Since the molecule has a hydroxyl (-OH) group, it is frequently bound to other lipids including fatty acids; most analytical methods, therefore, utilise a strong alkali (KOH or NaOH) to saponify the ester linkages. Typical extraction solvents include 6% KOH in methanol. The free sterols and stanols (saturated sterols) are then separated from the polar lipids by partitioning into a less polar solvent such as hexane. Prior to analysis, the hydroxyl group is frequently derivatised with BSTFA (bis-trimethyl silyl trifluoroacetamide) to replace the hydrogen with the less exchangeable trimethylsilyl (TMS) group. Instrumental analysis is frequently conducted on gas chromatograph (GC) with either a flame ionisation detector (FID) or mass spectrometer (MS). The mass spectrum for 5β-coprostanol - TMS ether can be seen in the figure. Alternatively, liquid-chromatography mass spectrometry (LC-MS) techniques that employ atmospheric pressure chemical ionization (APCI) may also be employed to detect coprostanol under positive mode.<br />