volumetric measurement & liquid handling
classification
meniscus line
All volumetric products are always calibrated as to contain (In) or to deliver (Ex) . They are classified in three groups; Class “B” or Class “A” or “AS” . Class “A” and “AS” carry exactly the same error and tolerance limits. The difference is in their “delivery” and “waiting times”. “S” means quick (swift) delivery. The classification as “A” or “B” indicates the degree of accuracy of related parameters. Class “A” or “AS” volumetric products carry highest level of accuracy and specially well accepted by laboratories looking for quality. The error limits, accuracy and variations are always in accordance with relevant ISO or DIN standard limits.
A simple definition of meniscus is the curve on the surface of the liquid. According to DIN , ISO and most other standards volume should be read at the lowest liquid level. The lowest level of the meniscus has to touch the upper edge of the graduation mark. On the volumetric glassware the form of the meniscus is concave. For the exact and most precise results, the eye of the observer must be exactly at the same level of meniscus line.
To have a better, faster and more accurate reading and measurement, a black strip should be held at the back side, just below of the graduation mark and meniscus line.
schellbach stripe
The schellbach stripe is a narrow blue band which takes place at the center of a wider white band on the burette tube background. Mostly printed at the backside of the burette tube for easier observation of meniscus line.
The penetrated light fraction two arrow head points that appear at the meniscus line. Exact meniscus line is exactly where two arrow heads touch each other.
delivery time
Delivery time is the time needed to deliver the liquid from the starting level to the final level. For burettes and pipettes final level is generally the tip of the product.
waiting time
The waiting time starts after complete transfer is finalised. After the transfer of the liquid usually liquid continues to flow down from the burette or pipette wall. For accurate volume measurement attention must be paid to the waiting time. Specially with pipettes the residual drop accumulated at the tip should be considered.
Made with FlippingBook - professional solution for displaying marketing and sales documents online