Automated sodium determination in various foods with 859 Titrotherm

Significance of the Topic

Monitoring sodium content in foods is essential for nutritional labeling, public health assessment and food quality control. Automated thermometric titration offers rapid, precise measurement of sodium by exploiting the exothermic precipitation of NaK2AlF6 in acidic media.

Objectives and Study Overview

This study aims to develop and validate an automated procedure using the Metrohm 859 Titrotherm system coupled with the 815 USB Robotic Sample Processor to determine total sodium in various food matrices including bouillon, gravy, tomato ketchup, corn chips, pretzel sticks and crackers. Key performance criteria were reproducibility, method blank stability and accuracy against labeled values.

Methodology and Instrumentation

Sample preparation involved homogenization by Polytron followed by addition of an NH4F·HF complexing solution and KNO3. The titrant was Al(NO3)3/KNO3 (0.5/1.1 mol/L). Thermometric end points were detected via the Titrotherm thermoprobe under constant titrant addition rate. Instrumentation:

• 859 Titrotherm with 800 Dosino dosing unit (20 mL)
• 815 USB Robotic Sample Processor XL
• Polytron PT 1300 D dispersing aggregate
• 843 Pump Station
• Various ETFE and glass dosing units

Blank and sample titrations were calibrated by linear regression of titrant consumption vs sample size. The method blank was determined from multiple blank analyses and subtracted from sample volumes.

Main Results and Discussion

Reproducibility across six replicates yielded relative standard deviations between 0.08 % and 3.75 % depending on the sample. Sodium recoveries closely matched labeled values with deviations typically within ±5 %, except for crackers (+15.8 %) and bouillon powder (+10.5 %), indicating matrix influences. Calibration curves exhibited excellent linearity (R² > 0.998). Total analysis time per sample, including homogenization, was approximately 8.5 minutes.

Benefits and Practical Applications

This thermometric titration approach provides high-throughput, robust sodium determination without electrode-based endpoints or insulated vessels. Automation reduces operator error and sample preparation time, making it ideal for routine quality control in food production and regulatory laboratories.

Future Trends and Applications

Integration with advanced robotics and inline sampling could further increase throughput. Expanding the method to multi-element thermometric titrations and miniaturized reaction vessels may reduce reagent consumption. Applying data analytics and machine learning to temperature profiles could enhance endpoint detection in complex matrices.

Conclusion

The automated sodium determination method using the 859 Titrotherm with robotic sample handling delivers accurate, precise and efficient quantification of sodium in diverse food products. Its reproducibility, speed and ease of operation support its adoption in food analysis laboratories.

References

• No external references provided