ASTM D7637 Determination of Glycerin Assay by Titration

ASTM D7637 test method determines the glycerin quantity by titration with sodium meta periodate. This test method can be applied for all glycerin or glycerin/water mixtures ˃75%. This method includes the cold oxidation of glycerol in the acidic medium. The final results of this test method are expressed in SI units.

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ASTM D7637 Determination of Glycerin Assay by Titration

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Overview
Scope, Applications, and Benefits
Test Process
Specifications
Instrumentation
Results and Deliverables

Overview

The ASTM D7637 glycerin assay is a standardized method for determining the content of crude and refined glycerin samples using periodic acid titration to measure the total concentration of glycerol in a sample by quantifying the periodate ion consumed by the hydroxyl groups in glycerin molecules. The ASTM D7637 process establishes methods for sample preparation and calculations to ensure accurate determination of glycerin purity and assay concentration across different samples.

Scope, Applications, and Benefits

Scope

ASTM D7637 determines glycerin assay concentration by reacting glycerin specimens with excess periodic acid and back-titrating the remaining periodate with sodium arsenite or sodium thiosulfate, measuring the moles of periodate consumed by the glycerin hydroxyl groups and calculating glycerin concentration from stoichiometric relationships between the titrant consumption and glycerol content.

ASTM D7637 glycerin assay testing evaluates:

Glycerin assay concentration and purity in crude, refined, and distilled glycerin grades
Periodate consumption measurements for calculating total glycerol content in glycerin samples
Compliance with minimum glycerin purity requirements for pharmaceutical, food, and industrial specifications
Comparative glycerin content across feedstock sources, production batches, and refining conditions
Process efficiency assessment for glycerin recovery and purification operations in biodiesel and oleochemical production

Applications

Crude and refined glycerin produced from biodiesel transesterification requires purity assay verification.
Pharmaceutical-grade and USP glycerin requiring glycerin content confirmation against compendial limits
Food-grade glycerin requires purity characterization for ingredient approval and supplier qualification
Oleochemical and soap-manufacturing glycerin requires content analysis for process quality control
Glycerin producers, biodiesel refiners, and specialty chemical suppliers requiring ASTM D7637 assay data

Benefits

Provides reliable glycerin assay concentration data for product release and specification compliance
Supports glycerin supplier qualification and incoming material verification programs
Identifies off-specification glycerin batches before formulation, blending, or further processing
Delivers traceable titration records for regulatory submissions and quality management systems
Reduces process and product risk by confirming glycerin purity early in production and distribution

Test Process

Sample Preparation

Glycerin specimens weighed and dissolved to defined concentration per ASTM D7637 preparation requirements.

Periodic Acid Oxidation

Prepared sample reacted with excess periodic acid solution for defined reaction period at controlled temperature.

Back Titration

Remaining periodate determined by back-titration with standardized sodium arsenite or sodium thiosulfate solution to endpoint.

Data Analysis & Reporting

Glycerin assay concentration calculated from titrant volume consumed and assessed against specification criteria for compliance result.

Technical Specifications

Parameter	Details
Applicable Materials	Crude glycerin, refined glycerin, distilled glycerin, USP glycerin, food-grade glycerin, and oleochemical glycerin streams
Measurement Technique	Periodic acid oxidation with back-titration using standardized sodium arsenite or sodium thiosulfate titrant
Titration Method	Volumetric back-titration with starch indicator endpoint detection per ASTM D7637 procedure
Glycerin Concentration Range	Applicable across crude glycerin (~40–80% glycerol) through refined and distilled glycerin (≥95–99.7% glycerol) grades
Measured Outputs	Periodate consumption volume, calculated glycerin assay percentage, and test compliance result

Instrumentation Used for Testing

Analytical balance for precise specimen weighing per ASTM D7637 sample preparation requirements
Calibrated volumetric burette for standardized back-titration of remaining periodate
Standardized periodic acid reagent solution for controlled glycerin oxidation reaction
Standardized sodium arsenite or sodium thiosulfate titrant for back-titration endpoint determination
Starch indicator solution for visual endpoint detection during titration
Temperature-controlled reaction vessel for the periodic acid oxidation step
Data recording and calculation system for glycerin assay concentration determination

Results and Deliverables

Titrant volume consumption data and calculated glycerin assay concentration for all tested specimens
Glycerin purity percentage expressed on an as-received and/or anhydrous basis per ASTM D7637 calculation requirements
Repeatability and reproducibility assessment for replicate titration measurements per ASTM D7637 precision criteria
Test compliance result assessed against the minimum glycerin content requirements per applicable specification
ASTM D7637 glycerin assay titration report

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Frequently Asked Questions

ASTM D7637 is the standardized periodic acid back-titration method for determining glycerin concentration in crude and refined glycerin samples — quantifying glycerol content by measuring periodate consumption during oxidation and calculating glycerin assay percentage from stoichiometric titrant relationships.

ASTM D7637 evaluates crude glycerin from biodiesel transesterification, refined and distilled glycerin, pharmaceutical-grade and USP glycerin, food-grade glycerin, and oleochemical glycerin streams — providing glycerin assay concentration data across all grades requiring purity characterization and specification compliance verification.

ASTM D7637 calculates glycerin assay by determining the moles of periodic acid consumed during glycerin oxidation from the back-titration volume difference between the blank and sample titrations — converting periodate consumption to glycerol mass using stoichiometric molar relationships and expressing the result as glycerin percentage on an as-received or anhydrous basis.

Glycerin purity directly affects downstream product quality in pharmaceutical formulations, food applications, and biodiesel co-product marketing — making accurate glycerin assay testing essential for confirming that glycerin streams meet minimum purity specifications, supporting product release decisions, and verifying supplier material quality before acceptance.

ASTM D7637 glycerin assay testing is commonly required by glycerin procurement specifications, biodiesel co-product standards, and pharmaceutical supplier qualification programs for glycerin materials requiring documented purity assay data. Always confirm specific requirements against your applicable glycerin grade specification and procurement quality standard.