Characterization of dissolved and particulate matter in urine

Noa Melman, Chemistry, Weizmann Institute of Science, Rehovot, Israel (noa.melman@weizmann.ac.il)
Ishai Dror, Chemistry, Weizmann Institute Of Science, Rehovot, Israel
Brian Berkowitz, Chemistry, Weizmann Institute Of Science, Rehovot, Israel

Urine has been employed in clinical diagnosis for several millennia, but definitive characterization remains incomplete because of matrix complexity, interindividual variability, and methodological limitations. In particular, the amount and nature of particulate content remains largely unknown, despite the potential of such information to expand diagnostic capabilities. A recent report showed that urine is rich in particulate matter for the size fraction spanning 0.33-70 µm, with approximately 10⁸ particles passing daily through the urinary tract. Additionally, baseline values for elemental content in urine have been established primarily for major elements whereas concentrations of minor/trace elements show substantial interstudy variability.

This presentation centers on detecting and characterization of the submicron (nano) fraction of the suspended particulate matter in urine (30-1000 nm), and on quantifying the elemental content of the particulate and the dissolved matter. Size distributions and concentrations of the submicron particles are determined using Nanoparticle Tracking Analysis (NTA), and elemental composition is measured by ICP-MS and ICP-OES.

Our analyses show that the concentrations of the urinary fraction of submicron particulates in a cohort of 56 samples (from 28 healthy donors) were on the order of 5 × 10¹⁰ mL^–1 which translates to a daily throughput of ~10¹³ submicron particles, with a mode of ~100 nm and similar size distribution pattern. No significant differences in results were found comparing between gender, ages, or time of sampling. Moreover, elemental profiling (n = 22 donors) identified measurable levels for 34 elements, overwhelmingly associated with dissolved species. Results from sequential pore-size filtration and concentrated acid digestion support a dissolved-phase origin of the elemental content, with the submicron particulate material being composed exclusively of organic constituents.

This work establishes an initial baseline for submicron particulate matter in the urine of healthy individuals, demonstrating the routine presence of organic nanoparticles with reproducible size distributions and compositions.