Automated determination of sodium in milk with 859 Titrotherm and 814 USB Sample Processor

Significance of the topic

The automated thermometric titration of sodium in milk addresses a critical need in the dairy industry for rapid, accurate, and reproducible sodium analysis. Sodium content impacts product quality, nutritional labeling, regulatory compliance, and consumer health. Thermometric titrimetry uses temperature change endpoints without requiring insulated vessels, making it ideal for high-throughput quality control.

Objectives and overview of the study

• Develop an automated method to quantify sodium in various milk matrices using 859 Titrotherm and 814 USB Sample Processor.
• Standardize the Al³⁺/K⁺ titrant by regression against a 0.25 mol/L NaCl standard.
• Validate precision, accuracy, and blank corrections for full cream, low-fat, and skim milk samples.
• Demonstrate workflow efficiency and data quality for routine dairy analysis.

Methodology and instrumentation used

Thermometric titration relies on a constant titrant addition rate to produce a predictable heat change until the sodium endpoint is reached, indicated by an inflection in the temperature curve. Milk samples are first deproteinized and defatted with 25% trichloroacetic acid, then clarified by filtration or centrifugation. An aliquot of serum is titrated with 0.5 mol/L Al(NO₃)₃ containing 1.1 mol/L KNO₃ after addition of 30% NH₄F·HF reagent to precipitate NaK₂AlF₆. Titrant molarity and method blanks are determined via linear regression in the tiamo software.

Instrumentation used

• 859 Titrotherm with 5 mL and 10 mL Dosino units
• 814 USB Sample Processor
• Multiposition sample rack, stirring propeller, titration head
• PP sample tubes, FEP tubing, reagent organizer, stacking frame

Main results and discussion

Calibration of the Al–K titrant yielded a slope of 1.8582, intercept 0.1889 mL, correlation R²=1.0000, and molarity 0.5382 mol/L. Method blanks ranged from 0.1295 to 0.1971 mL, with R² values >0.9994 across milk types. Sodium concentrations determined were:

• Full cream milk: 51.7 ± 0.38 mg/100 mL (label 46 mg/100 mL)
• Low-fat milk: 55.4 ± 0.32 mg/100 mL (label 67 mg/100 mL)
• Skim milk with solids and calcium: 62.7 ± 0.26 mg/100 mL (label 69 mg/100 mL)

The precision and accuracy demonstrate suitability for routine analysis despite minor deviations from label values.

Benefits and practical applications of the method

• Rapid endpoint detection without insulation
• High sample throughput with automation
• Minimal sample preparation and reagent consumption
• Robust blank correction and software integration
• Applicability to diverse dairy matrices

Future trends and possibilities for use

Advances may include integration with laboratory information management systems, miniaturized thermometric sensors for inline monitoring, extension to other food matrices, and further automation to support continuous process control in dairy production.

Conclusion

The automated thermometric method using 859 Titrotherm and 814 USB Sample Processor offers a reliable, efficient, and accurate solution for sodium determination in milk. Its straightforward workflow, precise blank correction, and high throughput make it a valuable tool for dairy quality control and nutritional analysis.

Reference

• Metrohm Application Bulletin 343/1e: Automated determination of sodium in milk with 859 Titrotherm and 814 USB Sample Processor.