Riboflavin and riboflavin 5′-phosphate sodium both deliver vitamin B2. The practical difference is solubility: riboflavin is very slightly soluble in water, and riboflavin 5′-phosphate sodium dissolves readily. Use riboflavin in tablets, capsules, dry premixes and feed. Use the phosphate sodium salt in liquids, drops and clear beverages.
Side by side
| Riboflavin | Riboflavin 5′-phosphate sodium | |
|---|---|---|
| CAS number | 83-88-5 | 130-40-5 |
| Other names | Vitamin B2, lactoflavin, E101(i) | Riboflavin sodium phosphate, FMN sodium, E101(ii) |
| Formula | C₁₇H₂₀N₄O₆ | C₁₇H₂₀N₄NaO₉P |
| Molecular weight | 376.36 | 478.33 (anhydrous) |
| Solubility in water | Very slightly soluble | Soluble |
| USP assay | 98.0–102.0% | 73.0–79.0%, expressed as riboflavin |
| U.S. food status | GRAS, 21 CFR 184.1695 | GRAS, 21 CFR 184.1697 |
| Typical products | Tablets, capsules, flour enrichment, feed | Liquid vitamins, syrups, shots, clear drinks |
Why the assay numbers look so different
A lot of riboflavin 5′-phosphate sodium that assays at 75% is not impure. The USP monograph reports the assay as riboflavin. The phosphate group, the sodium and the water of hydration account for the rest of the weight, so a fully conforming lot lands between 73.0% and 79.0%.
This catches people out when they compare quotations. If one supplier offers riboflavin 5′-phosphate sodium at “98% purity” and another quotes “73–79% as riboflavin”, they may be describing the same material measured two ways. Ask which test the figure comes from.
Converting a dose
To deliver a given amount of riboflavin from the phosphate sodium salt, divide by the assay on the certificate of analysis.
At 75% riboflavin content, 1.33 mg of riboflavin 5′-phosphate sodium supplies 1 mg of riboflavin.
Use the actual assay of the lot you are formulating with, and include the overage your stability data calls for.
Stability and handling
Both forms are sensitive to light, and far more so in solution than as dry powder. Clear beverages containing either one are normally packed in opaque or UV-blocking containers. Riboflavin 5′-phosphate sodium is also hygroscopic, so keep containers tightly closed.
How to choose
- Dry product, no dissolution needed: riboflavin. It costs less per unit of vitamin B2 and has the higher assay.
- Liquid or clear beverage: riboflavin 5′-phosphate sodium. Riboflavin will not stay in solution at useful concentrations.
- Powdered drink mix: either can work. Riboflavin is common in premixes; the phosphate sodium salt gives a cleaner dissolve.
- Animal feed: riboflavin, as the 80% feed grade.
See the full specifications for riboflavin and riboflavin 5′-phosphate sodium.
This article is general information for business customers. It is not legal or regulatory advice. Confirm requirements for your own products with qualified counsel or a regulatory consultant.