There are two important advantages that gas chromatography (GC) maintains over liquid chromatography, and they are high resolution and high sensitivity. The gas chromatograph can be more readily associated with other spectroscopic techniques without using involved interfaces and thus can easily provide unambiguous solute identification. However, it must be remembered that unless the components of a mixture are reasonably volatile (and derivatization has its limits) they cannot be separated by GC. This leaves the vast majority of separation problems to be solved by liquid chromatography, particularly in the areas of natural products and biotechnology. Until the advent of GC the analysis of essential oils was extremely difficult. Only the major components of the oils could be separated, and this was usually achieved by distillation with high efficiency columns. Due to their high sensitivity and resolution, spectroscopic and chromatographic techniques have played a particularly important part in providing analytical data.