Cubis II Ultra-High Resolution Balances: From Data Sheet to Reality
Peak Performance Under Your Laboratory Conditions
Repeatability Test and Determination of Minimum Sample Weight According to USP Chapter 41
Figure 1: Determining the minimum sample weight on a Cubis II MCA66S according to USP Chapter 41.
High-capacity micro balances are used to weigh small quantities of samples into larger flasks. For this reason it is important to understand how these balances meet the requirements for accuracy and repeatability over the entire weighing range. By adopting the requirements for minimum weight it is ensured that samples are being weighed according to the acceptance criteria for accuracy.
Test Setup: Repeatability tests were performed to define the minimum sample weight according to USP Chapter 41 with a test weight of 1 g at various preloads.
Results: Values between 2.6 mg and 2.9 mg were measured with Cubis II MCA66S through the entire weighing range (yellow bar, Figure 2). The deviation from zero preload (2.6 mg) is 12 % over the entire weighing range. The competitor balance showed rather larger deviation over the entire weighing range (black bar, Figure 2).
Conclusion: Cubis II MCA66S showed excellent repeatability and accuracy resulting in constant and low minimum sample weight values over the entire weighing range.
Figure 2: Minimum sample weight test result for different preloads.
Features and Benefits:
- Top of the class minimum sample weight saves precious materials
- Robust performance through the entire weighing range guarantees high level of accuracy and repeatability
Electrostatic Effects
Electrostatically charged samples or containers can be difficult to weigh. Static charges, which can occur e.g. when using gloves, weighing powders or at low humidity, can cause unstable balance readings and measurement drift leading to slow and inaccurate weighing results.
Figure 3: Weighing of charged samples is no problem thanks to the built-in ionizer in the Cubis II Ultra-High Resolution Balances.
Test Setup: The following samples: 10 ml beaker, 100 ml beaker and watch glass, were charged and then measured with a field mill. The charged samples were placed in the weighing chamber and the ionizer was activated. Once a stable value was shown, the sample was taken out and leftover charge was determined again.
In the case of Cubis II MCA66S the built-in ionizer was tested with a setting to activate the ionizer in combination with opening the door. Since this option was not available for the competitor balance, the ionizer started after the sample was put into the weighing chamber and the doors were closed. Additionally, both balances were tested against outer electrostatic fields. The electrostatic fields were induced by charged cellulose nitrate (CN) filters.
Results: Table 1 shows that the ionization of the different charged samples always led to a complete discharge for the MCA66S.
Table 1: Comparison of the built-in ionizer.
The test against outer electrostatic fields showed that the Cubis II MCA66S is not affected. The maximum deviation in digits is shown in Table 2.
Table 2: Comparison of the built-in ionizer.
The optimal positioning of the four ionizing nozzles and the unique technological solution enables full discharge, even when inner draft-shield is installed. The variety of setting options offer the preferred activation of the ionizer. For example, when the ionizer starts during draft-shield opening, this helps to efficiently neutralize any electrostatic charges that may have accumulated on the sample or container, not only ensuring accurate results but also stable readouts.
Additionally, the conductive coating of all glass parts (draft-shields) of the Cubis II MCA66S prevents outer electrostatic effects.
Conclusion: Cubis II MCA66S has demonstrated exceptional performance in mitigating the effects of electrostatic charges by 100 %. All tested vessels were fully discharged, and electrostatic charges were effectively neutralized.
In addition, the Cubis II MCA66S is designed to be highly resistant to external electrostatic fields. This feature ensures that even in environments where significant electrostatic activity is present, the balance system remains unaffected, allowing for accurate and reliable weighing results to be obtained.
Features and Benefits:
- Full discharge thanks to the optimal position of the 4 ionizing nozzles and the flexible setting options guarantee accurate results
- Protected from outer static effects thanks to the conductive coating of the draft-shields resulting in stable values without drift
- No cross-contamination because full discharge is guaranteed
Drafty Conditions – Performance in Fume Hood
Working in drafty environments, such as a fume hood or weighing cabinet, can greatly impact both the weighing values and prolong measurement time. Weighing quality is effected because of the decline in repeatability and increase in measurement uncertainty.
The influence of the airflow strongly depends on the readability of the balance. For a balance with a readability of 1 µg, draft can significantly influence the weighing results.
Figure 4: Receive accurate weighing results with the Cubis II MCA66S even under drafty conditions, like in a fume hood.
Test Setup: The standard deviation of the repeatability values and the measurement time were measured in a fume hood with an air-movement of 0.3 m/s to 0.4 m/s. Various laboratory vessels (vial, volumetric flask and weighing boat) were used as preload to simulate a workflow typical for high-capacity micro balances.
Please note, that the Cubis II MCA66S was tested with an automated inner draft shield as shown in Figure 5. The competitor balance had an inner draft shield installed.
Figure 5: Cubis II MCA66S with automated inner draft shield.
Results: The achieved standard deviations are remarkably low under drafty conditions with 6 µg for the vial, 19 µg for the volumetric flask and 6 µg for the weighing boat. (Figure 6).
Figure 6: Repeatability in drafty conditions test results. Both balances were tested with inner draft shield.
The measurement times were comparable in both devices measured for the tested vial and volumetric flask. However, for the weighing boat the Cubis II MCA66S achieved faster results (Figure 7).
Figure 7: Measurement times in drafty conditions test results.
Conclusion: The Cubis II MCA66S showed excellent repeatability values with all three different types of vessels. The measurement time is comparable or slightly better in contrast to the tested competitor.
Features and Benefits:
- High degree of repeatability in fume hood contributes to good performance
- Fast measurement time speeds up processes
