Metrohm Dosing Test

Metrohm Dosing Test
Calibration of Metrohm dosing and exchange units
Used every day – and always accurate ...
02
Everyday use
Your Metrohm dosing or exchange unit operates reliably
day in, day out, or even overnight if so configured. It al­­
ways dispenses an exact volume. The cylinder is filled
with titrant before the sequence starts again.
You base your decisions on the results obtained because
you know that you can rely on the values delivered by
your Metrohm titration system.
Alcoholic KOH, for example, attacks the glass cylinder
and can thus alter its inside diameter. Intensive use of the
internal buret or just simply aging may also compromise
the performance of the measuring system.
The Metrohm Dosing Test
The Metrohm Dosing Test has been developed to deal
with this situation: your dosing or exchange unit is perio­
dically inspected to verify that its accuracy and precision
are still within the required tolerances.
But are these values absolutely reliable?
Yes they are, provided that your Metrohm dosing or ex­­
change unit is new, or has been regularly serviced. Like
any instrument exposed to chemicals or which has mov­
ing parts, or both in the case of a Metrohm buret, it may
become less accurate over time.
Furthermore, the Metrohm Dosing Test is carried out by
specially trained Metrohm Service Engineers at your work­
­place using recognized standards and procedures.
The Metrohm Dosing Test can be conducted during an­­
nual servicing of the instrument, either as a component of
a Metrohm Care Contract or «on demand» to mi­­nimize
disruption to your laboratory workflow.
... for very demanding requirements
Piston burets have very demanding requirements with
respect to accuracy and precision of the dosed volumes,
as defined in ISO standard 8655-3:2002 «Piston-operated
volumetric apparatus – Part 3: Piston burettes».
When they leave factory, Metrohm burets fulfill these
strin­­gent requirements without exception, as confirmed
by the corresponding quality certificate. This means you
can rely on the accuracy and precision of your piston
buret right from the start.
The Metrohm Dosing Test checks that these require­
ments are still being fulfilled in your daily operations and
confirms continuous compliance with the respective
standards.
Maximum permissible errors for motor-driven
piston burets according to ISO 8655-3:2002:
Nominal
volume
mL
≤ 1
2
5
10
20
50
Maximum permissible errors
systematic
random
± µL
± µL
6.0
1.0
10
2.0
15
5.0
20
7.0
40
14
100
25
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One test method for every requirement
04
The Metrohm Dosing Test is based on a gravimetric
method. This means that the dispensed water is weighed
and the volume dosed is then calculated using the spe­
cific density of water. The calculated dosed volume is
subsequently compared to the displayed volume.
Procedure according to ISO 8655-6
In the procedure specified in the standard «ISO 8655­
6:2002 Piston­operated volumetric apparatus – Part 6:
Gravimetric methods for the determination of measure­
ment error», three different volumes are used in the test:
•10%ofthenominalcylindervolume
•50%ofthenominalcylindervolume
•100%ofthenominalcylindervolume
Ten individual measurements are carried out for each of
these three volumes. The test liquid is water conforming
with grade 3 as specified in ISO 3696. The systematic and
the random measurement errors are calculated from the
measured values.
Metrohm Dosing Test, cumulative procedure
The general conditions of the Metrohm Dosing Test cor­
respond to those of standard ISO 8655­6:2002. Details
of the test conditions, the test procedure, and the calcula­
tionsaregiveninMetrohmApplicationBulletin283/1e.
In the cumulative procedure, the test volumes are dis­
pensed from one cylinder filling without any refilling. The
smallest test volume is exactly 10% of the cylinder volume, the largest is exactly 100%. The remaining 8 test
volumes are randomly selected from the range between
these two limits.
This procedure ensures that the entire volume range of
the buret is covered. The linearity of the dosed volume
can thus be reliably checked.
The accuracy of the results depends not only on exact
determination of the mass, but on other parameters as
well. These are primarily the temperature of the water
and the ambient air as well as the barometric pressure.
This is why the Metrohm Service Engineers are equipped
with calibrated thermometers and barometers.
Metrohm Dosing Test, repetitive procedure
In the repetitive procedure of the Metrohm Dosing Test,
one test volume is dispensed and then the cylinder is
refilled. Each dosing thus starts with a cylinder that is
completely full.
Customer-specific Dosing Test
The Customer­specific Dosing Test is carried out in accor­
dance with the procedure and general conditions speci­
fied in standard ISO 8655­6:2002.
However, customers can select the following parameters:
• The selected test volume can be any value between
10%and100%ofthenominalcylindervolume.
• The number of repeated measurements can vary
between3and10,andthisnumbercanbevaried
for the individual test volumes.
This enables compliance with customer­specific require­
ments, e.g. those specified in an SOP.
Choosing the appropriate test procedure
Procedure according to ISO 8655­6
Metrohm Dosing Test, cumulative procedure
Metrohm Dosing Test, repetitive procedure
Customer­specific Dosing Test
Your advantages
• Official procedure according to an internationally
recognized standard
• Based on ISO 8665­6:2002
• Checks the entire volume range
• Quickest procedure
• Based on ISO 8665­6:2002
• Checks the entire volume range
• Simulates practical conditions
• Complies with the requirements of your SOP
• The buret can be checked in the volume range you
need
05
Stay on the safe side
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The Dosing Test gives you certainty – the certainty that
your Metrohm buret is dispensing the displayed value.
This in turn gives you assurance that you really can rely
on your results, and that this will not cause problems
during auditing.
Once the Metrohm Dosing Test has been successfully
completed, you will receive the corresponding certificate.
This certificate confirms clearly and traceable that your
buret continues to comply with the requirements as veri­
fied by the test, as well as the reference instruments used
in the test.
In short, you can focus on your work knowing that you
canrely100percentontheaccuracyofyourMetrohm
buret.
Good to know
The test includes inspection and maintenance of
your Metrohm buret
Every Metrohm Dosing Test includes inspection and
main­­­­tenance of your Metrohm buret.
The Metrohm Service Engineer checks the piston, cylin­
der, valve disc, connecting tubes, and other components
for any signs of damage or wear, and then cleans and
lubricates the parts as necessary.
If the buret no longer complies with the requirements,
the Metrohm Service Engineer can replace the corres­
pon­ding components directly on-site – and then repeats
the Dosing Test.
Inspection and maintenance of your drive unit
(Dosino, Titrino, Titrando)
The exchange unit or the dosing unit and the buret drive
form a unit, and the complete system is checked during
the Dosing Test.
The drive unit itself is also a high-precision instrument,
re­­­­­­gardless whether it is a Dosino, a Titrino or even a
Titrando. The piston stroke of 50 mm or 80 mm is di­­vi­­ded
into 10,000, respectively, 20,000 increments.
Legend:
Subsidiary
Independent
Distributor
Needless to say, this stroke is directly related to the dosed
volume. If the drive unit deviates from the spe­­­­cifi­cations,
it directly compromises the result of the Dosing Test.
Inspection and maintenance of your drive is thus worth­
while for several reasons:
•No unpleasant surprises during the Dosing Test.
•Error-free function of the drive unit, not only during
the Dosing Test itself, but also during operation.
•Maximum flexibility in combining the drive unit with
an exchange unit resp. a dosing unit.
Provided that all of your exchange, dosing, and drive
units have been calibrated, any ex­­change or dosing unit
can be combined with any drive unit.
07
Subject to change
Layout Ecknauer+Schoch ASW, printed in Switzerland by Metrohm AG, CH-9100 Herisau
8.000.5088EN – 2015-01
www.metrohm.com