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PubMed2004

An atmospheric pressure chemical ionization study of the positive and negative ion chemistry of the hydrofluorocarbons 1,1-difluoroethane (HFC-152a) and 1,1,1,2-tetrafluoroethane (HFC-134a) and of perfluoro-n-hexane (FC-72) in air plasma at atmospheric pressure.

A report is given on the ionization/dissociation behavior of the title compounds within air plasmas produced by electrical corona discharges at atmospheric pressure: both positive and negative ions were investigated at different temperatures using atmospheric pressure chemical ionization mass spectrometry (APCI-MS). CHF(2)CH(3) (HFC-152a) undergoes efficient ionic oxidation to C(2)H(5)O(+), in which the oxygen comes from water present in the plasma. In contrast, CF(3)CH(2)F (HFC-134a) does not produce any characteristic positive ion under APCI conditions, its presence within the plasma being revealed only as a neutral ligand in ion-molecule complexes with ions of the background (H(3)O(+) and NO(+)). Analogously, the perfluorocarbon FC-72 (n-C(6)F(14)) does not produce significant positive ions at 30 degrees C: at high temperature, however, it undergoes dissociative ionization to form many product ions including C(3)F(6)(+), C(2)F(4)(+), C(n)F(2n+1)(+) and a few families of oxygen containing cations (C(n)F(2n+1)OH(2)(+), C(n)F(2n)OH(+), C(n)F(2n-1)O(+), C(n)F(2n-1)O(2)H(2)(+), C(n)F(2n-2)O(2)H(+)) which are suggested to derive from C(n)F(2n+1)(+) in a cascade of steps initiated by condensation with water followed by steps of HF elimination and H(2)O addition. Negative ions formed from the fluoroethanes CHF(2)CH(3) and CF(3)CH(2)F (M) include complexes with ions of the background, O(2)(-)(M), O(3)(-)(M) and some higher complexes involving also water, and complexes of the fluoride ion, F(-)(H(2)O), F(-)(M) and higher complexes with both M and H(2)O also together. The interesting product O(2)(-)(HF) is also formed from 1,1-difluoroethane. In contrast to the HFCs, perfluoro-n-hexane gives stable molecular anions, M(-), which at low source temperature or in humidified air are also detected as hydrates, M(-)(H(2)O). In addition, in humidified air F(-)(H(2)O)(n) complexes are also formed. The reactions leading to all major positive and negative product ions are discussed also with reference to available thermochemical data and relevant literature reports. The effects on both positive and negative APCI spectra due to ion activation via increasing V(cone) are also reported and discussed: several interesting endothermic processes are observed under these conditions. The results provide important information on the role of ionic reactions in non-thermal plasma processes.

Air↗
PubMed2002

Characterization of triglycerides in vegetable oils by silver-ion packed-column supercritical fluid chromatography coupled to mass spectroscopy with atmospheric pressure chemical ionization and coordination ion spray.

Characterization of triglycerides in vegetable oils was achieved by silver-ion packed-column supercritical fluid chromatography (SI-pSFC) with mass spectrometric detection. Hyphenation was made using commercially available liquid chromatography-mass spectrometry (LC-MS) interfaces without any modification. A make-up fluid was delivered through a T-piece placed before or after the SFC restrictor by means of a high pressure pump. Atmospheric pressure chemical ionization (APCI) and coordination ion spray (CIS) with silver ions were used as ionization modes. Compared to UV detection, the sensitivity was increased by a factor of 100. Both ionization modes are generating similar structural information. Molecular ions [M-H]+ or [M-Ag(-)] are observed in the mass spectra with exception of the saturated triglycerides for which only CIS gives intense molecular ions. The position at which the fatty acids are esterified to the glycerol backbone can be elucidated by pSFC-APCI although it remains speculative whether this is valid for highly unsaturated triglycerides because reference compounds are not available to proof this.

Atmospheric Pressure↗
PubMed2006

Mode of action of a novel nonchemical method of insect control: atmospheric pressure plasma discharge.

Atmospheric pressure plasma discharge (APPD) has been applied to a number of industrial applications, including the bacterial sterilization of medical equipment of bacteria. APPD may also have applications in insect control. A positive correlation was found between exposure time to APPD and mortality of western flower thrips, Frankliniella occidentalis (Pergande); tobacco thrips, Frankliniella fusca (Hinds); Asian tiger mosquito, Aedes albopictus (Skuse); twospotted spider mite, Tetranychus urticae Koch; and German cockroach, Blattella germanica (L.), with the level of mortality also increasing with time after treatment. Cockroaches exposed to APPD for 60, 90, 120, and 180 s lost on average 7.5 +/- 0.8, 8.1 +/- 0.6, 8.7 +/- 0.4, and 10.1 +/- 1.1 (+/-1 SEM) mg of water weight, respectively, which was an increase over that of the controls. The metabolic rate of cockroaches exposed to plasma for 180 s increased from 0.79 +/- 0.03 to 1.07 +/- 0.04 ml of oxygen consumed mg-cockroach(-1) h(-1) at standard temperature and pressure. The level of cuticular hydrocarbons identified by electron impact gas chromatography-mass spectrometry were not significantly affected by plasma exposure in the green peach aphid, Myzus persicae (Sulzer), German cockroach, and citrus mealybug, Planococcus citri (Risso), except for a reduction in n-tritriacontane in the latter. However, changes in the behavior of cockroaches after plasma exposure, including the loss of photo-, vibro-, and thigmotropic responses, inability to right themselves, and hyperexcitatory symptoms, suggest that the site of action of APPD in insects is the nervous and/or neuromuscular system.

Acari↗
PubMedDate not supplied

Atmospheric pressure photoionization mass spectrometry.

Atmospheric pressure photoionization (APPI) is the last arrival in the family of atmospheric pressure ionization (API) methods to couple mass spectrometry (MS) to liquid-phase separation techniques. The basic idea was to further extend the fields of application of liquid chromatography (LC)-MS to those molecules that are not, or are poorly amenable, to electrospray (ESI) or APCI. The present review explores the literature. After a short introduction with an historical background and the premises for its development, we describe the technique, its physical principles, and the factors that affect its efficiency. The review also presents a survey of applications in different fields.

Atmospheric Pressure↗
PubMed1993

Detection of liquid injection using an atmospheric pressure ionization radiofrequency plasma source.

An atmospheric pressure rf plasma source which operates in a variety of different buffer gases has been developed as an ionization method for organic samples introduced by liquid injection into atmospheric pressure ionization mass spectrometry (API/MS). The rf source can operate in He at < 1 W of load power at 165 kHz. It can also be sustained in Ar, N2, air, and CO2 at a load power of < 15 W. In most cases studied, the protonated molecule, MH+, is observed with little or no fragmentation even under the relatively high current conditions of the discharge. However, using increasingly higher acceleration voltages between the skimmers in the differentially pumped region between atmospheric pressure and high vacuum, one can induce fragmentation via collision-induced dissociation. This can be assisted in these experiments via the use of a heavy buffer gas. The detection limits achieved for rf/API plasma detection are typically in the low femtomole region for small organic molecules including neurotransmitters, PTH-amino acids, steroids, drugs, pesticides, and explosives. The detection can be performed with quantitation over at least 4 orders of magnitude.

Air Ionization↗
PubMed1982

Pressure-volume relationships above and below atmospheric pressure in the synovial cavity of the rabbit knee.

1. The pressure-volume relationship in the synovial cavity of the rabbit knee was investigated by the infusion of a non-absorbable oil into the cavity. 2. The pressure (P)-volume (V) curve was sigmoid. Its slope dP/dV (elastance) was steep at subatmospheric, physiological pressures, least steep at 5 cm H2O, and steepened progressively at higher, pathological pressures. 3. Elastance dP/dV was a good approximation to linear functions of P below atmospheric pressure and above 5 cm H2O. Each part of the pressure-volume relationship could therefore be described by an exponential expression. 4. Flexion of the joint increased pressure at a given volume. This was mainly due to steepening of the pressure-volume curve, and also partly due to a shift towards the pressure axis. 5. Pressure-volume curves determined by the infusion of normal saline or Krebs solution were grossly distorted, because these fluids were absorbed across the permeable synovium. 6. The physiological significance of the synovial pressure-volume curve is discussed, and mechanical explanations of the curve are suggested.

Animals↗
PubMed2004

Determination of aldehydes and ketones using derivatization with 2,4-dinitrophenylhydrazine and liquid chromatography-atmospheric pressure photoionization-mass spectrometry.

Atmospheric pressure photoionization-mass spectrometry (APPI-MS) is used for the analysis of aldehydes and ketones after derivatization with 2,4-dinitrophenylhydrazine (DNPH) and liquid chromatographic separation. In the negative ion mode, the [M - H]- pseudomolecular ions are most abundant for the carbonyls. Compared with the established atmospheric pressure chemical ionization (APCI)-MS, limits of detection are typically lower using similar conditions. Automobile exhaust and cigarette exhaust samples were analyzed with APPI-MS and APCI-MS in combination with an ion trap mass analyzer. Due to improved limits of detection, more of the less abundant long-chain carbonyls are detected with APPI-MS in real samples. While 2,4-dinitrophenylazide, a known reaction product of DNPH with nitrogen dioxide, is detected in APCI-MS due to dissociative electron capture, it is not observed at all in APPI-MS.

Aldehydes↗
PubMed2003

The potential of organic (electrospray- and atmospheric pressure chemical ionisation) mass spectrometric techniques coupled to liquid-phase separation for speciation analysis.

The use of mass spectrometry based on atmospheric pressure ionisation techniques (atmospheric pressure chemical ionisation, APCI, and electrospray ionisation, ESI) for speciation analysis is reviewed with emphasis on the literature published in and after 1999. This report accounts for the increasing interest that atmospheric pressure ionisation techniques, and in particular ESI, have found in the past years for qualitative and quantitative speciation analysis. In contrast to element-selective detectors, organic mass spectrometric techniques provide information on the intact metal species which can be used for the identification of unknown species (particularly with MS-MS detection) or the confirmation of the actual presence of species in a given sample. Due to the complexity of real samples, it is inevitable in all but the simplest cases to couple atmospheric pressure MS detection to a separation technique. Separation in the liquid phase (capillary electrophoresis or liquid chromatography in reversed phase, ion chromatographic or size-exclusion mode) is particularly suitable since the available techniques cover a very wide range of analyte polarities and molecular mass. Moreover, derivatisation can normally be avoided in liquid-phase separation. Particularly in complex environmental or biological samples, separation in one dimension is not sufficient for obtaining adequate resolution for all relevant species. In this case, multi-dimensional separation, based on orthogonal separation techniques, has proven successful. ESI-MS is also often used in parallel with inductively coupled plasma MS detection. This review is structured in two parts. In the first, the fundamentals of atmospheric pressure ionisation techniques are briefly reviewed. The second part of the review discusses recent applications including redox species, use of ESI-MS for structural elucidation of metal complexes, characterisation and quantification of small organometallic species with relevance to environment, health and food. Particular attention is given to the characterisation of biomolecules and metalloproteins (metallothioneins and phytochelatins) and to the investigation of the interaction of metals and biomolecules. Particularly in the latter field, ESI-MS is the ideal technique due to the softness of the ionisation process which allows to assume that the detected gas-phase ions are a true representation of the ions or ion-biomolecule complexes prevalent in solution. It is particularly this field, important to biochemistry, physiology and medical chemistry, where we can expect significant developments also in the future.

Atmospheric Pressure↗
PubMed2001

Direct analysis of semivolatile organic compounds in air by atmospheric pressure chemical ionization mass spectrometry.

Atmospheric pressure chemical ionization is employed for direct air analysis, without ion source modification, by using the sheath gas as the sample transport agent. A simple modification of the sheath gas inlet line allows introduction of gaseous samples into a commercial atmospheric pressure chemical ionization source. Optimization and testing of this novel air sampling method are described and detection of semivolatile compounds is shown. The analytical performance of the technique is established with methyl salicylate, including a limit of quantification of 100 pptr, a limit of detection of 50 pptr, a linear response from 100 pptr to 20 ppb, and rise and fall times of 12 and 20 s, respectively. Using reagent ion monitoring, it is shown that the protonated methanol dimer is the principal CI reagent ion leading to protonated dimethyl methylphosphonate, while the monomer is mainly responsible for protonating methyl salicylate. Since the formation of the CI reagent (methanol clusters) can be controlled by simple variation of experimental parameters, the selectivity of the method can be easily adjusted to suit the targeted analyte. Performance is found to be independent of the choice of air or nitrogen as the sheath gas (and thus as the sample matrix) and this, together with the sensitivity and speed of the technique, make it promising for field studies.

Journal Article↗
PubMed2005

Ion/molecule reactions in the orifice-skimmer region of an atmospheric pressure Penning ionization mass spectrometer.

Atmospheric pressure Penning ionization mass spectra of methanol were measured as functions of Ar or He gas pressure in the first vacuum chamber, the position of the skimmer, and the voltage applied between the orifice and the skimmer. When the orifice and the skimmer were coaxial with a distance of 4 mm, the distribution of CH3OH2+(CH3OH)n clusters was only weakly dependent on both Ar pressure (in the range of 19-220 Pa) and orifice-skimmer voltage (in the range of 1-45 V). The ion/molecule reaction CH3OH2+ + CH3OH --> CH3+(CH3OH) + H2O was observed in the free jet expansion, especially at high orifice-skimmer voltage values. When the orifice and the skimmer were off-centered and the distance between them was increased to 18 mm, the formation of large CH3OH2+(CH3OH)n clusters, as well as their dissociation, were seen. The endothermic proton transfer reaction, CH3+(CH3OH) + CH3OH --> CH3OH2+ + CH3OCH3, occurred at high orifice-skimmer voltage. The collision-induced dissociation of cluster ions by He gas in the first vacuum chamber was much more efficient than by Ar. These results demonstrated that the mass spectra are highly dependent on skimmer position and on orifice-skimmer voltage and that ions observed by mass spectrometry do not necessarily reflect the abundance of ions produced in the atmospheric pressure ion source.

Journal Article↗
PubMed1984

Spontaneous pneumothorax related to falls in atmospheric pressure.

The relation of changes in atmospheric pressure to admissions due to radiologically verified spontaneous pneumothorax, was studied in 282 consecutive patients. A fall in atmospheric pressure of at least 10 mbar within 24 h was followed by a statistically significant increase in the number of admissions 2 days later.

Atmospheric Pressure↗
PubMed2003

Stability studies of propoxur herbicide in environmental water samples by liquid chromatography-atmospheric pressure chemical ionization ion-trap mass spectrometry.

Liquid chromatography-atmospheric pressure ionization ion-trap mass spectrometry has been investigated for the analysis of polar pesticides in water. The degradation behavior of propoxur, selected as a model pesticide belonging to the N-methylcarbamate group, in various aqueous matrices (Milli-Q water, drinking water, rain water, seawater and river water) was investigated. Two interfaces of atmospheric pressure ionization, atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI), were compared during the study. Propoxur and its transformation product (N-methylformamide) were best ionized as positive ions with both APCI and ESI, while another transformation product (2-isopropoxyphenol) yielded stronger signals as negative ions only with APCI. In addition, the effects of various pH, matrix type and irradiation sources (sunlight, darkness, indoor lighting and artificial UV lamp) on the chemical degradation (hydrolysis) were also assessed. From the kinetic studies of degradation, it was found that the half-life of propoxur was reduced from 327 to 161 h in Milli-Q water with variation of irradiation conditions from dark to sunlight exposure. Degradation rates largely increased with increasing pH. The half-life of the target compound dissolved in Milli-Q water under darkness decreased from 407 to 3 h when the pH of Milli-Q water was increased from 5 to 8.5. These suggest that hydrolysis of propoxur is light-intensity and pH-dependent. In order to mimic contaminated natural environmental waters, propoxur was spiked into real water samples at 30 microg/l. The degradation of propoxur in such water samples under various conditions were studied in detail and compared. With the ion trap run in a time-scheduled single ion monitoring mode, typical limits of detection of the instrument were in the range of 1-10 microg/l.

Atmospheric Pressure↗
PubMed1979

The survival and implantation of mouse blastocysts at varying degrees of reduced atmospheric pressure.

Pregnant mice were exposed to reduced atmospheric pressures ranging from 630 to 390 mm Hg during the pre-implantation and implantation periods and the numbers of embryos surviving 85 hours post coitum compared with those in litter-mate controls. Even at a pressure of 630 mm Hg (= 1,550 mm Hg) there was a significant fall in numbers of normal blastocysts and rise in abnormal forms before implantation, and implantation sites were reduced in number. The numbers of abnormal forms increased and implantation sites decreased at lower pressures, suggesting strongly that the hypoxia of reduce atmospheric pressure was responsible for the abnormalities observed. The pre-implantation period appears to be one during which the fertilised ovum is at particular risk, both of hypoxic damage and of failure to implant. Implantation may afford a degree of protection against hypoxia.

Animals↗
PubMed2001

Relationship of aneurysmal subarachnoid hemorrhage to changes in atmospheric pressure: results of a prospective study.

OBJECT: The purpose of this study was to evaluate the relationship between atmospheric pressure and subarachnoid hemorrhage (SAH) in a region in the English Midlands. METHODS: All patients with angiographically proven SAH for the calendar year 1998 were analyzed. A geographical allocation was made based on the patients' origin within the region. The events were then compared with the data available for the local atmospheric pressures. One hundred nine patients had an SAH during the time period studied. The median atmospheric pressure recorded was 1014.5 millibars. Atmospheric pressure was modestly correlated with the number of SAHs per day (Spearman's rank correlation, r = 0.33; p < 0.0001); the daily change in atmospheric pressure also correlated mildly (r = 0.34, p < 0.0001). No other statistically significant association was found. CONCLUSIONS: The authors have shown a relationship between high atmospheric pressure and increased incidence of SAH. The underlying reason for this remains obscure.

Atmospheric Pressure↗
PubMed2001

Discrepancies in the values of standard atmospheric pressure: the riddle resolved.

Over half a century ago, when I took Beginning Physics at university, I was bothered by the anomaly that normal air pressure (which is arbitrary anyhow) was taken to be 1.013250 bar instead of a sensible 1.000000 bar. My professor could not explain why, nor could any of the many other scientists whom I have asked since then. Now in retirement, I have made a laborious search in utterly uncharted territory and discovered the answer.

Air Pressure↗
PubMedDate not supplied

[The anodyne action of narcotic analgesics and clofelin under increased atmospheric pressure].

Rat experiments have revealed that gradual increases in atmospheric pressure up to 1.1 MPa progressively alters the vocalization threshold in electrical stimulation of the tail root. Substitution of air for heliox (79.1% helium and 20.9% oxygen) leads to attenuation of the analgesic effect of hyperbarism. It is postulated that hyperbaric analgesia is due mainly to the elevated partial pressure of nitrogen. Morphine and promedol in doses of 2.5 mg/kg and clofeline in a dose of 0.1 mg failed to change analgesic effects when atmospheric pressure was increased up to 0.7 and 1.1 MPa. The analgesic effect of morphine and promedol in doses of 5 mg/kg and buprenorphine in a dose of 0.035 mg/kg under similar conditions increased during the whole period of isopression, while that of clofeline in a dose of 0.5 mg/kg increased only in the first few minutes of isopression. The analgesic action of morphoeceptine in a dose of 5 mg/kg decreased during isopression. The possible mechanisms of hyperbaric analgesia and the specific features of the analgesic action of different drugs at elevated atmospheric pressure are discussed.

Analgesics, Opioid↗