Mass Specthoscope: A Hand-held Extendable Probe for Localized Noninvasive Sampling of Skin Volatome for Online Analysis.

Human skin emits a unique set of volatile organic compounds (VOCs). These VOCs can be probed in order to obtain physiological information about the individuals. However, extracting the VOCs that emanate from human skin for analysis is troublesome and time-consuming. Therefore, we have developed "Mass Specthoscope"─a convenient tool for rapid sampling and detecting VOCs emitted by human skin. The hand-held probe with a pressurized tip and wireless button enables sampling VOCs from surfaces and their transfer to the atmospheric pressure chemical ionization source of quadrupole time-of-flight mass spectrometer. The system was characterized using chemical standards (acetone, benzaldehyde, sulcatone, α-pinene, and decanal). The limits of detection are in the range from 2.25 × 10-5 to 3.79 × 10-5 mol m-2. The system was initially tested by detecting VOCs emanating from porcine skin spiked with VOCs as well as unspiked fresh and spoiled ham. In the main test, the skin of nine healthy participants was probed with the Mass Specthoscope. The sampling regions included the armpit, forearm, and forehead. Numerous skin-related VOC signals were detected. In the final test, one participant ingested a fenugreek drink, and the participant's skin surface was probed using the Mass Specthoscope hourly during the 8 h period. The result revealed a gradual release of fenugreek-related VOCs from the skin. We believe that this analytical approach has the potential to be used in metabolomic studies and following further identification of disease biomarkers─also in noninvasive diagnostics.

Robotized Noncontact Open-Space Mapping of Volatile Organic Compounds Emanating from Solid Specimens.

Analysis of volatile organic compounds (VOCs) is normally preceded by sample homogenization and solvent extraction. This methodology does not provide spatial resolution of the analyzed VOCs in the examined matrix. Here, we present a robotized pen-shaped probe for open-space sampling and mapping of VOCs emanating from solid specimens (dubbed "PENVOC"). The system combines vacuum-assisted suction probe, mass spectrometry, and robotic handling of the probe. The VOCs are scavenged from the sample surface by a gentle hydrodynamic flow of air sustained by a vacuum pump. The sampled gas is transferred to the proximity of corona discharge in an atmospheric pressure chemical ionization source of a tandem mass spectrometer. The PENVOC has been attached to a robotic arm to enable unattended scanning of flat surfaces. The specimens can be placed away from the mass spectrometer during the scan. The robotized PENVOC has been characterized using chemical standards (benzaldehyde, limonene, 2-nonanone, and ethyl octanoate). The limits of detection are in the range from 2.33 × 10-5 to 2.68 × 10-4 mol m-2. The platform has further been used for mapping of VOCs emanating from a variety of specimens: flowers, glove exposed to smoke, fuel stains, worn medical face mask, worn clothing, cheese, ham, and fruits. The chemical maps show unique distributions of the VOCs on the scanned surfaces. Obtaining comparable results (VOC maps) using other techniques (e.g., repetitive headspace sampling prior to offline analysis) would be time-consuming. The presented mapping technique may find applications in environmental, forensic, and food science.

On-Line Coupling of Simultaneous Distillation-Extraction Using the Likens-Nickerson Apparatus with Gas Chromatography.

Simultaneous distillation-extraction (SDE) using the Likens-Nickerson apparatus is a convenient technique used to isolate volatile organic compounds (VOCs) from complex liquid matrices. The technique combines steam distillation with solvent extraction. While analytical extractions are normally followed by off-line separation/detection, it is advantageous to couple extractions on-line with separation and detection systems that are employed in the same analytical workflow. Here, we have coupled the Likens-Nickerson apparatus on-line with a gas chromatograph hyphenated with a mass spectrometer. For that purpose, we have devised an automated liquid transfer setup comprising a peristaltic pump, control unit, customized transfer vial with a drain port, and an autosampler arm to deliver liquid extract aliquots at defined time points. The on-line SDE-GC/MS system enables one to record real-time extraction profiles. These profiles reveal extraction kinetics of various VOCs present in the extracted samples. The data sets were fitted with the first order kinetic equation to obtain numeric values characterizing the extraction process (rate constants ranging from 0.21 to 0.01 min-1 for the ethyl esters from C6 to C19). A comparison of on-line and off-line results reveals that the on-line system is more dependable, while the off-line analysis leads to artifacts. To demonstrate the operation of the on-line SDE-GC/MS system, we performed analyses of selected real samples (beer). The real-time data sets revealed extraction kinetics for VOCs present in these samples. The devised extraction-analysis system allows the analysts to make an evidence-based decision on the extraction time for different groups of analytes in order to maximize extraction yield and minimize analyte losses.