High-field asymmetric waveform ion mobility spectrometry (FAIMS) separates ions by utilizing the mobility differences of ions at high and low fields. The shape of the waveform is one of the essential features affecting the resolution, transmission, and separation of FAIMS. Due to practical circuitry advantages, sinusoidal asymmetric waveforms are typically used in FAIMS, whereas theoretical studies indicate that square asymmetric waveforms improve ion separation, resolution, and sensitivity. Results from FAIMS using square and sinusoidal waveforms are presented, and effects of the waveforms on ion separation are discussed. A FAIMS system interfaced with a quadrupole ion trap mass spectrometer was used in this study. FAIMS spectra were generated by scanning the compensation voltage (CV) while operating the mass spectrometer in total ion mode. The identification of ions was accomplished through mass spectra acquired at fixed values of ions' CVs. Square waveform evaluation was done by acquiring data at three frequencies and six duty cycles of the square waveform generator. The performance of FAIMS using square and sinusoidal waveforms at 250, 333, and 500 kHz frequencies was compared, and trends were identified. For all frequencies, the best response of FAIMS was achieved at the lower amplitudes and under the lower duty cycles of the square waveform generator. The separation of FAIMS was better at the higher frequencies. These results demonstrate the potential to incorporate square-wave FAIMS into the design of a miniature device for detection of explosives in the field. SIMION version 8.0, the ion trajectory modeling program, was utilized to optimize the performance of the miniature FAIMS cell and to validate experimental results.
High-field asymmetric waveform ion mobility spectrometry (FAIMS) can operate at atmospheric pressure to separate gas-phase ions on the basis of a difference in the mobility of an ion at high fields relative to its mobility at low field strengths. Several novel cell geometries have been proposed in addition to the commercially available planar and cylindrical designs. Nevertheless, there is still much to explore about three-dimensional (3-D) curved cell geometries (spherical and hemispherical) and comparison to twodimensional (2-D) curved geometries (cylindrical). The geometry of a FAIMS cell is one of the essential features affecting the transmission, resolution, and resolving power of FAIMS. Electric fields in a spherical design allow advantages such as virtual potential wells that can induce atmospheric-pressure near-trapping conditions and help reduce ion losses. Curvature of electrodes enables the ions to remain focused near the gap median, which help to improve sensitivity and ion trapping at higher pressures. Here we detail the design and characterization of a novel FAIMS cell having spherical electrode geometry and compare it to hemispherical and cylindrical cells. These FAIMS cells were interfaced with a quadrupole ion trap mass spectrometer in this study. Several structural classes of common explosives were employed to evaluate the separation power of these geometries. FAIMS spectra were generated by scanning the compensation voltage (CV) while operating the mass spectrometer in total ion mode. The identification of ions was accomplished through mass spectra acquired at fixed values of CVs. The performance of FAIMS using cylindrical, hemispherical, and spherical cells was compared and trends identified. For all trials, the best transmission was obtained by the spherical FAIMS cell while hemispherical FAIMS provided the best resolution and resolving power.
Background: Bats are reservoirs for several zoonotic pathogens, making human-bat interactions particularly concerning. Recent studies documented that Grenadian bats can be infected with Zika, dengue and Chikungunya viruses and Leptospira bacteria among other pathogens. The objective of this study was to estimate the number of homes in Grenada that have a bat infestation, and to determine whether there is a correlation between the number of bat infested homes with the type of roofing or the presence of arbovirus infections of human inhabitants. Methods: An institutional review board (IRB) approved questionnaire delivered through a semi-structured interview was administered at the central bus stop in St. George, Grenada to recruit participants from all six parishes and the island of Carriacou. Results determined the percentage of individuals that had bat roosts in their households, whether this was of concern to them, whether they had taken any steps to keep bats out of their residence, and whether they had confirmed or suspected cases of dengue, Zika or Chikungunya virus infections. Information on the type of roofing and presence of window screens were also documented. Bat type (fruit vs insect eating bats) was attempted by guano description. Results: Results from 210 individual responses provided data showing all six parishes were represented although not equally. Having bats at the household was not associated with parish of residence, roof type or presence or absence of window screens. The results showed 60% of homes in Grenada are bat-infested and 51% of people self-reported recent arbovirus infection; but no correlation between the two. Also, no correlation to a specific type of roof or type of bat was found.Conclusions: A statistically significant number of inhabitants had attempted to remove bats from their homes, indicating that bats are perceived as pest to homes in Grenada, and justifying further research into relocating bats through the use of construction changes, awareness, and the creation of bat houses.
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