08 TECHNICAL INFORMATION | PRODUCT-SPECIFIC SECTION
USP individual certificate – The volumetric flasks are labelled with an individual number. This is permanently laser-etched onto the base of the volumetric flask and is entered on the corresponding certificate. The accuracy limits for USP <31> compliant volumetric flasks are stricter than flasks conforming to ISO 1042 and therefore satisfy the requirements of the United States Pharmacopoeia (USP). The volume measured for the corresponding volumetric flask, the measurement uncertainty and the day of issue are documented on this certificate.
Volumetric flasks
DURAN® volumetric flasks are manufactured from the chemically highly resistant borosilicate glass 3.3. Used for the accurate measurement of specific quantities of liquid they are, like virtually all volumetric glassware, volumetric analysis aids. They are mainly used for preparation and storage of standard solutions. Calibration is based on the amount of fluid contained (“In”) at a + 20°C reference temperature, which means that when the circular graduation mark is reached, exactly the specified liquid amount is contained in the vessel. Thus the desired concentration can be precisely set. The volume content tolerances for volumetric flasks conform to accuracy class A, the accuracy limits of the German weights and measures regulation and to DIN and ISO guidelines.
Measuring and mixing cylinders
DURAN® measuring and mixing cylinders are manufactured from borosilicate glass 3.3 and therefore are very resistant to mechanical and thermal stresses. Measuring cylinders are for holding and simultaneously measuring different liquid amounts. Mixing cylinders are for diluting solutions and mixing several components in a given quantity ratio. Their large hexagonal base prevents the cylinder from rolling. The base is equipped with three knobs that increase its stability. The cylinders have uniform wall thickness over the entire measurement range, so wedge errors are avoided. Calibration is based on contained fluid (“In”) at a + 20 °C reference temperature, which means that when the circular graduation mark is reached, exactly the specified liquid amount is contained in the vessel. Thus the desired concentration can be precisely set. Volume content tolerances for measuring and mixing cylinders conform to DIN and ISO accuracy limits.
Burettes
DURAN® burettes are manufactured from chemically highly resistant borosilicate glass 3.3. They are primarily used for titration. The precise scale permits exact reading of the liquid quantity required for the titration. Calibration is based on the released volume (“Ex”) at a + 20°C reference temperature. The fluid quantity released can be taken exactly from the scale, as the liquid adhesion to the glass is taken into account in the calibration. This only applies, however, if the specified waiting times for reading the scale are adhered to. Volume content tolerances for burettes conform to DIN and ISO accuracy limits. The DURAN® Class B burettes’ accuracy limits are roughly one and a half times the Class AS accuracy limit. The tolerances are thus stricter than specified by DIN. The tried-and-tested DURAN® burettes are also available with PTFE keys. Work in the laboratory is simplified by the fact that unlike glass keys, these do not have to be lubricated. By the specification of a class “AS”, the German weights and measures regulations have, within the scope of the 15 th Amendment Regulations, acknowledged that the great majority of volumetric measurements, especially in clinical laboratories, are carried out with water or dilute aqueous solutions; thus apparatus with considerably shorter draining times than previously required but with the same accuracy limits is now admitted by the calibration regulations.
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