volumetric measurement & liquid handling
classification
volume graduation
All are manufactured based on volume (IN) or to deliver (EX). They are classified as Class “B”, “A”, or “AS”. Class “A” and “AS” have identical tolerances and error limits. volumetric products The only difference lies in waiting and delivery times. “S” refers to fast delivery. The difference between Classes A and B is the level of sensitivity in volumetric parameters. Class “A” and “AS” volumetric products are preferred for applications requiring high precision. Volume limit and sensitivity values are always defined according to the relevant ISO and DIN standards.
Due to surface tension of liquids, the curved structure formed is called the meniscus. According to DIN, ISO, and similar standards, volume measurement is performed at the lowest level of the meniscus. In evaluation, the lowest point of the graduation line is taken as reference. In volumetric glassware, the liquid forms a concave meniscus.
For precise and accurate results, the operator’s eye level and the graduation line must be aligned on the same plane.
schelbach stripe
The Schelbach stripe is located on the burette tube. It consists of a blue band in the center and is used for easier observation of the volume graduation.
For more accurate, clearer, and more precise measurements, it is fixed behind the graduation line of burette or pipette tubes. Reflected light ensures sharper visibility of the graduation line. The correct reading point of the volume is where the two lines intersect.
delivery time
Delivery time is the period between the upper starting line and the lower finishing line during liquid transfer. This point is where the tip of the pipette in burettes is located.
waiting time
Waiting time is the period after complete delivery during liquid transfer. After liquid transfer, residual liquid may continue to flow from the burette or pipette wall. For precise volumetric measurements, waiting time must be strictly observed. Especially in pipettes, the last remaining drop accumulated at the tip must be considered in volume measurement.
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