Daniel B. Milligan

Application of selected ion flow tube mass spectrometry to real-time atmospheric monitoring.

Data are presented for real-time atmospheric monitoring of volatile organic chemicals (VOCs) in air using selected ion flow tube mass spectrometry (SIFT-MS) technology. These measurements were made by one of the new generation of SIFT-MS instruments. Results are shown for five VOCs that were continually monitored from a stationary sampling point over a 4-day period: ethene, ethanol, 1,3-butadiene, benzene and toluene. All analytes except ethene in the study have at least two simultaneous and independent measures of concentration. These results demonstrate the great advances in SIFT-MS that have been made in recent years. 1,3-Butadiene is measured at a concentration of 9 pptv with a precision of 44%. For a 1-s integration time, a detection limit of 50 pptv is achieved. Instrument sensitivities are reported for all five analytes.

Emission of nitrogen oxides and ammonia from varying rates of applied synthetic urine and correlations with soil chemistry

Synthetic urine was applied at 5 rates, from 0 to 1000 kg synthetic urine-N/ha, to a pasture soil under controlled laboratory conditions. Gaseous emissions of NOx and NH3 were monitored for up to 21 days following application using selected ion flow tube mass spectrometry with N2O measured using electron-capture gas chromatography. During this period soil replicates were destructively sampled to measure changes in soil pH and inorganic-N concentrations. Comparisons were made between measured soil variables, calculated soil concentrations of NH3(g), HNO2, and the measured gas fluxes. At N rates up to 500 kg N/ha, inorganic-N concentrations increased as nitrification progressed over time. With the exception of the 1000 kg N/ha treatment, NO production followed the pattern of increasing nitrification, reaching a maximum of 905 ng NO-N/cm2.h in the 500 kg N/ha treatment 14 days after synthetic urine application. At this time the NO flux was associated best with soil pH, NH4+, and NO2– levels. Over 21 days the maximum cumulative loss as NO-N and N2O-N occurred under the 100 kg N/ha urine treatment, with 6.6 and 6.4% of N applied lost as gas, respectively. NO2 gas fluxes paralleled the NO emissions but were an order of magnitude smaller. Nitrification was inhibited in the 1000 kg N/ha treatment due to the sustained high ammoniacal-N and pH conditions present. These conditions prolonged the NH3 volatilisation from this treatment. NH3 volatilisation, as determined by selected ion flow tube-mass spectrometry, was linearly related to calculated soil NH3 gas concentrations up to 500 kg N/ha on Day 1.

Quantitative analysis of trace gases of breath during exercise using the new SIFT–MS technique

Abstract We show how the concentration of the breath gases ammonia, acetone, and isoprene vary with time during exercise using the new selected ion flow tube mass spectrometry (SIFT–MS) technique. The expired breath concentrations of ammonia, acetone and isoprene were observed within the range of 50–500, 100–1400 and 5–400 ppb, respectively. Increasing acetone levels were observed for most subjects during the exercise period. However, isoprene levels decreased with time during exercise. Older subjects showed higher levels of isoprene compared with younger subjects. The ammonia time profile with exercise showed both decreasing and increasing patterns for different subjects.

A flowing afterglow selected ion flow tube (FA/SIFT) comparison of SIFT injector flanges and H3+ + N revisited

Abstract The performances of two different but interchangeable Venturi injectors (an annulus and a hole injector) have been compared in a new flowing afterglow source-selected ion flow tube (FA/SIFT) instrument built at the University of Canterbury. The tests applied compared the relative “pumping efficiencies” of the two injectors; their ion transmission using (O 2 + ); the relative ease of injecting cluster ions subject to collision induced dissociation (H 3 O · + H 2 O); and the extent of isomerization of ions sensitive to structural changes during the injection process (C 3 H 5 + ). The annulus injector was clearly superior to the hole injector in pumping efficiency. Thereafter the improvement in performance was only marginal. The greater difficulty of construction and maintenance of the annulus injector needs to be balanced against the slightly less versatile hole injector. It was necessary to direct a significant fraction of the total helium buffer gas flow through an outer, noncritical orifice to maintain satisfactory performance in the hole injector when injecting ions susceptible to collision induced dissociation. Finally, the new instrument was used to reexamine the reaction of H 3 + and N atoms, which was found to be a nonreactive system, k −11 cm 3 s −1 .

Real time analysis of breath volatiles using SIFT-MS in cigarette smoking.

Abstract The selected ion flow tube mass spectrometry (SIFT-MS) technique enables real time analysis of trace volatiles at ppb levels without preconcentration steps or chemical derivatization. Most previous studies of trace compounds on the breath were analyzed using gas chromatography where enhanced detection sensitivity was achieved by concentrating the breath using cryogenic or adsorption trapping techniques. In this paper, we have examined volatile organic substances, isoprene, acetone, ammonia and ethanol in breath before and after smoking a cigarette. It is interesting that isoprene levels increased in all the subjects after smoking one cigarette with a mean increase of 70%. The mean increase for acetone was found to be 22%. In contrast to isoprene, a decreasing ethanol level was observed in all the subjects except one with the negative mean decrease of 28%. Further SIFT-MS studies also have high-lighted some organic substances produced even by unburned cigarettes, US and New Zealand products. Certain US brands have shown much higher levels of volatile species than cigarettes produced in New Zealand.

Detection and Quantification of Chemical Warfare Agent Precursors and Surrogates by Selected Ion Flow Tube Mass Spectrometry

The rate coefficients and branching ratios of 15 chemical warfare agent precursor and surrogate compounds reacting with H(3)O(+), NO(+), and O(2)(+) have been measured in the laboratory using the selected ion flow tube (SIFT) technique. Measurement of the relevant kinetic parameters for these agents has enabled quantitative monitoring using the SIFT-MS analytical technique. Thirteen of the 15 compounds studied were found to have real-time detection limits in the parts-per-trillion-by-volume concentration range when measured on a standard commercial Voice100 instrument, with specific compounds having detection limits below 100 parts-per-trillion-by-volume.

H3++O: an experimental study

Abstract We have measured the reaction rate coefficient and branching ratios for the H 3 + +O atom reaction using a flowing afterglow/selected ion flow tube operating at room temperature (295±5 K). The measured rate coefficient was k =(1.2±0.5)×10 −9 cm 3 s −1 and the branching ratios were OH + +H 2 , (70%) and H 2 O + +H (30%). This reaction has some relevance to the synthesis of water in interstellar clouds.

COMPETITIVE ASSOCIATION AND CHARGE TRANSFER IN THE REACTIONS OF NO+ WITH SOME KETONES : A SELECTED ION FLOW DRIFT TUBE STUDY

The rate coefficients and product ion branching ratios have been determined for reactions between NO+ and three ketones, acetone, 2-butanone, and 3-pentanone, as a function of NO+/reactant ketone centre-of-mass energy, Er, and NO+/helium carrier gas atom centre-of-mass energy, Ec, in a flowing afterglow selected ion flow drift tube apparatus. In these experiments, the helium carrier gas was maintained at a temperature of 300 K. At zero drift field, association was the dominant channel occurring at close to the collision rate forming NO·+ ketone adduct ions. At higher drift fields (Er, Ec < 1 eV), charge transfer and dissociative charge transfer channels became the major channels forming fragment ions of the ketones. The decrease in the association rate coefficient with increasing Ec exhibits an inverse power law dependence k3 ∝ Ec−n where n ∼ 2.5 for all three ketones. This dependence is much larger than predicted by simple theory and may be indicative of low energy vibrations contributing to the total energy pool in the (NO· ketone)+∗ excited complex. Keywords: Ion/molecule association; SIFT; Drift tube; Charge transfer

Termolecular ion-molecule reactions in titan's atmosphere. II : The structure of the association adducts of HCNH+ with C2H2 and C2H4

The ion—molecule reactivity of the products formed in the association reactions of HCNH+ with C2H2 (C3H4N+) and C2H4 (C3H6N+) has been investigated to provide information on the structures of the adducts thus formed. The C3H4N+ and C3H6N+ adducts were formed in the reaction flow tube of a flowing afterglow sourced-selected ion flow tube (FA-SIFT) and their reactivity with a neutral molecular “probe” examined. The reactivity of possible known structural isomers for the C3H4N+ and C3H6N+ ions was investigated in both the FA-SIFT and an ion cyclotron resonance spectrometer (ICR). Ab initio investigations of the potential energy surfaces for both structures at the G2(MP2) level have also been performed and structures corresponding to local minima on both surfaces have been identified and evaluated. The results of these experimental and theoretical studies show that at room temperature, the C3H4N+ adduct ion contains two isomers; a less reactive one that is likely to be a four-membered cyclic covalent isomer (∼70%) and a faster reacting component that is probably an electrostatic complex (∼30%). The C3H6N+ adduct ion formed from HCNH+ + C2H4 at room temperature is a single isomer that is likely to be the four-membered covalently bound cyclic CH2CH2CHNH+ species.

Real-Time Monitoring of Hazardous Air Pollutants

Selected ion flow tube mass spectrometry (SIFT-MS) is a technique that offers real-time alternatives to existing methods for monitoring hazardous air pollutants (HAPs) in the environment using chemical ionization. The use of this technique requires knowledge of the kinetic parameters of the reagent ions H(3)O(+), NO(+), and O(2)(+) that are most commonly used. We report here measurements with these reagent ions of kinetic parameters for 17 HAP molecules ranging from 1,1-dichloroethene to nitrobenzene. From these data, limits of quantitation are established for all 17 compounds on a commercial SIFT-MS instrument and are found to be well below the time-weighted averages required by legislating bodies for workplace conditions.