Quality control methods for

General aspects of analytical methodology 
The samples should be tested as quickly as possible after collection, before any 
physical or chemical changes occur. If prolonged storage is envisaged, the 
samples should preferably be stored in air-tight containers under refrigeration. 
Light can cause degradation of many pesticides, and it is therefore advisable to 
protect the samples and any extracts or solutions from undue exposure. 
The type of container or wrapping material used should not interfere with the 
sample or affect the analytical results. 
Solvents and reagents used in the analytical method should be free from sub-
stances that may interfere with the reaction, alter the results or provoke 
degradation of the pesticide residue in the sample. It is usually necessary to 
employ specially purified solvents or to distil them freshly in an all-glass 

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Quality control methods for medicinal plant materials 
apparatus. Blank determinations with the solvents should be carried out, 
concentrating and testing them as specified in the test procedure for the plant 
material concerned. 
The simplest and quickest procedure should be used to separate unwanted 
material from the sample (clean-up procedure) in order to save time when many 
samples have to be tested. 
The process of concentrating solutions should be undertaken with great care, 
especially during the evaporation of the last traces of solvent, in order to avoid 
losses of pesticide residues. For this reason, it is often not advisable to remove 
the last traces of solvent. Agents, such as mineral oil or other oils of low 
volatility, that may help to preserve the solution could be added to retard the 
loss of the relatively volatile pesticides, especially when the last traces of solvent 
are being evaporated. However, these agents, while satisfactory in colorimetric 
procedures, are usually not desirable in gas chromatographic methods. It may 
be necessary to evaporate heat-labile compounds using a rotary vacuum 
apparatus.