Citric Acid, Magnesium Oxide, and Sodium Carbonate Irrigation

This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition

Issued and maintained by the United States Pharmacopeial Convention (USP)

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1 DEFINITION 

Citric Acid, Magnesium Oxide, and Sodium Carbonate Irrigation is a sterile solution of Citric Acid, Magnesium Oxide, and Sodium Carbonate in Water for Injection. It contains NLT 95.0% and NMT 105.0% of the labeled amounts of citric acid (C₆H₈O₇. H₂O), magnesium oxide (MgO), and sodium carbonate (Na₂CO₃). 

2 IDENTIFICATION 

A. Identification Tests—General, Sodium〈191〉andMagnesium〈191〉 

B. 

Sample solution: 10 mL of Irrigation 

Analysis: Add 1 mL of mercuric sulfate TS to the Sample solution, heat to boiling, and add a few drops of potassium permanganate TS. Acceptance criteria: A white precipitate is formed. 

3 ASSAY 

Citric Acid 

Mobile phase, Standard preparation 1, and Chromatographic system: Proceed as directed in Assay for Citric Acid/Citrate and Phosphate 〈345〉. 

Assay preparation for citric acid/citrate assay: Nominally 20 µg/mL of citrate from Irrigation in 1 mM of sodium hydroxide prepared as follows. Transfer a suitable volume of Irrigation to an appropriately sized volumetric ask, and proceed as directed in Assay for Citric Acid/Citrate and Phosphate 〈345〉,Sample solution (for the assay of citric acid/citrate). 

Analysis 

Samples: Standard preparation 1 and Assay preparation for citric acid/citrate assay 

Proceed as directed in Assay for Citric Acid/Citrate and Phosphate 〈345〉, Procedure. 

Calculate the percentage of the labeled amount of citric acid monohydrate (C₆H₈O₇. H₂O) in the portion of Irrigation taken: 

Result = (r_U/r_S) × (C_S/C_U) × (M_r1 /M_r2) × 100 

r_U = peak response of citrate from the Assay preparation for citric acid/citrate assay

r_S = peak response of citrate from Standard preparation 1

C_S = concentration of Standard preparation 1 (μg/mL)

C_U = nominal concentration of citric acid monohydrate in the Assay preparation for citric acid/citrate assay (μg/mL)

M_r1 = molecular weight of citric acid monohydrate, 210.14

M_r2 = molecular weight of citrate, 189.10

Acceptance criteria: 95.0%–105.0% 

Magnesium Oxide 

Sample solution: A volume of Irrigation, nominally equivalent to 40 mg of magnesium oxide 

Analysis: Transfer the Sample solution to a beaker containing 130 mL of water heated to 75° ± 5°, and add 4 mL of ammonium chloride TS and then 5 mL of ammonium hydroxide. Mix, and add slowly, with stirring, 8 mL of 8-hydroxyquinoline TS. After allowing to stand for 30 min at 75°, filter through a sintered-glass crucible, previously dried and weighed. Wash the precipitate with 50 mL of a warm mixture of water and 6 N ammonium hydroxide (45:5), followed by 50 mL of cool water. Dry the crucible and contents at 105° for 3 h, cool, and weigh. Determine the equivalent of magnesium oxide (MgO) in the portion of Irrigation taken by multiplying the weight of the C₁₈H₁₂MgN₂O₂. 2H₂Oso obtained by 0.1156 (mg of MgO). 

Calculate the percentage of the labeled amount of magnesium oxide (MgO) in the portion of Irrigation taken. Acceptance criteria: 95.0%–105.0% 

Sodium Carbonate 

Sodium chloride stock solution: 4.75 mg/mL of sodium chloride, previously dried at 105° for 2 h, in water 

Internal standard solution: 0.636 mg/mL of lithium chloride in water 

Standard solution: 0.0475 mg/mL of sodium chloride and 0.6296 mg/mL of lithium chloride prepared from an appropriate mixture of Sodium chloride stock solution and Internal standard solution 

Sample stock solution: Nominally equivalent to 4.4 mg/mL of sodium carbonate from Irrigation diluted with water Sample solution: 0.044 mg/mL of sodium carbonate and 0.6296 mg/mL of lithium chloride prepared from an appropriate mixture of Sample stock solution and Internal standard solution 

Instrumental conditions 

Mode: Flame photometer 

Analytical wavelengths: 591 and 671 nm 

Analysis 

Samples: Internal standard solution, Standard solution, and Sample solution 

Concomitantly determine the emittances of the Standard solution and the Sample solution, adjusting the instrument with Internal standard solution to zero emittance. 

Calculate the percentage of the labeled amount of sodium carbonate (Na₂CO₃) in the portion of Irrigation taken: 

Result = (r_U,591/r_U,671) × (r_S,671/r_S,591) × × (C_S/C_U) (M_r1 /M_r2) × 100 

r_U,591 = emittance reading from the Sample solution at 591 nm

r_U,671 = emittance reading from the Sample solution at 671 nm

r_S,671 = emittance reading from the Standard solution at 671 nm

r_S,591 = emittance reading from the Standard solution at 591 nm

C_S = concentration of sodium chloride in the Standard solution (mg/mL)

C_U = nominal concentration of sodium carbonate in the Sample solution (mg/mL)

M_r1 = molecular weight of sodium carbonate, 105.99

M_r2 = two times the molecular weight of sodium chloride, 116.88

Acceptance criteria: 95.0%–105.0% 

4 SPECIFIC TESTS 

pH 〈791〉: 3.8–4.2 

Bacterial Endotoxins Test 〈85〉: It contains not more than 2.80 USP Endotoxin Units per mL. 

Other Requirements: It meets the requirements in Injections and Implanted Drug Products 〈1〉, except that the container may be designed to empty rapidly and may exceed 1000 mL in capacity. 

5 ADDITIONAL REQUIREMENTS 

Packaging and Storage: Preserve in single-dose containers, preferably of Type I or Type II glass.