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PubMed2006

Factors affecting primary ionization in dopant-assisted atmospheric pressure photoionization (DA-APPI) for LC/MS.

The sensitivity of dopant-assisted atmospheric pressure photoionization (DA-APPI) for LC/MS is generally reduced at higher solvent flow rates. Theory suggests that quenching of excited-state precursors to the dopant ions, via collisions with vaporized solvent molecules, may be one mechanism responsible for this trend. To ascertain if the primary rate of ionization is affected by quenching, experiments were performed utilizing an ionization detector to determine the primary ion current generated by irradiating vaporized mixtures of toluene dopant and methanol solvent. The results indicate that no loss of primary ion current occurs as the solvent flow is increased, provided the dopant-to-solvent ratio is held constant. Additional primary ion current can always be generated by increasing the dopant flow rate and/or the lamp power. Thus, quenching of excited-state precursors to the dopant ions, leading to a reduction in the primary rate of ionization, is not the mechanism responsible for the observed loss of sensitivity at higher liquid solvent flow rates.

Journal Article↗
PubMed2005

Determination of linear response in the detection of aroma compounds by atmospheric pressure ionization-mass spectrometry (API-MS).

Linearity and detection thresholds of atmospheric pressure ionization-mass spectrometry (API-MS) were determined for 11 aroma compounds in air at concentrations ranging from 50 ppb to approximately 450 ppm (moles of volatile per mole of air). In most cases, the protonated molecular ion (i.e., m/z = M + 1) was the base peak throughout the range; however, some compounds showed an increase in fragmentation at lower concentrations. Detection limits varied greatly (from 50 ppb to 14 ppm) depending upon the aroma compound being measured. The linear range was also strongly dependent upon the aroma compound, with values ranging from <10-fold change in concentration to >4000-fold change in concentration depending upon the volatile being studied. The two volatiles with poor detection thresholds also exhibited the smallest linear range. Most compounds had linear ranges of >200. There was no apparent relationship between gas-phase basicity and either detection limit or linear range.

Chemical Phenomena↗
PubMed1979

Real-time analysis of breath using an atmospheric pressure ionization mass spectrometer.

A new technique is reported resulting in the direct, instantaneous analyses of trace compounds in breath. The analyses were performed using a commercial atmospheric pressure chemical ionization mass spectrometer (TAGA TM2000 APCI mass spectrometer). A known flow of breath sample is introduced into the ionization region of the mass spectrometer. The study includes the measurement and monitoring in real-time, of breath ammonia during a 24 hour and a 48 hour period. The ammonia profiles indicate a personalized daily pattern associated with each subject. This method appears to be of potential value in routine detection and treatment of hyperammonemia patients. Results also show that it is possible to obtain instantaneous analyses of several naturally occurring metabolites and other substances on breath in the ppm to ppt range, suggesting a number of diagnostic research applications.

Air↗
PubMed2001

Fragmentation of N-oxides (deoxygenation) in atmospheric pressure ionization: investigation of the activation process.

The diagnostic fragmentation of N-oxides resulting from loss of the oxygen atom (MH+ --> MH+-O) in electrospray and atmospheric pressure chemical ionization (APCI) mass spectra was investigated. When the temperature of the heated capillary tube was elevated, the ratio of the intensity of the [MH+ -16] fragment to the precursor ion (MH+) increased. This 'deoxygenation' process was associated with thermal activation and did not result from collisional activation in the desolvation region of the API source. Although the extent of 'deoxygenation' is compound-dependent, it can provide evidence for the presence of an N-oxide in a sample and can be used to distinguish N-oxides from hydroxylated metabolites (Ramanathan et al. Anal. Chem. 2000; 72: 1352). To demonstrate the practical application of thermal fragmentation of N-oxides, liquid chromatography (LC)/APCI-MS was used to distinguish an N-oxide drug from its hydroxylated metabolite in an unprocessed rat urine sample, despite the fact that the drug and its metabolite were not fully resolved by HPLC.

Animals↗
PubMed2005

Quantitative determination of endogenous sorbitol and fructose in human nerve tissues by atmospheric-pressure chemical ionization liquid chromatography/tandem mass spectrometry.

Attachment of anions to sorbitol and fructose has been shown to enhance sensitivity in both electrospray ionization (ESI) and atmospheric-pressure chemical ionization (APCI) mass spectrometry. The post-column addition of CHCl3 produced Cl-adducts of sorbitol and fructose but their signals were suppressed due to the elevated background. Different chlorinated compounds and different additive methods were systematically investigated to form more abundant Cl-adduct precursor ions and deprotonated product ions. The major causes of the high background were explored and effective methods were developed to improve the signal-to-noise ratios and reproducibility. The compositions of mobile phase, percentages of organic modifiers (MeCN, MeOH and water), columns, oven temperature, flow rates and different gradients were investigated to separate sorbitol from fructose along with their isomers including glucose, galactose, mannose, sorbose, mannitol, and dulcitol. The optimized separation was achieved on a Luna 5 mu NH2 100A column (150 x 4.6 mm) using a mobile phase containing MeCN with 0.1% of CH2Cl2 and 50% MeOH in water at a flow rate of 800 microL/min and an oven temperature of 40 degrees C using a gradient liquid chromatography (LC) system. Human nerve tissue samples were extracted by protein precipitation followed by mixed-mode solid-phase extraction. The LC/ESI-MS/MS method produced higher peak intensities than LC/APCI-MS/MS. However, there were matrix effects from extracted tissues in LC/ESI-MS/MS but not in LC/APCI-MS/MS. Consequently, APCI proved to be the more effective method of ionization. Then the LC/APCI-MS/MS method was fully validated and successfully applied to analysis of clinical samples. The concentrations of endogenous sorbitol and fructose were determined using calibration curves employing sorbitol-13C6 and fructose-13C6 as surrogate analytes. The method has provided excellent intra- and inter-assay precision and accuracy with linear ranges of 0.2-80 ng/mg for sorbitol and 1-400 ng/mg for fructose in human nerve tissues.

Atmospheric Pressure↗
PubMed2006

Rectilinear ion trap mass spectrometer with atmospheric pressure interface and electrospray ionization source.

A rectilinear ion trap (RIT) mass analyzer was incorporated into a mass spectrometer fitted with an electrospray ionization source and an atmospheric pressure interface. The RIT mass spectrometer, which was assembled in two different configurations, was used for the study of biological compounds, for which performance data are given. A variety of techniques, including the use of a balanced rf, elevated background gas pressure, automatic gain control, and resonance ejection waveforms with dynamically adjusted amplitude, were applied to enhance performance. The capabilities of the instrument were characterized using proteins, peptides, and pharmaceutical drugs. Unit resolution and an accuracy of better than m/z 0.2 was achieved for mass-to-charge (m/z) ratios up to 2000 Th at a scan rate of approximately 3000 amu/(charge.s) while reduced scan rates gave greater resolution and peak widths of less than m/z 0.5 over the same range. The mass discrimination in trapping externally generated ions was characterized over the range m/z 190-2000 and an optimized low mass cutoff value of m/z 120-140 was found to give equal trapping efficiencies over the entire range. The radial detection efficiency was measured as a function of m/z ratio and found to rise from 35% at low m/z values to more than 90% for ions of m/z 1800. The way in which the ion trapping capacity depends on the dc trapping potential was investigated by measuring the mass shift due to space charge effects, and it was shown that low trapping potentials minimize space charge effects by increasing the useful volume of the device. The collision-induced dissociation (CID) capabilities of the RIT instrument were evaluated by measuring isolation efficiency as a function of mass resolution as well as measuring peptide CID efficiencies. Overall CID efficiencies of more than 60% were easily reached, while isolation of an ion with unit resolution at m/z 524 was achieved with high rejection (>95%) of the adjacent ions. The overall analytical capabilities of the ESI-RIT instrument were demonstrated with the analysis of a mixture of pharmaceutical compounds using multiple-stage mass spectrometry.

Apoproteins↗
PubMed1999

Determination of nivalenol and deoxynivalenol in wheat using liquid chromatography-mass spectrometry with negative ion atmospheric pressure chemical ionisation.

A new, rapid and sensitive method has been developed for the determination of nivalenol (NIV) and deoxynivalenol (DON) by using HPLC in combination with an atmospheric pressure chemical ionization (APCI)-interface and a single quadrupole mass spectrometer. Different LC and MS parameters have been optimized prior to this in order to obtain better results and sensitivity. The effect of nebulizing temperature on the sensitivity and fragmentation of NIV and DON in an APCI interface was investigated. Also, the influence of the cone voltage on the fragmentation pattern was studied, which was shown to have a tremendous effect. Furthermore, the effect of modifiers such as ammonium acetate, acetic acid and ammonia on the ionisation yield of the above substances have been investigated. The extraction was carried out using acetonitrile-water. A two step purification was then applied on two different Mycosep clean up columns. We have used a modified, rapid and isocratic HPLC method combined with a negative ion APCI-MS for the separation and quantitative determination of NIV and DON in wheat extract. An RP C18 column was used for the separation of selected compounds in wheat extract with water-acetonitrile-methanol (82:9:9, v/v/v) at a flow-rate of 1 ml/min without a split. Calibration curves show good linearity and reproducibility. The detection limit and precision were determined for NIV and DON. Both compounds could be detected down to microg/kg level in wheat using selected ion monitoring of the [M-H]- ions and the main fragments.

Atmospheric Pressure↗
PubMed1999

Cheek and tongue pressures in the molar areas and the atmospheric pressure in the palatal vault in young adults.

The pressures acting on the maxillary and mandibular posterior teeth from the tongue and cheeks were measured in 24 adults aged 22-29 years. In addition, the pressure in the palatal vault was recorded. The pressure at two maxillary (buccal and lingual) and two mandibular (buccal and lingual) measuring points, and in the palatal vault was recorded simultaneously. Repeated recordings of the pressures at rest, and during chewing and swallowing were made. The pressures at rest were of similar magnitude (about 2 g/cm2) at the buccal and lingual sides of the mandibular posterior teeth. The median resting pressure at the maxillary posterior teeth was 2.7 g/cm2 on the buccal side and 1.0 g/cm2 on the lingual side. The difference in the maxilla was significant, but not in the mandible. It was concluded that the equilibrium of tooth position is maintained by the pressure from the cheeks and the tongue. During chewing and swallowing the pressures on the lingual side of the teeth were greater than those on the buccal side. At rest about half of the subjects had a negative pressure at the palatal vault, but no correlations between the resting pressure at the palatal vault and the resting pressures on the teeth were found.

Adult↗
PubMed2003

Simultaneous determination of selected endocrine disrupters (pesticides, phenols and phthalates) in water by in-field solid-phase extraction (SPE) using the prototype PROFEXS followed by on-line SPE (PROSPEKT) and analysis by liquid chromatography-atmospheric pressure chemical ionisation-mass spectrometry.

In this study, a new procedure, based on on-line solid-phase extraction (SPE) and analysis by liquid-chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS), has been developed for the simultaneous, multianalyte determination of 21 selected pesticides, phenols and phthalates in water. SPE was carried out on polymeric PLRP-s cartridges by percolating 20 mL-samples. For sample preconcentration, the performance of a prototype programmable field extraction system (PROFEXS) was evaluated against the commercial laboratory bench Prospekt system used for method development. The Profexs is designed for the automated on-site sampling, SPE preconcentration, and storage of up to 16 samples in SPE cartridges. These cartridges are further eluted and on-line analyzed with the Prospekt coupled to the chromatographic system. In the optimized method, where completely on-line SPE-LC-MS analysis of the samples is carried out with the Prospekt in the laboratory, detection limits lower than 100 ng/L, and satisfactory precision (relative standard deviations <25%) and accuracies (recovery percentages >75%) were obtained for most investigated compounds from the analysis of spiked Milli-Q water. The extraction efficiency achieved with the Profexs was comparable to that of the Prospekt for most compounds and somewhat lower for the most apolar analytes, probably due to adsorption on the pump filters. The completely on-line optimized method was applied to the analysis of surface water, ground water and drinking water from a waterworks in Barcelona. Some pesticides and phenols were found in both surface water and groundwater at ng/L or microg/L levels, but not in the final drinking water. Di(2-ethylhexyl)phthalate (DEHP) was present in all samples investigated, including blanks. To the author's knowledge, this is the first work describing the application of a fully automated on-line SPE-LC-MS method for the simultaneous analysis of pesticides, phenols, and phthalates in water, and the second one that examines the possibilities of the prototype Profexs for automated on-site SPE preconcentration of organic pollutants from water samples.

Atmospheric Pressure↗
PubMed1998

Determination of LY355703 in dog and mouse plasma by positive ion liquid chromatography/tandem mass spectrometry with atmospheric pressure chemical ionization.

A liquid chromatographic/mass spectrometric assay was developed for the determination of LY355703, a potent anti-tumor drug, in mouse and dog plasma. Empore (3M) C18 solid-phase extraction cartridges were used for sample preparation in conjunction with a positive pressure manifold. Chromatographic separation was obtained with a cyano high-performance liquid chromatographic column and detection was conducted using atmospheric pressure chemical ionization tandem mass spectrometry in the selected reaction monitoring mode. A structural analog, compound LY354504, was used as the internal standard. The assay was validated for the determination of LY355703 in mouse (ICR and NuNu) and dog (beagle) plasma. The lower and upper limits of quantitation were 2.1 and 527 ng ml-1, respectively, using a 0.1 ml plasma aliquot. The signal-to-noise ratio of a typical 2.1 ng ml-1 standard was approximately 40:1. The inter-day precision (relative standard deviation) and accuracy (relative error) derived from the analysis of validation samples at five concentrations ranged from 2.7 to 7.6% and from 4.8 to 4.5%, respectively. Throughput is approximately one sample every 3 min. This assay is simple, sensitive, accurate, precise and is being used to support toxicokinetic studies in dog and mouse.

Animals↗
PubMed2001

Sensitive and specific determination of clindamycin in human serum and bone tissue applying liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry.

A method for the quantification of clindamycin in human serum and in human bone tissue samples applying high-performance liquid chromatography with atmospheric pressure chemical ionization-mass spectrometry (APCI-MS) is presented. Lincomycin is used as the internal standard. Serum samples are prepared only by protein precipitation with acetonitrile. Bone tissue samples have to be crushed and homogenized in extraction buffer prior to analysis. The chromatographic separation is achieved on an RP-18 stationary phase with 0.02% trifluoroacetic acid in water 60%/ acetonitrile 40% v/v as mobile phase. The limits of quantification are 0.1 microg/ml for serum samples and 0.1 microg/g for bone tissue samples. The coefficients of variation for the assays are 4.48 and 8.41% at the limit of quantification for serum and bone tissue samples, respectively. Bone tissue samples as small as 50 mg can be used.

Animals↗
PubMed1998

Determination of lycopene, alpha-carotene and beta-carotene in serum by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry with selected-ion monitoring.

A selected-ion monitoring (SIM) determination of serum lycopene, alpha-carotene and beta-carotene by an atmospheric pressure chemical ionization mass spectrometry (APCI-MS) was developed. A large amount of serum cholesterols disturbed the SIM determination of carotenoids by contaminating the segment of interface with the LC-MS. Therefore, separation of carotenoids from the cholesterols was performed using a mixed solution of methanol and acetonitrile (70:30) as the mobile phase on a C18 column of mightsil ODS-5 (75 mm x 4.6 mm I.D.). The SIM determination was carried out by introducing only the peak portions of carotenoids and I.S. (squalene) by means of an auto switching valve. In the positive mode of APCI-MS, lycopene, alpha-carotene and beta-carotene were monitored at m/z 537 and I.S. was monitored at m/z 411. This method was linear for all analytes in the range of 15-150 ng for lycopene, 7-70 ng for alpha-carotene and 25-50 ng for beta-carotene. The detection limit of LC-APCI-MS-SIM for carotenoids was about 3 ng per 1 ml of serum (S/N = 3). The repeatabilities, expressed as C.V.s, were 10%, 8.4% and 5.3% for lycopene, alpha-carotene and beta-carotene, respectively. The intermediate precisions, expressed as C.V.s, were 11.2%, 8.8% and 6.5% for lycopene, alpha-carotene and beta-carotene, respectively.

Atmospheric Pressure↗
PubMed2001

Relationship between atmospheric pressure and mortality in the Madrid Autonomous Region: a time-series study.

This study set out to determine the possible influence of variations in atmospheric pressure on mortality in the Madrid Autonomous Region (MAR), taking into account the possible confounding effect of other atmospheric variables. The study was based on daily mortality data from the MAR Revenue and Excise Authority, meteorological data from Getafe Observatory and air pollution data from the Madrid Municipal Automatic Air Pollution Monitoring Grid. A time-series analysis was performed, using Box-Jenkins modelling and controlling for the respective confounding variables. Furthermore, the different variables studied (pressure, temperature, pollutants, etc.) were used to produce a multivariate model of the different causes of mortality. A significant association was found between anticyclonic trend and mortality with circulatory causes in the medium-long term and anticyclonic trend and mortality with respiratory causes in the long term.

Air Pollution↗
PubMed2000

Comparison of on-line coupling of ion-chromatography with atmospheric pressure ionization mass spectrometry and with inductively coupled plasma mass spectrometry as tools for the ultra-trace analysis of bromate in surface water samples.

Ion chromatography in combination with atmospheric pressure ionization mass spectrometry (API-MS) as well as with inductively coupled plasma mass spectrometry (ICP-MS) had been compared for trace analysis of bromate. The results indicate that both techniques yield comparable results, which are in excellent agreement with standard methods for bromate determination. Furthermore, both techniques showed almost equal absolute detection limits (approximately 50 pg bromate injected). Contrary to IC-API-MS, IC-ICP-MS can tolerate a higher salt concentration in the mobile phase. This allows the use of high-capacity columns combined with large sample volumes. This lowered the concentration based detection limits by one order of magnitude for IC-ICP-MS compared to IC-API-MS (0.06 microg/l vs. 0.5 microg/l). On the other hand, IC-API-MS is able to allow a positive identification of bromate even in cases when IC does not fully separate bromate from other bromine-containing species. The performance data of both IC-MS techniques have been established by participation in an international round robin test.

Atmospheric Pressure↗
PubMed2002

Analysis of beta-lactam antibiotics by high performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry using bromoform.

The novel identification method for a heat-unstable antibiotic, FC/TA-891 and its active metabolite (FCE22101) by high-performance liquid chromatography (HPLC)-atmospheric pressure chemical ionization mass spectrometry (APCI-MS) employing bromoform as an ionization acceleration solvent, was applied to eight penicillins and 13 cephalosporins which are groups of beta-lactam antibiotics. The conditions of HPLC-APCI-MS were examined with ampicillin. Bromoform or chloroform was added to the mobile phase in HPLC to compare the difference between bromine and chlorine adducted ions. For all penicillins except sulbenicillin, both chlorine adducted and bromine adducted ions were observed with a flow injection method. The results indicated that the relative sensitivity ratios of bromine adducted ions to [M-H](-) were higher than those of chlorine adducted ions. These bromine adduct ions could be clearly distinguished from other ions due to its isotopical ratio (1:1), leading to an easy identification of the compounds. For 13 cephalosporins, bromine adducted ions were detected in nine compounds, and chlorine adducted ions were detected in four compounds. The separation of four antibiotics was investigated with an HPLC column to apply this technique to the actual analysis. The capability was equal as in the flow injection method and it found that this technique, i.e. APCI-MS with bromoform could be applicable in the separation analysis.

Anti-Bacterial Agents↗
PubMed2004

Identification of hydroxy fatty acids by liquid chromatography-atmospheric pressure chemical ionization mass spectroscopy in Euglena gracilis.

Hydroxy fatty acids from Euglena gracilis were identified by reverse-phase high performance liquid chromatography coupled to a mass spectrometer run in atmospheric pressure chemical ionization positive ion mode. These metabolites were converted to methyl esters to improve stability and chromatographic properties. A detection limit of 20 pg/microl per injection was determined for 5-HETE methyl ester based on the signal to noise ratio of the m/z 317 ion which corresponds to the loss of a hydroxyl group (M-17) and the major fragment in all HETE methyl esters studied. This is the first report for these metabolites in E. gracilis.

Animals↗