Citric Acid, Anhydrous, and Citric Acid, Monohydrate - ACS Publications

Monograph pubs.acs.org/doi/book/10.1021/acsreagents

Citric Acid, Anhydrous, and Citric Acid, Monohydrate (2-Hydroxy-1,2,3-propanetricarboxylic Acid)

Downloaded by CORNELL UNIV on May 11, 2017 | http://pubs.acs.org Publication Date (Web): February 28, 2017 | doi: 10.1021/acsreagents.4096

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 Citric Acid, Anhydrous, and Citric Acid, 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, corresponding tests for verifying that a substance meets ACS Reagent Grade specifications including: Assay, Insoluble Matter, Residue after Ignition, Chloride, Oxalate, Phosphate, Sulfur Compounds (as SO, Iron, Lead, and Substances Carbonizable by Hot Sulfuric Acid (Tartrates, etc.).

C8H8O7 (anhydrous) C8H8O7·H2O (monohydrate)

Formula Wt 192.12 Formula Wt 210.14

CAS No. 77-92-9 CAS No. 5949-29-1

Note: This reagent is available as either the anhydrous or monohydrate form. The label should identify the specific form.

GENERAL DESCRIPTION Typical appearance . . . . . . . . . . . . . . . . . . . colorless or white solid

© 2017 American Chemical Society

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ACS Reagent Chemicals ACS Reagent Chemicals; American Chemical Society: Washington, DC, 2017.

DOI:10.1021/acsreagents.4096 ACS Reagent Chemicals, Part 4

ACS Reagent Chemicals

Monograph

pubs.acs.org/doi/book/10.1021/acsreagents

Applications . . . . . . . . . . . . . . . . . . . . . . . . sequestering agent for trace metals; determination of citrate-soluble phosphorus pentoxide Change in state (approximate) . . . . . . . . . . . . melting point, 100 °C (monohydrate), 153 °C (anhydrous) Aqueous solubility . . . . . . . . . . . . . . . . . . . . 165 g in 100 mL at 20 °C


SPECIFICATIONS Assay (anhydrous) . . . . . . . . . . . . . . . . . . . . 99.5% C6H8O7 Assay (monohydrate) . . . . . . . . . . . . . . . . . . 9.0–102.0% C6H8O7 · H2O Maximum Allowable Insoluble matter . . . . . . . . . . . . . . . . . . . . . 0.005% Residue after ignition. . . . . . . . . . . . . . . . . . 0.02% Chloride (Cl) . . . . . . . . . . . . . . . . . . . . . . . 0.001% Oxalate (C2O4) . . . . . . . . . . . . . . . . . . . . . . Passes test Phosphate (PO4) . . . . . . . . . . . . . . . . . . . . . 0.001% Sulfur Compounds (as SO4) . . . . . . . . . . . . . . 0.002% Iron (Fe) . . . . . . . . . . . . . . . . . . . . . . . . . . 3 ppm Lead (Pb) . . . . . . . . . . . . . . . . . . . . . . . . . 2 ppm Substances carbonizable by hot sulfuric acid . . . Passes test

TESTS Assay (By acid–base titrimetry). Weigh accurately about 2.7 g, dissolve in about 40 mL of water, and add 0.15 mL of phenolphthalein indicator solution. Titrate with 1 N sodium hydroxide volumetric solution to a pink color that persists for 5 min. One milliliter of 1 N sodium hydroxide corresponds to 0.06404 g of C6H8O7 or 0.07005 g of C6H8O7 · H2O.

Insoluble Matter [Part 2: Gravimetric Methods; Insoluble Matter]. Use 20 g dissolved in 150 mL of water.

Residue after Ignition [Part 2: Gravimetric Methods; Residue after Ignition]. Ignite 5.0 g. Use 2 mL of sulfuric acid to moisten the residue.

Chloride [Part 2: Colorimetry and Turbidimetry; Chloride]. Use 1.0 g.


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ACS Reagent Chemicals

Monograph

pubs.acs.org/doi/book/10.1021/acsreagents

Oxalate Dissolve 5 g in 25 mL of water and add 2 mL of 10% aqueous calcium acetate solution. No turbidity or precipitate should appear after standing 4 h. (Limit about 0.05%.)

Phosphate [Part 2: Colorimetry and Turbidimetry; Phosphate; Procedure for Phosphate, Method 1 (Direct Molybdenum Blue)]. Mix 2.0 g with 0.5 g of magnesium nitrate in a platinum dish, and ignite. Dissolve the residue in 5 mL of water, add 5 mL of nitric acid, and evaporate to dryness. Dissolve the residue in 25 mL of approximately 0.5 N sulfuric acid, and continue as described.


Sulfur Compounds (as SO4) To 3.0 g, add 0.2–0.5 mg of ammonium metavanadate and 10 mL of nitric acid. Digest in a covered beaker on a hot plate (~100 °C) until the reaction ceases, remove the cover, and evaporate to dryness. Add 10 mL of nitric acid, and repeat the digestion and evaporation. Add 5 mL of dilute hydrochloric acid (1:1), and evaporate to dryness. Dissolve the residue in 4 mL of water plus 1 mL of dilute hydrochloric acid (1:19), filter if necessary through a small filter, wash with two 2 mL portions of water, and dilute with water to 10 mL. Add 1 mL of 12% barium chloride reagent solution. Any turbidity should not exceed that produced by 0.06 mg of sulfate ion (SO4) treated in the same manner as the sample. Compare 10 min after adding the barium chloride to the sample and standard solutions.

Iron [Part 2: Colorimetry and Turbidimetry; Iron; Procedure for Iron, Method 1 (Ammonium Thiocyanate)]. Use 3.3 g.

Lead Dissolve 1.5 g in 10 mL of water, adjust the pH to between 9 and 10 (using a pH meter) with ammonium hydroxide, and dilute with water to 15 mL. Prepare a control containing 0.003 mg of lead and the amount of ammonium hydroxide required to neutralize the sample, and evaporate it to dryness on a hot plate (~100 °C). Moisten the residue from the control with 0.1 mL of nitric acid, dissolve in 5 mL of water, and add 5 mL of ammonium citrate (lead-free) reagent solution. Adjust the pH to between 9 and 10 (using a pH meter) with ammonium hydroxide, and dilute with water to 15 mL. Transfer the sample solution and the control solution to separatory funnels, add to each 5 mL of dithizone extraction reagent solution (in chloroform), and shake vigorously for 2 min. Let the layers separate, draw off the dithizone–chloroform layers into clean, dry comparison tubes, and dilute to 10 mL with chloroform. Any red color producing a purplish hue in the chloroform from the sample solution should not exceed that in the chloroform from the control.

Substances Carbonizable by Hot Sulfuric Acid (Tartrates, etc.) Carefully powder about 1.0 g of the sample, and take precautions to prevent contamination during the powdering. Mix 0.30 g with 10 mL of sulfuric acid in a test tube previously rinsed with the acid. Heat the mixture at 110 °C (in a brine bath) for 30 min, and keep the test tube covered during the heating. Any color should not exceed that produced in a color standard of the following composition: 1 part of cobalt chloride reagent solution, 2.4 parts of ferric chloride reagent solution, 0.4 parts of cupric sulfate reagent solution, and 6.2 parts of water.


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Citric Acid, Anhydrous, and Citric Acid, Monohydrate - ACS Publications

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