Analysis of Phosphate and Other Phosphorus Anions Using the Agilent 7100 CE

Importance of the Topic

The determination of phosphates and related phosphorus anions is vital for monitoring nutrient pollution in surface and industrial waters, as well as for ensuring quality and compliance in food and beverage products. Elevated phosphorus levels can induce eutrophication in aquatic ecosystems, and phosphorus-based additives are widely used in the food industry for emulsification, stabilization and acidity control.

Objectives and Study Overview

This study demonstrates a capillary electrophoresis (CE) method using the Agilent 7100 CE system for the simultaneous separation and quantification of phosphate, diphosphate, triphosphate, phosphite, hypophosphite and common inorganic anions in various complex sample matrices. The goal is to establish a reproducible, sensitive and straightforward protocol suitable for routine analysis.

Methodology and Instrumentation

The method employs indirect UV detection with an Agilent plating bath buffer containing a UV-absorbing component and an electroosmotic flow modifier to reverse EOF. Key parameters include:

• Instrument: Agilent 7100 Capillary Electrophoresis System
• Capillary: fused silica, 50 µm ID, 72 cm length
• Injection: 30 s at 50 mbar, followed by 5 s at 50 mbar
• Detection: indirect UV at 350 nm (signal) and 245 nm (reference)
• Voltage: –30 kV with 0.3 min ramp
• Temperature: 20 °C

Reagents and consumables are commercially available from Merck, Sigma-Aldrich and Agilent, including standard salts (e.g., sodium dihydrogen phosphate, pyrophosphate, tripolyphosphate) and pre-filled electrolyte vials.

Main Results and Discussion

The optimized CE method achieves baseline separation of chloride, nitrate, sulfate, triphosphate, diphosphate, hypophosphite, phosphite and phosphate within 7 min.

• Migration time reproducibility: RSD ≤ 0.05 %
• Peak area reproducibility: RSD 1–3 %
• Detection limit for phosphate: ≈ 1 mg/L
• Linearity: 10–100 mg/L with correlation coefficients > 0.999

Applications tested include:

• Surface water samples: direct detection of common anions and phosphate after fortification
• Industrial wastewater: dilution and cleansing steps reduce matrix peaks and remove phosphate
• Detergents and fertilizers: simple dilution yields clear identification of phosphate species without column fouling
• Food samples (baking powder, cake mix, soft cheese): ultrasonic water extraction allows quantification of diphosphate and phosphate despite complex matrices

Benefits and Practical Applications

This CE approach offers:

• Minimal sample preparation and avoidance of column coatings
• Rapid analysis with broad anion coverage
• High reproducibility supporting routine QA/QC workflows
• Flexibility to analyze various environmental, industrial and food matrices

Future Trends and Applications

Potential advancements include coupling CE with mass spectrometry for enhanced sensitivity and structural confirmation, development of eco-friendly buffer systems, miniaturization for field-deployable instruments and expansion to additional inorganic and organic anions.

Conclusion

The described method on the Agilent 7100 CE system provides a robust, sensitive and efficient solution for simultaneous analysis of phosphate and related anions across diverse sample types. Its excellent reproducibility, linearity and minimal sample preparation make it well suited for routine environmental and food industry monitoring.