Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Lactic Acid, 85% (2-Hydroxypropanoic 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 Lactic Acid, 85% 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, Substances Darkened by Sulfuric Acid, Residue after Ignition, Chloride, Sulfate, Heavy Metals, and Iron.
CH3CHOHCOOH
Formula Wt 90.08
CAS No. 50-21-5
Note: The reagent generally available is a mixture of lactic acid, CH3CHOHCOOH, and lactic acid lactate, C6H10O5.
GENERAL DESCRIPTION Typical appearance . . . . . . . . Applications . . . . . . . . . . . . . Change in state (approximate) . Aqueous solubility . . . . . . . . .
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clear, odorless, syrupy liquid clinical standard boiling point, 122 °C miscible
SPECIFICATIONS Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85.0–90.0% C3H6O3 Substances darkened by sulfuric acid . . . . . . . . Passes test
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4183 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Residue after ignition. Chloride (Cl) . . . . . . Sulfate (SO4) . . . . . . Heavy metals (as Pb) . Iron (Fe) . . . . . . . . .
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Maximum Allowable 0.02% 0.001% 0.002% 5 ppm 5 ppm
TESTS Assay (By indirect acid–base titrimetry). Weigh accurately 3 mL in a tared, glass-stoppered flask. Add 50.0 mL of 1 N sodium hydroxide volumetric solution, boil gently for 20 min, and titrate the excess alkali with 1 N sulfuric acid volumetric solution, using 0.15mL of phenolphthalein indicator solution. Correct for a blank test. One milliliter of 1 N sodium hydroxide corresponds to 0.09008 g of C3H6O3.
Substances Darkened by Sulfuric Acid Cool 5 mL of sulfuric acid to 15 °C, and transfer to a clean, dry test tube. Cool 5 mL of the sample to 15 °C, and add to the test tube in such a way as to form a distinct layer over the sulfuric acid. A dark color should not develop at the interface of the two layers within 10 min.
Residue after Ignition [Part 2: Gravimetric Methods; Residue after Ignition]. In a tared, preconditioned crucible, ignite 10 g (8 mL), and moisten the char with 1 mL of sulfuric acid. Retain the final residue for the test for iron.
Chloride [Part 2: Colorimetry and Turbidimetry; Chloride]. Dilute 12 g (10 mL) with water to 60 mL, mix, and use 5 mL of this solution. Retain the remainder of the solution for the test for sulfate.
Sulfate [Part 2: Colorimetry and Turbidimetry; Sulfate; Procedure for Sulfate, Method 1]. Use 12.5 mL of the solution prepared in the test for chloride.
Heavy Metals [Part 2: Colorimetry and Turbidimetry; Heavy Metals (as Lead); Procedure for Heavy Metals, Method 2]. Test a 4.0 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 2 mL of water and 2 mL of hydrochloric acid, and evaporate to dryness on a hot plate
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4183 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
(~100 °C). Take up the residue in 1 mL of hydrochloric acid and 20 mL of water, filter if necessary, and dilute with water to 50 mL in a volumetric flask. Use 10 mL.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4183 ACS Reagent Chemicals, Part 4
