AUTOMATED WEIGHING OPTION: PROVING THE ACCURACY OF AUTOMATED SAMPLE PREP

Importance of Gravimetric Automation in Sample Preparation

Automated sample preparation ensures consistent control of critical variables such as timing, temperature and mixing speeds. Integrating gravimetric approaches further improves accuracy by directly measuring added solids and liquids, reducing out-of-specification results and providing insight into preparation errors.

Study Objectives and Overview

This application note by Liscio et al. at Anatune evaluates the accuracy and precision of an integrated weighing module on a GERSTEL Multipurpose Sampler (MPS). The focus is on assessing liquid handling performance across multiple experiments and examining the impact of gravimetric recording on method robustness.

Methodology and Instrumentation

The MPS was equipped with:

• Sartorius Cubis I automated balance (4-decimal precision)
• Capper/decapper module
• Solvent reservoirs and trays for 10 mL vials
• Pipette Tool (1 mL tips) and Large Liquid Tool (10 mL syringe)
• Prep Syringe Module PSM (2.5 mL syringe)

Five experiments were conducted:

1. Weighing repeatability of empty and filled vials
2. Liquid handling accuracy for water, methanol and dichloromethane
3. Syringe performance across volume range with and without “Accurate Add”
4. Gravimetric preparation of calibration curves
5. Dispensing viscous samples (avocado oil)

Main Results and Discussion

Experiment 1 demonstrated an RSD of 0.001% for five weighings of 10 mL vials, with liquid additions averaging 0.9992 mL (RSD 0.03%).
In Experiment 2, syringe tool achieved 100% accuracy for water, 99.2% for methanol and 97.3% for dichloromethane; pipette tool showed lower accuracy, especially for dichloromethane (65.5%). Solvent loss was negligible for water and methanol; DCM losses of up to 0.6% reflected volatility.
Syringe performance (Experiment 3) across 0.25–2.5 mL volumes improved at the bottom end when using the “Accurate Add” feature, achieving up to 100.1% accuracy. Large volume dispensing (4.25–4.75 mL) showed accuracy above 98.8%, increasing to 99.4% with a 10 mL syringe and Accurate Add.
Calibration curves (Experiment 4) prepared gravimetrically yielded volumetric accuracies of 98.8–100% across solvent, internal standard and analyte additions. Gravimetric data improved linearity assessment with R2 0.9996.
Viscous sample tests (Experiment 5) delivered average RSDs of 4.0% for 900 µL and 5.1% for 500 µL of avocado oil after optimizing fill speed and air gap to limit dripping.

Practical Benefits and Applications

• Enhanced analytical robustness through direct weight measurements
• Minimization of pipetting errors and solvent losses
• Automated data logging into spreadsheets for QA/QC and method validation
• Insight into error sources by reviewing gravimetric records

Future Trends and Potential Uses

Progress in automation will integrate advanced sensors and AI-driven workflows to further reduce variability. Wider implementation in pharmaceutical QC, environmental monitoring and high-throughput screening is anticipated. Real-time data analytics may enable predictive maintenance and dynamic method adjustments.

Conclusion

The integrated gravimetric option on the GERSTEL MPS offers a robust means to prove and enhance liquid handling performance. By combining automated weighing with precise liquid dispensing, laboratories can achieve higher accuracy, reduced variability and greater confidence in analytical results.

Reference

Liscio C. Automated Weighing Option: Proving the Accuracy of Automated Sample Prep. Anatune Ltd., 2020.