| HS Code | 765284 |
| Chemical Name | Sodium Selenite |
| Cas Number | 10102-18-8 |
| Molecular Formula | Na2SeO3 |
| Molecular Weight | 172.94 g/mol |
| Grade | USP |
| Appearance | White to off-white crystalline powder |
| Odor | Odorless |
| Solubility | Freely soluble in water; slightly soluble in alcohol |
| Assay | 98.0%–100.5% Na2SeO3 on dried basis |
| Selenium Content | Approximately 45.7% (theoretical) |
| Melting Point | Decomposes at approximately 710°C |
As an accredited Sodium Selenite USP factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Sodium Selenite USP is packaged in a 25 kg drum with an inner polyethylene liner for safe, secure chemical containment. |
| Container Loading (20′ FCL) | 20′ FCL: packed on pallets, secured drums/bags, proper labeling, moisture protection, safe handling for Sodium Selenite USP. |
| Shipping | Ship as UN 2630 Sodium Selenite, Class 6.1 (Toxic), Packing Group II. Use UN-approved packaging with proper toxic hazard labels. Avoid dust, moisture, acids, oxidizers, and food contact. Include required transport documentation per DOT/IATA/IMDG regulations. Handlers should wear appropriate personal protective equipment. |
| Storage | Store Sodium Selenite USP in a tightly sealed, clearly labeled container in a cool, dry, well-ventilated area. Protect from moisture, direct sunlight, and heat. Keep away from acids, reducing agents, and incompatible materials. Ensure segregation from food and beverages, and follow all hazardous chemical storage regulations. |
| Shelf Life | Shelf life is typically 24 months from manufacture date when stored in original unopened containers at controlled room temperature. |
Sodium selenite USP enters animal nutrition not as a direct loose salt but through validated sequential dilution in mineral premix plants. The USP assay is normally read against the sodium selenite monograph, and the selenium fraction of Na₂SeO₃ is 45.66% by mass; this conversion factor governs every downstream addition calculation. In the United States, selenium as sodium selenite is permitted under 21 CFR 573.920, with a maximum of 0.3 mg/kg selenium in complete feed for major livestock species. European Union complete-feed limits under Regulation (EC) No 1334/2003 permit total selenium up to 0.5 mg/kg at 12% moisture. Expressed as the pure USP salt, the finished-feed working window is therefore 0.66–1.10 mg/kg sodium selenite, which is too small for direct addition at the weigh hopper. Production-scale mixing therefore begins with a 1% selenium premix, typically prepared by blending sodium selenite with calcium carbonate or wheat middlings in a stainless-steel ribbon mixer; the 1% premix is then incorporated at 30–50 g/t of final complete feed, depending on the jurisdictional selenium ceiling. The premix sequence is validated to a coefficient of variation below 5% using microtracer recovery or ICP-MS after acid digestion. Although feed-grade sodium selenite is common in cost-sensitive operations, USP-grade material is specified where compendial documentation and lower heavy-metal profiles are required for export premixes.
Process bottlenecks arise from selenium’s narrow margin between nutritional requirement and toxicity. Premix plants therefore use dedicated or sequenced lines for selenium-containing premixes to prevent carryover into selenium-free feeds. Retention samples are quantified by hydride-generation atomic absorption or ICP-MS using feed-specific methods such as AOAC 986.15. Batch-to-batch variance is managed by limiting each geometric dilution step to no more than 1:10 and by controlling mixer fill volume; vertical mixers with poorly sealed discharge gates are avoided because low-density selenium premix can segregate and escape at the gate seal. Terminal product forms include broiler starter/grower mineral premixes, swine grower-finisher premixes, dairy transition-cow trace-mineral packs, and ovine trace-mineral salt blocks.
In the manufacture of sterile multi-trace-element injections and parenteral nutrition additives, sodium selenite USP is dissolved into Water for Injection at acidic pH and sterile-filtered before filling. The formulation objective is to deliver selenium in the adult parenteral nutrition range of 60–100 µg/day as recommended in ASPEN trace-element dosing guidelines, without generating insoluble elemental selenium in the final admixture. To prepare a concentrate at 40 µg/mL selenium, 87.6 mg of sodium selenite USP is required per liter of solution; because the salt contains 45.66% selenium, the dissolution calculation is linear and is confirmed by ICP-MS against a selenite standard. The concentrate is adjusted to pH 2.0–3.0 with hydrochloric acid and filtered through a 0.22 µm polyvinylidene fluoride membrane. Terminal sterilization may be employed where container-closure integrity and stability data support moist heat at 121 °C for 15 min; otherwise aseptic processing is used.
Downstream manufacturing constraints are defined by redox incompatibility. In total nutrient admixtures containing ascorbic acid, selenite can be reduced to red elemental selenium, and visual inspection for red particulate formation is required at compounding and before administration. For this reason, selenium-containing trace-element injections are often presented as separate ampules or added through a dedicated port at the time of admixture, and storage time after mixing is minimized. Compliance documents follow 21 CFR Part 211, USP <797>, and elemental-impurity review under USP <232>/<233>. Terminal product types are single-entity selenium injection vials, multi-trace-element concentrate vials, and pediatric trace-element injection solutions for parenteral nutrition.
Compressed oral dosage forms use sodium selenite USP not as a direct salt addition to a 500 mg tablet blend but as a 1% selenium trituration on microcrystalline cellulose or dicalcium phosphate because the target elemental selenium dose is in the microgram range. For a 55 µg selenium tablet, the pure salt requirement is 120.4 µg; for a 200 µg selenium tablet, the requirement is 438 µg. This corresponds to 0.024–0.088 wt% of a 500 mg tablet blend before considering overages. The trituration is geometrically diluted in a V-blender or bin blender, and content uniformity is verified under USP <905>. Granulation is usually dry or roller-compacted because aqueous wet granulation in the presence of ascorbic acid creates a reducing environment that converts selenite to red elemental selenium; if ascorbic acid is included in the same formula, separate granulations or coated ascorbic acid are used.
Manufacturing under 21 CFR Part 111 requires raw-material identity testing against the USP Sodium Selenite monograph, heavy-metal and elemental-impurity review under USP <232>/<233>, and adherence to the Institute of Medicine selenium upper intake level of 400 µg/day from food and supplements. Finished dosage forms include selenium 55 µg and 200 µg tablets, multivitamin-mineral tablets, and selenium-containing trace-mineral capsules. Dissolution testing under USP <2040> is used to confirm selenium release from the tablet matrix, and accelerated stability samples are visually inspected for red speck formation caused by selenite reduction.
Within chemically defined Chinese hamster ovary perfusion processes, sodium selenite USP serves as the trace selenium source for selenoprotein synthesis, particularly cytosolic glutathione peroxidase and thioredoxin reductase. The salt is selected because it is water-soluble, filterable, and can be added as a separate trace-element supplement after basal-media heat treatment. The working concentration in basal media is commonly 5–10 µg/L sodium selenite, equivalent to 2.3–4.6 µg/L elemental selenium; in high-density fed-batch or perfusion cultures, cumulative feed concentrations may be increased to 10–30 µg/L, although published cell-line-specific titration data remain limited. A 10 g/L sodium selenite stock solution in Water for Injection therefore requires subsequent dilution of 1:1,000,000 to reach 10 µg/L in basal medium. The dilution is performed by single-use mixing systems rather than by direct weighing at the bioreactor scale.
Raw material qualification follows ancillary-material guidance under USP <1043> and ICH Q7, with compendial identity and purity testing against the USP Sodium Selenite monograph and elemental impurity review under USP <232>/<233>. The manufacturing process involves dissolving the salt in Water for Injection, aseptic filtration through 0.1 µm durapore or polyethersulfone filters, and storage in light-protected single-use bags at 2–8 °C until supplementation. A process boundary is imposed by selenite reactivity: concentrated feed solutions containing cysteine or ascorbic acid above molar parity can reduce selenite to elemental selenium, fouling sterilizing-grade filters and creating visible red particles. Terminal product types are chemically defined CHO media, serum-free HEK293 media, and perfusion feed supplements for monoclonal antibody, viral-vector, and vaccine production.
The substitution of sodium selenate with sodium selenite in foliar biofortification changes selenium mobility and leaf absorption kinetics. Sodium selenite is less phloem-mobile than sodium selenate, so grain deposition depends more on application timing, leaf retention, and repeated low-dose spraying. Reported foliar trial rates for cereal biofortification fall mainly within 10–50 g Se/ha, equivalent to 22–110 g/ha sodium selenite USP on an elemental selenium basis. In a tank-mix volume of 200 L/ha, the working spray concentration is 110–550 mg/L sodium selenite. The spray solution is adjusted to pH 5.0–6.0 and applied at tillering to booting; flat-fan nozzles are used to maximize leaf interception, and application is separated from acid phosphate fertilizers to avoid precipitation.
Regulatory compliance is jurisdiction-dependent: in some markets, selenium biofortification agents are registered under national fertilizer or plant biostimulant frameworks, and maximum selenium levels in final foods are subject to national food-safety legislation. Published data for this specific USP-grade configuration are limited; most agronomic studies use technical-grade sodium selenite, and the USP specification adds cost without changing agronomic selenium equivalence. Terminal product types include selenium-enriched wheat flour, rice, and processed cereal fractions intended for human consumption in selenium-deficient regions. The lower soil mobility of selenite also requires leaf residue analysis before harvest to ensure final grain selenium does not exceed target levels.
In neonatal ruminant veterinary practice, selenium deficiency is corrected by intramuscular injection of sodium selenite combined with vitamin E, typically in the form of a sterile emulsion or micellar solution. Injectable products contain elemental selenium at 1–5 mg/mL as sodium selenite; to prepare 1 mg/mL selenium, 2.19 mg of sodium selenite USP is required per milliliter of finished injection. The formulation is compounded under injectable good manufacturing practice, with bacterial endotoxin limits tested under USP <85> and injectable quality attributes under USP <1>. The manufacturing process involves dissolving sodium selenite in Water for Injection, adding vitamin E acetate with polysorbate 80 as an emulsifier, and homogenizing the mixture before 0.22 µm filtration and filling into multi-dose rubber-stoppered vials.
Terminal products are selenium and vitamin E injection for calves, lambs, and piglets, labeled for prevention and correction of white muscle disease. The operational boundary is species-specific dose volume: selenium has a narrow toxicity margin, and accidental overdose in sheep is documented with acute selenium toxicosis; therefore filling lines must be calibrated to exact fill weights and batch reconciliation is mandatory.
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Sodium Selenite USP is the pharmacopeial-grade sodium salt of selenious acid, Na2SeO3, CAS 10102-18-8, molecular weight 172.94 g/mol. The compendial article is supplied as a white to off-white crystalline powder, very soluble in water and practically insoluble in ethanol. No model designation is assigned under the United States Pharmacopeia monograph “Sodium Selenite”; the product is identified by compendial name, chemical formula, and grade. Unlike technical-grade sodium selenite used in metallurgical or glass applications, the USP-grade material is released under current good manufacturing practice and is evaluated for identity, assay, loss on drying, and elemental impurity controls intended for pharmaceutical use. The selenium center exists in the +4 oxidation state as the selenite anion, which is reducible to elemental selenium under acidic reducing conditions. The product is therefore not interchangeable with sodium selenate (+6) or selenomethionine without formulation and bioequivalence considerations.
The analytical basis for the assay is an iodometric titration. In acidic solution, selenite oxidizes iodide to iodine; each mole of selenite accepts 4 electrons and releases 2 mol of iodine. The equivalent weight of sodium selenite in this reaction is molecular weight divided by 4, or 43.235 g/eq. A 0.25 g sample is dissolved in 25 mL of water, treated with potassium iodide TS and hydrochloric acid, and held for 10 min. The liberated iodine is titrated with 0.1 N sodium thiosulfate VS; each milliliter of titrant corresponds to 4.324 mg of Na2SeO3. The acceptance interval is 98.0% to 100.5% on the dried basis. The +4 oxidation state is chemically significant because it is the state measured in this titration; any sodium selenate impurity (+6) would not be captured by the iodometric reaction and would require an orthogonal method such as ion chromatography.
Because the iodometric titration is selective for selenite, it does not provide a mass balance across all selenium species. When the synthesis route or downstream formulation may generate selenate, speciation by ion chromatography with conductivity detection or HPLC-ICP-MS is used as an additional in-house control. The USP monograph does not assign a limit for selenate; therefore, a finished product manufacturer that requires control of the +6 oxidation state must validate a separate analytical procedure and establish internal acceptance criteria.
Identity testing includes a sodium flame test and a wet-chemical precipitation procedure for selenite. The precipitation test differentiates selenite from sulfate and selenate by its behavior under ammoniacal conditions; the compendial procedure uses ammonium chloride TS and ammonia TS followed by acidification to give a characteristic precipitate. Loss on drying is performed according to USP <731> and is limited to ≤1.0%, which controls surface moisture and loosely bound water. The monograph storage statement requires tight containers, because moisture pickup can alter assay results and powder flow. Elemental impurities are controlled by USP <232> and <233>. The finished product sponsor is responsible for establishing elemental impurity limits that reflect the dosage form, daily exposure, and route of administration; the API supplier typically reports results against an agreed panel of elements. Residual solvent testing is not automatically part of the monograph unless solvents are used in the manufacturing process; if the API is crystallized from water, no organic volatile impurity control beyond USP <467> may be required.
| Parameter | Acceptance criterion | Method reference |
|---|---|---|
| Assay (Na2SeO3, dried basis) | 98.0%–100.5% | USP monograph iodometric titration; 0.1 N Na2S2O3 VS, 4.324 mg/mL equivalence |
| Loss on drying | ≤1.0% | USP <731> |
| Identification | Sodium flame test; selenite precipitation | USP monograph |
| Elemental impurities | Risk-based limits | USP <232>, <233> |
| Residual solvents | If applicable | USP <467> |
In oral solid dosage manufacturing, Sodium Selenite USP is typically handled as a low-dose active ingredient in a preblend. Tablets or capsules containing 50–100 µg of selenium per unit require geometric dilution with a directly compressible filler such as microcrystalline cellulose or dibasic calcium phosphate dihydrate. High-shear wet granulation is avoided unless the formulation can prevent acidic degradation; direct compression and dry blending are preferred because the API is water-soluble and can dissolve during granulation, creating nonuniform distribution after drying. Segregation risk is controlled by matching the particle-size distribution of the active preblend to the filler and by limiting transfer steps. Blend uniformity is evaluated by USP <905>, with acceptance value ≤15 for dosage units. Incoming identity testing under 21 CFR 211.84 is required before release for production; the certificate of analysis is not a substitute for identity confirmation.
Wet granulation with Sodium Selenite USP presents a redox stability boundary. The selenite ion is capable of oxidizing ascorbic acid and sulfite salts in acidic granulating fluids, producing elemental selenium as a red-brown precipitate. This incompatibility is most pronounced at pH values below 4.0; if the formulation requires ascorbic acid, the granulating fluid should be buffered to a higher pH or the ascorbic acid should be incorporated in an external phase. Forced-degradation studies under ICH Q1A(R2) are used to confirm that the chosen granulation process does not reduce assay below the specification. Published data for this specific configuration is limited; therefore, process validation should include selenium speciation analysis rather than total selenium alone.
Quantification of selenium in finished dosage forms is commonly performed by ICP-MS after microwave-assisted acid digestion with nitric acid and hydrogen peroxide. The argon plasma generates 40Ar40Ar dimer interference at m/z 80, so selenium is measured at m/z 78 or 82 using collision cell technology. Method validation follows ICH Q2(R1), with linearity typically established across 0.5–50 µg/L and LOQ at or below 0.5 µg/L for selenium in the digest. Published data for this specific configuration is limited because instrumental detection limits depend on sample dilution and digest matrix. When flame atomic absorption is used instead, the sensitivity is lower and more sample mass is required; the method is adequate for higher-dose products but not for trace-level uniformity testing.
Because Sodium Selenite USP is hygroscopic, moisture control during weighing and blending is a production bottleneck. Exposure to relative humidity above 60% can cause surface moisture uptake and powder caking; pre-drying in a vacuum oven at temperatures below 105 °C may be used if the API has been exposed to ambient humidity. The compendial loss on drying method at 105 °C is a quality control method, not a processing instruction; production drying should be evaluated for chemical stability because prolonged heating can alter the fraction of oxidized selenium species.
Sodium selenite differs from sodium selenate in both redox behavior and solution stability. Selenate (+6) is the oxidized form and is less prone to reduction to elemental selenium in acidic media; selenite (+4) is thermodynamically capable of being reduced by ascorbic acid, sulfite, and cysteine at low pH. The reduction of selenious acid to elemental selenium is favorable under acidic conditions, although kinetic rates are matrix-dependent. In aqueous multi-trace element admixtures, this creates a compatibility boundary: selenite should not be compounded in strongly acidic solutions with high concentrations of reducing agents unless the final pH is raised, the reducing agent is omitted, or forced-degradation data support the holding time.
Compared with selenomethionine, Sodium Selenite USP has no chiral center, no amino acid moiety, and is not nonspecifically incorporated into proteins in place of methionine. Selenomethionine is a selenoamino acid that enters the methionine pool and can be stored in tissue proteins, producing different retention kinetics. Selenite must be reduced to selenide before incorporation into selenocysteine; this metabolic reduction consumes reducing equivalents and makes the acute toxicity profile of selenite generally higher per milligram of selenium than selenomethionine. The USP monograph does not equate these sources; substitution between them requires a clinical or nutritional rationale and is outside the scope of the compendial grade definition.
| Property | Sodium selenite USP | Sodium selenate | Selenomethionine |
|---|---|---|---|
| Selenium oxidation state | +4 | +6 | −2 |
| Water solubility | Very soluble | Very soluble | Soluble |
| Reduction to elemental selenium in acidic reducing media | High | Low | Low |
| Metabolic incorporation | Reduced to selenide before selenoprotein synthesis | Reduced to selenide after two-electron reduction | Nonspecific incorporation into proteins as methionine analog |
| Compendial monograph | USP Sodium Selenite | Not a USP monograph in the same class | USP dietary ingredient monograph where applicable |
In parenteral trace element compounding, Sodium Selenite USP is dissolved in Water for Injection under USP <797> controls. A Class 5 environment defined by ISO 14644-1 is used for aseptic processing, and filtration through a 0.22 µm polyvinylidene fluoride membrane provides sterility assurance when the solution is not terminally sterilized. Selenium recovery across the membrane should be confirmed, because adsorption can occur on some nylon or mixed cellulose ester membranes at low selenium concentrations. The dissolution vessel is usually glass-lined or 316L stainless steel; prolonged contact with unpassivated metal surfaces can introduce elemental impurities. Nitrogen sparging is used to displace oxygen when the formula contains oxidizable amino acids or when selenium is held in solution for more than 24 h. The pH of the final admixture is ordinarily adjusted to a slightly acidic to neutral range to reduce precipitation of selenium with divalent cations. Calcium and magnesium salts in total parenteral nutrition can form insoluble precipitates; selenium itself may participate in particulate formation if the admixture is exposed to rapid pH shifts or high calcium concentrations. Compatibility testing under simulated infusion conditions is therefore required before routine preparation.
Solution stability at 2–8 °C is typically longer than at room temperature, but specific stability intervals must be established by the compounding facility. The USP monograph does not provide a beyond-use date for compounded preparations. In the absence of product-specific data, USP <797> default beyond-use dating applies for low-risk compounded sterile preparations; any extended dating requires a stability study with sterility and chemical assay data.
For parenteral applications, the bulk monograph does not impose a sterility or bacterial endotoxin requirement. The finished manufacturer must establish a bacterial endotoxin limit using USP <85> and sterility using USP <71>. If the API is received as a non-sterile powder, sterilization is accomplished by filtration after dissolution or by an aseptic compounding sequence; dry-heat sterilization of the powder is not typical because of stability and airborne contaminant risks.
The USP grade is distinguished from feed-grade sodium selenite not by a different molecular structure but by the audit trail and impurity controls. Feed-grade material may be sold under AAFCO definitions and may contain sulfate, selenate, or metal residues that are not controlled to pharmaceutical limits. USP-grade material is released under current good manufacturing practice for APIs as described in 21 CFR 211, and the accompanying certificate of analysis supports use in FDA-regulated finished drugs and dietary supplements under 21 CFR 111. The certificate of analysis does not replace incoming identity testing under 21 CFR 211.84 or 21 CFR 111.75. For a pharmaceutical formulation, the supplier should be qualified through an on-site audit that verifies batch-to-batch consistency, investigation procedures, and analytical instrument qualification under 21 CFR 211.160.
Supplier qualification for Sodium Selenite USP includes review of the manufacturing process starting with selenium dioxide or selenious acid neutralization. The route of synthesis can influence trace selenate and heavy metal profiles. A supplier using purified selenium dioxide and sodium hydroxide may produce lower sulfate and chloride content than a route using technical-grade selenious acid. The USP monograph does not require disclosure of the synthesis route, but the finished product manufacturer should assess residual element profiles through supplier questionnaires and periodic third-party testing. Warehouse storage conditions should include temperature mapping and humidity logging because the API is hygroscopic; high-density polyethylene drums with low moisture vapor transmission rate are common for bulk packaging, and desiccants are not placed in direct contact with the API unless qualified.