Calcium Gluconate: Physicochemical Properties, Pharmacopoeial Quality Control, and Application Guidelines

Calcium gluconate is the calcium salt of D-gluconic acid and is commonly available in anhydrous and monohydrate forms. Owing to its characteristic compatibility and solubility behavior in aqueous systems, calcium gluconate is widely used in medicine, occupational-safety emergency response, food processing and nutritional fortification, as well as laboratory and process applications. Its practical value is rooted in the central roles of Ca2+ in physiology and material systems, while its performance is jointly constrained by solution chemistry conditions, impurity profiles, and regulatory/standard boundaries.

Keywords: calcium gluconate; D-gluconic acid; calcium ion; hyperkalemia; hydrofluoric acid exposure; soy-product coagulation; pharmacopeial standards; quality control

I. Basic Information and Physicochemical Characteristics

1.1 Snapshot of Key Properties

Item	Information	Item	Information
English name	Calcium Gluconate	Appearance	White crystalline powder, odorless and tasteless
Molecular formula	C12H22O14Ca	Water solubility	Readily soluble in boiling water; slowly soluble in water
Molecular weight	430.37	CAS No.	299-28-5
Melting point	195 °C	EINECS No.	206-075-8
Exact mass	430.0635	Boiling point	673.6 °C
Flash point	375.2 °C	PSA	291.79000
Hazard symbol	Xn	Safety statements	S24/25
Application overview	Calcium fortification; buffering; setting/firming; chelation	Hazard statements	R20/21/22; R36/37/38

1.2 Structural Features and Solubility Behavior

Calcium gluconate is an organic-acid calcium salt. The gluconate anion contains multiple hydroxyl groups and a carboxyl group, providing strong hydration capacity and, therefore, generally favorable solvation and formulation compatibility in aqueous systems. Pharmacopeial descriptions typically emphasize that it is readily soluble in boiling water, slowly soluble in water at room temperature, and insoluble in anhydrous ethanol, chloroform, or ether. In practice, this means that dissolution at room temperature may be kinetically limited and should be supported by adequate stirring and sufficient time. In complex matrices, solution clarity and particulate control should be assessed concurrently.

1.3 Solution-Chemistry Constraints and Compatibility Risks

(1) pH and precipitation tendency

In systems containing carbonate, phosphate, oxalate, or other multivalent anions, Ca2+ may form low-solubility salts, leading to turbidity or precipitation. The risk generally increases as pH rises, and a stability window should be established by small-scale compatibility tests.

(2) Ionic strength and complexation equilibria

Changes in ionic strength can shift ionic activity and complexation/precipitation equilibria, thereby affecting apparent solubility, turbidity points, and gel-forming behavior. Multi-component formulations should be validated experimentally rather than inferred.

(3) Temperature and mixing order

Elevated temperature can accelerate dissolution but may also affect the stability of other components. The mixing order can influence local supersaturation and transient precipitate formation; therefore, key operational parameters should be fixed and documented in process records.

II. Physiological Roles of Calcium Ions and Medical-Related Uses

2.1 Physiological basis of Ca2+

Calcium ions participate in neurotransmitter release, excitation–contraction coupling in neuromuscular systems, maintenance of cardiac electrical activity and contractility, as well as skeletal mineralization and bone-metabolism homeostasis. Serum calcium homeostasis is jointly regulated by endocrine signaling, renal handling, and exchange with the bone reservoir. Calcium supplementation is conceptually distinct from etiological management and should be discussed within a clear clinical boundary.

2.2 Calcium supplementation in hypocalcemia-related settings

As a calcium source, calcium gluconate can be used for supplementation or management of hypocalcemia-related conditions. Oral dosage forms are more commonly used for long-term supplementation, whereas injectable calcium gluconate is used in acute, symptomatic hypocalcemia requiring rapid correction. Such use involves route, administration rate, and electrocardiographic monitoring and belongs to professional medical care.

2.3 Intravenous calcium in emergency management of hyperkalemia

In severe hyperkalemia, especially when electrocardiographic abnormalities are present, intravenous calcium is administered to counteract adverse effects of hyperkalemia on cardiac excitability and to reduce the risk of malignant arrhythmias. Intravenous calcium does not directly lower serum potassium and must be integrated with potassium-lowering or potassium-removal measures to complete the therapeutic loop.

2.4 Other supportive contexts and statement boundaries

(1) Calcium-channel blocker toxicity

Intravenous calcium may be part of comprehensive supportive care to offset selected pharmacodynamic effects, typically requiring multi-modal strategies and close monitoring.

(2) Management of hypermagnesemia

Calcium salts may be used to antagonize neuromuscular transmission depression caused by elevated magnesium, which is likewise a specialist emergency-care scenario.

(3) Background of adjunctive use in allergy-related conditions

Calcium preparations have appeared as adjunctive medications in certain allergy-related contexts. In scientific communication, adjunctive backgrounds should not be overstated as definitive primary therapeutic conclusions; statement strength should be bounded by approved labeling or authoritative guidance.

III. Occupational Safety and Emergency Use

3.1 Hazard profile of hydrofluoric acid exposure

The hazards of hydrofluoric acid (HF) exposure extend beyond acid burns. Fluoride ions can penetrate deeply and bind endogenous Ca2+ and Mg2+, potentially causing persistent local injury and systemic electrolyte disturbances. Calcium gluconate provides Ca2+ to complex free fluoride and is a key component of HF skin-exposure management strategies.

3.2 On-site response and laboratory management essentials

(1) On-site response principles

After thorough irrigation, calcium gluconate gel should be applied as soon as possible, followed by continued treatment and medical evaluation based on symptom evolution. Specific actions should follow institutional SOPs and professional medical advice.

(2) Emergency-system readiness

Laboratories handling HF should stock calcium gluconate gel, flushing facilities, and personal protective equipment, and should establish exposure assessment, transfer, and follow-up workflows. Emergency supplies should be accessible and usable, supported by periodic checks and drills.

IV. Food Processing and Nutritional Fortification

4.1 Soy-product coagulation and texture control

In soy-milk systems, soybean proteins can form gel networks under suitable conditions. After calcium gluconate is added, Ca2+ participates in protein interactions and network formation, shifting the system from a liquid state to a gel state and enabling products such as tofu pudding or heat-set tofu. Key variables include protein concentration, heating profiles, pH, calcium-salt dosage, addition mode, stirring intensity, and setting time. Process optimization can be built around gel strength, water-holding capacity, and syneresis rate as evaluation metrics.

4.2 Functional positioning in food formulations and system validation

In food systems, calcium gluconate can serve as a calcium source for fortification and can also contribute to buffering, firming/setting, and chelation objectives. Sensitivity to Ca2+ varies across matrices; in particular, systems containing multivalent anions, proteins, or polysaccharides may exhibit turbidity or texture shifts upon Ca2+ addition and should be validated via small-scale trials. Scope and use levels must be bounded by local regulations and standards.

4.3 Formulation stability considerations for fortification

(1) Aqueous beverages

Clarity, mouthfeel, and storage stability should be assessed; pH adjustment and compatibility strategies may be required to reduce turbidity and precipitation risks.

(2) Solid or semi-solid matrices

Mixing uniformity, hygroscopicity, and storage stability are key. If phosphate or carbonate components are present, precipitation risks and grittiness should be verified.

(3) Synergy with colloidal or chelation systems

Colloids and chelating ingredients can alter Ca2+ activity and microstructure. Formulation balancing and validation should be guided by critical quality attributes.

V. Pharmacopeial Standards and Quality Control Essentials for Calcium Gluconate Monohydrate

5.1 Standards and assay (potency)

This product is calcium D-gluconate monohydrate. The content of C12H22CaO14·H2O should be 99.0%–104.0%.

5.2 Description and solubility

This product is a white granular powder, odorless and tasteless. It is readily soluble in boiling water, slowly soluble in water, and insoluble in anhydrous ethanol, chloroform, or ether.

5.3 Identification

(1) Ferric chloride reaction

After adding ferric chloride reagent, the solution shows a dark-yellow coloration.

(2) Thin-layer chromatography (TLC) identification

On silica gel G TLC plates, develop with ethanol–water–concentrated ammonia solution–ethyl acetate (50:30:10:10), air-dry, heat at 110 °C for 20 min, cool, spray with ammonium molybdate–ceric sulfate reagent, heat again at 110 °C for 10 min, cool, and inspect after 10 min; the principal spot should match the reference in position and color.

(3) Infrared spectroscopy

The infrared absorption spectrum should be consistent with the reference spectrum.

(4) Calcium-salt identification reaction

The aqueous solution should give the characteristic identification reaction of calcium salts.

5.4 Tests

(1) Clarity of solution

Dissolve 4.0 g of the product in 40 mL of water by boiling until completely dissolved. The solution should be clear (for injection).

(2) Chloride

Take 0.10 g of the product and test for chloride in accordance with the General Methods. The turbidity produced, if any, must not be more intense than that of the control solution prepared with 5.0 mL of standard sodium chloride solution (limit: 0.05%).

(3) Sulfate

Take 0.50 g of the product and test for sulfate in accordance with the General Methods. The turbidity produced, if any, must not be more intense than that of the control solution prepared with 5.0 mL of standard potassium sulfate solution (limit: 0.1%).

(4) Sucrose or reducing sugars

Dissolve 0.50 g of the product in 10 mL of water with heating. Add 2 mL of dilute hydrochloric acid and boil for 2 minutes. Cool, add 5 mL of sodium carbonate reagent solution, and allow to stand for 5 minutes. Dilute with water to 20 mL and filter. To 5 mL of the filtrate add 2 mL of alkaline copper tartrate reagent solution, and boil for 1 minute; no red precipitate should form immediately.

(5) Magnesium salts and alkali metals

Dissolve 1.0 g of the product in 40 mL of water. Add 0.5 g of ammonium chloride and bring to boiling. Add an excess of ammonium oxalate reagent solution to precipitate calcium completely. Heat on a water bath for 1 hour, cool, dilute with water to 100 mL, mix well, and filter. Take 50 mL of the filtrate, add 0.5 mL of sulfuric acid, evaporate to dryness, and ignite to constant mass; the residue must not exceed 5 mg.

(6) Heavy metals

Dissolve 1.0 g of the product in 2 mL of 1 mol/L hydrochloric acid solution and sufficient water to make 25 mL, warming gently to dissolve if necessary. Cool and test for heavy metals in accordance with the General Methods; the content of heavy metals must not exceed 15 ppm.

(7) Arsenic

Dissolve 1.0 g of the product in 5 mL of hydrochloric acid and 23 mL of water. Test for arsenic in accordance with the General Methods; it must comply with the limit of 0.0002%.

5.5 Assay

Assay is commonly performed by complexometric titration with disodium EDTA using an appropriate indicator, titrating to the prescribed endpoint color change. Each 1 mL of 0.05 mol/L disodium EDTA is equivalent to 22.42 mg of C12H22CaO14·H2O.

VI. Laboratory and Process Use Considerations

6.1 Solution preparation and concentration reporting

(1) Dissolution strategy

① If dissolution is slow at room temperature in aqueous media, use a warm-water bath and continuous stirring to promote dissolution.

② After preparation, check solution clarity and, if necessary, filter to remove insoluble particulates.

③ For systems with strict particulate requirements, evaluate membrane material and pore size for potential impacts on effective components.

(2) Concentration reporting and equivalence conversion

① It is recommended to record both the mass concentration of the salt and the elemental-calcium equivalent concentration to improve cross-experiment comparability.

② In precipitation-sensitive systems, elemental-calcium equivalents better reflect the driving force of the system and should be treated as a core recording metric.

(3) Storage and stability

① Solution stability can be affected by microbial contamination, pH drift, and CO2 absorption; storage conditions and shelf-life should be defined.

② Before critical experiments, re-check clarity and pH to avoid systematic bias introduced by solution-state changes.

6.2 Compatibility with common matrix components

(1) With phosphate systems

① Calcium-phosphate precipitation may occur; control concentration and pH and fix the mixing order.

② Turbidity or particle counting can be used as a process-monitoring metric.

(2) With carbonate/bicarbonate systems

① Carbonate readily forms low-solubility salts with calcium, especially under alkaline conditions; formulation should be designed cautiously.

② Where needed, consider alternative buffers or reduce carbonate activity to maintain clarity.

(3) With protein or polysaccharide systems

① Ca2+ may induce protein aggregation or polysaccharide crosslinking, which can be harnessed for structure formation but may also cause unintended flocculation.

② Establish a safe window via gradient addition, and quantify effects using rheology, particle size, and turbidity metrics.

VII. Aladdin-Related Products

Catalog No.	Product Name	CAS No.	Grade and Purity
C580335	Calcium D-gluconate monohydrate	66905-23-5	2mM in Water
C171268	Calcium D-gluconate monohydrate	66905-23-5	≥98%
C352040	Calcium α-D-heptagluconate hydrate	17140-60-2	≥98%
C422111	Calcium α-D-heptagluconate hydrate	17140-60-2	10mM in Water
G1499481	Gluconate Calcium	299-28-5	Moligand™, 10 mM in Water
C110858	Calcium Gluconate Monohydrate	66905-23-5	≥99%
C110859	Calcium Gluconate Monohydrate	66905-23-5	PharmPure™, USP

Calcium gluconate is widely used as a calcium source and as a tool for ionic-environment control and texture formation, largely because of its solubility and compatibility behavior in aqueous systems. In research and technical communication, the key technical focus points include how solution chemistry conditions affect stability, precipitation risks in multivalent-anion matrices, structure-coupling effects in protein/polysaccharide systems, and the constraints imposed by pharmacopeial quality-control items on raw-material consistency and safety. Establishing standardized preparation records, compatibility verification, and quality traceability around these points can substantially improve interpretability and reproducibility.

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