Direct analysis of volatile organic compounds in foods by headspace extraction atmospheric pressure chemical ionisation mass spectrometry.

RATIONALE: The rapid screening of volatile organic compounds (VOCs) by direct analysis has potential applications in the areas of food and flavour science. Currently, the technique of choice for VOC analysis is gas chromatography/mass spectrometry (GC/MS). However, the long chromatographic run times and elaborate sample preparation associated with this technique have led a movement towards direct analysis techniques, such as selected ion flow tube mass spectrometry (SIFT-MS), proton transfer reaction mass spectrometry (PTR-MS) and electronic noses. The work presented here describes the design and construction of a Venturi jet-pump-based modification for a compact mass spectrometer which enables the direct introduction of volatiles for qualitative and quantitative analysis. METHODS: Volatile organic compounds were extracted from the headspace of heated vials into the atmospheric pressure chemical ionization source of a quadrupole mass spectrometer using a Venturi pump. Samples were analysed directly with no prior sample preparation. Principal component analysis (PCA) was used to differentiate between different classes of samples. RESULTS: The interface is shown to be able to routinely detect problem analytes such as fatty acids and biogenic amines without the requirement of a derivatisation step, and is shown to be able to discriminate between four different varieties of cheese with good intra and inter-day reproducibility using an unsupervised PCA model. Quantitative analysis is demonstrated using indole standards with limits of detection and quantification of 0.395 µg/mL and 1.316 µg/mL, respectively. CONCLUSIONS: The described methodology can routinely detect highly reactive analytes such as volatile fatty acids and diamines without the need for a derivatisation step or lengthy chromatographic separations. The capability of the system was demonstrated by discriminating between different varieties of cheese and monitoring the spoilage of meats.

Evaluation of an isotope dilution liquid chromatography tandem mass spectrometry method for pharmaceuticals in fish.

An isotope dilution liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was successfully developed and applied for analysis of 15 pharmaceuticals and 2 pharmaceutically active metabolites in fish tissues. This method relied on electrospray ionization (ESI), for which the influence of sample matrix on analyte ionization efficiencies remains a persistent challenge to environmental analysis. Statistically derived method detection limits (MDLs) for most analytes ranged from 1 to 10 ng/g, independent of sample matrix, and were as low as 0.04 ng/g for the most sensitive compounds in fillet tissue. MDLs for fish fillets were determined for both 10 µL and 100 µL injection volumes; however, results showed that detection limits did not scale linearly with injection volume. Direct comparison of spike recoveries from fish liver demonstrated that isotope dilution was superior to matrix-matched calibration in compensating for matrix interference. Spike recoveries for the isotope dilution approach generally ranged from 91 to 112%, independent of tissue (i.e., fillet or liver). The developed method was applied to examine target analytes in brown trout (Salmo trutta), collected upstream and downstream from a municipal effluent discharge to East Canyon Creek, Park City, UT, USA. Though no pharmaceuticals were detected in fish samples from the upstream location, 3 and 10 compounds (out of 17 target analytes) were detected in fish fillet and liver samples, respectively, from the downstream sampling site. Pharmaceuticals in fish fillets were observed at concentrations ranging from 0.14 to 12 ng/g, while levels were markedly higher in liver tissues (range: 0.27-600 ng/g).