Development Of A New Analytical Method For Isolation And Easier Identification Of Aldehydes By Derivatization, Solid Phase Extraction, And GC-MS Analysis Of The Derivatives

Aldehydes are a class of important components in the flavor and fragrance industry. They generally play a crucial role in contributing to the total aromas of many kinds of flavors and fragrances. In fact, aldehydes exist widely in various natural plant extracts and food flavors. For example, citrus oil often contains many aldehydes present in trace amounts, including citral, etc. On the other hand, aldehydes also make very important contributions to many kinds of meat flavors, such as pork flavor, etc. Therefore, the identification of trace aldehydes is very essential in the analytical field of the flavor and fragrance industry.However, the identification of the trace aldehydes in natural samples with complex matrices is always difficult if the sample is not pretreated and purified before analysis by GC-MS because the small peaks of trace aldehydes are often covered or interfered by the peaks of other components in GC-MS chromatogram. Consequently, it is often necessary to isolate the aldehyde components from the complex matrix before GC-MS analysissince this facilities detection and identification of the aldehyde components. Additionally, the determination of the positions of the carbon-carbon double bond in some unsaturated aldehydes may be difficult due to their non-diagnostic EI-MS spectra.In order to facilitate the identification of trace aldehydes in natural products with complex matrices, we have developed a new analytical method to achieve this goal. This new analytical method can not only isolate the aldehydes from complex matrices by means of derivatization with 1,1-dimethylhydrazine, cation exchanged solid phase extraction (SPE) and subsequent hydrolysis, but also allows more easy interpretation of the EI-MS spectra of the resulting derivatives. In our approach aldehydes are first converted into dimethylhydrazones by reaction with 1,1-dimethylhydrazine. Then, the resulting dimethyhydrazones can be isolated from the other compounds by an MCX SPE method. Finally, the original aldehydes can be recovered through the hydrolysis of the isolated dimethyhydrazones. However, the dimethylhydraoznes are also volatile enough to be directly analyzed by GC-MS. Moreover, the mass spectra of the dimethyl-hydrazones not only show obvious molecular ions but also a lot of other important fragments that are very useful for deduction of the structures of the original aldehydes. We initially proved the feasibility of the new analytical method with a model mixture containing aldehydes. The results obtained from the model mixture showed relatively high recoveries of the aldehydes (63%-89%) and successful isolation of aldehydes relative to other matrix components. We analyzed two real samples containing aldehydes, namely the extract of rosted pork fat sample and citrus oil sample, to further demonstrate the utility of this new analytical method. The results we obtained indicated that the method was successful for the easy identification of more aldehydes, compared with the results obtained from the direct GC-MS analysis. Moreover, the identification of aldehydes was also more reliable based on the diagnostic EI-MS spectra of the resulting dimethylhydrazone derivatives.This is the first report that aldehydes can be isolated from other matrix components by means of derivatization with 1,1-dimethylhydrazine combined with cation exchanged solid phase extraction (SPE) and hydrolysis.