July 26, 2021
Keywords or phrases:
Lab weighing, Balances, Microbalances,
The Perfect Microbalance for Every Application
New Innovations for Microbalances
Dr. Thomas Pertsch, Dr. Holger Densow
Sartorius Lab Instruments GmbH & Co. KG, Otto-Brenner-Straße 20, 37079 Goettingen
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weigh very small sample amounts. Obtaining reliable weighing results with these balances requires special considerations
regarding the installation site in addition to optimized ergonomics and technical controls. Sartorius’s innovative micro- and
ultra-microbalances offer both accuracy and ease of use for routine measurement.
It is fascinating that we can use micro- and ultra-
microbalances to weigh sample amounts so small that they
are invisible to the naked eye. Considering the conventional
visual range of 25 cm, some people can still distinguish
viewing angle of approximately 2 arc minutes. Others can
minutes. On average, the healthy human eye can resolve
(the normal visual acuity of the human eye at a comfortable
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3 and a weight equal
to the smallest scale interval of a microbalance has a
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the particle size is below the visual acuity of the human eye,
the weight can be accurately determined. That is why
touching a sample or vessel with bare fingers must be
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has a major impact on measurement accuracy. To put it in
another perspective, an ultra-microbalance with a scale
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resolution in 21 million steps. That is comparable to
measuring a distance less than 2 meters of the earth’s
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million meters). In weight units, this is fine enough to
measure a weight of 1 g of a total mass of 21 tons. This high
resolution provides ideal support for measuring the
smallest sample weights below 1 mg within one part per
thousand. For such applications, micro- and ultra-
microbalances with ten time greater accuracy are needed.
Typical areas of application for the micro- and ultra-range
weight measurement are filter weighing (filter particulate
matter and residual dirt analysis), pipette calibration,
measuring the coating of medical products (stent
weighing), pesticide analysis, measuring the incineration or
drying of chemicals or finished goods and the dispensing of
medical drugs. Micro- and ultra-microbalances therefore
play an essential role in R&D and industrial quality control
laboratories in the automotive, pharmaceutical, chemical,
food, mining industry, and medical device manufacturing.
Most of these industries are subject to strict legal
regulations. In particular, the international pharmaceutical
industries like the United States Pharmacopeia (USP),
European Pharmacopoeia (Ph. Eur.) and Japanese Pharmacopeia (JP) set stringent requirements to meet the
highest weighing standards. Therefore, the manufacturers
of micro- and ultra-microbalances offer technical features
and controls that ensure the instrument specifications are
not only maintained under optimal conditions in the
manufacturer’s testing laboratory, but also at the
Ideally, micro- and ultra-microbalances are set up on a
stable worktable, preferably on a weighing table specially
designed for this purpose and optimized accordingly. In
addition to the ideal installation location, the weighing
module must be properly leveled to give reliable results.
The new technical feature on the Sartorius micro- and ultra-
balances offer motorized automatic leveling. The user
can check the leveling in the balance Status center and
start the automatic leveling function with a single push of a
button (Figure 1).
Additionally, the balance continuously monitors the
leveling status and other factors, such as the temperature
and the time since the last internal adjustment, and alerts
the operator as needed. This is achieved by setting the Safe
Weighing mode to Warning, and the isoCAL execution
mode to Manual (Figure 2).
Figure 1 . The Status center displays the leveling status of the weighing
module. If the weighing module is not properly leveled, the virtual spirit
level is out of center, colored red and the Perform leveling button is
active. Pressing the Perform leveling button initiates the automatic
motorized leveling function. After leveling, the virtual spirit level is
centered, colored green and the button Perform leveling is inactive.
Figure 3. The external tower with climate modules transfers data to the
balance. The real-time temperature, air humidity and air pressure can be
viewed on the balance status center.
When the Safe Weighing mode is set to strict, weighing
applications will not initiated if the balance is not properly
leveled or an internal adjustment is needed. These
automatic safeguards ensure the reliability of weighing
results and provide peace of mind for the user.
Even with proper leveling and the optimal installation
location, micro- and ultra-microbalances are susceptible to
changes in environmental conditions, such as temperature,
air pressure and relative humidity. Air pressure changes, for
example, affect the air buoyancy, and low relative humidity
can increase interference by static electricity. Both air
buoyancy and static electricity can affect weight readings.
Therefore, it is important to monitor the laboratory climate
and maintain a constant environment around the weighing
stations. The Sartorius micro- and ultra-microbalances
come with an optional climate module tower that measures
temperature, humidity, and the barometric air pressure. The
data is accessible on the unit Status center (Figure 3) and is
used to perform corrective weight adjustments by some
Figure 2. If the Safe Weighing mode is set to Warning and the isoCAL
execution mode is set to Manual execution, the display buttons for
leveling or isoCAL are highlighted yellow when the balance must be
leveled or if an internal adjustment is needed. The yellow color provides
the operator with direct visual feedback when an action is necessary to
ensure proper weighing results. If the Safe Weighing mode is set to Strict,
weighing measurement only begins once the balance is properly leveled
or the internal adjustment is performed.
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interference by static electricity raises significantly.
lectrostatic influences are easy to detect by the continuous
drift of displayed weight readouts. Increasing the air
effects of static electricity. Ionization can neutralize electric
charges on surfaces, such as glass vessels.
Magnetism is another factor that impairs weight
measurement. Weighing magnetic materials, or
magnetizable tare vessels or samples may compromise the
weighing accuracy and reproducibility. Using tare vessels or
samples containing iron, steel, cobalt, or nickel can lead to
stable, but non-repeatable weight readings. Depending on
the position of the vessel or sample on the weighing pan,
different weight values are displayed. Magnetism could also
be caused by the weighing pan or a sample holder made of
steel. If the sample holder or weighing pan is rotated to
achieve a better vessel accessibility, the orientation of the
magnetic fields changes and can influence the weight
measurement. This is why the sample holders, weighing
pans and the draft shield base plate of Sartorius’s micro-
and ultra-microbalances are made of titanium as this metal
Figure 4. Microbalance weighing module with crystal clear glass draft
shield and sample holder for stent weighing. The draft shield base plate
and sample holder are made of titanium. The round, flat weighing pans
with a diameter of 20/30 mm and 50 mm, which are part of the standard
delivery contents, are also made of high-quality, non-magnetic titanium.
The weighing chamber can be dissembled easily and within a few
seconds for cleaning purposes.
Cleanability is also important for routine maintenance.
Titanium is easy to clean and offers high resistance against
many corrosive chemicals. The weighing chamber of micro-
and ultra-microbalances is made of high-quality materials
with smooth surfaces and can be easily disassembled for
Ergonomics plays an essential role in accurate weighing of
very small sample amounts. Transferring sample from a
piece of weighing paper or foil into a vessel carries the risk
of sample loss. Depending on the sample properties, a
significant portion of weighed sample might remain on the
paper or foil during transfer, leading to inaccurate sample
preparation. Direct weighing into the vessel requires a
specific set of accommodation from the balance unit.
Balancing powdery or granular samples on a spatula and in
parallel opening the draft shield manually is distracting for
the operator. In regulated pharmaceutical industry settings
where highly active substances are measured, this could
not only fatigue the user, but also be dangerous. Sartorius’s
micro- and ultra-microbalances with glass draft shield have
proximity sensors that detect the operator’s hand in front of
smooth-action draft shield, facilitating fast and ergonomic
work procedures (Figure 5).
Figure 5. The proximity sensors are located on the left and right of the
glass draft shield. The sensors detect the operator’s hand and
automatically open the draft shield, and close it when the hand is moved
out of the sensor’s detection range.
The sensitivity range for the left and right proximity sensor
can be adjusted independently of each other in three steps
(short, medium, and long) under the balance settings menu
(Figure 6). A fourth option allows for switching off a
proximity sensor to prevent the draft shield opening to the
Figure 6. Settings menu for proximity sensors and palm keys. The
proximity sensor sensitivity range can be adjusted in three steps or the
sensor can be switched off. Under the settings menu, the operator can
use the palm keys to define (in degrees) the draft shield opening angle.
The automatic draft shield functions and settings
significantly increase safe sample handling and prevent the
interruptions from manual operations. However, users who
prefer not to use the proximity sensors can control the draft
Figure 7. Removable palm keys located at the Cubis
® II MCA display.
Gentle pressing on the palm key opens or closes the
automated glass draft shield to the opening angle defined
in the balance settings menu (Figure 6). The palm keys are
held in place by magnets and can be removed from the
display for easy cleaning.
Another factor influencing sample weighing ergonomics is
the visual workflow control. Sartorius’s micro- and ultra-
microbalances are equipped with a crystal-clear tempered
glass draft shield plus LED backlight illumination. The LEDs
are located in the weighing module and light the draft
shield interior (Figure 8).
Figure 8. The crystal-clear glass and LED backlight illumination improve
visibility of all the actions inside the draft shield. The LEDs are located in
the weighing module and their intensity can be adjusted under the
balance settings menu.
The illuminated draft shield allows for clear sample viewing
and optimal handling of even the smallest sample amounts.
For light sensitive samples the LED intensity is adjustable in
three steps or can be switched off (bright, medium, dark, or
Figure 9. Settings menu for the LED intensity.
In addition to the LED illumination, the round glass draft
shield has no frame components that interfere with the
operator’s line of sight on the small – sometimes
microscopic – samples and provides a learning function.
The desired opening angle can be adjusted in the balance
settings menu by entering the angle (in degrees) using the
numeric keypad, or by manually opening the draft shield to
the desired position. The balance software saves the actual
angle and opens the draft shield to the same angle
the next time. Using the draft shield learning capability,
the balance can be adapted quickly and easily to changing
routines. Furthermore, the glass shield is treated with a
special conductive coating that helps to prevent static
electricity, which often occurs under conditions of low
humidity (see above, paragraph on static electricity).
® II micro- and ultra-microbalances series offers
models with different weighing capacities and scale
intervals. For the highest sensitivity, the ultra-microbalance
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microbalance models 6.6S and 10.6S offer a maximum
capacity of 6.1 g and 10.1 g, respectively, and a scale interval
microbalance portfolio with the model 3.6P. Here, the
weighing capacity is divided into three ranges, 1.1 g, 2.1 g
and 3.1 g, with different resolutions. At up to 1.1 g the balance
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the balance automatically switches between the different
resolutions. It is important to note the shift of the resolution
range; if using a high tare load, the highest resolution is
applied for the first 1.1 g of sample weight.
Cubis ® II MCA micro- and ultra-microbalances have
approximately sixty preinstalled weighing applications and
extended functions in the QApp Center. In the QApp
Center, applications are grouped by topic into different
packages. The Essentials package offers thirteen different
license-free weighing applications, covering basic weighing
applications. Other applications or extended functions are
grouped into five additional packages (Pharma, Advanced
Applications, Utilities, Connectivity, and Specials). Except
for the Specials software application, the remaining four
software packages can be factory licensed at the time of
purchase. Software applications and extended functions in
these packages offer optimal support and technical controls
for 21 CFR part 11 (audit trail, electronic signatures and user
monitoring of the minimum sample weight) or
EURAMET cg-18 compliance (measurement uncertainty)
and for guided weighing applications for filter or stent
weighing (filter particulate matter, backweighing).
For further contacts, visit
Specifications subject to change without notice.
Copyright Sartorius Lab Instruments GmbH & Co. KG.
Status: 08 | 2021
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