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Table 2 Summary of the methods for determination of “loss on drying” and “water” in European Pharmacopoeia and Chinese Pharmacopoeia

From: Quality standard of traditional Chinese medicines: comparison between European Pharmacopoeia and Chinese Pharmacopoeia and recent advances

European Pharmacopoeia Chinese Pharmacopoeia
Loss on drying
 Dry the sample under the specified temperature to constant mass (Δma ≤ 0.5 mg) or for the prescribed time by one of the following procedures and calculate the difference in the mass of the sample before and after drying, expressed as a percentage (m/m):
    In a desiccator
    In vacuo
    In an oven at a specified temperature
Place about 1 g or specified amount of sample in a tared, shallow weighing bottle and dry the sample under 105 °C until constant weight (Δm ≤ 0.3 mg) except as otherwise herein provided. Calculate the loss of mass expressed as per cent
Test may also be done with desiccator with temperature control or vacuum
 Distillation with toluene (procedure similar to method 4 in Chinese Pharmacopoeia) Method 1: Karl-Fischer’s titration
Method 2: Drying in the oven (100–105 °C until Δm ≤ 5 mg)
Method 3: Drying under reduced pressure (≤ 2.67 kPa at room temperature for 24 h)
Method 4: Toluene distillation
Method 5: Gas chromatography
  1. a Δm: the difference in the mass of the sample between two consecutive weighings