ISO 18068:2014

Overview - ISO 18068:2014 (Cotton fibres - Sugar content - Spectrophotometry)

ISO 18068:2014 specifies a laboratory test method to determine the total sugar content in cotton fibres using spectrophotometry. The method quantifies sugars (reducing and non‑reducing) after extraction with a non‑ionic surfactant and chemical degradation to furfural derivatives. A 3,5‑dihydroxytoluene–sulfuric acid reagent acts as the colour developer to form an orange‑yellow complex measured at 425 nm. The standard is applicable to cotton fibres and provides procedures for sampling, reagents, apparatus, calibration and result reporting.

Key topics and technical requirements

• Principle: sugars are extracted from cotton with a fatty acid alkanolamide surfactant, degraded in concentrated H2SO4 to furfural derivatives, then reacted with 3,5‑dihydroxytoluene; absorbance at 425 nm is compared to a calibration curve.
• Sampling & specimen size: laboratory sample prepared per ISO 1130; minimum laboratory sample 50 g; three test portions of 2.000 g each are used.
• Calibration: stock D‑fructose standard (2.0 mg/ml) is diluted to prepare a series of standards; absorbance (minus blank) builds the calibration curve for mg/ml → percentage sugar.
• Apparatus & conditions:
  • Spectrophotometer (200–800 nm) and 1 cm cuvettes
  • Water bath maintained at (70 ± 2) °C
  • Mechanical shaker for extraction (specified amplitudes/frequencies)
  • Filters (heat‑resistant glass, pore 40–100 μm)
• Reagents: analytical-grade D‑fructose, 3,5‑dihydroxytoluene, sulfuric acid (1.84 g/ml), and fatty acid alkanolamide (extraction and determination concentrations provided).
• Calculation & reporting: results expressed as percentage of sugars (formula specified), mean of three determinations, and full test-report requirements (reference to ISO 18068, dates, sample description, calibration range, deviations).

Practical applications and who uses it

• Textile testing laboratories use ISO 18068 to monitor cotton fibre quality and to detect elevated sugar levels that can cause storage mildew, fibre metamorphism, or problems during spinning (twining, breakage, lower yarn quality).
• Cotton growers & brokers may test batches to support quality specifications.
• Spinners and textile manufacturers can apply the method for incoming fibre acceptance and process troubleshooting.
• Research institutions studying fibre chemistry or improving pretreatment and storage methods.

Keywords: ISO 18068, cotton fibres sugar content, spectrophotometry, 3,5‑dihydroxytoluene, sulfuric acid, D‑fructose calibration, textile testing.

Related standards

• ISO 139:2005 - standard atmospheres for conditioning and testing
• ISO 1130:1975 - textile fibre sampling methods
• ISO 3696:1987 - water for analytical laboratory use
• ISO 4793:1980 - laboratory sintered filters

This standard provides a reproducible, spectrophotometric procedure to quantify sugars in cotton, supporting quality control and process optimization across the textile supply chain.