di-Sodium Hydrogen Phosphate Dodecahydrate: Lab Use Guide

di-Sodium hydrogen phosphate dodecahydrate is a widely used inorganic phosphate salt that serves as a critical component in buffer preparation, biological media, and analytical chemistry applications across research and clinical laboratories.

Chemical Name

di-Sodium hydrogen phosphate dodecahydrate

Molecular Formula

Na2HPO4·12H2O

Molecular Weight

358.14 g/mol

Appearance

White crystalline powder or colorless crystals

Solubility

Freely soluble in water; insoluble in ethanol

pH of 1% aqueous solution

Approximately 9.0–9.5

Aladdin SKU

D431179

Chemical Properties and Identification

di-Sodium hydrogen phosphate dodecahydrate (Na₂HPO₄·12H₂O) is the dodecahydrate form of disodium hydrogen phosphate, a dibasic sodium phosphate salt. It has a molecular weight of approximately 358.14 g/mol and appears as white crystalline powder or colorless transparent crystals at room temperature.

The compound is freely soluble in water, producing a mildly alkaline solution. A freshly prepared 1% (w/v) aqueous solution typically exhibits a pH in the range of 9.0–9.5. It is essentially insoluble in ethanol and most organic solvents. Upon heating above 35°C, the dodecahydrate loses water of crystallization and transitions to lower hydrate forms, eventually yielding the anhydrous salt at higher temperatures. This hygroscopic and efflorescing behavior must be considered during weighing and storage.

The phosphate anion (HPO₄²⁻) acts as the conjugate base of the dihydrogen phosphate ion (H₂PO₄⁻), giving this salt excellent buffering capacity in the physiological pH range when combined with an appropriate acid or monbasic phosphate salt.

Laboratory Applications

di-Sodium hydrogen phosphate dodecahydrate is one of the most versatile inorganic salts used in life science and analytical chemistry laboratories. Its primary applications include:

• Phosphate-Buffered Saline (PBS) Preparation: Together with sodium chloride, potassium chloride, and potassium dihydrogen phosphate, disodium hydrogen phosphate is a core component of PBS, the most widely used isotonic buffer in cell biology, immunology, and molecular biology.
• Buffer Formulation: Combined with monosodium phosphate (NaH₂PO₄), it forms sodium phosphate buffer systems effective in the pH range 5.8–8.0, suitable for enzyme assays, protein purification, and chromatography.
• Microbiological and Cell Culture Media: Used as a phosphate source and pH stabilizer in bacteriological culture media and mammalian cell culture supplements.
• Analytical Chemistry: Employed as an ion-pairing reagent in HPLC mobile phases and as a standard for calibration in ion chromatography.
• Chemical Synthesis: Acts as a mild base and phase-transfer catalyst in certain organic synthesis protocols.

Because of its high water content (approximately 60% by mass as water of crystallization), researchers must account for the hydrated form when calculating molar quantities, and use the molecular weight of 358.14 g/mol rather than that of the anhydrous salt (141.96 g/mol).

Buffer Preparation Protocol

The following outlines a standard procedure for preparing 0.1 M sodium phosphate buffer (pH 7.4) and 1× PBS using di-Sodium hydrogen phosphate dodecahydrate (Aladdin SKU: D431179).

0.1 M Sodium Phosphate Buffer, pH 7.4 (1 L)

1. Weigh 20.0 g (approximately 55.9 mmol) of di-Sodium hydrogen phosphate dodecahydrate and dissolve in approximately 800 mL of ultrapure water.
2. Separately dissolve an appropriate quantity of sodium dihydrogen phosphate (monohydrate or dihydrate) to prepare a 0.1 M stock solution.
3. Combine the two phosphate solutions, monitoring pH with a calibrated pH meter. Adjust the ratio to achieve pH 7.4 at the working temperature (typically 25°C).
4. Adjust the final volume to 1 L with ultrapure water and re-verify pH.
5. Sterilize by autoclaving or passing through a 0.22 µm membrane filter if required for biological applications.

10× PBS Stock Solution (1 L)

1. Dissolve the following in 800 mL ultrapure water: 80 g NaCl, 2 g KCl, 14.4 g Na₂HPO₄·12H₂O (or approximately 7.2 g anhydrous Na₂HPO₄), and 2.4 g KH₂PO₄.
2. Adjust pH to 7.4 with HCl or NaOH as needed.
3. Bring to 1 L final volume with ultrapure water.
4. Autoclave or filter-sterilize; dilute 1:10 for 1× working solution.

Note: All quantities are approximate. Verify pH at working temperature. Use reagent-grade or higher purity materials to avoid interference in sensitive assays.

Storage, Handling, and Safety

Storage Conditions: Store di-Sodium hydrogen phosphate dodecahydrate in a tightly sealed container at room temperature (15–25°C), away from moisture and heat sources. The dodecahydrate is efflorescent and may lose water of crystallization upon prolonged exposure to dry air or elevated temperature, shifting the effective molarity of prepared solutions if the salt has partially dehydrated. Confirm the hydration state if reagent has been stored for extended periods.

Handling Precautions: While di-Sodium hydrogen phosphate dodecahydrate is considered a low-hazard material, standard laboratory precautions apply:

• Wear appropriate personal protective equipment (PPE): laboratory coat, chemical-splash safety goggles, and nitrile gloves.
• Avoid generating and inhaling dust during weighing. Work in a well-ventilated area or use a dust mask if handling large quantities.
• Avoid contact with eyes and skin; flush with copious water if contact occurs.

Disposal: Dilute aqueous solutions may generally be disposed of via the drain in accordance with local institutional and municipal regulations. Consult your institution's Environmental Health and Safety (EHS) office for guidance specific to your jurisdiction.

Incompatibilities: Avoid contact with strong acids, strong oxidizers, and alkaline earth metal salts that may cause precipitation of insoluble phosphate salts.

Quality, Specifications, and Purchasing Guidance

When selecting di-Sodium hydrogen phosphate dodecahydrate for research applications, purity grade is a critical consideration. For most biochemical and cell biology applications, ACS reagent grade (≥99.0%) or higher is recommended. For sensitive analytical techniques such as HPLC or trace-metal analysis, consider ultra-pure or trace-metal-free grades.

Key specification parameters to verify upon receipt include:

• Assay (purity): ≥99.0% (ACS grade) based on titrimetric or gravimetric analysis
• pH of solution: Within specified range for the stated concentration
• Heavy metals: ≤5 ppm (for standard reagent grade)
• Insoluble matter: ≤0.005%
• Chloride (Cl): ≤0.0005%

Aladdin Scientific offers di-Sodium hydrogen phosphate dodecahydrate under SKU D431179, referenced to Sigma catalog number 1.06579. Procurement teams should verify the current certificate of analysis (CoA) for each lot to confirm compliance with internal quality standards before use in regulated or GMP-adjacent workflows.

For bulk or custom orders, contact Aladdin Scientific's sales team for volume pricing and documentation support.

Frequently asked questions

What is the difference between di-Sodium hydrogen phosphate dodecahydrate and anhydrous disodium phosphate?

Both compounds contain the same active phosphate anion (HPO4²⁻) but differ in water of crystallization content and molecular weight. The dodecahydrate (Na2HPO4·12H2O) has a molecular weight of 358.14 g/mol and contains approximately 60% water by mass, while the anhydrous form (Na2HPO4) has a molecular weight of 141.96 g/mol. When preparing solutions, it is essential to use the correct molecular weight for the specific hydrate form in hand to achieve the desired molar concentration.

How should I store di-Sodium hydrogen phosphate dodecahydrate to prevent degradation?

Store the reagent in a tightly sealed container at room temperature (15–25°C), protected from excess heat and moisture. Because the dodecahydrate is efflorescent, prolonged exposure to dry air or temperatures above 35°C can cause loss of crystallization water, altering the effective weight-based concentration of your solutions. Always reseal the container promptly after use and check the physical appearance of the crystals before use.

Can di-Sodium hydrogen phosphate dodecahydrate be used to prepare PBS for cell culture?

Yes, di-Sodium hydrogen phosphate dodecahydrate is a standard component for preparing phosphate-buffered saline (PBS) for cell culture applications. When preparing PBS for cell culture, use reagent-grade or higher purity material, prepare the solution with ultrapure or tissue-culture-grade water, and sterilize by autoclaving or filtration through a 0.22 µm membrane. Verify the final pH (typically 7.2–7.4) before use.

Why does my di-Sodium hydrogen phosphate dodecahydrate appear clumped or wet?

Clumping or apparent wetness can result from exposure to humid air, as the dodecahydrate is hygroscopic. Conversely, if stored in very dry conditions, the salt may effloresce and appear powdery or opaque, indicating partial loss of crystallization water. In either case, re-weigh carefully and consider the potential shift in effective purity. If significant alteration is suspected, replace with a fresh lot to ensure reproducibility.

What pH range is achievable with sodium phosphate buffer made from di-Sodium hydrogen phosphate dodecahydrate?

Sodium phosphate buffer systems prepared by mixing di-Sodium hydrogen phosphate (dibasic) with monosodium phosphate (monobasic, NaH2PO4) can effectively buffer in the pH range of approximately 5.8 to 8.0, with optimal buffering capacity around pH 7.2. This range covers most physiological and biochemical assay requirements.

References

1. Merck KGaA / Sigma-Aldrich. Product Information: di-Sodium hydrogen phosphate dodecahydrate. Catalog No. 1.06579.
2. Gomori, G. (1955). Preparation of buffers for use in enzyme studies. Methods in Enzymology, 1, 138–146.
3. Dulbecco, R. & Vogt, M. (1954). Plaque formation and isolation of pure lines with poliomyelitis viruses. Journal of Experimental Medicine, 99(2), 167–182.
4. Lide, D.R. (Ed.). CRC Handbook of Chemistry and Physics, 97th Edition. CRC Press, Boca Raton, FL.

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