In Aqueous Normal Phase (ANP) on Cogent TYPE‑C™ silica (e.g., Diamond Hydride™), the usual best practice is to inject samples prepared in a high‑organic diluent to maximize focusing and minimize band distortion.

However, in many real‑world applications you can inject entirely aqueous diluents (100% water) and still obtain sharp, symmetrical peaks—as demonstrated in an application analyzing folic acid (standards and juice samples) on a Cogent Diamond Hydride™ column with 100% water as the sample diluent. 

When 100% Water Works (and Why)

• For certain highly polar, ionizable analytes (e.g., folic acid), the hydrated silica‑hydride interface plus ANP’s high‑organic mobile phase start can still provide strong focusing, even if the injection plug is fully aqueous. In practice, excellent peak shape has been observed under these conditions. 

• This approach is particularly helpful when matrix compatibility or sample preparation constraints require water‑only diluents (e.g., food/beverage extracts), and you wish to avoid non‑volatile additives or excessive sample manipulation. 

Key point: Although a high‑ACN diluent is still the default recommendation for ANP, 100% water can be a viable, validated option for specific targets and matrices, with minimal compromise to peak integrity. 

Practical Setup & Method Tips

1. Mobile‑phase strategy (ANP):

   • Start at high %B (ACN) with standard volatile additives (e.g., 0.1% formic acid or 10 mM ammonium acetate) to ensure MS compatibility and robust retention of polar analytes. 

2. Injection volume & focusing:

   • If switching from high‑organic to 100% water diluent, consider slightly smaller injection volumes or a brief high‑%B pre‑segment to preserve focusing at the column head. (This preserves the focusing advantage typically delivered by an organic‑rich plug.) 

3. Gradient design:

   • Maintain a high‑organic start (typical ANP), then decrease %B to elute the most strongly retained polar species. This approach has produced sharp, symmetrical folic acid peaks with 100% aqueous sample diluent.

4. Matrix robustness:

   • For food/juice/bio‑like matrices, add a short clean‑out hold (e.g., 50:50 water/MeOH or water/IPA) after the gradient or between runs to prevent matrix build‑up; this practice complements the aqueous‑diluent approach and protects column longevity. 

When to Prefer High‑Organic Diluents

• Very early eluters (extremely hydrophilic analytes) that risk partial breakthrough with water‑only plugs.

• Large injection volumes or high‑salt samples that can disrupt focusing or increase band broadening.

• Highly throughput‑sensitive assays where the tightest possible focusing is required across diverse analyte classes.
  
  In these cases, revert to ACN‑rich diluents or reduce injection volume for optimal focusing. 

Summary

• Default ANP guidance favors high‑organic sample diluents, but 100% water can absolutely work on Cogent TYPE‑C™ columns for specific analytes and matrices. This has been shown for folic acid (standards and juice) on Cogent Diamond Hydride™ with sharp, symmetrical peaks even from fully aqueous injections. 

• Use ANP‑consistent gradients (high %B start), adjust injection volume, and include clean‑out holds as needed for robust performance over complex matrices.