Rapid analysis of critical electrolytes and impurities in dialysis solutions

Rapid analysis of critical electrolytes and impurities in dialysis solutions — Expert summary

Importance of the topic

Dialysis solutions (dialysate), used in hemodialysis and peritoneal dialysis, act effectively as medicinal fluids that must match tight compositional and purity specifications to protect vulnerable patients. Accurate, rapid determination of electrolytes, organic acids and sugar-related impurities (including glucose degradation products) is essential for batch release, process control and patient safety. Consolidating multiple routine assays into a single high-throughput workflow reduces turnaround time, labor, instrument footprint and per-test cost in regulated production and clinical laboratory environments.

Objectives and overview of the article

- Present analytical needs for dialysis-related fluids (dialysate, CPDA anticoagulant solutions, peritoneal dialysis fluids). - Summarize common target analytes and process impurities relevant to product quality and biocompatibility. - Introduce a consolidated wet-chemistry, discrete analyzer approach (Thermo Scientific Gallery series) as a high-throughput alternative to multiple separate instruments. - Compare methods typically used (ion chromatography, HPLC, spectrophotometry, gravimetry) with an automated discrete photometric/enzymatic/electrochemical workflow and discuss practical benefits.

Methodology and analytical approaches described

- Typical analytes and tests: pH, conductivity, electrolytes (chloride, sulfate, phosphate, sodium, potassium, calcium, magnesium, ammonium), organic acids or their salts (acetic/acetate, lactic/lactate, citric/citrate), glucose/dextrose/fructose, total oxidizable nitrogen (TON), nitrate, total phosphorus, and glucose degradation products (HMF, acetaldehyde, formaldehyde). - CPDA anticoagulant-specific constituents: citric acid/sodium citrate, monobasic sodium phosphate, dextrose and adenine. Regulatory methods: citrate and phosphate by ion chromatography (USP General Chapter <345>), adenine by HPLC-UV, dextrose historically by gravimetric methods. - GDPs (e.g., HMF, acetaldehyde) are determined using derivatization followed by HPLC or by UV spectrophotometry. - The discrete analyzer strategy automates colorimetric/photometric and enzymatic assays and integrates electrochemical measurements (pH and conductivity), enabling parallel measurement of multiple parameters from the same sample with miniaturized cuvettes and low reagent consumption.

Used instrumentation

• Thermo Scientific Gallery and Gallery Plus discrete analyzers — automated discrete photometric/enzymatic/electrochemical platform for simultaneous multi-analyte testing and walkaway operation.
• Ion chromatography (IC) — used for citrate and phosphate quantification per USP guidance.
• High-performance liquid chromatography (HPLC) with UV detector — used for adenine and for GDPs after derivatization.
• Spectrophotometers — for select colorimetric and UV assays.
• Auto titrator, pH and conductivity meters, and ion meters — for routine water and solution quality parameters.

Main results and discussion (key points summarized)

- Analytical coverage: The combined use of conventional chromatographic techniques and an automated discrete analyzer covers the broad range of required assays for dialysis fluids including electrolytes, organic acids, sugars and low-level impurities. - Throughput and efficiency: Discrete analyzers enable simultaneous processing of many parameters from a single sample with reduced operator intervention, faster turnaround and lower reagent consumption due to miniaturized cuvettes. - Method complementarity: While the discrete analyzer handles many routine colorimetric and enzymatic tests efficiently, certain analytes (e.g., citrate/phosphate by IC, adenine and some GDPs by HPLC) still rely on chromatographic separation for specificity and regulatory compliance. - Quality and regulatory relevance: Automated, validated discrete methods increase reproducibility and support routine QC needs for sterile water for injection, concentrates and finished dialysis solutions.

Benefits and practical applications

• Consolidation of assays reduces the number of separate instruments and technician time required for routine QC testing of dialysate and related solutions.
• Improved lab productivity through walkaway automation and parallel measurement capabilities.
• Lower reagent usage and waste via small-volume cuvettes, contributing to reduced cost-per-test.
• Suitable for production release testing, in-process monitoring of concentrate manufacture and routine checks of finished dialysis fluids, including CPDA anticoagulant solutions and peritoneal dialysis fluids.
• Maintains traceability to regulatory methods by combining discrete assays with chromatographic techniques where necessary.

Future trends and potential applications

- Greater integration between discrete analyzers and chromatographic instruments to provide hybrid workflows that maximize throughput while maintaining chromatographic specificity where required. - Expansion of validated, automated assays for additional clinically relevant impurities (broader GDP panels, advanced organic contaminants) to improve biocompatibility screening. - On-line or at-line process analytical technology (PAT) implementations for continuous monitoring of dialysis concentrate production lines. - Enhanced data connectivity, laboratory information system (LIS) integration and application of machine learning for trend detection and predictive QC interventions. - Continued miniaturization, sensor development and single-use assay cartridges to further reduce sample/reagent volumes and contamination risk.

Conclusion

Comprehensive QC of dialysis solutions requires multiple complementary analytical approaches. Automated discrete analyzers provide a practical, high-throughput platform for many routine colorimetric, enzymatic and electrochemical assays, substantially improving laboratory efficiency and reducing cost-per-test. Chromatographic techniques remain necessary for certain regulated or specificity-demanding assays (e.g., citrate/phosphate by IC, adenine and some GDPs by HPLC). A combined analytical strategy yields robust, regulatory-aligned testing workflows suitable for manufacturing release, clinical quality control and safety monitoring of dialysis fluids.

References

• Thermo Fisher Scientific. Rapid analysis of critical electrolytes and impurities in dialysis solutions. SMART NOTE 73707; 2020.
• USP General Chapter <345> (referenced method for citrate and phosphate by ion chromatography).