AS burettes and pipettes are calibrated to the same accuracy tolerances as Class A, but are designed to permit a more rapid outflow time than the standard Class A equivalents.
Volumetrics contain or Deliver?
- All volumetric products are calibrated either ‘to contain’ or ‘to deliver’ at a specific temperature, usually 20oC. For example, a 50ml volumetric flask that is calibrated ‘to contain’ is calibrated at 20oC to precisely contain 50ml when filled to the graduation mark. Volumetric products usually calibrated ‘to contain’ are measuring cylinders and volumetric flasks.
- With a product calibrated ‘to deliver’, the delivered volume of liquid corresponds to the graduation mark on the vessel. The drainage holdback error (i.e. the amount of liquid remaining within the vessel to wet the inner surface or the liquid remaining in the jet of a pipette or burette) has already been taken into account during calibration. All volumetric glassware is marked either ‘to contain’ (ISO designation ‘IN’) or ‘to deliver’ (ISO designation ‘EX’) to indicate which type of calibration applies to that product.
All SciLabware manufactured Pyrex and MBL volumetric products are tested and calibrated in an ISO/IEC 17025 UKAS (United Kingdom Accreditation Service) accredited calibration laboratory located at SciLabware’s glass manufacturing facility in Stoke-on-Trent.
To receive ISO/IEC 17025 accreditation, SciLabware had to demonstrate the highest levels of competency in a number of areas of its calibration procedures. The achievement of this accreditation provides customers with an additional assurance of the accuracy and precision of SciLabware’s volumetric glassware.
- Pyrex and MBL Class A/AS volumetric glassware is available with different types of certification depending on what level of product traceability is required.
- All Pyrex and certain MBL volumetric products can be supplied either batch certification or individual calibration certificates. Pyrex Class A volumetric flasks and measuring cylinders can also be supplied with individual UKAS calibration certificates, where certification proving compliance to the highest levels of accuracy is required.