Propylene Glycol (PG) Testing Procedure

Propylene glycol (PG) is commonly tested using gas chromatography (GC) or high-performance liquid chromatography (HPLC). Propylene Glycol (PG) Testing Procedure and methods use separation techniques to isolate and quantify the PG from a sample, which is then measured using a detector. The choice of method depends on the specific requirements of the test, such as the sample size, level of precision, and required analysis time. Other methods, such as infrared spectroscopy (IR), can also be used but may not be as accurate as GC or HPLC. It’s recommended to consult with a specialist or refer to industry-specific standards for the best testing method for a particular application.

A step-by-step procedure for testing propylene glycol (PG) using gas chromatography (GC) is as follows:

  1. Sample Preparation: Prepare a representative sample of the material to be tested. Depending on the sample type, this may involve homogenizing, diluting, or extracting the PG.
  2. Injection: Introduce the prepared sample into the GC system. This is typically done by injecting a small aliquot of the sample into the inlet of the GC.
  3. Separation: The sample is separated into its individual components by passing it through a column packed with a stationary phase. The PG is separated from other components in the sample based on its boiling point and partitioning between the stationary and mobile phases.
  4. Detection: The separated PG is detected by the GC system’s detector, which typically measures the amount of PG in the sample based on its specific retention time and peak height.
  5. Data Analysis: The data collected by the detector is analyzed to determine the concentration of PG in the sample. This may involve comparing the sample data to a standard PG calibration curve or using software to calculate the PG concentration.
  6. Reporting: The results of the test are reported, including the concentration of PG in the sample and any relevant quality control measures such as instrument performance or sample preparation checks.


To ensure the quality of incoming raw material of Propylene Glycol.


It is applicable for the analysis of Propylene Glycol in the quality control department.


  1. Quality Control Manager
  2. Assist. Q.C. Manager
  3. Q.C Analyst


  1. SAP: Standard Analytical Procedure
  2. QC: Quality control


Propylene Glycol (PG) Testing Procedure


  1. Analytical Balance
  2. Filter Paper
  3. Glassware
  4. Hot Plate
  5. Nessler Cylinder
  6. Oven
  7. Pycnometer
  8. Refractometer
  9. Karl Fischer Titrator
  10. Water Bath


  1. Distilled Water
  2. Chloroform
  3. Ethanol
  4. Methanol
  5. Sodium Hydrogen Carbonate


  1. Potassium Iodide Solution
  2. 1M Sulphuric Acid
  3. 0.05M Sodium Thiosulphate
  4. Starch Solution
  5. 6M Ammonia Solution
  6. 0.1M Silver Nitrate
  7. Acetate Buffer Solution pH 3.5
  8. Thioacetamide Reagent
  9. Lead Standard Solution 1ppm

Physical Analysis

Test of Physical Form:

Check the sample and confirm its physical form; it should be viscous liquid, hygroscopic.

Test of Colour:

Confirm the colour of the material with naked eye; it should be clear & colourless.

Test of Solubility:

  1. Ethanol (96%): Miscible.
  2. Water: Miscible.

Acidity or Alkalinity:

To 10 ml add 40 ml of water R and 0.1 ml of bromothymol blue solution R1. The solution is greenish-yellow. Not more than 0.05 ml of 0.1 M sodium hydroxide is required to change the colour of the indicator to blue.

Refractive index:

Cool the liquid at 20oC and check its refractive index using Refractometer at 20oC.
It should be 1.431 – 1.433.


Determine the water constants of the sample (Take 5g) by Karl Fischer Titrator.
It should not be more than 0.2% of its weight.

Relative Density:

Cool the liquid and water at 20oC.
Weigh a dry pycnometer (X gm)
Fill the pycnometer with water and weigh (Y gm)
Dry and fill the same pycnometer with liquid and weigh (A gm)

Weight of Water = Y – X = A
Weight of Liquid = Z – X = B

d = ——–
d = Relative Density of Liquid when temperature of both liquid and water is 20oC.
It should be 1.035 to 1.040.

Limit Test:

Test of Oxidizing Substances:

To 10 ml add 5 ml of water, 2 ml of Potassium Iodide Solution and 2 ml of 1M Sulphuric Acid and allow to stand in a ground-glass-stoppered flask protect from light for 15 minutes. Titrate the librated iodine with 0.05M Sodium Thiosulphate VS using 1 ml of Starch Solution as indicator. Not more than 0.2 ml of 0.05M Sodium Thiosulphate VS is required.

Test of Reducing Substances:

Mix 1 ml with 1 ml of 6M Ammonia and heat in a water bath at 60o for 5 minutes; the solution is not yellow. Immediately add 0.15 ml of 0.1M Silver Nitrate; the solution does not change its appearance within 5 minutes.

Heavy Metals:

Sample Preparation:

  1. Take 3 ml of solution and dilute to 15 ml with water.
  2. To 12 ml of resulting solution.
  • Add 2 ml of acetate buffer pH 3.5 and mix.
  • Add 1.2 ml of thioacetamide reagent. Mix immediately and allow to stands for two minutes.

Standard Preparation:

  1. Mix 10 ml of 1ppm lead standard solution with 2 ml of above sample solution being examined.
  • Add 2 ml of acetate buffer pH 3.5 and mix.
  • Add 1.2 ml of thioacetamide reagent. Mix immediately and allow to stands for two minutes.


  1. Mix 10 ml of distilled water with 2 ml of prescribed solution.
  • Add 2 ml of acetate buffer pH 3.5 and mix.
  • Add 1.2 ml of thioacetamide reagent. Mix immediately and allow to stands for two minutes.


Any brown colour produced in sample is not more intense than standard. The standard solution exhibits slightly brown colour when compared to blank.

Quality Record(s)/Form(s):

  1. The following Quality Records shall be generated and managed in accordance with the Procedure for Control of Company Quality Records.

Note that this procedure may vary slightly depending on the specific GC system and method used. It’s recommended to consult the instrument manual or seek the assistance of a specialist if necessary.

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