Objective: The purpose of this SOP is to provide guidelines for accurately measuring the peroxide value in oil samples. Peroxide value is a crucial parameter used to assess the extent of oxidation and rancidity in oils, which affects their quality and shelf life.
Applicable Standards and References:
- AOCS Official Method Cd 8b-90 - Peroxide Value Acetic Acid-Isooctane Method
- ASTM D3702 - Standard Test Method for Hydrogen Peroxide Value of Fats and Oils
Materials and Equipment:
- Oil samples to be tested
- Acetic acid-isooctane solution (3:2 v/v)
- Potassium iodide-starch solution
- Titration apparatus (burette, pipettes, and conical flask)
- Volumetric flasks
- Magnetic stirrer and stir bars
- Glassware (beakers, test tubes, etc.)
- Weighing balance
- Distilled water
- Safety equipment (lab coat, gloves, goggles)
- Waste disposal containers
Procedure:
Preparation of Reagents:
a. Prepare the acetic acid-isooctane solution by mixing acetic acid and isooctane in a 3:2 ratio by volume. Store the solution in a labeled, tightly sealed container.
b. Prepare the potassium iodide-starch solution by dissolving potassium iodide and starch in distilled water. Mix until the solution becomes clear and store it in a dark container to avoid degradation.
Sample Preparation:
a. Ensure that oil samples are at room temperature before analysis.
b. Mix the oil samples thoroughly to ensure homogeneity.
c. Weigh accurately 5-10 grams of the oil sample using a clean and dry weighing balance.
Titration Procedure:
a. Transfer the weighed oil sample to a clean and dry conical flask.
b. Add 30 mL of the acetic acid-isooctane solution to the flask.
c. Insert a magnetic stir bar into the flask and place it on a magnetic stirrer.
d. Stir the mixture gently at room temperature for 1-2 minutes to dissolve the oil.
e. Remove the flask from the stirrer and add 0.5 mL of the potassium iodide-starch solution.
f. Immediately titrate the solution with standardized 0.01 N sodium thiosulfate (Na2S2O3) until the appearance of a pale-yellow color. This indicates the endpoint of the titration.
Calculation:
a. Calculate the peroxide value (PV) using the following formula:
PV (meq/kg) = (V * N * 56.1) / W,
where:
V = volume of sodium thiosulfate used in mL
N = normality of sodium thiosulfate
W = weight of the oil sample in grams
Reporting: Record all observations, calculations, and results in a laboratory notebook or electronic data management system. Report the peroxide value in meq/kg.
Safety Precautions:
a. Wear appropriate personal protective equipment (PPE) such as lab coats, gloves, and goggles.
b. Work in a well-ventilated area to avoid inhalation of volatile solvents.
c. Handle all chemicals with care, following their Material Safety Data Sheets (MSDS).
d. Dispose of waste and hazardous materials in designated containers according to laboratory protocols.
