ISO 9289:1991

Overview

ISO 9289:1991 specifies a precise analytical method for the determination of free residual hexane in oilseed residues following extraction with hydrocarbon-based solvents. This standard ensures consistent and accurate measurement of hexane volatile content, critical for quality control and safety in the edible oil industry. It provides detailed instructions covering the principle, reagents, apparatus, sampling, test procedure, and result reporting.

Free residual hexane refers to the portion of hexane that can be desorbed from oilseed residues by direct heating at 80 °C without prior humidification. This measurement is distinct from total residual hexane and reflects the immediate volatile hexane content after extraction processes using solvents like technical hexane or n-hexane.

Key Topics

• Scope and Definition
  The standard focuses on quantifying volatile free hexane residues in oilseed cakes and meals resulting from solvent extraction. Free residual hexane is expressed as mg of n-hexane per kg of sample.

• Reagents and Materials

  • Technical hexane or light petroleum solvent similar to industrial extraction mixtures.
  • Internal standards such as cyclohexane or n-heptane.
  • Carrier gases free of oxygen and impurities, including hydrogen, nitrogen, or helium.

• Apparatus Requirements

  • Gas chromatograph with flame ionization detector (FID).
  • Heating bath maintained at 80 ± 2 °C for hexane desorption.
  • Gas syringes, septum flasks, crimping pliers, and inert septa.

• Sample Handling and Storage
  Sampling follows ISO 5500 protocols, emphasizing prevention of hexane loss. Samples must be stored airtight at 4 °C, preferably in hermetically sealed metal containers.

• Method Principle and Procedure
  Hexane is desorbed by heating the oilseed residue at 80 °C in sealed flasks, and the volatile hexane vapors are analyzed via gas chromatography. Calibration uses oilseed residues with known low hexane content spiked with measured solvent volumes.

• Data Processing and Results Expression
  The free residual hexane content is calculated using chromatographic peak areas, internal standard amounts, and calibration factors, ensuring accuracy in reporting mg/kg hexane values.

• Precision and Repeatability
  The standard includes inter-laboratory test data demonstrating reproducibility and repeatability with specified coefficients of variation, vital to laboratory quality assurance.

Applications

• Agricultural and Food Industry:
  Used by edible oil producers and quality control laboratories to monitor residual solvents in oilseed meals ensuring regulatory compliance and product safety.

• Environmental and Safety Testing:
  Helps evaluate hexane emissions and residual solvent safety levels in by-products of oil extraction plants.

• Research and Development:
  Facilitates studies on solvent extraction efficiency and the impact of processing variables on residual hexane levels.

• Regulatory Compliance:
  Supports adherence to international regulations limiting solvent residues in food and feed products.

Related Standards

• ISO 5500:1986 - Oilseed residues sampling methods, vital for ensuring representative sampling for hexane analysis.
• ISO 8892:1987 - Determination of total residual hexane content, complementary to free residual hexane measurement.
• ISO 5725:1986 - Guidelines on precision of test methods, including repeatability and reproducibility evaluation.

Understanding and implementing ISO 9289:1991 enhances the consistency of hexane residue testing in oilseed processing, promoting food safety and quality assurance across international markets.