Calcium Silicate
(kal' see um sil' i kate).
DEFINITION
Calcium Silicate, crystalline or amorphous, is a compound of calcium oxide and silicon dioxide. It contains NLT 4.0% of calcium oxide and NLT 35.0% of silicon dioxide.
IDENTIFICATION
• A. Identification Tests—General, Calcium 
191
191
Sample solution:
Mix 0.5 g with 10 mL of 3 N hydrochloric acid. Filter, and neutralize the filtrate to litmus paper with 6 N ammonium hydroxide.
Acceptance criteria:
The neutralized filtrate meets the requirements.
• B.
Analysis:
Prepare a bead by fusing a few crystals of sodium ammonium phosphate on a platinum loop in the flame of a gas burner. Place the hot, transparent bead in contact with the specimen of Calcium Silicate, and again fuse.
Acceptance criteria:
Silica floats about in the bead, producing, upon cooling, an opaque bead having a web-like structure.
ASSAY
• Silicon Dioxide
Sample:
Calcium Silicate in the appropriate amount (see Table 1)
Table 1
| Sample Weight (mg) |
Calcium Oxide Content (%) |
|---|---|
| 400 | >25 |
| 600 | 11–25 |
| 1000 | 4–10 |
Analysis:
Transfer the Sample to a beaker, add 5 mL of water and 10 mL of perchloric acid, and heat until dense white fumes of perchloric acid are evolved. Cover the beaker with a watch glass, and continue to heat for 2 h. Allow to cool, add 30 mL of water, filter, and wash the precipitate with 200 mL of hot water. [Note—Retain the combined filtrate and washings for use in the assay for Calcium Oxide. ]
Transfer the filter paper and its contents to a platinum crucible, heat slowly to dryness, then heat sufficiently to char the filter paper. Ignite at about 900
–1000 to constant weight. Moisten the residue with 5 drops of perchloric acid, add 15 mL of hydrofluoric acid, heat cautiously on a hot plate until all of the acid is driven off, and ignite at a temperature NLT 1000 to constant weight. Cool in a desiccator, and weigh: the loss in weight represents the weight of SiO2.
–1000 to constant weight. Moisten the residue with 5 drops of perchloric acid, add 15 mL of hydrofluoric acid, heat cautiously on a hot plate until all of the acid is driven off, and ignite at a temperature NLT 1000 to constant weight. Cool in a desiccator, and weigh: the loss in weight represents the weight of SiO2.
Acceptance criteria:
NLT 35.0% of silicon dioxide (SiO2) and 90.0%–110.0% of the content stated in the labeling, or within the range of percentages stated in the labeling
• Calcium Oxide
Sample solution:
Use the combined filtrate and washings retained from the assay for Silicon Dioxide.
Titrimetric system
(See Titrimetry 541.)
541.)
Mode:
Direct titration
Titrant:
0.05 M edetate disodium VS
Endpoint detection:
Visual
Analysis:
Neutralize the Sample solution to litmus with 1 N sodium hydroxide. Add, while stirring, 10 mL of 0.05 M edetate disodium VS from a 50-mL buret. Add 15 mL of 1 N sodium hydroxide and 300 mg of hydroxy naphthol blue, and continue the titration to a blue endpoint.
Calculate Z, the percentage of calcium oxide (CaO) in the sample taken:
Z = [(V × M × F)/W] × 100
| V | = | = volume of Titrant consumed by the Sample solution (mL) |
| M | = | = actual molarity of the Titrant (mmol/mL) |
| F | = | = equivalency factor, 56.08 mg/mmol |
| W | = | = weight of the sample (mg) |
Calculate the percentage of the labeled amount of calcium oxide (CaO):
Result = (Z/L) × 100
| Z | = | = percentage of CaO in the sample taken as calculated above |
| L | = | = labeled amount of CaO |
Acceptance criteria:
NLT 4.0% of calcium oxide (CaO) and 90.0%–110.0% of the content stated in the labeling, or within the range of percentages stated in the labeling
IMPURITIES
• Loss on Ignition 733:
Transfer 1 g to a suitable tared crucible, dry at 105 for 2 h, and ignite at 900 to constant weight: it loses NMT 20.0% of its weight.
733:
Transfer 1 g to a suitable tared crucible, dry at 105 for 2 h, and ignite at 900 to constant weight: it loses NMT 20.0% of its weight.
• Heavy Metals 231
231
Test preparation:
Boil 4.0 g with a mixture of 50 mL of water and 10 mL of hydrochloric acid for 20 min, adding water to maintain the volume during the boiling. Add ammonium hydroxide until the mixture is only slightly acid to litmus paper. Filter with the aid of suction, and wash with 15–20 mL of water, combining the washing with the original filtrate. Add 2 drops of phenolphthalein TS, then add a slight excess of 6 N ammonium hydroxide. Discharge the pink color with dilute hydrochloric acid (1 in 100). Dilute with water to 100 mL, and use 25 mL of the solution for the test.
Acceptance criteria:
NMT 20 ppm
• Limit of Lead
Palladium matrix modifier:
Palladium nitrate (1% Pd)1
Magnesium matrix modifier:
Magnesium nitrate (2% Mg)2
Nitric acid, 65% [7697-37-2]:
Use a suitable grade with a content of NLT 65.0%.3
Nitric acid diluent:
Transfer 42 mL of Nitric acid, 65% to a 1000-mL volumetric flask. Dilute with water to volume.
Matrix modifier solution:
Transfer 1.0 mL of Palladium matrix modifier and 100 µL of Magnesium matrix modifier to a 20-mL volumetric flask. Dilute with water to volume, and mix.
Lead standard solution:
A solution containing Pb(NO3)2 in 0.5 M nitric acid corresponding to 1000 mg of lead/mL4
Standard solution:
Transfer 100 µL of Lead standard solution to a 100-mL volumetric flask. Dilute with water to volume, and mix. This solution contains the equivalent of 1.0 µg/mL of lead.
Calibration solutions
Calibration solution A:
Transfer 50 mL of Nitric acid diluent to a 100-mL volumetric flask, and dilute with water to volume (0 µg/mL of lead).
Calibration solution B:
Transfer 1 mL of Standard solution and 50 mL of Nitric acid diluent to a 100-mL volumetric flask, and dilute with water to volume (0.01 µg/mL of lead).
Calibration solution C:
Transfer 5 mL of Standard solution and 50 mL of Nitric acid diluent to a 100-mL volumetric flask, and dilute with water to volume (0.05 µg/mL of lead).
Sample solution:
Weigh 2.0 g of Calcium Silicate into a 150-mL beaker. Mix with 50 mL of Nitric acid diluent. Cover with a watch glass, and boil for 20 min. Allow to cool. With the aid of a vacuum, pass through a glass filter,5 and wash the filter several times with water. Transfer the filtrate into a 100-mL volumetric flask. Dilute with water to volume, and mix.
System suitability solution:
Transfer 5 mL of Standard solution and 50 mL of Nitric acid diluent into a 100-mL volumetric flask. Dilute with water to volume, and mix. This solution contains the equivalent of 0.05 µg of lead/mL.
Instrumental conditions
Mode:
Graphite furnace atomic absorption spectrophotometer
Analytical wavelength:
283.3 nm (lead emission line)
Lamp:
Lead hollow-cathode lamp and an adequate means of Zeeman background correction
Carrier gas:
Argon
Under typical conditions, the Sample solution and Calibration solutions volumes are 20 µL, the volume of the Matrix modifier solution is 10 µL, the injection temperature is 20, and the oven conditions are as follows (see Table 2).
, and the oven conditions are as follows (see Table 2).
[Note—These conditions may be optimized for each instrument. ]
Table 2
| Step | Temperature () |
|---|---|
| Drying 1 | 110 |
| Drying 2 | 130 |
| Pyrrolysis | 950 |
| Read | 1800 |
| Clean out | 2450 |
Analysis
Samples:
Calibration solutions, Sample solution, and System suitability solution
Plot the absorbance of each Calibration solution versus its content of lead, in µg/mL, and draw the best straight line fitting the three points. From this plot, determine the concentration, in µg/mL, of lead in the Sample solution: the correlation coefficient is NLT 0.99, and the recovery for the System suitability solution is 85%–115%.
Calculate the quantity, in ppm, of lead in the Sample solution.
Result = (C × V)/W
| C | = | = concentration of the Sample solution (µg/mL) |
| V | = | = volume of the Sample solution (mL) |
| W | = | = weight of sample taken (g) |
Acceptance criteria:
NMT 10 ppm
• Limit of Fluoride
[Note—Store all solutions in polytef containers. ]
Buffer solution:
294 mg/mL of sodium citrate
Ionic strength adjustment buffer:
Transfer 42 mL of hydrochloric acid, 121 g of tris(hydroxymethyl)aminomethane, and 115 g of sodium tartrate to a 500-mL volumetric flask containing 250 mL of water. Stir to dissolve, and dilute with water to volume.
Standard stock solution:
221 µg/mL of USP Sodium Fluoride RS. This stock solution contains 100 µg/mL of fluoride ion.
Sample solution:
Transfer 2.0 g of Calcium Silicate to a 100-mL polytef beaker containing a magnetic stir bar. Add 20 mL of water and 2.0 mL of hydrochloric acid. Cover with a watch glass, and heat to a vigorous boil for 1 min, stirring continuously. Remove from heat, and cool. Transfer the cooled suspension to a 100-mL polytef beaker. Add 25 mL of Buffer solution, and adjust with ammonium hydroxide or hydrochloric acid to a pH of 5–6. Add 50 mL of Ionic strength adjustment buffer and water to make 100 mL of solution.
Electrode system:
Use a fluoride-specific ion-indicating electrode and a suitable reference electrode connected to a pH meter capable of measuring potentials with a reproducibility of ±0.2 mV (see pH 791).
791).
Standard response line:
Obtain a standard response line with four standard solutions containing 0, 0.10, 0.20, and 0.40 µg/mL of fluoride as follows. Add 23 mL of water, 2 mL of hydrochloric acid, and 25 mL of Buffer solution to a 100-mL plastic beaker. Adjust with ammonium hydroxide to a pH of 5–6, and add Ionic strength adjustment buffer to obtain 100 mL of solution. Insert the electrode into the solution, stir for at least 15 min, and record the potential for the standard solution containing 0 µg/mL of fluoride. When the electrode has stabilized, add 100 µL of the Standard stock solution to the beaker, and stir. Allow the electrode to stabilize for 5 min, and measure the potential for the standard solution containing 0.10 µg/mL of fluoride. Similarly add another 100 and 200 µL of the Standard stock solution and record the potential for the standard solutions, containing 0.20 µg/mL of fluoride and 0.40 µg/mL of fluoride, respectively. After each addition, continue to stir for 5 min before recording the reading.
Analysis:
Insert the calibrated electrode into the Sample solution, stir for 5 min, and record the measurement. From the measured potential of the Sample solution and the Standard response line, determine the concentration, C, in µg/mL, of fluoride ion in the Sample solution.
Calculate the quantity, in ppm, of fluoride in Calcium Silicate:
Result = (C × V)/W
| C | = | = concentration of fluoride ion in the Sample solution (µg/mL) |
| V | = | = volume of the Sample solution (mL) |
| W | = | = weight of Calcium Silicate in the Sample solution (g) |
Acceptance criteria:
NMT 50 ppm
SPECIFIC TESTS
• pH 791:
8.4–11.2, determined in a well-mixed aqueous suspension (1 in 20)
791:
8.4–11.2, determined in a well-mixed aqueous suspension (1 in 20)
• Ratio of Silicon Dioxide to Calcium Oxide:
Divide the percentage of silicon dioxide obtained in the test for Silicon Dioxide by the percentage of calcium oxide obtained in the test for Calcium Oxide.
Acceptance criteria:
0.5–20
• Sum of CaO, SiO2, and Loss on Ignition:
The sum of the percentages obtained in the three tests is NLT 90.0%.
ADDITIONAL REQUIREMENTS
• Packaging and Storage:
Preserve in well-closed containers.
• Labeling:
The labeling states the claimed percentage or range of percentages for the content of calcium oxide and for the content of silicon dioxide.
• USP Reference Standards 11
11
USP Sodium Fluoride RS
1
A suitable grade is available as catalog number RCMMPD10KN-50 from VWR, www.vwr.com.
2
Available as catalog number RCMMMG20KN-50, from VWR, www.vwr.com.
3
A suitable grade is available as catalog number 441-2 from EMD Chemicals, www.emdchemicals.com.
4
A suitable grade is available as catalog number 1.19776 from EMD Chemicals, www.emdchemicals.com.
5
Glass filter: Whatman GF/B glass microfiber filters, 1.0 µm, Whatman no. 1821-090, is suitable. Available as catalog number 28497-492, from VWR, www.vwr.com.
Auxiliary Information—
Please check for your question in the FAQs before contacting USP.
| Topic/Question | Contact | Expert Committee |
|---|---|---|
| Monograph | Robert H. Lafaver, M.S.
Scientific Liaison 1-301-816-8335 |
(EXC2010) Monographs - Excipients |
| Reference Standards | RS Technical Services 1-301-816-8129 rstech@usp.org |
USP35–NF30 Page 1722
Pharmacopeial Forum: Volume No. 33(3) Page 484