Browsing by Author "Saowapon, Matthew T."

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    Dehydration of a Water Stationary Phase as a Novel Separation Gradient in Capillary Supercritical Fluid Chromatography
    (Elsevier, 2019-06-27) Thurbide, Kevin B.; Saowapon, Matthew T.
    A novel alternative to gradient elution in capillary supercritical fluid chromatography (SFC) based upon the systematic removal of a water stationary phase from the column, using a pure CO 2 mobile phase, is introduced. By adjusting the flow of water used to humidify the system, the stationary phase can be removed at different rates and this results in proportionately faster analyte elution. As well, the phase can be readily restored within a few minutes. The method demonstrates good reproducibility with analyte retention times yielding an RSD of 1.2% in consecutive trials. Further, it provides results that compare well to a conventional pressure program in capillary SFC, but without the problematic convolution of system pressure and flow rate. The technique also demonstrated the ability to refocus analytes into sharper peaks, resulting in a 30-fold increase in their peak height. This effect can improve detection limits and also allow ionizable analytes like amines and dicarboxylic acids to be eluted with improved peak shape. Results indicate that systematic removal of a water stationary phase from the column is an interesting and potentially effective alternate means of controlling and improving analyte elution in capillary SFC.
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    Quantification of peroxynitric acid and peroxyacyl nitrates using an ethane-based thermal dissociation peroxy radical chemical amplification cavity ring-down spectrometer
    (European Geosciences Union, 2018-07-17) Taha, Youssef M.; Saowapon, Matthew T.; Assad, Faisal V.; Ye, Connie Z.; Chen, Xining; Garner, Natasha M.; Osthoff, Hans D.
    Peroxy and peroxyacyl nitrates (PNs and PANs) are important trace gas constituents of the troposphere which are challenging to quantify by differential thermal dissociation with NO2 detection in polluted (i.e., high-NOx) environments. In this paper, a thermal dissociation peroxy radical chemical amplification cavity ring-down spectrometer (TD-PERCA-CRDS) for sensitive and selective quantification of total peroxynitrates (ΣPN  =  ΣRO2NO2) and of total peroxyacyl nitrates (ΣPAN  =  ΣRC(O)O2NO2) is described. The instrument features multiple detection channels to monitor the NO2 background and the ROx ( =  HO2 + RO2 + ΣRO2) radicals generated by TD of ΣPN and/or ΣPAN. Chemical amplification is achieved through the addition of 0.6 ppm NO and 1.6 % C2H6 to the inlet. The instrument's performance was evaluated using peroxynitric acid (PNA) and peroxyacetic or peroxypropionic nitric anhydride (PAN or PPN) as representative examples of ΣPN and ΣPAN, respectively, whose abundances were verified by iodide chemical ionization mass spectrometry (CIMS). The amplification factor or chain length increases with temperature up to 69 ± 5 and decreases with analyte concentration and relative humidity (RH). At inlet temperatures above 120 and 250 °C, respectively, PNA and ΣPAN fully dissociated, though their TD profiles partially overlap. Furthermore, interference from ozone (O3) was observed at temperatures above 150 °C, rationalized by its partial dissociation to O atoms which react with C2H6 to form C2H5 and OH radicals. Quantification of PNA and ΣPAN in laboratory-generated mixtures containing O3 was achieved by simultaneously monitoring the TD-PERCA responses in multiple parallel CRDS channels set to different temperatures in the 60 to 130 °C range. The (1 s, 2σ) limit of detection (LOD) of TD-PERCA-CRDS is 6.8 pptv for PNA and 2.6 pptv for ΣPAN and significantly lower than TD-CRDS without chemical amplification. The feasibility of TD-PERCA-CRDS for ambient air measurements is discussed.
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    Quantification of peroxynitric acid and peroxyacyl nitrates using an ethane-based thermal dissociation peroxy radical chemical amplification cavity ring-down spectrometer
    (Copernicus, 2018-07-17) Taha, Youssef M.; Saowapon, Matthew T.; Assad, Faisal V.; Ye, Connie Z.; Chen, Xining; Garner, Natasha M.; Osthoff, Hans D.
    Peroxy and peroxyacyl nitrates (PNs and PANs) are important trace gas constituents of the troposphere which are challenging to quantify by differential thermal dissociation with NO2 detection in polluted (i.e., high-NOx) environments. In this paper, a thermal dissociation peroxy radical chemical amplification cavity ring-down spectrometer (TD-PERCA-CRDS) for sensitive and selective quantification of total peroxynitrates (ΣPN = ΣRO2NO2) and of total peroxyacyl nitrates (ΣPAN = ΣRC(O)O2NO2) is described. The instrument features multiple detection channels to monitor the NO2 background and the ROx ( = HO2+RO2+ΣRO2) radicals generated by TD of ΣPN and/or ΣPAN. Chemical amplification is achieved through the addition of 0.6ppm NO and 1.6% C2H6 to the inlet. The instrument's performance was evaluated using peroxynitric acid (PNA) and peroxyacetic or peroxypropionic nitric anhydride (PAN or PPN) as representative examples of ΣPN and ΣPAN, respectively, whose abundances were verified by iodide chemical ionization mass spectrometry (CIMS). The amplification factor or chain length increases with temperature up to 69±5 and decreases with analyte concentration and relative humidity (RH). At inlet temperatures above 120 and 250°C, respectively, PNA and ΣPAN fully dissociated, though their TD profiles partially overlap. Furthermore, interference from ozone (O3) was observed at temperatures above 150°C, rationalized by its partial dissociation to O atoms which react with C2H6 to form C2H5 and OH radicals. Quantification of PNA and ΣPAN in laboratory-generated mixtures containing O3 was achieved by simultaneously monitoring the TD-PERCA responses in multiple parallel CRDS channels set to different temperatures in the 60 to 130°C range. The (1s, 2σ) limit of detection (LOD) of TD-PERCA-CRDS is 6.8pptv for PNA and 2.6pptv for ΣPAN and significantly lower than TD-CRDS without chemical amplification. The feasibility of TD-PERCA-CRDS for ambient air measurements is discussed.