Quality control methods for

Preparation of standard stain 
Add 10 ml of stannated hydrochloric acid (~250g/l) AsTS and 1 ml of dilute 
arsenic AsTS to 50 ml of water. The resulting solution, when treated as described 
in the general test, yields a stain on mercuric bromide paper AsR referred to as 
the standard stain (10 µg of As). 
Limit test for cadmium and lead 
The method of determination is left to the analyst. Nevertheless, the 
determination must be consistent and sensitive enough to allow comparison 
with a reference material. 

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Quality control methods for medicinal plant materials 
Recommended procedure 
 
Apparatus 
The equipment consists of a digestion vessel, consisting of a vitreous silica 
crucible (DIN 12904), "tall form", height 62mm, diameter 50mm, capacity 75ml, 
with a vitreous silica cover. 
Materials used are: 
- 
digestion mixture: 2 parts by weight of nitric acid (~1000g/l) TS and 1 part 
by weight of perchloric acid (~1170g/l) TS. 
- 
reference materials: olive leaves (Olea europaea)
1
 and hay powder
2
. 
Clean scrupulously with nitric acid (~1000g/l) TS the digestion vessel and all 
other equipment to be used for the determination, rinse thoroughly several 
times with water and dry at 120°C. 
Preparation of the sample 
For the wet digestion method in an open system, place 200-250mg of air-dried 
plant material, accurately weighed, finely cut and homogeneously mixed, into a 
cleaned silica crucible. Add 1.0ml of the digestion mixture, cover the crucible 
without exerting pressure and place it in an oven with a controlled temperature 
and time regulator (computer-controlled, if available). 
Heat slowly to 100°C and maintain at this temperature for up to 3 hours; then 
heat to 120°C and maintain at this temperature for 2 hours. Raise the 
temperature very slowly to 240°C, avoiding losses due to possible violent 
reactions especially in the temperature range of 160-200°C, and maintain at this 
temperature for 4 hours. Dissolve the remaining dry inorganic residue in 2.5 ml 
of nitric acid (~1000g/l) TS and use for the determination of heavy metals. 
Every sample should be tested in parallel with a blank. 
Method 
The contents of lead and cadmium may be determined by inverse voltametry or 
by atomic absorption spectrophotometry. 
The following maximum amounts in dried plant materials, which are based on 
the ADI values, are proposed: 
- 
lead, 10 mg/kg; 
- 
cadmium, 0.3 mg/kg. 
1
BCR reference material CRM No. 62 Community Bureau of Reference, obtainable from BCR, 
Directorate-General X11, Commission of the European Communities, 200 rue de la Loi, B-1049 
Brussels, Belgium. 
2
Obtainable from IAEA/V-10, International Atomic Energy Agency, Analytical Quality Control 
Services, Laboratory Geibersdorf, P.O. Box 1'00, A-Vienna, Austria.

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Quality control methods for medicinal plant materials