Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Ascorbic Acid 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 Ascorbic Acid 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, Specific Rotation, Residue after Ignition, Heavy Metals, and Iron.
C6H8O6
Formula Wt 176.12
CAS No. 50-81-7
GENERAL DESCRIPTION Typical appearance . . . . . . . . Applications . . . . . . . . . . . . . Change in state (approximate) . Aqueous solubility . . . . . . . . .
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white solid antioxidant melting point, 191 °C with decomposition 30 g in 100 mL at 25 °C
SPECIFICATIONS Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . ≥99.0% C6H8O6 Specific rotation [α]25°D . . . . . . . . . . . . . . . . +21.0° ± 0.5°
© 2017 American Chemical Society
A
DOI:10.1021/acsreagents.4042 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Maximum Allowable Residue after ignition. . . . . . . . . . . . . . . . . . 0.1% Heavy metals (by ICP–OES) . . . . . . . . . . . . . . 0.002% Iron (Fe) . . . . . . . . . . . . . . . . . . . . . . . . . . 0.001%
TESTS Assay (By oxidation–reduction titration). Weigh accurately 0.4 g, and in a conical flask, dissolve in a mixture of 100 mL of water (made oxygen-free by bubbling nitrogen gas through it) and 25 mL of 10% sulfuric acid. Nitrogen gas used in this procedure must be of a high purity grade. Swirl and titrate immediately with 0.1 N iodine, adding 3 mL of starch indicator near the end of the titration. One milliliter of 0.1 N iodine corresponds to 0.008806 g of C6H8O6.
Specific Rotation [Part 2: Measurement of Physical Properties; Specific Rotation]. Weigh accurately about 10 g, dissolve in 90 mL of oxygen free water in a 100 mL volumetric flask, and dilute with water to volume. Adjust the temperature of the solution to 25 °C. Observe the optical rotation in a polarimeter at 25 °C using the sodium line, and calculate the specific rotation.
Residue after Ignition [Part 2: Gravimetric Methods; Residue after Ignition]. Ignite 1.0 g in a tared, preconditioned crucible. Moisten the char with 1 mL of sulfuric acid. Retain the residue for the test for iron.
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 2.0 g sample.
Iron [Part 2: Colorimetry and Turbidimetry; Iron; Procedure for Iron, Method 1 (Ammonium Thiocyanate)]. To the residue from the test for residue after ignition, add 3 mL of dilute hydrochloric acid (1:1) and 0.10 mL of nitric acid, cover with a watch glass, and digest on a hot plate (~100 °C) for 15–20 min. Remove the watch glass, and evaporate to dryness. Dissolve the residue in a mixture of 2 mL of hydrochloric acid and 10 mL of water, dilute with water to 50 mL, and use without further acidification.
© 2017 American Chemical Society
B
DOI:10.1021/acsreagents.4042 ACS Reagent Chemicals, Part 4
