Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Sodium Phosphate, Monobasic, Monohydrate (Sodium Dihydrogen Phosphate Monohydrate) Part 4, Monographs for Reagent Chemicals: General Descriptions, Specifications, and Tests eISBN: 9780841230460 Tom Tyner Chair, ACS Committee on Analytical Reagents James Francis Secretary, ACS Committee on Analytical Reagents
ABSTRACT This monograph for Sodium Phosphate, Monobasic, Monohydrate provides, in addition to common physical constants, a general description including typical appearance, applications, change in state (approximate), and aqueous solubility. The monograph also details the following specifications and corresponding tests for verifying that a substance meets ACS Reagent Grade specifications including: Assay, pH of a 5% Solution at 25.0 °C, Insoluble Matter, Chloride, Sulfate, Calcium, Potassium, Heavy Metals, and Iron.
NaH2PO4 • H2O
Formula Wt 137.99
CAS No. 10049-21-5
GENERAL DESCRIPTION Typical appearance . . . . . . . . Applications . . . . . . . . . . . . . Change in state (approximate) . Aqueous solubility . . . . . . . . .
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white or colorless solid buffering agent loses all water at 100 °C freely soluble
SPECIFICATIONS Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98.0–102.0% NaH2PO4 · H2O pH of a 5% solution at 25.0 °C . . . . . . . . . . . . 4.1–4.5 Maximum Allowable Insoluble matter . . . . . . . . . . . . . . . . . . . . . 0.01% Chloride (Cl) . . . . . . . . . . . . . . . . . . . . . . . 5 ppm Sulfate (SO4) . . . . . . . . . . . . . . . . . . . . . . . 0.003% Calcium (Ca) . . . . . . . . . . . . . . . . . . . . . . . 0.005% Potassium (K) . . . . . . . . . . . . . . . . . . . . . . . 0.01% Heavy metals (by ICP–OES) . . . . . . . . . . . . . . 0.001% Iron (Fe) . . . . . . . . . . . . . . . . . . . . . . . . . . 0.001%
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4365 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
TESTS Assay (By acid–base titrimetry). Weigh accurately about 5.0 g, and dissolve in 50 mL of water. Titrate with 1 N sodium hydroxide volumetric solution to the inflection point at about pH 8.8, as measured with a pH meter. One milliliter of 1 N sodium hydroxide corresponds to 0.1380 g of NaH2PO4 · H2O.
pH of a 5% Solution at 25.0 °C [Part 2: Direct Electrometric Methods; pH Potentiometry; pH Range; Procedure for pH of a 5% Solution at 25.0 °C].
Insoluble Matter [Part 2: Gravimetric Methods; Insoluble Matter]. Dissolve 10.0 g in 100 mL of water.
Chloride [Part 2: Colorimetry and Turbidimetry; Chloride]. Use 2.0 g of sample and 2 mL of nitric acid.
Sulfate Dissolve 1.0 g in 15 mL of water, and add 2.5 mL of 10% hydrochloric acid (solution pH approximately 2). Filter through washed filter paper, and add 10 mL of water through the same filter. For control, add 0.03 mg of sulfate ion (SO4) in 20 mL of water, and add 1.0 mL of (1:19) hydrochloric acid. Dilute both to 35 mL with water, add 5.0 mL of 40% barium chloride solution, and mix. Observe turbidity after 10 min. Sample solution turbidity should not exceed that of the control solution.
Calcium and Potassium (By flame AAS, [Part 2: Trace and Ultratrace Elemental Analysis; Atomic Absorption Spectroscopy; Analysis; Procedure for Flame AAS]).
For the Determination of Calcium and Potassium
S a m p l e S t o c k S o l u t i o n . Dissolve 10.0 g of sample in 70 mL of water, and transfer to a 100 mL volumetric flask. Add 5 mL of nitric acid, and dilute to the mark with water (1 mL = 0.10 g).
For the Determination of Calcium and Potassium
Element
Wavelength (nm)
Sample Wt (g)
Standard Added (mg)
Flame Type*
Background Correction
Ca
422.7
0.40
0.02; 0.04
N/A
No
K
766.5
0.40
0.02; 0.04
A/A
No
*A/A is air/acetylene; N/A is nitrous oxide/acetylene.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4365 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Heavy Metals ([Part 2: Trace and Ultratrace Elemental Analysis; Inductively Coupled Plasma−Optical Emission Spectroscopy (ICP–OES); Calculation of Heavy Metals (by ICP–OES) Results], by ICP–OES). Use 1.0 g sample.
Iron [Part 2: Colorimetry and Turbidimetry; Iron; Procedure for Iron, Method 2 (Hydroxylamine and 1,10-Phenanthroline)]. Use 1.0 g.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4365 ACS Reagent Chemicals, Part 4
