Solid-phase microextraction (SPME) for determination of geosmin and 2-methylisoborneol in volatile emissions from soil disturbance

A method is described here for the concentration and determination of geosmin and 2-methylisoborneol (2-MIB) from the gaseous phase, with translation to field collection and quantification from soil disturbances in situ. The method is based on the use of solid-phase microextraction (SPME) fibers for adsorption of volatile chemicals from the vapor phase, followed by desorption into a gas chromatograph-mass spectrometer (GC-MS) for analysis. The use of a SPME fiber allows simple introduction to the GC-MS without further sample preparation. Several fiber sorbent types were studied and the 50/30 μm DVB/CAR/PDMS was the best performer to maximize the detected peak areas of both analytes combined. Factors such as extraction temperature and time along with desorption temperature and time were explored with respect to analyte recovery. An extraction temperature of 30 ◦C for 10 min, with a desorption temperature of 230 ◦C for 4 min was best for the simultaneous analysis of both geosmin and 2-MIB without complete loss of either one. The developed method was used successfully to measure geosmin and 2-MIB emission from just above disturbed and undisturbed soils, indicating that this method detects both compounds readily from atmospheric samples. Both geosmin and 2-MIB were present as background concentrations in the open air, while disturbed soils emitted much higher concentrations of both compounds. Surprisingly, 2-MIB was always detected at higher concentrations than geosmin, indicating that a focus on its detection may be more useful for soil emission monitoring and more sensitive to low levels of soil disturbance.

Nitrogen as a Probe Molecule for the IR Studies of the Heterogeneity of OH Groups in Zeolites

One of the methods of IR studies of the heterogeneity of Si–OH–Al groups in zeolites is the investigation of the frequency shift of the band of free OH bands restored upon the adsorption of ammonia and subsequent desorption at increasing temperatures. We extended this method by following the shift of the band of the OH group interacting by hydrogen bonding with nitrogen. The advantage of nitrogen, compared with CO, which has been commonly used as a probe molecule in studies on hydrogen bonding, is that for nitrogen the frequency shift is smaller than for CO and therefore there is no overlapping of shifted OH band with the bands of ammonium ions. For zeolites NaHY, HMFI, and HBEA, the frequency shift of IR bands of both free and hydrogen-bonded Si–OH–Al with the increase of ammonia desorption temperature evidences the heterogeneity of these hydroxyls. On the other hand, in zeolite HFAU of Si/Al = 31, Si–OH–Al were found to be homogeneous. Heterogeneity of OH groups may be explained both by the presence of Si–OH–Al of various number of Al near the bridge and of Si–OH–Al of various geometry.

A new method to quantify particulate sodium and potassium salts (nitrate, chloride, and sulfate) by thermal desorption aerosol mass spectrometry

The reaction of sea salt (or biomass burning) particles with sulfuric acid and nitric acid leads to the displacement of chloride relative to sodium (or potassium). We have developed a new particle mass spectrometer to quantify non-refractory and refractory sulfate aerosols (referred to as refractory aerosol thermal desorption mass spectrometer: rTDMS). The combination of a graphite particle collector and a carbon dioxide laser enables high desorption temperature (up to 930 °C). Ion signals originating from evolved gas molecules are detected by a quadrupole mass spectrometer. Here we propose a new method to quantify the mass concentrations of sodium nitrate (NaNO3: SN), sodium chloride (NaCl: SC), sodium sulfate (Na2SO4: SS), potassium nitrate (KNO3: PN), potassium chloride (KCl: PC), and potassium sulfate (K2SO4 : PS) particles by using the rTDMS. Laboratory experiments were performed to test the sensitivities of the rTDMS to various types of particles. We measured ion signals originating from single-component particles for each compound, and found a good linearity (r2 > 0.8) between the major ion signals and mass loadings. We also measured ion signals originating from internally mixed SN + SC + SS (or PN + PC + PS) particles, and found that the temporal profiles of ion signals at m/z 23 (or 39) were characterized by three sequential peaks associated with the evolution of the desorption temperature. We tested potential interferences in the quantification of sea salt particles under real-world conditions by artificially generating "modified" sea salt particles from a mixture of diluted seawater and SS/SN solution. Based on these experimental results, the applicability of the rTDMS to ambient measurements of sea salt particles is discussed.

Experimental Study of O2-Enriched CO2 Production by BaCo0.8B0.2O3−δ (B=Ce, Al, Fe, Cu) Perovskites Sorbent for Marine Exhaust CO2 Capture Application

An effective approach for reducing CO2 emissions from marine exhaust is adopting oxyfuel combustion technology. A series of B-site doped BaCo0.8B0.2O3−δ (B=Ce, Al, Fe, Cu) perovskites as novel oxygen carrier applications were prepared by the sol-gel method. The oxygen desorption characteristics of the B-site doped BaCo0.8B0.2O3−δ perovskites and the effects of adsorption/desorption temperature, CO2 volume flow rate, CO2 partial pressures, and adsorption time were researched in the fixed bed reactor. The surface morphology and size of the oxygen carrier was observed by scanning electron microscope (SEM). Results showed that BaCo0.8Al0.2O3−δ and BaCo0.8Ce0.2O3−δ have comparable performance, considering the cost of the raw materials. BaCo0.8Al0.2O3−δ was selected as candidate for further study. The optimal adsorption/desorption temperature, CO2 volume flow rate, CO2 partial pressure and adsorption time for BaCo0.8Al0.2O3−δ were studied in detail. Results showed that the best operating parameters were determined to be 850 °C/850 °C for adsorption/desorption temperature, 200 mL/min for CO2 volume flow rate, 100% CO2 partial pressure, and 30 min for absorption time, respectively. Furthermore, multiple cycle results indicate that BaCo0.8Al0.2O3−δ sorbent has high reactivity and cyclic stability.

Using Design of Experiments to Optimize a Screening Analytical Methodology Based on Solid-Phase Microextraction/Gas Chromatography for the Determination of Volatile Methylsiloxanes in Water

Volatile methylsiloxanes (VMSs) constitute a group of compounds used in a great variety of products, particularly personal care products. Due to their massive use, they are continually discharged into wastewater treatment plants and are increasingly being detected in wastewater and in the environment at low concentrations. The aim of this work was to develop and validate a fast and reliable methodology to screen seven VMSs in water samples, by headspace solid-phase microextraction (HS-SPME) followed by gas chromatography with flame ionization detection (GC-FID). The influence of several factors affecting the extraction efficiency was investigated using a design of experiments approach. The main factors were selected (fiber type, sample volume, ionic strength, extraction and desorption time, extraction and desorption temperature) and optimized, employing a central composite design. The optimal conditions were: 65 µm PDMS/Divinylbenzene fiber, 10 mL sample, 19.5% NaCl, 39 min extraction time, 10 min desorption time, and 33 °C and 240 °C as extraction and desorption temperature, respectively. The methodology was successfully validated, showing low detection limits (up to 24 ng/L), good precision (relative standard deviations below 15%), and accuracy ranging from 62% to 104% in wastewater, tap, and river water samples.

Seasonal changes of sources, processes, and volatility of organic aerosol at urban, coastal and forest sites in Eastern Europe

<p>The stable carbon isotope <sup>13</sup>C has the potential to give insights into sources and processing of organic aerosol. However, the use for source apportionment has been somewhat limited, because the <sup>13</sup>C source signatures vary and show some overlap. <sup>13</sup>C/<sup>12</sup>C ratios are usually reported as δ<sup>13</sup>C indicating a permil deviation from the international reference standard Vienna Pee Dee Belemnite (V-PDB).</p><p>We use a method to measure δ<sup>13</sup>C  in OC desorbed from filter samples at three different temperature steps: 200 °C, 350°C and 650°C (Zenker et al.,2020). The results give a rough indication of aerosol volatility, as more volatile compounds usually desorb at lower temperatures.</p><p>We demonstrate with an extensive source study that in Lithuania and likely other Eastern European regions, the main anthropogenic primary sources for organic carbon (OC) have distinct isotopic signatures. δ<sup>13</sup>C  values of vehicular emissions show the most negative values around - 29 ‰, emissions from combustion of the most common wood types are more enriched with values around -26 to -27 ‰, and coal burning is around -25‰. For source samples d<sup>13</sup>C values at the three desorption temperature steps usually do not differ more than 1 ‰.</p><p>For ambient aerosol samples, the differences in δ<sup>13</sup>C values at different desorption temperatures are usually larger. This indicates varying source contribution or different chemical processes leading to the different volatility fractions. Combined isotopic and chemical analysis showed that in winter was a clear distinction in source contribution between the less refractory OC and the more refractory OC. We were able to identify fossil fuel burning as predominant source of the less refractory OC in the small particle size range (D<sub></sub>< 0.18 μm), and biomass burning as predominant source of the more refractory OC in the larger size range (0.32< D<sub></sub><1 μm).</p><div><span>At all three sites, </span><span>OC had more negative δ<sup>13</sup>C values in summer than in winter which can be explained by the contribution of biomass/coal burning sources in winter. At the urban site δ<sup>13</sup>C of OC did not change much with increasing desorption temperature in winter, which is typical for primary sources. In the summer δ<sup>13</sup>C of OC was clearly more negative for lower desorption temperatures at all three sites. This is likely due to the influence of secondary organic aerosol formation in summer, which should have depleted (more negative) isotopic signature and contributes strongly to the more volatile fraction.</span></div><div> <p>A higher fraction of more refractory OC in summer compared to winter-time suggests active photochemical processing of the primary organic aerosol as an important process at all three sites. During a pollution episode transporting aged pollution from Poland and southern Europe to the otherwise clean forest site, a potential isotopic signature for photochemical aging was identified.</p> </div>

Temporally resolved thermal desorption of volatile organics from nanoporous silica preconcentrator

Gas-phase volatile organic compounds (VOCs) are collected in a nanoporous silica preconcentrator, then released slowly by heating onto a detector. Desorption temperature depends on VOC properties, allowing potential discrimination.