Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Congo Red (Direct Red 28, C.I. 22120) 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 Congo Red provides, in addition to common physical constants, a general description including typical appearance, applications, and aqueous solubility. The monograph also details the following specifications and corresponding tests for verifying that a substance meets ACS Reagent Grade specifications including: Clarity of Solution, Visual Transition Interval, and Loss on Drying.
C32H22N6O6S2Na2
Formula Wt 696.66
CAS No. 573-58-0
GENERAL DESCRIPTION Typical appearance . . . . . . . . . . . . . . . . . . . brownish-red solid Applications . . . . . . . . . . . . . . . . . . . . . . . . pH indicator; nitrogen analysis Aqueous solubility . . . . . . . . . . . . . . . . . . . . soluble
SPECIFICATIONS Clarity of solution . . . . . . . . . . . . . . . . . . . . Passes test Visual transition interval . . . . . . . . . . . . . . . . pH 3.0 (blue) to pH 5.2 (red) Maximum Allowable Loss on drying . . . . . . . . . . . . . . . . . . . . . . 3.0%
© 2017 American Chemical Society
A
DOI:10.1021/acsreagents.4100 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
TESTS Clarity of Solution Dissolve 0.10 g in 100 mL of water. Not more than a trace of turbidity or insoluble matter should remain. Reserve the solution for the test for visual transition interval.
Visual Transition Interval Dissolve 1.0 g of potassium chloride in 100 mL of water. Adjust the pH of the solution to 3.0 (using a pH meter) with 0.01 N hydrochloric acid. Add 0.15 mL of the 0.1% solution reserved from the clarity of solution test. The solution should be blue. Titrate with 0.01 N sodium hydroxide to pH 4.0. The solution should be violet. Continue the titration to pH 5.2. The solution should be red.
Loss on Drying [Part 2: Gravimetric Methods; Loss on Drying]. Use 1 g. Dry at 105 °C.
© 2017 American Chemical Society
B
DOI:10.1021/acsreagents.4100 ACS Reagent Chemicals, Part 4
