Analysis of model Titan atmospheric components using ion mobility spectrometry

The Gas Chromatograph-Ion Mobility Spectrometer (GC-IMS) was proposed as an analytical technique for the analysis of Titan's atmosphere during the Cassini Mission. The IMS is an atmospheric pressure, chemical detector that produces an identifying spectrum of each chemical species measured. When the IMS is combined with a GC as a GC-IMS, the GC is used to separate the sample into its individual components, or perhaps small groups of components. The IMS is then used to detect, quantify, and identify each sample component. Conventional IMS detection and identification of sample components depends upon a source of energetic radiation, such as beta radiation, which ionizes the atmospheric pressure host gas. This primary ionization initiates a sequence of ion-molecule reactions leading to the formation of sufficiently energetic positive or negative ions, which in turn ionize most constituents in the sample. In conventional IMS, this reaction sequence is dominated by the water cluster ion. However, many of the light hydrocarbons expected in Titan's atmosphere cannot be analyzed by IMS using this mechanism at the concentrations expected. Research at NASA Ames and PCP Inc., has demonstrated IMS analysis of expected Titan atmospheric components, including saturated aliphatic hydrocarbons, using two alternate sample ionizations mechanisms. The sensitivity of the IMS to hydrocarbons such as propane and butane was increased by several orders of magnitude. Both ultra dry (waterless) IMS sample ionization and metastable ionization were successfully used to analyze a model Titan atmospheric gas mixture

Advanced modulation technology development for earth station demodulator applications

The purpose of this contract was to develop a high rate (200 Mbps), bandwidth efficient, modulation format using low cost hardware, in 1990's technology. The modulation format chosen is 16-ary continuous phase frequency shift keying (CPFSK). The implementation of the modulation format uses a unique combination of a limiter/discriminator followed by an accumulator to determine transmitted phase. An important feature of the modulation scheme is the way coding is applied to efficiently gain back the performance lost by the close spacing of the phase points

Clinically useful predictors for premature mortality among psychiatric patients visiting a psychiatric emergency room

OBJECTIVE: The aim of this study was to examine changes in the distribution of causes of death and mortality rates among psychiatric patients visiting a psychiatric emergency room (PER), to determine clinically useful predictors for avoiding premature mortality among these patients and to discuss possible interventions.METHOD: The study was designed as a historical prospective record linkage study of patients with at least one visit to a Danish PER in 1995-2007. Five consecutive 3-year cohorts of individuals aged 20 to &lt;80 years were identified. Data from the Danish Civil Registration System were linked to the Cause of Death Register and the Central Psychiatric Research Register, and logistic predictor analyses for premature death were performed.RESULTS: The standardised mortality ratio (SMR) of all visitors compared to the general Danish population was approximately 5. Overall, patients with drug and/or alcohol use disorder experienced at least a twofold increase in SMR compared to patients without substance use disorder. In the case of patients with schizophrenia and a concurrent substance use disorder, the SMR increased considerably. During the period, substance use disorder was the strongest predictor of premature death among visitors to a PER (odds ratio (OR) = 1.8; 95% confidence interval (CI) = 1.5, 2.2).CONCLUSION: Persons visiting the PER had an increased SMR and substance use disorders were the strongest predictor of premature death within 3 years. However, death caused by substance use disorder is preventable, and PERs are ideal points of early intervention. Systematic screening for substance use disorder at the PER and/or crisis intervention teams may be effective intervention strategies.</p

For recent reviews of ion mobility studies of biomolecules, see

An ion mobility/mass spectrometry technique has been developed to record mass-resolved ion mobility distributions for multiple ions simultaneously. The approach involves a new instrument that couples an electrospray ion source to an injected-ion drift tube/time-of-flight mass spectrometer. Individual components in a mixture of ions are separated by mobility differences in a drift tube and subsequently dispersed by mass-to-charge ratios in a time-of-flight instrument. Flight times in the mass spectrometer are much shorter than residence times in the drift tube, making it possible to record mass-resolved ion mobilities for all ions simultaneously. The result is a three-dimensional spectrum that contains collision cross section, mass-to-charge, and ion abundance information. The instrument and data acquisition system are described. Examples of combined ion mobility/time-of-flight data are presented for distributions of electrosprayed bradykinin and ubiquitin ions. Ion mobility techniques 1,2 combined with mass spectrometry (MS) make it possible to distinguish between many types of ions that have identical mass-to-charge (m/z) ratios. A limitation of these methods is that mobilities and m/z ratios are measured independently. Ion mobility distributions are typically recorded for mass-selected ions by fixing a mass spectrometer to transmit only a narrow m/z window. 1,2 For systems where multiple ions are present, such as the charge state distributions formed by electrospray ionization (ESI), 3 separate ion mobility distributions must be recorded for each m/z ion. Recently, Guevremont et al. have reported essentially the reverse approach: 4 ions are selected by differences in their mobilities in a drift tube, and mass spectra are subsequently recorded using a time-of-flight (TOF) mass spectrometer. This requires that separate mass spectra be recorded for ions with different mobilities. In both the mass-and mobility-selected approaches, ions which are not selected are discarded during experiments. This introduces an inherent inefficiency in the method and precludes direct measurements of m/z-and conformer-resolved abundance information for the total ion system. In this paper, we describe an injected-ion mobility/TOF mass spectrometer that is designed to record ion mobilities and m/z ratios for multiple ions simultaneously. Charge state distributions formed by ESI are separated by differences in their mobilities in a drift tube and then dispersed by their m/z ratios in the TOF instrument. This strategy makes it possible to record massresolved mobilities for all ions present in ESI distributions simultaneously. Thus, conformer-and m/z-resolved abundances for the total distribution of ions can be measured directly. A number of recent studies have reported ion mobility distributions for biomolecular ions. Much of the recent interest in this approach is due to the fact that information about gasphase conformations and the dynamics of folding and unfolding can be obtained. 2 Most work has involved peptides 5,6 or proteins, 2,7,8 and recently mobilities of oligosaccharides 9,10 and cross sections of DNA 11 have been reported. Several other ion mobility measurements have been made for biomolecules, with no attempt to extract information about conformations. [12][13