Quality control methods for

Silica gel HF
254
 
Description. A fine, white, homogeneous powder with an average particle size of 
between 10 and 40 µm containing about 150g of a fluorescent indicator per kg 
with an optimal intensity at 254 nm. 
pH. Shake 1 g with 10 ml of carbon-dioxide-free water R for 5 minutes. Measure 
the pH potentiometrically (The international pharmacopoeia, Vol. 1, page 96); pH is 
about 7. 

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Quality control methods for medicinal plant materials 
Preparation. Suspend 30g in 60 ml of water, shaking vigorously for 30 seconds. 
Carefully coat the cleaned plates with a layer 0.25 mm thick using a spreading 
device. Allow the coated plates to dry in air. 
Separating power. Apply separately to the adsorbent layer 10 µl of 0.10 mg/ml 
solutions containing respectively indophenol blue R, sudan red G R and 
dimethyl yellow R in toluene R. Develop the plate with the same solvent over a 
distance of 10 cm. The chromatogram shows three clearly separated spots, the 
spot of indophenol blue near the point of application, that of dimethyl yellow in 
the middle of the chromatogram, and that of sudan red G between the two. 
Fluorescence. Prepare a 1.0 mg/ml solution of benzoic acid R in a mixture of 9 
volumes of 2-propanol R and 1 volume of formic acid (~1080g/l) TS. Apply to 
the adsorbent layer at 10 points of application, increasing the quantities of the 
solution from 1 µl to 10 µl. Develop the chromatogram using a mixture of 9 
volumes of 2-propanol R and 1 volume of formic acid (~1080g/l) TS. Allow the 
solvents to evaporate and examine the chromatogram in ultraviolet light at 254 
nm. The benzoic acid appears as dark spots on a fluorescent background in the 
upper third of the chromatogram for amounts of 2 µg and more.