Cyclomethicone
;)
Cyclopolydimethylsiloxane.
Cyclomethicone [69430-24-6].
»Cyclomethicone is a fully methylated cyclic siloxane containing repeating units of the formula:
[–(CH3)2SiO–]n,
in which nis 4,5,or 6,or a mixture of them.It contains not less than 98.0percent of (C2H6OSi)n,calculated as the sum of cyclomethicone 4,cyclomethicone 5,and cyclomethicone 6,and not less than 95.0percent and not more than 105.0percent of the labeled amount of any one or more of the individual cyclomethicone components.
Packaging and storage—
Preserve in tight containers.
Labeling—
Label it to state,as part of the official title,the n-value of the Cyclomethicone.Where it is a mixture of 2or 3such cyclic siloxanes,the label states the n-value and percentage of each in the mixture.
Identification—
The IRabsorption spectrum,determined in a 0.1-mm cell,exhibits maxima only at the same wavelengths as that of a similar preparation of USP Cyclomethicone 4RS,USP Cyclomethicone 5RS,or USP Cyclomethicone 6RS.
Limit of nonvolatile residue—
Evaporate 2.0g in an open,tared aluminum dish in a circulating air oven at 150
for 2hours,allow to cool in a desiccator,and weigh:the weight of the residue so obtained does not exceed 3.0mg,corresponding to not more than 0.15%(w/w).
for 2hours,allow to cool in a desiccator,and weigh:the weight of the residue so obtained does not exceed 3.0mg,corresponding to not more than 0.15%(w/w).
Assay—
The gas chromatograph is equipped with a thermal conductivity detector and a suitable recorder,and contains a 3.66-m ×3-mm column packed with 20%liquid phase G1on 60-to 80-mesh packing S1A(see Gas Chromatographyunder Chromatography á621ñ).The column is temperature-programmed at a rate of about 8per minute from 125to 320,the injection port is maintained at a temperature of about 300,and the detector block is maintained at a temperature of about 350.Helium is used as the carrier gas,flowing at a rate of about 20mLper minute.Separately inject about 1µLof USP Cyclomethicone 4RS,USP Cyclomethicone 5RS,and USP Cyclomethicone 6RSinto the gas chromatograph,record the chromatograms,and note the retention times of the peaks.Similarly inject about 1µLof Cyclomethicone,record the chromatogram,and measure the responses of the major peaks.Calculate the percentage of cyclomethicone 4,cyclomethicone 5,and cyclomethicone 6by dividing 100times the response of each peak at the retention time of the corresponding reference standard by the sum of all of the responses in the chromatogram.The percentages obtained from duplicate injections agree to within 1.0%.Calculate the percentage purity by adding the percentages of cyclomethicone 4,cyclomethicone 5,and cyclomethicone 6.
per minute from 125to 320,the injection port is maintained at a temperature of about 300,and the detector block is maintained at a temperature of about 350.Helium is used as the carrier gas,flowing at a rate of about 20mLper minute.Separately inject about 1µLof USP Cyclomethicone 4RS,USP Cyclomethicone 5RS,and USP Cyclomethicone 6RSinto the gas chromatograph,record the chromatograms,and note the retention times of the peaks.Similarly inject about 1µLof Cyclomethicone,record the chromatogram,and measure the responses of the major peaks.Calculate the percentage of cyclomethicone 4,cyclomethicone 5,and cyclomethicone 6by dividing 100times the response of each peak at the retention time of the corresponding reference standard by the sum of all of the responses in the chromatogram.The percentages obtained from duplicate injections agree to within 1.0%.Calculate the percentage purity by adding the percentages of cyclomethicone 4,cyclomethicone 5,and cyclomethicone 6.
Auxiliary Information—
Staff Liaison:Elena Gonikberg,Ph.D.,Scientist
Expert Committee:(PA4)Pharmaceutical Analysis 4
USP28–NF23Page 2994
Phone Number:1-301-816-8251