Overview
ISO 4735:2002 specifies a laboratory method for determining the CD value of essential oils of Citrus using ultraviolet (UV) spectrometric analysis. The standard defines how to prepare an ethanolic solution of a citrus oil, record its UV absorbance curve in the 220–440 nm range, and calculate the CD value (expressed in absorbance units per gram). The method is intended for quality control, characterization and specification of citrus essential oils.
Key topics and requirements
- Scope: Measurement of the CD value for citrus essential oils by UV spectrometry.
- Wavelength range: Record absorbance between 220 nm and 440 nm using an appropriate UV spectrometer.
- Reagent: Ethanol, 95% (spectrometric grade); the standard requires high UV transmittance (minimum specified at 210 nm).
- Apparatus:
- UV spectrometer suitable for 220–440 nm,
- Quartz cells (optical path length 1 cm),
- One-mark volumetric flasks (100 ml) and pipettes compliant with ISO glassware standards,
- High-precision analytical balance.
- Sample preparation: Prepare test samples according to ISO 356 and dissolve the weighed test portion in ethanol in a 100 ml volumetric flask.
- Measurement procedure:
- Use ethanol as the reference (blank) and record the absorbance curve.
- Identify the CD segment on the absorbance curve by applying the tangent/parallel construction described in the standard (points A, B, C, D, E on the curve).
- The CD value is calculated from the measured segment and the mass of the test portion and is reported to two decimal places in absorbance units per gram.
- Reporting: Include full sample identification, sampling method (if known), the test method reference, any non‑standard operating details, incidents affecting results, and the measured value(s).
Applications and who uses it
- Essential oil producers and processors use ISO 4735 to characterize citrus oils for quality control and batch release.
- Analytical laboratories performing compositional and purity testing of citrus essential oils.
- Flavor and fragrance manufacturers who need standard measurements to specify raw materials and ensure consistency.
- Regulatory bodies and standards organizations referencing reproducible methods for product specifications.
Practical benefits: provides a standardized UV spectrometric procedure to compare CD values across laboratories, aiding product specification, adulteration detection and quality assurance.
Related standards
- ISO 356 - Preparation of test samples (essential oils)
- ISO 212 - Sampling of essential oils (recommended)
- ISO 1042 - One-mark volumetric flasks
- ISO 648 - One-mark pipettes
Keywords: ISO 4735, CD value, citrus oils, essential oils, ultraviolet spectrometric analysis, UV spectrometry, absorbance, citrus essential oil testing.