Cross-Validation of Low-Cost Potentiometric and Colorimetric Methods for Urinary Urea Quantification: Toward Accessible Monitoring of Protein Metabolism

Supplementary Information: Figure S1: Ammonium ISE schematic representation. Figure S2: Urease volume optimization for the ISE potentiometric method. Figure S3: Berthelot reaction. Figure S4: The schematic of urine color changes following salicylate addition. Figure S5: Calibration of the API® colorimetric assay for direct urea quantification. Figure S6: Direct ammonia calibration of the API® colorimetric reagent system. Figure S7: Step-by-step protocol for the API® colorimetric urea assay developed in this work. Figure S8: ISE potentiometric method for urinary urea and ammonia. Figure S9: API colorimetric method for urinary urea and ammonia. Figure S10: Per-run ISE urea calibration. Figure S11: Per-run ISE ammonia calibration. Figure S12: Per-run API calibration curves for urinary urea. Figure S13: Per-run API calibration curves for urinary ammonia. Table S1: Detailed per-sample reagent-cost breakdown for the evaluated methods. Table S2: Per-run ISE calibration parameters. Table S3: Per-run API calibration parameters. Table S4: Paired Cobas C311 and ISE ammonia measurements. Table S5: Paired Cobas C311 and API-urea measurements. Table S6: Paired ISE and API for urinary urea. Table S7: Side-by-side performance comparison of the three methods for urinary urea and urinary ammonia quantification. Urea data: Excel file with all experimental raw data used in the main manuscript and Supplementary Information.