Factors influencing the analytical performance of an atmospheric sampling glow discharge ionization source as revealed via ionization dynamics modeling. (1/24)

A kinetic model is developed for the dynamic events occurring within an atmospheric sampling glow discharge that affect its performance as an ion source for analytical mass spectrometry. The differential equations incorporate secondary electron generation and thermalization, reagent and analyte ion formation via electron capture and ion-molecule reactions, ion loss via recombination processes, diffusion, and ion-molecule reactions with matrix components, and the sampling and pumping parameters of the source. Because the ion source has a flow-through configuration, the number densities of selected species can be estimated by applying the steady-state assumption. However, understanding of its operation is aided by knowledge of the dynamic behavior, so numerical methods are applied to examine the time dependence of those species as well. As in other plasma ionization sources, the ionization efficiency is essentially determined by the ratio of the relevant ion formation and recombination rates. Although thermal electron and positive reagent ion number densities are comparable, the electron capture/ion-molecule reaction rate coefficient ratio is normally quite large and the ion-electron recombination rate coefficient is about an order of magnitude greater than that for ion-ion recombination. Consequently, the efficiency for negative analyte ion formation via electron capture is generally superior to that for positive analyte ion generation via ion-molecule reaction. However, the efficiency for positive analyte ion formation should be equal to or better than that for negative analyte ions when both ionization processes occur via ion-molecule reaction processes (with comparable rate coefficients), since the negative reagent ion density is considerably less than that for positive reagent ions. Furthermore, the particularly high number densities of thermal electrons and reagent ions leads to a large dynamic range of linear response for the source. Simulation results also suggest that analyte ion number densities might be enhanced by modification of the standard physical and operating parameters of the source.  (+info)

Millisecond pulsed radio frequency glow discharge time of flight mass spectrometry: temporal and spatial variations in molecular energetics. (2/24)

The internal energy distributions, P(epsilon), of a millisecond pulsed radio frequency glow discharge plasma were investigated using tungsten hexcarbonyl W(CO)(6) as a "thermometer molecule". Vapor of the probe molecule, W(CO)(6), was introduced into the plasma and subjected to various ionization and excitation processes therein. The resultant molecular and fragment ions were monitored using a Time-of-Flight mass spectrometer. Ion abundance data were utilized in combination with the known energetics of W(CO)(6) to construct the P(epsilon) plots. The P(epsilon) of W(CO)(6) exhibited strong temporal dependence over the pulse cycle: Distinct internal energy distributions were found at the discharge breakdown period (prepeak), the steady state period (plateau), and the post-pulse period (afterpeak). Spatial variation in P(epsilon) was also observed, especially during the plateau regime. The observations suggest that this pulsed glow discharge affords excellent energy tunability that can be used to perform selective ionization and fragmentation for molecular, structural, and elemental information. Parametric studies were performed to evaluate the effects of discharge pressure and operating power on P(epsilon). These studies also provided insight into the correlation of the observed P(epsilon)s with the fundamental ionization and excitation mechanisms in the plasma. The temporal and spatial variations in P(epsilon) were hence attributed to changes in the dominant energy transfer processes at specific times in specific regions of the plasma. These data will be useful in future efforts to optimize the analytical performance of this source for chemical speciation.  (+info)

Comparison of electrospray ionization, atmospheric pressure chemical ionization, and atmospheric pressure photoionization for the analysis of dinitropyrene and aminonitropyrene LC-MS/MS. (3/24)

The only relevant source for human exposure to dinitropyrenes is diesel engine emissions. Due to this specificity, dinitropyrenes may be used as biomarkers for monitoring human exposure to diesel engine emissions. Only few analytical methods have been described for the quantitation of dinitropyrenes and their metabolites, aminonitropyrenes, and diaminopyrenes. Therefore, for dinitropyrenes, aminonitropyrenes, and diaminopyrenes were selected as model compounds for the development of a sensitive HPLC-MS/MS method (high performance liquid chromatography coupled to triple quadrupole mass spectrometry) was to quantify polyaromatic amines and nitroarenes in biological matrices was developed optimal methods by comparing electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photoionization (APPI) sources. Dinitropyrene was not effectively ionized and diaminopyrene yielded mainly [M(.)](+) ions by electrospray ionization. With APCI and APPI, precursor ions of diaminopyrene and aminonitropyrene were [M + H](+) and [M(.)](-) for dinitropyrene. Precursor ions with [M - 30(.)](-) for dinitropyrene and [M - 30 + H](+) for aminonitropyrene were observed. Reversed and normal phase HPLC-MS/MS with ESI, APCI and APPI were optimized separately with respect to unequivocal analyte identification and sensitivity. Normal phase HPLC coupled to APPI-MS/MS gave the highest precision and sensitivity for aminonitropyrene (6%/0.2 pg on column) and dinitropyrene (9%/0.5 pg on column). The limit of detection in spiked rat plasma was 5 pg/100 microL for aminonitropyrene (accuracy 82%) and 10 pg/100 microL for dinitropyrene (accuracy 105%). In plasma of rats treated with dinitropyrene by oral administration, no detectable levels of dinitropyrene but higher aminonitropyrene levels compared with intratracheal instillation were observed. These findings clearly demonstrate that dinitropyrene was absorbed after oral and intratracheal application and that a reduction of nitro groups occurs to a high extent in the reductive environment of the intestine. To our knowledge, this is the first time that aminonitropyrene was observed in plasma after intratracheal or oral administration directly demonstrating the reductive metabolism of dinitropyrene in vivo.  (+info)

Studies on the effects of ionization on bacterial aerosols in a burns and plastic surgery unit. (4/24)

The effect of the ionization of the air on the decay of bacterial aerosols was studied in a Burns and Plastic Surgery Unit. Ions were generated by free corona needles. The air content of bacteria measured by settle plates was found to be smaller during the ionization period than during the controls period. The number of individual phage typed Staph. aureus strains was especially found to be lower during ionization. The opposite potential increased the disappearance of bacteria from the air. The size of skin particles carrying bacteria is not optimum, but the results obtained show that the ionization may have applications in controlling airborne infection.  (+info)

Reduced flavin: NMR investigation of N5-H exchange mechanism, estimation of ionisation constants and assessment of properties as biological catalyst. (5/24)

BACKGROUND: The flavin in its FMN and FAD forms is a versatile cofactor that is involved in catalysis of most disparate types of biological reactions. These include redox reactions such as dehydrogenations, activation of dioxygen, electron transfer, bioluminescence, blue light reception, photobiochemistry (as in photolyases), redox signaling etc. Recently, hitherto unrecognized types of biological reactions have been uncovered that do not involve redox shuffles, and might involve the reduced form of the flavin as a catalyst. The present work addresses properties of reduced flavin relevant in this context. RESULTS: N(5)-H exchange reactions of the flavin reduced form and its pH dependence were studied using the 15N-NMR-signals of 15N-enriched, reduced flavin in the pH range from 5 to 12. The chemical shifts of the N(3) and N(5) resonances are not affected to a relevant extent in this pH range. This contrasts with the multiplicity of the N(5)-resonance, which strongly depends on pH. It is a doublet between pH 8.45 and 10.25 that coalesces into a singlet at lower and higher pH values. From the line width of the 15N(5) signal the pH-dependent rate of hydrogen exchange was deduced. The multiplicity of the 15N(5) signal and the proton exchange rates are little dependent on the buffer system used. CONCLUSION: The exchange rates allow an estimation of the pKa value of N(5)-H deprotonation in reduced flavin to be >or= 20. This value imposes specific constraints for mechanisms of flavoprotein catalysis based on this process. On the other hand the pK asymptotically equal to 4 for N(5)-H protonation (to form N(5)+-H2) would be consistent with a role of N(5)-H as a base.  (+info)

Hospital-acquired legionnaires disease in a university hospital: impact of the copper-silver ionization system. (6/24)

We evaluated the impact of the copper-silver ionization system in a hospital where hyperendemic nosocomial legionellosis and was present and all previous disinfection measures had failed. After implementation of the copper-silver ionization system, environmental colonization with Legionella species decreased significantly, and the incidence of nosocomial legionellosis decreased dramatically, from 2.45 to 0.18 cases per 1000 patient discharges.  (+info)

Bactericidal action of positive and negative ions in air. (7/24)

BACKGROUND: In recent years there has been renewed interest in the use of air ionisers to control of the spread of airborne infection. One characteristic of air ions which has been widely reported is their apparent biocidal action. However, whilst the body of evidence suggests a biocidal effect in the presence of air ions the physical and biological mechanisms involved remain unclear. In particular, it is not clear which of several possible mechanisms of electrical origin (i.e. the action of the ions, the production of ozone, or the action of the electric field) are responsible for cell death. A study was therefore undertaken to clarify this issue and to determine the physical mechanisms associated with microbial cell death. RESULTS: In the study seven bacterial species (Staphylococcus aureus, Mycobacterium parafortuitum, Pseudomonas aeruginosa, Acinetobacter baumanii, Burkholderia cenocepacia, Bacillus subtilis and Serratia marcescens) were exposed to both positive and negative ions in the presence of air. In order to distinguish between effects arising from: (i) the action of the air ions; (ii) the action of the electric field, and (iii) the action of ozone, two interventions were made. The first intervention involved placing a thin mica sheet between the ionisation source and the bacteria, directly over the agar plates. This intervention, while leaving the electric field unaltered, prevented the air ions from reaching the microbial samples. In addition, the mica plate prevented ozone produced from reaching the bacteria. The second intervention involved placing an earthed wire mesh directly above the agar plates. This prevented both the electric field and the air ions from impacting on the bacteria, while allowing any ozone present to reach the agar plate. With the exception of Mycobacterium parafortuitum, the principal cause of cell death amongst the bacteria studied was exposure to ozone, with electroporation playing a secondary role. However in the case of Mycobacterium parafortuitum, electroporation resulting from exposure to the electric field appears to have been the principal cause of cell inactivation. CONCLUSION: The results of the study suggest that the bactericidal action attributed to negative air ions by previous researchers may have been overestimated.  (+info)

The detection of airborne transmission of tuberculosis from HIV-infected patients, using an in vivo air sampling model. (8/24)

BACKGROUND: Nosocomial transmission of tuberculosis remains an important public health problem. We created an in vivo air sampling model to study airborne transmission of tuberculosis from patients coinfected with human immunodeficiency virus (HIV) and to evaluate environmental control measures. METHODS: An animal facility was built above a mechanically ventilated HIV-tuberculosis ward in Lima, Peru. A mean of 92 guinea pigs were continuously exposed to all ward exhaust air for 16 months. Animals had tuberculin skin tests performed at monthly intervals, and those with positive reactions were removed for autopsy and culture for tuberculosis. RESULTS: Over 505 consecutive days, there were 118 ward admissions by 97 patients with pulmonary tuberculosis, with a median duration of hospitalization of 11 days. All patients were infected with HIV and constituted a heterogeneous group with both new and existing diagnoses of tuberculosis. There was a wide variation in monthly rates of guinea pigs developing positive tuberculin test results (0%-53%). Of 292 animals exposed to ward air, 159 developed positive tuberculin skin test results, of which 129 had laboratory confirmation of tuberculosis. The HIV-positive patients with pulmonary tuberculosis produced a mean of 8.2 infectious quanta per hour, compared with 1.25 for HIV-negative patients with tuberculosis in similar studies from the 1950s. The mean monthly patient infectiousness varied greatly, from production of 0-44 infectious quanta per hour, as did the theoretical risk for a health care worker to acquire tuberculosis by breathing ward air. CONCLUSIONS: HIV-positive patients with tuberculosis varied greatly in their infectiousness, and some were highly infectious. Use of environmental control strategies for nosocomial tuberculosis is therefore a priority, especially in areas with a high prevalence of both tuberculosis and HIV infection.  (+info)

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