Determination of Chloride in Infant Formula and Adult Nutritionals

Importance of the Topic

The accurate measurement of chloride content in infant formulas and adult nutritional products is critical for ensuring proper nutrient intake, regulatory compliance, and consumer safety. Chloride plays a vital role in maintaining electrolyte balance and preventing metabolic disorders in vulnerable populations, particularly infants.

Study Objectives and Overview

This study aimed to develop and validate a robust ion chromatography (IC) method for quantifying chloride in various product forms, including powdered, ready-to-feed (RTF), and liquid concentrates, following AOAC SPIFAN Single Laboratory Validation (SLV) and Standard Method Performance Requirements (SMPR) guidelines.

Methodology and Instrumentation

Sample Preparation:

• Powders: Reconstitution in water, centrifugation using ultracentrifugal filter units, and 0.2 μm filtration.
• RTF and liquids: Direct centrifugation and filtration.

Chromatographic Conditions:

• System: Thermo Scientific Dionex ICS-5000+ Reagent-Free HPIC.
• Column: IonPac AS15 analytical (2 × 250 mm) with AG15 guard (2 × 50 mm) at 30 °C.
• Eluent: KOH gradient (5–60 mM) generated in-line; flow rate 0.4 mL/min; injection volume 2.5 μL.
• Detection: Suppressed conductivity (AERS 500 suppressor, recycle mode, 60 mA).

Results and Discussion

Separation and Detection:
Chloride was baseline-resolved from other anions with a retention time of ~15.4 min. The RFIC system provided high-purity eluent without manual preparation.

Linearity and Sensitivity:
Calibration over 5–2000 mg/L showed R² > 0.9995. Estimated LOD and LOQ were 0.006 and 0.02 mg/100 g, well below SMPR requirements.

Precision and Accuracy:
Intermediate precision (n=2 per day) and overall reproducibility (n=12) across 14 fortified matrices yielded RSDs < 2.5% and < 3.2%, respectively. NIST SRM 1849a chloride recovery averaged 106% of certified value with 1.9% RSD. Spike recoveries in placebo matrices ranged from 94.7% to 106%, largely within the 95–105% SMPR range.

Benefits and Practical Applications

This IC method offers:

• High accuracy and reproducibility for routine quality control in food and nutrition labs.
• Simplified operation via reagent-free eluent generation.
• Rapid sample turnaround with minimal matrix interference.
• Compliance with regulatory standards (Infant Formula Act, AOAC SPIFAN SMPR).

Future Trends and Opportunities

Emerging directions include:

• Integration of mass spectrometric detection for multi-element profiling.
• Automation and inline sample processing to increase throughput.
• Development of novel stationary phases for faster separations.
• Adoption of miniaturized and portable IC systems for on-site testing.

Conclusion

The validated IC procedure using a Dionex ICS-5000+ system and IonPac AS15 column achieves precise, accurate, and sensitive chloride determination in diverse nutritional matrices, meeting or exceeding AOAC SPIFAN and regulatory performance criteria. Its streamlined workflow and reagent-free design make it well suited for high-throughput quality assurance laboratories.

Used Instrumentation

• Thermo Scientific Dionex ICS-5000+ Reagent-Free HPIC System.
• IonPac AS15 analytical and AG15 guard columns.
• EGC III KOH eluent generator and CR-ATC II trap column.
• AERS 500 electrolytic suppressor.
• AS-AP autosampler; Chromeleon Chromatography Data System.

References

1. Linshaw MA et al. Hypochloremic alkalosis in infants associated with soy protein formula. J. Pediatr. 1980;96(4):635–640.
2. Reznik VM et al. Neo-Mull-Soy metabolic alkalosis: a model of Bartter’s syndrome? Pediatrics. 1980;66(5):784–786.
3. Newberry RE. The Infant Formula Act of 1980. J. Assoc. Off. Anal. Chem. 1982;65(6):1472–1473.
4. AOAC SMPR 2014.015 Standard Method Performance Requirements for Chloride in Infant and Adult/Pediatric Nutritional Formula. 2014.
5. AOAC International. Recommended Guidelines for SPIFAN SLV. 2010.