Browsing by Author "Chang, Cheng-Hao"

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Automated Dual-Chamber Sampling System to Follow Dynamics of Volatile Organic Compounds Emitted by Biological Specimens
(2018-12-04)
Chang, Cheng-Hao
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Urban, Pawel L.
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應用化學系
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Department of Applied Chemistry
Growth of microorganisms is often accompanied by the release of volatile organic compounds (VOCs). The released VOCs may qualitatively or quantitatively reflect the physiological states of microbial cultures. A number of VOCs are produced during microbial degradation of organic matter accompanying food spoilage. In order to characterize the dynamics of microbial VOC production, and enable time-dependent analysis, we have constructed a dual-chamber sampling system and coupled it online with mass spectrometry (MS). The biological specimen is placed in a gas-tight sampling chamber. A carrier gas is introduced to the chamber periodically to transfer the VOCs present in the specimen headspace to the atmospheric-pressure chemical-ionization interface of a triple-quadrupole mass spectrometer. A control or blank spectrum is recorded before the specimen spectrum is recorded at each time point, enabling signal comparison and subtraction. The custom-made electronic control unit, incorporating three Arduino microcontrollers, operates six pinch valves and a miniature air compressor and triggers MS-data acquisition. The automated dual-chamber sampling system was first tested using standard mixtures to verify its analytical performance. To demonstrate the usefulness of this system in the studies of microbial volatomes, we implemented it in real-time monitoring of the growth of bakers yeast (Saccharomyces cerevisiae), fructification of golden oyster mushroom (Pleurotus citrinopileatus), and microbial degradation of a food-related sample (Pacific white shrimp, Litopenaeus vannamei). The recorded VOC signals show characteristic temporal profiles with transient bands or plateaus corresponding to different stages of microbial growth and putrefaction processes.
Fizzy Extraction of Volatile and Semivolatile Compounds into the Gas Phase
(2016-09-06)
Chang, Cheng-Hao
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Urban, Pawel L.
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應用化學系
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Department of Applied Chemistry
Extraction of volatile and semivolatile compounds from liquid matrixes with high yields, and transferring the extracts to detectors in real time, is challenging. Common extraction procedures involve heating the samples to release the analytes to the gas phase and, in some cases, trapping the gas-phase analytes into sorbents or containers. Here, we propose a new method for fast extraction of volatile and semivolatile compounds from liquid matrixes. This method involves dissolution of a carrier gas in the liquid sample by applying a moderate overpressure (similar to 150 kPa) and stirring the sample. An abrupt decompression of the extraction chamber leads to effervescence. In this step, many bubbles are instantly formed in the sample matrix. The dissolved carrier gas as well as dissolved volatiles are liberated into the headspace of the extraction chamber within a short period of time (few seconds). The gaseous effluent of the extraction chamber is immediately transferred to the online detector; in this case, an atmospheric pressure chemical ionization interface of a triple quadrupole mass spectrometer. The fast release of the gas-phase extract gives rise to a high signal recorded by the detector; several times higher than the signal recorded during direct infusion of headspace vapors without fizzy extraction. This feature provides the means to detect and quantify analytes present in solutions in a short period of time. Here we show that fizzy extraction is suitable for analysis of volatile/semivolatile compounds present in various samples, including those containing complex matrixes.
Fizzy Extraction of Volatile Organic Compounds Combined with Atmospheric Pressure Chemical Ionization Quadrupole Mass Spectrometry
(2017-07-01)
Yang, Hao-Chun
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Chang, Cheng-Hao
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Urban, Pawel L.
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應用化學系
;
Department of Applied Chemistry
Chemical analysis of volatile and semivolatile compounds dissolved in liquid samples can be challenging. The dissolved components need to be brought to the gas phase, and efficiently transferred to a detection system. Fizzy extraction takes advantage of the effervescence phenomenon. First, a carrier gas (here, carbon dioxide) is dissolved in the sample by applying overpressure and stirring the sample. Second, the sample chamber is decompressed abruptly. Decompression leads to the formation of numerous carrier gas bubbles in the sample liquid. These bubbles assist the release of the dissolved analyte species from the liquid to the gas phase. The released analytes are immediately transferred to the atmospheric pressure chemical ionization interface of a triple quadrupole mass spectrometer. The ionizable analyte species give rise to mass spectrometric signals in the time domain. Because the release of the analyte species occurs over short periods of time (a few seconds), the temporal signals have high amplitudes and high signal-to-noise ratios. The amplitudes and areas of the temporal peaks can then be correlated with concentrations of the analytes in the liquid samples subjected to fizzy extraction, which enables quantitative analysis. The advantages of fizzy extraction include: simplicity, speed, and limited use of chemicals (solvents).
Microanalysis Using Acoustically Actuated Droplets Pinned Onto a Thread
(2019-01-01)
Yang, Tzu-Hsien
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Yang, Hao-Chun
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Chang, Cheng-Hao
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Prabhu, Gurpur Rakesh D.
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Urban, Pawel L.
An acoustic wave-assisted microscale assay platform is demonstrated. Liquid droplets containing samples and reagents are dispensed and pinned onto a hydrophobic thread, and actuated by sound waves. The transport of droplets is achieved by modulating sound emitted by two sources. The resulting sound intensity gradient pushes the droplets in one direction. The available distance of droplet actuation is related to droplet size. The moving droplets merge at the end of their actuation range, and the merged droplet travels further due to its greater size. Fluorometric analysis of the merged droplet is accomplished by positioning an excitation light source above a defined interrogation zone along the thread. The emitted light is analyzed by a miniature spectrometer positioned orthogonally to the excitation light beam. The sound sources and detection system are controlled by universal electronic modules (Raspberry Pi, Arduino). The system is operated automatically with the aid of a custom-developed graphical user interface. Here, we demonstrate its application in enzyme assays (trypsin, beta-galactosidase). In-droplet enzymatic reaction progress curves are readily obtained. The actuated droplets can be put in motion and stopped without a significant delay. Only microliter-range volumes of sample and reagent are consumed in every analysis, while sub-milliliter volumes of chemical waste are produced.