Overview
ISO 4876:1980 specifies a standardized analytical method for the determination of maleic hydrazide residues in tobacco and tobacco products. The method is based on reduction of maleic hydrazide to hydrazine by nascent hydrogen (granulated zinc), steam distillation of the liberated hydrazine and spectrophotometric measurement of the yellow complex formed with 4-dimethylaminobenzaldehyde. The standard also covers residues from maleic hydrazide sucker-control agents used on tobacco crops and provides optional clean-up procedures in Annex A and distillation notes in Annex B.
Key Topics
- Principle: Alkaline digestion, zinc reduction to succinic hydrazide/hydrazine, steam distillation and spectrophotometric detection of the hydrazine–4-dimethylaminobenzaldehyde complex.
- Sample preparation: Grind sample to pass a 2 mm mesh; typical test portion is 1 g (weighed to 0.01 g).
- Reagents & apparatus: Analytical-grade reagents including 4-dimethylaminobenzaldehyde reagent, sodium hydroxide solutions, iron(II) chloride, and specified volumetric glassware. A steam distillation apparatus and a spectrophotometer capable of 425, 455 and 485 nm measurements are required.
- Measurement & calibration: Distillate is reacted with 4-dimethylaminobenzaldehyde, and absorbances at 425, 455 and 485 nm are used to calculate a corrected absorbance. Calibration is prepared by fortifying tobacco with known maleic hydrazide aliquots (0–80 µg range) and constructing a calibration curve.
- Quality & repeatability: Duplicate determinations are performed; repeatability limits are provided in the standard (difference not to exceed 5% of mean when >10 µg/g, or 1 µg/g when
