Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Potassium Phosphate, Tribasic (Tripotassium Orthophosphate) 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 Potassium Phosphate, Tribasic provides, in addition to common physical constants, a general description including typical appearance and applications. The monograph also details the following specifications and corresponding tests for verifying that a substance meets ACS Reagent Grade specifications including: Assay, Dibasic Potassium Phosphate, Excess Alkali, Insoluble Matter, Chloride, Heavy Metals, Iron, Sulfate, and Sodium.
K3PO4 (anhydrous) K3PO4•7H2O (heptahydrate)
Formula Wt 212.26 Formula Wt 338.37
CAS No. 7778-53-2 CAS No. 22763-02-6
Note: This reagent must be labeled to indicate whether it is the anhydrous form or one of the hydrated forms.
GENERAL DESCRIPTION Typical appearance . . . . . . . . . . . . . . . . . . . solid Applications . . . . . . . . . . . . . . . . . . . . . . . . buffering agent
SPECIFICATIONS Assay (as-is basis) . . . . . . . . . . . . . . . . . . . . ≥98% K3PO4 or K3PO4 · 7H2O Maximum Allowable Dibasic potassium phosphate (K2HPO4) . . . . . . . 1% Excess alkali (as KOH) . . . . . . . . . . . . . . . . . 1% Insoluble matter . . . . . . . . . . . . . . . . . . . . . 0.01% Chloride (Cl) . . . . . . . . . . . . . . . . . . . . . . . 0.005% Heavy metals (by ICP–OES) . . . . . . . . . . . . . . 0.002% Iron (Fe) . . . . . . . . . . . . . . . . . . . . . . . . . . 0.001%
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4306 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Sulfate (SO4) . . . . . . . . . . . . . . . . . . . . . . . 0.005% Sodium (Na) . . . . . . . . . . . . . . . . . . . . . . . . 0.1%
TESTS Assay (By indirect acid–base titrimetry). Weigh accurately about 4.0 g for the anhydrous salt and 6.5 g for the heptahydrate salt, and dissolve in 50 mL of water and exactly 50.0 mL of 1 N hydrochloric acid volumetric solution. Heat to boiling to expel carbon dioxide. While protecting the solution from absorbing carbon dioxide, cool, and titrate with 1 N sodium hydroxide volumetric solution to the inflection point at about pH 4, as measured with a pH meter. Calculate A, the equivalent of 1 N hydrochloric acid consumed by the sample. Continue the titration with 1 N sodium hydroxide to the inflection point at about pH 8.8. Calculate B, the equivalent of 1 N sodium hydroxide required in the titration between the two inflection points.
If A is equal to or greater than 2B, then
If A is less than 2B, then
where F is 0.2123 for the anhydrous salt and 0.3384 for the heptahydrate salt.
Dibasic Potassium Phosphate and Excess Alkali Calculate the amount of dibasic potassium phosphate as K2HPO4 or the amount of excess alkali as potassium hydroxide from the titration values obtained in the assay. If A is less than 2B, then
If A is greater than 2B, then
Insoluble Matter [Part 2: Gravimetric Methods; Insoluble Matter]. Dissolve 10.0 g in 100 mL of water, add 0.10 mL of methyl red indicator solution, add hydrochloric acid until the solution is slightly acid to the indicator, and continue as described.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4306 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Chloride [Part 2: Colorimetry and Turbidimetry; Chloride]. Dissolve 0.20 g of sample in 10 mL of water, add 3 mL of nitric acid, and dilute to 20 mL.
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 0.5 g sample.
Iron [Part 2: Colorimetry and Turbidimetry; Iron; Procedure for Iron, Method 2 (Hydroxylamine and 1,10-Phenanthroline)]. Use 1.0 g.
Sulfate Dissolve 1.0 g in 15 mL of water, and add 4.0 mL of 10% hydrochloric acid (solution pH 2). Filter through washed filter paper, and add 10 mL of water through the same filter. For the control, add 0.05 mg of sulfate ion (SO4) in 20 mL of water, and then add 1.0 mL of dilute hydrochloric acid (1:19). Dilute both to 35 mL with water, add 5.0 mL of 40% barium chloride solution, and mix. Observe turbidity after 10 min. The turbidity of the sample solution should not exceed that of the control.
Sodium (By flame AAS, [Part 2: Trace and Ultratrace Elemental Analysis; Atomic Absorption Spectroscopy; Analysis; Procedure for Flame AAS]).
For the Determination of Sodium
S o d i u m S t o c k S o l u t i o n . Dissolve 1.0 g of sample in water, and dilute to 100 mL in a volumetric flask with water (1 mL = 0.01 g).
For the Determination of Sodium
Element
Wavelength (nm)
Sample Wt (g)
Standard Added (mg)
Flame Type*
Background Correction
Na
589.0
0.02
0.01;0.02
A/A
No
*A/A is air/acetylene.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4306 ACS Reagent Chemicals, Part 4
