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THE PHARMA REVIEW (FEBRUARY - MARCH, 2008)

Gas Chromatographic Determination of Methanol and Isopropyl
Alcohol Impurities in Herbal Extracts

S. B. Puranik, Varun R. Pawar, Lalitha N, P. N. Sanjay Pai, G. K.Rao

Abstract: Residual solvents in herbal extracts were monitored using gas chromatography (GC) with Flame Ionisation detector (FID). As per GMP, measuring residual solvents is mandatory. It is now possible to take advantage of GC equipment with faster temperature ramping capabilities, in combination with shorter capillary GC columns, to achieve considerable gain in efficiency and reduction in analysis time. In the present study Gas chromatographic method for the determination of methanol and isopropyl alcohol at residual levels in herbal extracts was developed using a flame ionization detector and the separation was carried out on BP 624 column (30m X 0.53mm i.d. X 0.25µm coating thickness), using GC 17 A shimadzu, with nitrogen as carrier gas in the split mode by direct injection method. The retention time for standard methanol and isopropyl alcohol was found to be 3.095 and 4.097 respectively. The linearity for methanol and Isopropyl alcohol was found to be in the range of 10-400 µLmL-1 and 1-240 µLmL-1 respectively. The method was validated according to ICH guidelines. The method described is simple, sensitive, rugged, reliable and reproducible for the quantitation of methanol and isopropyl levels from herbal extracts and their levels are found to be within the ICH limits.

Introduction: Herbal extract1 is a liquid extract of herbs, dried or fresh herbs are combined with solvent, and then the solid matter is removed leaving only the required active constituents of the herbs mixed in the solvent. Herbal extracts are sold as dietary supplements and alternative medicine. The active constituents in the herbs are extracted by using various solvents methanol, isopropyl alcohol, acetone, toluene, butanol, dichloromethane etc. These solvents cannot be completely removed by practical processes such as freeze drying and drying at higher temperature under vaccum. The fraction of solvents always remains with the extract and are referred as residual solvents or organic volatile impurities. The residual solvents have no therapeutic benefits and are toxic and hazardous to human health. ICH has prescribed the limits for the solvents in herbal extracts and formulations. The content of residual solvents in herbal extracts is routinely measured by gas chromatography. Routine GC applications include analysis of herbal extracts to comply to good laboratory and good manufacturing practices as well as in process testing of residual solvents to optimize drying procedure. Over the last decade, several GC methods to monitor residual solvents have been reported in the literature. For the said purpose, method has been developed and validated for detection and quantification of residual solvents methanol, isopropyl alcohol in herbal extracts of Momardica charentia, Morinda Citrifolia, Rosemary, Curcumin, Green tea, Gymnema, Phyllantus niruri.

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