Edition: BP 2025 (Ph. Eur. 11.6 update)
Action and use
Organophosphorus insecticide.
DEFINITION
Malathion Shampoo contains Malathion in a suitable vehicle.
The shampoo complies with the requirements stated under Liquids for Cutaneous Application and with the following requirements.
Content of malathion, C10H19O6PS2
95.0 to 105.0% of the stated amount.
IDENTIFICATION
In the Assay, the chromatogram obtained with solution (1) shows a peak with the same retention time as that of the principal peak in the chromatogram obtained with solution (2).
TESTS
Related substances
Carry out the method for liquid chromatography, Appendix III D, using the following solutions in a mixture of 1 volume of water and 3 volumes of acetonitrile (solvent A).
(1) Dilute a quantity of the preparation being examined with sufficient solvent A to produce a solution containing 0.2% w/v of Malathion.
(2) Dilute 1 volume of solution (1) to 500 volumes.
(3) 0.0002% w/v each of malathion impurity A EPCRS and malathion impurity B EPCRS.
CHROMATOGRAPHIC CONDITIONS
(a) Use a stainless steel column (15 cm × 4.6 mm) packed with octadecylsilyl silica gel for chromatography (10 µm) (Nucleosil C18 is suitable).
(b) Use isocratic elution and the mobile phase described below.
(c) Use a flow rate of 1 mL per minute.
(d) Use a column temperature 35°.
(e) Use a detection wavelength of 210 nm.
(f) Inject 20 µL of each solution.
MOBILE PHASE
45 volumes of acetonitrile and 55 volumes of water.
When the chromatograms are recorded under the prescribed conditions, the relative retentions with reference to Malathion (retention time = about 16 minutes) are: impurity B = about 0.2 and impurity A = about 0.3.
SYSTEM SUITABILITY
The test is not valid unless, in the chromatogram obtained with solution (3), the resolution factor between the peaks due to impurity A and impurity B is at least 2.0.
LIMITS
In the chromatogram obtained with solution (1):
the area of any peak corresponding to malathion impurity A is not greater than three times the area of the corresponding peak in the chromatogram obtained with solution (3) (0.3%);
the area of any peak corresponding to malathion impurity B is not greater than the area of the corresponding peak in the chromatogram obtained with solution (3) (0.1%);
the area of any other secondary peak is not greater than the area of the principal peak in the chromatogram obtained with solution (2) (0.2%);
the sum of the areas of any other secondary peaks is not greater than five times the area of the principal peak in the chromatogram obtained with solution (2) (1.0%).
Disregard any peak with an area less than half the area of the principal peak in the chromatogram obtained with solution (3) (0.1%).
ASSAY
Carry out the method for liquid chromatography, Appendix III D, using the following solutions in a mixture of 1 volume of water and 3 volumes of acetonitrile (solvent B).
(1) Dilute a quantity of the preparation being examined with sufficient solvent B to produce a solution containing 0.2% w/v of Malathion.
(2) 0.2% w/v of malathion EPCRS.
(3) 0.0002% w/v each of malathion impurity A EPCRS and malathion impurity B EPCRS.
CHROMATOGRAPHIC CONDITIONS
The chromatographic conditions described under Related substances may be used.
SYSTEM SUITABILITY
The test is not valid unless, in the chromatogram obtained with solution (3), the resolution factor between the peaks due to impurity A and impurity B is at least 2.0.
DETERMINATION OF CONTENT
Calculate the content of C10H19O6PS2 using the declared content of C10H19O6PS2 in malathion EPCRS.
STORAGE
Malathion Shampoo should be stored in an airtight container, protected from light.
IMPURITIES
The impurities limited by the requirements of this monograph include those listed under Malathion.
