Direct Sample Inlet Mass Spectrometry for the Determination of Volatile Organic Compounds in Vegetable Oils

Introduction: The composition of volatile organic compounds (VOCs) in agricultural products provides information about their quality. The standard approach to VOC analysis involves sample preparation and resource- and time-intensive chromatographic separation methods. Recently developed direct sample introduction mass spectrometry methods significantly accelerate and simplify analysis. One such method, proposed by the authors and named APLPI (Atmospheric Pressure Laser Plasma Ionization), stands out. The key feature of this analytical method is the analyte ionization occurring at atmospheric pressure under UV radiation from laser-induced plasma. The method's advantage lies in ion formation efficiency for VOCs exceeding that of common approaches by over an order of a half magnitude for certain compounds, with minimal dependence on the analyte's nature.​

Purpose: To investigate the feasibility of using the novel direct sample introduction mass spectrometric analysis method APLPI for determining alcohol and ketone concentrations in vegetable oils without sample preparation, target compound extraction, or chromatographic separation.​

Materials and Methods: Vegetable oil samples (olive, linseed, sunflower) purchased from local supermarkets served as research objects. All samples remained within their shelf life throughout the experiment. Mass spectra of VOCs released from oil samples were recorded using a reflectron time-of-flight mass spectrometer with orthogonal injection. Laser plasma generated by a pulsed Nd:YAG laser (wavelength 1.06 μm, pulse duration 0.5 ns) ionized the organic compounds. Volatile compounds from the oil sample vial were delivered via argon gas flow.​

Results: For the first time, a method was implemented using a direct sample introduction mass spectrometer with laser plasma radiation ionization of VOCs to determine alcohol and acetone concentrations in vegetable oil samples across the 0.4 ng/mL – 20 μg/mL range. The relative standard deviation of three parallel experiments did not exceed 5%. Measurements were performed on unprepared oil samples without chromatographic separation, with each analysis taking 200 seconds. Complex mass spectra characteristic of each oil type were recorded.​

Conclusion:  APLPI mass spectrometry with direct sample introduction, tailored for VOC analysis, eliminates concentration and chromatographic separation steps while reducing analysis time and maintaining high sensitivity. The method suits high-throughput sample measurements. The obtained complex VOC mass spectra of vegetable oils can identify oil origins and detect potential adulterations.​

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