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PubMed2003

Characterization of hydrophobic peptides by atmospheric pressure photoionization-mass spectrometry and tandem mass spectrometry.

The use of photoionization at atmospheric pressure shows great potential for the mass analysis of large apolar or hydrophobic peptides. Mass spectra that were obtained using this technique showed mainly singly charged ions. While polar peptides spectra do not produce fragment ions, others lead to B-type or C-type in-source fragmentation. These dissociation reactions, which could involve electron capture dissociation processes in the case of the C-type ions, are observed for hydrophobic peptides. Both the compatibility of this ionization mode with reversed- or normal-phase liquid chromatographic separation and its sensitivity allow liquid chromatography coupling to both mass spectrometry and tandem mass spectrometry for the analyses of hydrophobic peptide mixtures. Atmospheric pressure photoionization seems to be an interesting alternative method to study hydrophobic peptides that are not easily ionizable by more classical ionization techniques such as electrospray ionization and matrix-assisted laser desorption/ionization.

Amino Acid Sequence↗
PubMed1994

Effect of atmospheric pressure on hearing in normal subjects.

Hearing is assumed to be altered during or immediately after a change in atmospheric pressure, although this has not been tested experimentally. We used a soundproof pressure chamber to examine the effect of alterations in atmospheric pressure on hearing in 26 normal healthy subjects. The subjects were placed in the soundproof pressure chamber in a supine position and instructed to actively equilibrate middle ear pressure or to abstain from doing so. When the pressure was changed to +/- 500 mmH2O at 33 mmH2O/s the results were as follows: When subjects did not equilibrate middle ear pressure, air conduction at low frequency tones increased more than bone conduction. The degree of deterioration in hearing was greater when the chamber pressure was increased (descent) than where pressure was decreased (ascent). When the subjects equilibrated middle ear pressure, little change in the levels of air or bone conduction was observed. Most of the deterioration in bone conduction was considered to reflect functional loss due to increased stiffness and damping of the sound transmission mechanism.

Adult↗
PubMed2005

Advantages of atmospheric pressure photoionization mass spectrometry in support of drug discovery.

The performance of the atmospheric pressure photoionization (APPI) technique was evaluated against five sets of standards and drug-like compounds and compared to atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI). The APPI technique was first used to analyze a set of 86 drug standards with diverse structures and polarities with a 100% detection rate. More detailed studies were then performed for another three sets of both drug standards and proprietary drug candidates. All 60 test compounds in these three sets were detected by APPI with an overall higher ionization efficiency than either APCI or ESI. Most of the non-polar compounds in these three sets were not ionized by APCI or ESI. Analysis of a final set of 201 Wyeth proprietary drug candidates by APPI, APCI and ESI provided an additional comparison of the ionization techniques. The detection rates in positive ion mode were 94% for APPI, 84% for APCI, and 84% for ESI. Combining positive and negative ion mode detection, APPI detected 98% of the compounds, while APCI and ESI detected 91%, respectively. This analysis shows that APPI is a valuable tool for day-to-day usage in a pharmaceutical company setting because it is able to successfully ionize more compounds, with greater structural diversity, than the other two ionization techniques. Consequently, APPI could be considered a more universal ionization method, and therefore has great potential in high-throughput drug discovery especially for open access liquid chromatography/mass spectrometry (LC/MS) applications.

Animals↗
PubMed2002

Influence of the eluent composition on the ionization efficiency for morphine of pneumatically assisted electrospray, atmospheric-pressure chemical ionization and sonic spray.

A comparative study of three atmospheric-pressure ionization (API) sources for liquid chromatography/mass spectrometry (LC/MS), namely pneumatically assisted electrospray or ionspray (IS), atmospheric-pressure chemical ionization (APCI), and sonic spray (SS), with respect to the influence of the eluent composition on the ionization of morphine, is presented. The effect of organic modifiers, volatile acids, and buffer systems (with and without pH adjustment) in the LC mobile phase on the ionization efficiency of each interface is described. We conclude that for all three ion sources, the composition of the liquid phase had a serious impact on the ionization of the target compound. For IS and SS, very similar behavior towards the LC eluent was observed. In both cases, an increase in organic modifier resulted in an increase in ionization, while an increasing amount of volatile acid or buffer caused signal suppression. APCI, on the other hand, proved to respond completely differently towards the changes in the eluent. Again, an increased ionization was observed with an increase in organic modifier content but this time also in the presence of mobile phase additives like acids or buffers. Finally, we concluded that APCI proved to be the preferred ion source for the test compound because of its robust character and its direct applicability in traditional LC analysis.

Chromatography, Liquid↗
PubMed1989

Liquid chromatographic-atmospheric pressure ionization mass spectrometric analysis of toremifene metabolites in human urine.

A liquid chromatographic-atmospheric pressure ionization mass spectrometric method has been developed for the analysis of toremifene metabolites in human urine after oral administration. This ionization source is a useful device for studying metabolites of toremifene because the total effluent from high-performance liquid chromatography is fed through an interface with a direct heating nebulizer and vaporizer at atmospheric pressure. To obtain good sensitivity the use of the right mobile phase is very important: ammonium acetate in methanol in the case of toremifene and its metabolites. Four unconjugated and three glucuronide-conjugated metabolites were detected in human urine. The majority of these were new and distinguishable from known metabolites.

Antineoplastic Agents↗
PubMed1988

Critical water temperature during water immersion at various atmospheric pressures.

The present work was undertaken to determine the effect of atmospheric pressure [ranging from a high altitude of 4,300 m above sea level or 0.6 atmospheres absolute (ATA) to depths of 10 m deep or 2 ATA] on the critical water temperature (Tcw), defined as the lowest water temperature a subject can tolerate at rest for 2 h without shivering, of the unprotected subject during water immersion. Nine healthy males wearing only shorts were subjected to immersion to the neck in water at 0.6, 1, and 2 ATA while resting for 2 h. Continuous measurements included esophageal (Tes) and skin (Tsk) temperatures, direct heat loss from the skin (Htissue), and insulation of the tissue (Itissue). The Tcw was significantly higher at 0.6 ATA than 1 and 2 ATA: however, Tcw at 1 ATA was identical to that at 2 ATA. The metabolic heat production remained unchanged among the pressures. During the 2-h immersion in Tcw, Tes was identical among all atmospheric pressures: however, Tsk was significantly higher (P less than 0.05) at 0.6 ATA and was identical between 1 and 2 ATA. The overall mean Itissue was near maximal during immersion in Tcw in each pressure, and no difference was detected among the pressures. However, Itissue at the acral extremities (arm, hand, and foot) decreased significantly at 0.6 ATA, and subsequently heat loss from these parts was increased, which elevated an extremity-to-trunk heat loss ratio to 1.4 at 0.6 ATA from 1.1 at 1 and 2 ATA.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2002

Atmospheric pressure photoionization liquid chromatographic-mass spectrometric determination of idoxifene and its metabolites in human plasma.

This paper describes a comparison between atmospheric pressure chemical ionization (APCI) and the recently introduced atmospheric pressure photoionization (APPI) interface for the LC-MS determination of idoxifene and its major metabolite, SB245419 (SB19), in human plasma. The results indicate that analyte response in APPI is highly dependent on the solvent composition, especially to water in the mobile phase. Other parameters investigated are the mobile phase flow-rate, the chemical noise, and signal suppression by matrix interferences. APPI appears to be six to eight times more sensitive than APCI for idoxifene and its SB245419 metabolite; the response for the SB245420 metabolite is considerably better than for APCI conditions, but still not sufficient for trace level pharmacokinetic determinations in human plasma. The LOQ for the parent drug and its major metabolite were 10 and 25 ng/ml, respectively, in human plasma. From post-column infusion experiments we conclude that there is little difference in matrix suppression between APCI and APPI. From these studies we suggest APPI may be an additional tool in pharmaceutical LC-MS applications.

Atmospheric Pressure↗
PubMed1998

Determination of n-hexane metabolites by liquid chromatography/mass spectrometry. 1. 2,5-hexanedione and other phase I metabolites in untreated and hydrolyzed urine samples by atmospheric pressure chemical ionization.

The capabilities of atmospheric pressure chemical ionization liquid chromatography/mass spectrometry (APCI-LC/MS) were investigated for the analysis of urinary 2,5-hexanedione (2,5-HD) and for the identification and characterization of other n-hexane Phase I metabolites in hydrolized urine samples. Chromatography was performed under reversed phase conditions at 0.75 mL min-1 flow rate. The ionization of 2,5-HD and other n-hexane metabolites was obtained in positive ion mode. After optimization of several interface parameters, the linearity, sensitivity and precision of the method were determined operating in the selected ion monitoring mode. Detection limits were 0.02 and 0.05 mg L-1 in water and urine respectively, with linear calibration curves in the 0.05-10 L-1 concentration range. Repeatability and both intra-day and inter-day precision were determined at two concentration levels (0.5 and 5.0 mg L-1), and relative standard deviations were in the 1.3%-5.3% range. The method was applied to the quantitative analysis of 2,5-HD in urine samples from an external Quality Assurance Programme for Organic Solvent Metabolites. Moreover, the metabolites 5-hydroxy-2-hexanone, 2,5-hexanediol and 4,5-dihydroxy-2-hexanone were identified and confirmed in hydrolyzed urine of rats exposed to n-hexane.

Air Ionization↗
PubMed1996

Quantitative analysis of triglycerides using atmospheric pressure chemical ionization-mass spectrometry.

Atmospheric pressure chemical ionization-mass spectrometry (APCI-MS) was used for quantitative analysis of triglycerides (TG) separated by reverse-phase high-performance liquid chromatography. APCI-MS was used for analysis of mono-acid TG standards containing deuterated internal standard, of a synthetic mixture of heterogeneous TG, of randomized and normal soybean oils and of randomized and normal lard samples. Quantitation of the TG by four approaches based on APCI-MS were compared, and these were compared to quantitation obtained using liquid chromatography (LC) with flame-ionization detection (FID). The APCI-MS methods were based on (i) calibration curves from data for mono-acid TG standards, (ii) response factors obtained from a synthetic mixture of TG, (iii) response factors calculated from comparison of randomized samples to their statistically expected compositions, and (iv) response factors calculated from comparison of fatty acid (FA) compositions calculated from TG compositions to FA compositions obtained by calibrated gas chromatography (GC) with FID. Response factors derived from a synthetic mixture were not widely applicable to samples of disparate composition. The TG compositions obtained using APCI-MS data without application of response factors had average relative errors very similar to those obtained using LC-FID. Numerous TG species were identified using LC/APCI-MS which were undetected using LC-FID. Two quantitation methods, based on response factors calculated from randomized samples or on response factors calculated from FA compositions, both gave similar results for all samples. The TG compositions obtained using response factors calculated from FA compositions showed less average relative error than was obtained from LC-FID data, and were in good agreement with predicted compositions for the synthetic mixture and for randomized soybean oil and lard samples.

Chromatography, High Pressure Liquid↗
PubMed2001

Organic chloramine analysis and free chlorine quantification by electrospray and atmospheric pressure chemical ionization tandem mass spectrometry.

Atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI), together with tandem mass spectrometry (MSn), are used to study the mechanism of chlorination of amines and to develop a method for qualitative and quantitative determination of organic chloramines. Cyclohexylamine and 1,4-butanediamine (putrescine) are used as model compounds to investigate the mechanisms of the reactions between primary aliphatic amines and hypochlorous acid (aqueous Cl2). The chlorination products are identified and characterized by collision-induced dissociation (CID) and H/D exchange. Chlorination occurs by electrophilic addition of Cl+ and may be followed by HCl elimination, hydrolysis, or, in the case of diamines, amine elimination by intramolecular nucleophilic substitution. The relative rates of chlorination at amine and chloramine nitrogens are a function of pH and depend on the basicity of the amine. A novel method for active chlorine quantification using ESI or APCI mass spectrometry is suggested on the basis of the extent of chlorination of a sacrifical amine standard. This measurement has a limit of detection for N-chlorocyclohexylamine in the range of 0.1-10 microM, a linear dynamic range of 10(2)-10(3), and an accuracy of +/-10%, as determined for wastewater samples.

Journal Article↗
PubMed2000

Determination of glucosinolates in rapeseed and Thlaspi caerulescens plants by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.

Liquid chromatography-atmospheric pressure chemical ionization mass spectrometry was used to identify glucosinolates in plant extracts. Optimization of the analytical conditions and the determination of the method detection limit was performed using commercial 2-propenylglucosinolate (sinigrin). Optimal values for the following parameters were determined: nebulization pressure, gas temperature, flux of drying gas, capillar voltage, corona current and fragmentor conditions. The method detection limit for sinigrin was 2.85 ng. For validation of the method the glucosinolates in reference material (rapeseed) from the Community Bureau of Reference Materials (BCR) were analyzed. The method was applied for the determination of glucosinolates in Thlaspi caerulescens plants.

Atmospheric Pressure↗
PubMed1993

Analysis of polyols in uremic serum by liquid chromatography combined with atmospheric pressure chemical ionization mass spectrometry.

Liquid chromatography with atmospheric pressure chemical ionization mass spectrometry in the negative-ion mode was used to analyse polyols in uremic serum obtained from haemodialysis patients. With post-column addition of 1% chloroform-methanol as an ionization accelerating solvent, the chloride addition ions, [M+Cl]-, were detected as base peaks, and the molecular masses of the polyols were easily determined by comparing [M+Cl]- and [M - H]- ions. Concentrations of erythritol, myoinositol, mannitol and sorbitol were markedly increased, and that of 1,5-anhydroglucitol was markedly decreased in the uremic serum compared with normal serum. After haemodialysis, the serum concentration of these polyols decreased significantly. This method was found to be useful in analysing the profile of polyols.

Atmospheric Pressure↗
PubMed2006

Sterilization of bacteria, yeast, and bacterial endospores by atmospheric-pressure cold plasma using helium and oxygen.

Atmospheric-pressure cold plasma (APCP) using helium/oxygen was developed and tested as a suitable sterilization method in a clinical environment. The sterilizing effect of this method is not due to UV light, which is known to be the major sterilization factor of APCP, but instead results from the action of reactive oxygen radicals. Escherichia coli, Staphylococcus aureus, and Saccharomyces cerevisiae deposited on a nitrocellulose filter membrane or Bacillus subtilis spores deposited on polypropylene plates were exposed to helium/oxygen plasma generated with AC input power at 10 kHz, 6 kV. After plasma treatment, nitrocellulose filter membranes were overlaid on fresh solid media and CFUs were counted after incubation overnight. D-values were 18 sec for E. coli, 19 sec for S. aureus, 1 min 55 sec for S. cerevisiae, and 14 min for B. subtilis spores. D-values of bacteria and yeast were dependent on the initial inoculation concentration, while the D-value of B. subtilis spores showed no correlation. When treated cells were observed with a scanning electron microscope, E. coli was more heavily damaged than S. aureus, S. cerevisiae exhibited peeling, and B. subtilis spores exhibited shrunken morphology. Results showed that APCP using helium/oxygen has many advantages as a sterilization method, especially in a clinical environment with conditions such as stable temperature, unlimited sample size, and no harmful gas production.

Atmospheric Pressure↗
PubMed1980

Applications of a versatile technique for trace analysis: atmospheric pressure negative chemical ionization.

The ability to use ambient air as a carrier and reagent gas in an atmospheric pressure chemical ionization source allows instantaneous air analysis to be combined with hypersensitivity toward a wide variety of compounds. The TAGA (Trace Atmospheric Gas Analyser) is an instrument which is designed to use both positive and negative atmospheric pressure chemical ionization (APCI) for trace gas analysis; this paper describes several applications of negative APCI which demonstrates that the technique is not limited to environmental monitoring. Examples are described which suggest that the TAGA can be used for the detection of illicit drugs and explosives, and for the analysis of breath or skin emissions, as well as for air pollution measurements. The applications are not restricted by the use of ambient air as a reagent gas; addition to the air carrier of various gases allows specific reagent ions such as Cl- or Br- to be generated. Furthermore, in certain situations pure gas carriers can be used to provide even more flexibility in the ion chemistry, with a short term absorber-desorber system used to transfer the sample from the ambient air into the ion source region. The potential uses for APCI are expanding continuously as the understanding of the complex ion-molecule chemistry grows. This paper underlines the complementary relation between the development of new negative chemical ionization (NCI) techniques and practical applications using the TAGA system.

Air↗
PubMed2001

Pure atmospheric pressure promotes an expression of osteopontin in human aortic smooth muscle cells.

Although the types of pathophysiological stimulation that initiate an overexpression of OPN have yet to be determined, we hypothesized that mechanical stress is one of the candidates which initiates OPN expression in vascular smooth muscle cells. Cell proliferation assay indicated that a pure atmospheric pressure of 160 mmHg activated cell proliferation by 11% in human aortic smooth muscle cells (HASMC) compared to nonpressurized controls. Immunoblot analysis probed with an anti-OPN antibody demonstrated a 50% increase in OPN. Dual-luciferase reporter assay demonstrated that OPN promoter, corresponding to the -771 through -1 region of OPN gene, was highly responsive to pure atmospheric pressure by ten times that of the control. From these observations, we concluded that pure atmospheric pressure directly promotes an expression of OPN in HASMC, with these results also suggesting that high blood pressure-mediated mechanical compression is involved in the process of atherosclerosis and remodeling via OPN expression in HASMC.

Animals↗
PubMed2002

Laser desorption-atmospheric pressure chemical ionization mass spectrometry for the analysis of peptides from aqueous solutions.

A recently reported ionization method, comprising an infrared (IR) laser pulse to desorb (LD) analyte species, followed by atmospheric pressure chemical ionization (APCI) with a corona discharge (LD-APCI) to effect ionization of the desorbed neutral analyte molecules, is described for the direct analysis of aqueous peptide solutions. The source employs a heated capillary atmospheric pressure (AP) inlet coupled to a quadrupole ion trap mass spectrometer and allows sampling under normal ambient air conditions. By use of the corona discharge, signals of the atmospheric pressure infrared matrix-assisted laser desorption/ionization (AP-IR-MALDI)-generated analyte protonated molecule were enhanced by factors as large as 1400. In addition, the acid modifier trifluoroacetic acid (TFA) was found to improve the AP-IR-MALDI-generated signal by a factor of approximately 10, whereas the LD-APCI generated signal yielded a 100-fold increase. In this study, the use of the corona discharge is described to enhance the analyte signal generated via AP-IR-MALDI and, as a tool, to probe the gas-phase neutral molecule population generated by the MALDI process. Finally, through the decoupling of desorption from ionization, implications regarding the application of LD-APCI for the direct analysis of numerous new analyte containing matrixes (e.g., polyacrylamide gel electrophoresis (PAGE), tissue, etc.) are discussed.

Peptides↗
PubMedDate not supplied

Influence of tapping-time and atmospheric pressure on concentrations of monoamine metabolites in the cerebrospinal fluid: a prospective study in female volunteers.

Lumbar puncture was performed on 12 healthy female volunteers at the L4-5 level. CSF concentrations of 5-HIAA, HVA and HMPG were included in turn as dependent variables in repeated analyses of covariance with age, height, tapping-time, atmospheric pressure and the distance on the spine in the lying position as regressors. Use or non-use of oral contraceptives was included as a nominal variable. Results obtained were confirmed by nonparametric statistics. We found significant relationships between 5-HIAA and HVA, respectively, and height when the concentrations per minute of tapping-time (nM/min) were used as dependent variables. Hypothetically, the tapping-time mirrors the transport of concentrated CSF from the cranial to the caudal region when sitting up. We also found significant influences of atmospheric pressure and the use or non-use of oral contraceptives on HMPG. The role of atmospheric pressure is not clear but it might contribute to the transport of HMPG from the periphery to the CSF or affect the outflow of HMPG from the lumbar CSF compartment. The contribution of oral contraceptives might reflect interactions in the cerebral catecholamine metabolism.

Adult↗