The use of fragrances to generate pleasant and attractive smells in human bodies goes back thousands of years. These sample-types may be characterized by a considerable degree of complexity, as the number of natural and synthetic perfume formulation constituents in use is extremely high.¹ The relationship between contact allergy and perfume ingredients has been widely discussed.² Under a European regulation called the 7th Amendment of the Cosmetic Directive the twenty-six most frequently recognized skin allergens must be labelled on the final cosmetic product if specific concentrations are reached: 10 mg/L and 100 mg/L in "leave-on" and "rinse-off" substances respectively. Twenty-four of the twenty-six skin sensitizors are volatile and can, therefore, be analysed by GC.

Recently, a sample classification for the analysis of skin sensitizors was introduced: perfumes were included in class II, considering their medium to high complexity (commonly containing more than a hundred analytes). In these cases, a monodimensional gas chromatography (GC) application could be sufficient for satisfactory analyte determination. Whenever the complexity of a class II matrix exceeds the peak capacity of a single capillary column, then a multidimensional method must be used.³

Comprehensive multidimensional gas chromatography (GC×GC) has been used for the analysis of complex perfumes.^3,4 It was demonstrated that a single peak eluting from the primary column consisted of eight overlapping components.⁴ In such a situation, the reliable determination of a fragrance ingredient by using any of the most common gas chromatogrpahy mass spectrometry (GC–MS) approaches — such as full scan monitoring, multi-ion chromatogram (MIC), single ion monitoring (SIM) or peak deconvolution — is an arduous task. Classical MDGC has also been used for the analysis of allergens contained in a fragrance.³ The target analytes were freed from co-eluting compounds through two 1 min heart cuts, performed on the perfume. The extensive degree of overlapping was evident in the second dimension chromatogram.

The research described in this article focuses on the use of an innovative valveless MDGC–MS system for the analysis of allergens in a complex perfume. The transfer device, which achieves two-dimensional (2D) analysis by pressure tuning at the column conjunction point, is simple to use and enables the transfer of multiple fractions during each application. Fourteen cuts were performed on the sample, with time windows determined using linear retention indices (LRIs).

Experimental

Sample and standard compounds: A commercial perfume was purchased from a local store in Messina, Italy. Amyl cinnamaldehyde, anisyl alcohol, benzyl alcohol, benzyl cinnamate, methyl 2-octynoate, citral, cinnamaldehyde, benzyl benzoate, benzyl salicylate, cinnamyl alcohol, amyl cinnamyl alcohol, coumarin, eugenol, isoeugenol, farnesol (four isomers with the Z,E and E,E isomers predominant), citronellol, geraniol, hydroxycitronellal, hexyl cinnamaldehyde, limonene, α-isomethylionone, lilial, linalool, lyral and and 1,4-dibromobenzene — the internal standard (IS) — were purchased from Sigma–Aldrich (Milan, Italy). The purity of each standard was verified and was accounted for prior to use, using GC–MS. A stock allergen solution (10000 mg/L) was prepared in ethanol and used for calibration purposes. Solutions containing all the 24 allergens were injected at different concentrations (from 1–10000 mg/L) considering their original purity.

A 1000 mg/L n-alkane mix (C₇–C₃₀) was purchased from Supelco (Bellefonte, Philadelphia, USA).

Instrumentation and operational conditions: The Shimadzu MDGC system consisted of two GC–2010 gas chromatographs (defined as GC 1 and GC 2), an MS-QP2010 quadrupole mass spectrometer and an AOC-20i autosampler (Shimadzu Corporation, Kyoto, Japan). GC 1 presents a split/splitless injector and a flame ionization detector (FID), while GC 2 presents a split/splitless injector (not used for MDGC analysis), a FID (not used for for this application) and a rapid scanning quadrupole mass spectrometer. The MDGC transfer device, located in GC 1, is connected to an advanced pressure control (APC) unit which supplies carrier gas (He), at constant pressure.