Determination of pyrophosphate, trimetaphosphate, tripolyphosphate and standard ions in detergents or fertilizers using IC with a high-capacity suppressor

Importance of the topic

This study addresses the critical need for reliable determination of various phosphate species and common anions in complex matrices such as detergents and fertilizers. Excess phosphate discharge into the environment drives eutrophication, making rapid and accurate measurement essential for environmental monitoring, regulatory compliance, and industrial quality control.

Objectives and study overview

The primary aim was to develop a direct-injection ion chromatography method capable of simultaneously separating and quantifying ortho-, pyro-, trimeta-, and tripolyphosphate alongside monovalent (fluoride, chloride, bromide, nitrate) and divalent (sulfate, citrate) anions. Both isocratic and binary gradient elution modes were evaluated, and three suppressor configurations were compared for sensitivity and peak performance.

Methodology and instrumentation used

A Metrohm IC system was deployed, comprising:

• 820 IC Separation Center
• 819 Advanced IC Detector
• 818 Advanced IC Pump
• 830 Advanced IC Interface
• 838 Advanced IC Sample Processor
• 833 Advanced IC Liquid Handling
• Suppressors: 828 IC Dual Suppressor, XL Suppressor with and without subsequent CO2 suppression
• Columns: A Supp 5 – 100 for isocratic mode; Metrosep A Supp 3 – 250 for gradient mode

Isocratic conditions employed 40 mmol/L NaOH at 0.7 mL/min, 20 µL injection volume. Gradient elution used ultrapure water (eluent A) and 40 mmol/L NaOH (eluent B) with a stepwise program (85:15 to 30:70 A:B over 30 min) at 1.0 mL/min.

Main results and discussion

Under isocratic conditions, sulfate, citrate, and all four phosphate species were baseline-resolved. The 828 IC Dual Suppressor provided exceptionally low background conductivity and superior peak heights for early eluting anions, while the XL Suppressor combined with CO2 suppression enhanced sensitivity for strongly retained phosphates. Gradient separation successfully resolved halides without coelution with sulfate or orthophosphate. Calibration curves for each analyte demonstrated excellent linearity (r2 ≥ 0.998), confirming the method’s quantitative robustness.

Benefits and practical applications

The proposed IC method offers:

• Direct injection with minimal sample preparation
• High sensitivity and low detection limits across a wide ionic strength range
• Simultaneous multi-analyte determination in a single run
• Faster turnaround and greater reproducibility compared to traditional wet-chemical assays
• Applicability in environmental monitoring, detergent and fertilizer QC, and process control

Future trends and potential use

Emerging directions include integration with mass spectrometric detection for enhanced selectivity, miniaturized and portable IC platforms for field analysis, and advanced suppressor technologies to further lower background noise. Automation of sample handling and data processing will support high-throughput screening in industrial and environmental laboratories.

Conclusion

Direct-injection suppressed ion chromatography with high-capacity suppression provides a versatile, sensitive, and reliable approach for comprehensive phosphate and anion analysis in complex samples. The method’s flexibility in elution modes and suppressor selection makes it a valuable tool for diverse analytical challenges.

Reference

• S. Czyborra, R. Odermatt, H. Schäfer. Determination of pyrophosphate, trimetaphosphate, tripolyphosphate and standard ions in detergents or fertilizers using IC with a high-capacity suppressor. Metrohm Application Note 8.000.6075 EN.