The Sincerest Form of Flattery
One of the most common ways of duplicating a fragrance is by using a technology called Gas Chromatography and Mass Spectrometry, or GC-MS for short.
This technology works by injecting a small sample of fragrance oil into a tiny capillary column, which is located in the oven of the GC. The temperature is set to rise at a steady rate, and as it does, different molecules burn off at different temperatures. In this way the relative concentrations of the different components of the fragrance are determined.
After passing through the column, the sample is then passed into the Mass Selective Detector for the Mass Spectrometry analysis. As the components of the fragrance pass into the Mass Spectrometer, they are bombarded by ions and each break apart in a unique way. This "fingerprint" is then used to identify each fragrance compound as it passes through.
By combining the data from the GC and MSD the analytical perfumers are able to identify which exact components are present in the sample as well as their approximate percentage. This procedure can provide a starting formula, but it requires the nose of the perfumer to create the exact duplication.