Understanding Precipitation with Sodium Ascorbyl Phosphate (SAP) and Magnesium Ascorbyl Phosphate (MAP)

Thank you for sharing your formulation experience. It's common to encounter solubility challenges when working with high concentrations of active ingredients like Sodium Ascorbyl Phosphate (SAP) and Magnesium Ascorbyl Phosphate (MAP).

You are correct that both SAP and MAP are most stable and soluble within a pH range of 7-9. While you adjusted your formula to pH 7, which is within this range, there are a few factors that could be contributing to the precipitation you observed with a combined concentration of 15% (5% SAP + 10% MAP):

• Concentration Limits: The product descriptions for both SAP and MAP indicate that using concentrations exceeding 8% individually may cause dissolution problems. A combined concentration of 15% is quite high, and it's possible this exceeds the total solubility limit in your specific formulation, even at the optimal pH.
• Formulation Complexity: The original product you like contains a variety of other ingredients, including solvents like Butylene Glycol and thickeners/stabilizers like Sodium Hyaluronate and Xanthan Gum. These ingredients play a crucial role in maintaining the stability and solubility of active compounds in a complex formula. Your test formulation, being simpler, might lack the necessary components to keep 15% combined SAP and MAP fully dissolved over time.
• Interaction with Citric Acid: While Citric Acid is used for pH adjustment, its interaction with SAP and MAP at high concentrations and in the absence of other formula components might also contribute to instability or localized precipitation.

Recommendations to Address Precipitation:

1. Try Lower Concentrations: Consider testing lower combined concentrations of SAP and MAP, perhaps starting with the recommended 3% for each, or up to 8% each, to see if precipitation is avoided. This can help determine if the issue is purely related to exceeding the solubility limit at 15%.
2. Include a Chelating Agent: The product descriptions for both SAP and MAP recommend including Disodium EDTA at 0.05% in the formula. Chelating agents help to bind metal ions that can interfere with the stability and solubility of these Vitamin C derivatives. Incorporating this could help.
3. Consider the Full Formulation: Replicating the stability of a commercial product often requires understanding and incorporating the full range of ingredients used, as they work synergistically to maintain the formula's integrity.

If you continue to experience precipitation even at lower concentrations and with the addition of a chelating agent, it may indicate that achieving a stable solution with a combined 15% concentration of SAP and MAP requires a more complex formulation approach than a simple water-based system allows.