Cosmetic products such as soap, shampoo, lotions and creams are often scented with suitable compounds to improve their appeal. This application note describes an analytical method to identify the fragrance and other compounds contained within these cosmetic formulations.
Because of the solid or viscous nature of these formulations, direct sample injection into a gas chromatograph is not feasible and some form of analyte extraction is normally required. The approach taken in this work was to place a small amount of the sample in a thermal desorption tube and use an inert carrier gas to purge the volatile sample constituents into a cooled secondary trap. The secondary trap was then rapidly heated to desorb the collected components into a gas chromatographic column for separation and subsequent detection and identification by mass spectrometry.
This thermal desorption gas chromatography mass spectrometry (TD-GC-MS) technique may be fully automated using standard instrumentation and so provides a convenient and easy way of screening difficult sample matrices such as cosmetic products for constituent volatile compounds.
Approximately 120 mg of sample was placed within a glass wool plug in a PTFE thermal desorption tube insert as shown in Figure 1a. The flexible tube was squeezed to disperse liquid samples into the glass wool and so ensure an open pathway for carrier gas to flow through it.
The PTFE insert was then placed in an empty stainless steel desorption tube, as shown in Figure 1b, ready for analysis.
The following samples were examined:
Each sample tube was analyzed using TD-GC-MS under the conditions listed in Table 1.
Results and Discussion
Figure 2 shows a total ion chromatogram (TIC) obtained from the liquid soap sample. Despite the messy nature of this sample, clean chromatography has been obtained thus enabling easy data processing. The TurboMass software was used to examine the mass spectral data of each of the major components and to perform a library search to identify each of these. Figures 3, 5 and 7 show some typical mass spectra taken from the liquid soap chromatogram and Figures 4, 6 and 8 show the corresponding results from the spectral library search. Figures 9 to 15 show the total ion chromatograms, with annotated peak identities, for the remaining samples.
This note has described a simple means of identifying fragrance and other volatile compounds in cosmetic preparations without the need for tedious and lengthy sample extractions.