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volumetric measurement & liquid handling
006
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.
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.
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.
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 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.
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.
classification
meniscus line
schellbach stripe
delivery time
waiting time