What is Riboflavin Sodium Phosphate? Uses, Grade & Applications

If you are a formulator, procurement manager, or product developer working with vitamin B2, you have likely encountered multiple names for what is essentially the same ingredient. Riboflavin sodium phosphate, riboflavin 5-phosphate sodium, FMN sodium salt, E101(ii) — the terminology can be inconsistent depending on whether you are reading a pharmacopoeia, a food additive register, or a supplier datasheet.

This post covers everything a technical buyer or formulator needs to know in one place: what the compound actually is, how it differs from regular riboflavin, what grades exist, where it is used, and how to handle and store it correctly.

Chemical Identity

Riboflavin sodium phosphate is the sodium salt of riboflavin 5-phosphate, which is the phosphorylated, biologically active form of vitamin B2. In biochemistry it is known as flavin mononucleotide (FMN).

Its empirical formula is C17H20N4NaO9P with a molecular weight of 478.33 (anhydrous basis) and a CAS number of 130-40-5. The EC number is 204-988-6.

It exists in both an anhydrous form and as a dihydrate. The dihydrate form carries the molecular formula C17H20N4NaO9P·2H2O with a molecular weight of 514.36. Most pharmacopoeial specifications and commercial supply is in the dihydrate form, though both are referenced under CAS 130-40-5.

All names refer to the same compound:

• Riboflavin sodium phosphate
• Riboflavin 5-phosphate sodium
• Riboflavin 5'-monophosphate sodium salt
• Riboflavin 5'-(dihydrogen phosphate), monosodium salt, dihydrate
• Flavin mononucleotide sodium (FMN-Na)
• R5P (used informally in supplement and clinical communities)
• Active B2
• E101(ii) — the EU food additive designation
• Vitamin B2 phosphate sodium salt

For full technical specifications, Certificate of Analysis, and purchase enquiries, visit our Riboflavin Sodium Phosphate product page.

Physical and Chemical Properties

Riboflavin sodium phosphate appears as a yellow or orange-yellow, crystalline, hygroscopic powder. It is soluble in water and very slightly soluble in ethanol.

It is odorless and has a slightly bitter taste. It is soluble in water and practically insoluble in ethanol, chloroform, and diethyl ether.

Solubility in water is approximately 100 g/L at 20°C. This is substantially higher than plain riboflavin, which dissolves at only around 10-13 mg/dL at room temperature — a difference of nearly 100-fold that makes the sodium phosphate form the preferred choice for any liquid formulation.

The pH of solution ranges from 6.0 to 7.5 and the compound decomposes above 280°C.

It is stable but incompatible with strong oxidants, reducing agents, alkalis, calcium, and metal salts.

The Key Difference from Regular Riboflavin

Regular riboflavin (CAS 83-88-5) is the unconverted free form of vitamin B2. When ingested, the body must phosphorylate it in the intestinal wall to produce FMN, which is then further converted to FAD (flavin adenine dinucleotide). Both FMN and FAD function as coenzymes in hundreds of enzymatic reactions.

Riboflavin sodium phosphate skips the first conversion step. It is already in the phosphorylated form, meaning it is ready to function as a coenzyme without further transformation in healthy individuals.

From a formulation standpoint, the practical difference is solubility. Regular riboflavin is poorly soluble in water, which limits its use in liquid and injectable formats. Riboflavin sodium phosphate is highly water-soluble, which is why it is the form used in oral solutions, injectables, and parenteral nutrition.

For a full comparison of the two forms, see our post on Riboflavin 5-Phosphate vs Regular Riboflavin: What's the Difference?

Pharmacopoeial Grades

Riboflavin sodium phosphate is monographed in all major pharmacopoeias. The assay specification is consistent across them.

Under USP, BP, and Ph. Eur. specifications, riboflavin sodium phosphate contains not less than 73.0% and not more than 79.0% of riboflavin (C17H20N4O6), calculated on the dried basis.

This range exists because the compound contains a variable quantity of water and may include minor proportions of other riboflavin monophosphate isomers alongside the primary 5'-isomer.

Available pharmacopoeial grades:

• USP (United States Pharmacopeia)
• BP (British Pharmacopoeia)
• Ph. Eur. (European Pharmacopoeia)
• IP (Indian Pharmacopoeia)

For manufacturers and formulators, the grade selected should match the regulatory jurisdiction of the finished product. All four are substantively aligned in their specifications for this compound.

Food Grade and Regulatory Status

In the EU, riboflavin-5'-phosphate sodium is authorised as a food colour and is designated E101(ii). EFSA has re-evaluated it as a food additive and concluded it is unlikely to pose a safety concern at current reported uses and exposure levels. Internationally, JECFA (Joint FAO/WHO Expert Committee on Food Additives) has assigned a group ADI of "not specified" for riboflavin and related riboflavin sources, meaning a numerical ADI is not considered necessary when used as intended. In the United States, riboflavin is recognised as GRAS (Generally Recognized as Safe) for certain direct-food uses.

The FCC (Food Chemicals Codex) designation is Flavin Mononucleotide, Sodium Salt, with INS number 101(ii).

Food grade riboflavin sodium phosphate is used both as a nutrient and as a natural yellow colorant in food applications.

Applications

Pharmaceutical: Oral Liquid Formulations

The high water solubility of riboflavin sodium phosphate makes it the standard form for oral solutions and syrups. Plain riboflavin cannot be dissolved at meaningful concentrations in water-based systems, whereas the sodium phosphate form dissolves readily. This makes it suitable for paediatric liquid vitamins, multivitamin syrups, and oral B-complex preparations.

Pharmaceutical: Injectable and Parenteral Nutrition

Riboflavin 5'-phosphate sodium is used in parenteral formulations including total parenteral nutrition (TPN). In parenteral nutrition products such as Infuvite Adult, riboflavin is included as riboflavin 5-phosphate sodium, with each 5 mL providing 3.6 mg of riboflavin (as riboflavin 5-phosphate sodium). Riboflavin 5'-phosphate sodium has been nominated and used in intravenous (IV) and intramuscular (IM) injections at concentrations of 2-100 mg/mL, as both single-dose and multi-dose products, for indications including riboflavin deficiency, migraine, muscle cramp, and as part of vitamin B complex injections.

For more on the clinical use case in migraine, see our post on Riboflavin for Migraines.

Pharmaceutical: Ophthalmic Applications

A topical ophthalmic preparation of FMN was approved by the FDA in October 2025 for use as a photoenhancer in epithelium-on corneal collagen cross-linking. This is a specific clinical application where riboflavin sodium phosphate is applied to the cornea in combination with UV-A light to treat progressive keratoconus — a condition that causes thinning and irregular shaping of the cornea.

Nutraceuticals and Dietary Supplements

Riboflavin sodium phosphate is used in dietary supplements where the active, pre-converted form of B2 is preferred. It appears in capsules, tablets, and powder blends targeting methylation support, energy metabolism, and MTHFR-related formulations. For context on the MTHFR use case, see our post on Riboflavin 5-Phosphate and MTHFR.

Food Fortification and Functional Foods

Riboflavin sodium phosphate is found in several foodstuffs, energy drinks, and vitamin formulations. In food applications, it serves a dual role: as a nutrient providing bioavailable vitamin B2, and as a natural yellow colorant designated E101(ii). It is used in fortified beverages, dairy products, breakfast cereals, and functional food products where regular riboflavin's poor solubility would create formulation challenges.

Cosmetic and Topical Formulations

Riboflavin 5'-phosphate sodium is used in topical formulations for dermatological and cosmetic applications, primarily for its antioxidant properties and role in supporting skin cell metabolism.

Animal Nutrition and Veterinary Applications

Riboflavin sodium phosphate is an authorised feed additive for all animal species, covering vitamin B2 requirements when administered via feed or water. It is used in poultry, swine, aquaculture, and companion animal supplements. The sodium phosphate form is preferred over plain riboflavin in liquid and water-soluble feed formats for the same reason it is preferred in pharmaceutical liquids, its significantly higher water solubility makes it practical where plain riboflavin cannot dissolve at the required concentration.

Stability and Storage

Riboflavin sodium phosphate requires careful handling due to its sensitivity to light and moisture.

It should be protected against light, air, and moisture. It is stable when stored away from light and moisture at a storage temperature of 10-25°C, with a shelf life of 24-36 months in sealed containers.

The light sensitivity is important for formulation. When dry, it is not affected by diffused light, but when in solution, light induces deterioration rapidly. Liquid formulations containing riboflavin sodium phosphate should be packaged in amber or light-protective containers.

In alkaline conditions, stability decreases. It is incompatible with alkalis, so formulation pH should be controlled within the recommended range of 6.0 to 7.5.

Practical storage checklist for bulk material:

• Store in sealed, moisture-resistant containers
• Keep away from direct light and UV exposure
• Maintain temperature between 10 and 25°C
• Avoid contact with alkaline materials, calcium, and heavy metal salts
• Once opened, use promptly or reseal under dry conditions

Why Riboflavin Sodium Phosphate Specifically, Not Plain Riboflavin?

For a formulator, the choice between the two forms typically comes down to three factors:

Solubility is the primary driver. Any formulation requiring significant dissolved riboflavin in a water-based matrix needs the sodium phosphate form. Plain riboflavin simply cannot dissolve at the concentrations required for injectables, oral solutions, or fortified beverages.

Bioavailability is the secondary consideration. For populations where the conversion of plain riboflavin to its active form may be impaired, the pre-activated sodium phosphate form is preferred. This is relevant for MTHFR-variant populations and for parenteral applications where the conversion pathway is bypassed entirely.

Cost is the third factor. Plain riboflavin remains less expensive and is suitable for solid dose forms, dry mixes, and applications where solubility is not a constraint. Riboflavin sodium phosphate commands a premium, which is justified in formulations where its specific properties are needed.