Substances Detected in Dialysis Water: A Comprehensive Analysis

In a typical dialysis experiment (e.g., dialysis tubing model), substances found in the external water bath represent molecules small enough to diffuse across the semipermeable membrane:

• Sodium chloride (NaCl): Dissociates to Na⁺ and Cl⁻ — small ions, readily diffuse
• Glucose (C₆H₁₂O₆): Small molecule (180 Da) — diffuses slowly
• Urea (CH₄N₂O): Very small (60 Da) — diffuses rapidly

Larger molecules (proteins, starch, polysaccharides) remain inside the tubing. This demonstrates selective permeability based on molecular size—principle of hemodialysis and peritoneal dialysis.