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PubMed2003

Characterization of phthalides in Ligusticum chuanxiong by liquid chromatographic-atmospheric pressure chemical ionization-mass spectrometry.

High-performance liquid chromatography (HPLC) with diode-array detection interfaced to atmospheric pressure chemical ionization (APCI)-mass spectrometry (MS) is applied to analyze phthalides from Chuanxiong (the rhizome of Ligusticum chuanxiong). This herb material, containing plenty of phthalide compositions, is selected as the analytical target in this paper for its hematological activity. Some of the phthalides are not stable and are difficult to analyze by gas chromatography-MS. Under optimized LC-MS-MS conditions, six phthalides in the methanol extract of Chuanxiong are unambiguously identified, and characteristic fragments are obtained using homemade reference standards. Ten other phthalides in the extract are confirmed by means of LC-APCI-MS with positive-negative ion mode and collision-induced dissociation in combination with UV spectrophotometry. The results show that LC-MS-MS is a method of choice for fast detection and detailed structural analysis of such mixtures in the crude extract of Chuanxiong.

Atmospheric Pressure↗
PubMed1999

Combination of suppressed and non-suppressed ion chromatography with atmospheric pressure ionization mass spectrometry for the determination of anions.

Non-suppressed and suppressed ion chromatography in combination with atmospheric pressure ionization mass spectrometry are compared with special respect to sensitivity for the analysis of low-molecular-mass anions. Iodate, bromate, bromide, sulfate, thiosulfate and bromide could be separated by non-suppressed ion chromatography using a low-capacity anion-exchange column and ammonium citrate as mobile phase. Absolute detection limits between 0.4 and 0.7 ng could be achieved; employing a column requiring a flow-rate of 1 ml/min for optimum performance, splitting was necessary so that only 120 microliters/min entered the interface of the mass spectrometer resulting in detection limits between 0.03 and 0.06 mg/l. The same stationary phase (packed into a narrow-bore column which allowed operation without splitting) was suitable for the separation of oxyhalides in the suppressed mode with detection limits of 0.5 microgram/l (50 pg) with sodium carbonate as eluent. The method was applied to the analysis of drinking water for oxyhalides. The sample pretreatment for the removal of matrix anions (sulfate, chloride and hydrogencarbonate) is described.

Anions↗
PubMed2000

Rapid and sensitive analysis of azadirachtin and related triterpenoids from Neem (Azadirachta indica) by high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.

Based on reversed-phase high-performance liquid chromatography (RP-HPLC) and atmospheric pressure chemical ionization (APCI) mass spectrometry, a HPLC-MS method was developed to permit the rapid qualitative and quantitative analysis of azadirachtin and related tetranortriterpenoids from seeds and tissue cultures of Neem (Azadirachta indica). APCI+ standard scanning mass spectra of the major Neem triterpenoids were recorded and utilized to select suitable ions for selected ion monitoring (SIM). Transitions for selective reaction monitoring (SRM) were based on MS-MS experiments. Using SIM, major Neem triterpenoids were detected in callus culture material and seed kernels of A. indica. The limit of detection for azadirachtin in extract samples (approximately 1 ng ml(-1) or 10 pg in SIM mode) was determined to be (with respect to injected absolute amounts) approximately 1000-times lower than values quoted in the literature for existing HPLC methods (approximately 200 ng ml(-1) or 10 ng). In addition to high sensitivity, the HPLC-MS method is able to tolerate minimal sample preparation and purification, dramatically reducing total analysis time.

Atmospheric Pressure↗
PubMed1999

Separation and identification of various carotenoids by C30 reversed-phase high-performance liquid chromatography coupled to UV and atmospheric pressure chemical ionization mass spectrometric detection.

In this paper the application of on-line HPLC-UV-APCI (atmospheric pressure chemical ionization) mass spectrometry (MS) coupling for the separation and determination of different carotenoids as well as cis/trans isomers of beta-carotene is reported. All HPLC separations were carried out under RP conditions on self-synthesized polymeric C30 phases. The analysis of a carotenoid mixture containing astaxanthin, canthaxanthin, zeaxanthin, echinenone and beta-carotene by HPLC-APCI-MS was achieved by scanning the mass range from m/z 200 to 700. For the characterization of a sample containing cis/trans isomers of beta-carotene as well as their oxidation products, a photodiode-array UV-visible absorbance detector was used in addition between the column and the mass spectrometer for structural elucidation of the geometrical isomers. The detection limit for beta-carotene in positive-ion APCI-MS was determined to be 1 pmol. In addition, an extract of non-polar substances in vegetable juice has been analyzed by HPLC-APCI-MS. The included carotenoids could be identified by their masses and their retention times.

Atmospheric Pressure↗
PubMed2005

Positive ion chemistry of esters of carboxylic acids in air plasma at atmospheric pressure.

Ionization of esters of carboxylic acids RCOOR' (R = H, alkyl; R' = alkyl) within the air plasma of the Atmospheric Pressure Chemical Ionization (APCI) source occurs largely via H(+)-transfer and, to a minor extent, via NO(+) association. The protonated ester MH(+) is normally observed as M(2)H(+) and as higher aggregates (M(3)H(+), M(3)H(+)(H(2)O)) also at high source temperature. The behavior of M(2)H(+) upon collisional activation is consistent with the reported dissociation of proton-bound dimers to MH(+) species that, in turn, fragment according to the known paths of lowest energy. In addition, other important product ions form within the plasma, some in very high relative abundance, which are attributed to ion-molecule condensation reactions between neutral M and either MH(+) or M(2)H(+) resulting in the elimination of CO, R'OH, alkene from the alkoxy moiety of the ester and HCOOH. A general scheme is proposed to account for the experimental observations, which suggest that the encounter complex formed between MH(+) and M or between M(2)H(+) and M may either collisionally relax to the protonated dimer or trimer, respectively, or react via covalent bond forming and cleaving steps to eliminate stable neutral molecules. The proposed scheme is supported by both the observed concentration dependence and the temperature dependence of the products relative abundances within the plasma. Such reactions can be the dominant process, as in the case of formate esters. A second significant ionization route involves addition of NO(+) to form M(n)NO(+) (n = 1, 2, 3). An additional product corresponding to [M(2)NO(+) - CO(2)] is also observed with iso- and n-butyl formate esters.

Acetates↗
PubMed2002

Quantitative determination of polar and ionic compounds in petroleum fractions by atmospheric pressure chemical ionization and electrospray ionization mass spectrometry.

The capabilities of atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) methods for quantitative analysis of polar and ionic compounds in petroleum fractions have been examined. The requirements of the analysis for sensitivity, linear dynamic range, and structural characterization have been discussed. ESI was found to be approximately two orders of magnitude more sensitive than APCI and is most suitable for the detection of analytes in weak concentrations. Equivalent relative linear dynamic ranges were observed by the two methods (at least three orders of magnitude). For the relatively high analyte concentrations examined here (e.g., 1-100 ppm or higher), the absolute area counts increased linearly with the analyte amount only in APCI, making this method more attractive for quantitative liquid chromatography/mass spectrometry (LC/MS) applications. Nevertheless, a wider range of ionic compounds can be detected by ESI than by APCI.

Air Pressure↗
PubMed2004

Negative ion-atmospheric pressure photoionization-mass spectrometry.

The ionization mechanism in the novel atmospheric pressure photoionization mass spectrometry (APPI-MS) in negative ion mode was studied thoroughly by the analysis of seven compounds in 17 solvent systems. The compounds possessed either gas-phase acidity or positive electron affinity, whereas the solvent systems had different polarities and gas-phase acidities and some of them positive electron affinities. The analytes that possessed gas-phase acidity formed deprotonated ions in proton transfer; in addition, fragments and solvent adducts were observed. The compounds of positive electron affinity formed negative molecular ions by electron capture or charge exchange and substitution products of form [M - X + O](-) by substitution reactions. The efficiency of deprotonation was decreased if the solvent used possessed higher gas-phase acidity than the analyte. Solvents of positive electron affinity captured thermal electrons and deteriorated the ionization of all the analytes. Also, the proportion of substitution products was affected by the solvent. Finally, the performances of negative ion APPI and negative ion APCI were compared. The sensitivity for the studied compounds was better in APPI, but the formation of substitution products was lower in APCI.

Journal Article↗
PubMed2002

An atmospheric pressure ion lens that improves nebulizer assisted electrospray ion sources.

An atmospheric pressure ion lens improves the performance and ease of use of a nebulizer assisted electrospray (ion spray) ion source. The lens is comprised of an oblong-shaped stainless steel ring attached to an external high voltage power supply. The lens is located near the tip of the conductive sprayer, and is maintained at a potential less than that of the sprayer. The ion lens improves the shape of the equipotential lines in the vicinity of the sprayer tip. This lens gives approximately a 2-fold reduction in the signal RSD, a 2-fold increase in the ion signal, an increase in the number of multiply charged ions, and a much broader range of usable sprayer positions.

Journal Article↗
PubMed2006

Optimization of the dopant for the trace determination of polycyclic aromatic hydrocarbons by liquid chromatography/dopant-assisted atmospheric-pressure photoionization/mass spectrometry.

The composition of the dopant for the analysis of polycyclic aromatic hydrocarbons (PAHs) by liquid chromatography/dopant-assisted atmospheric-pressure photoionization/mass spectrometry under reversed-phase conditions was optimized to enhance the ionization efficiency for PAHs. The most suitable dopant was a toluene/anisole mixture (99.5:0.5, v/v) and it could improve limit of detections (LODs) to 0.79-168 ng mL(-1) (signal-to-noise (S/N)=3) for 16 common PAHs. The LODs are 3.8-40 times lower than those obtained with toluene alone and are comparable to those obtained using gas chromatography/mass spectrometry.

Atmospheric Pressure↗
PubMed2001

Elucidation of the composition of bovine milk fat triacylglycerols using high-performance liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry.

Bovine milk fat triacylglycerols (TAGs) have been characterised using high-performance liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry (HPLC-APCI-MS) and high-temperature gas chromatography-mass spectrometry (GC-MS). The complex nature of the fat meant that prefractionation was necessary to provide simpler fractions for more detailed molecular analyses. Silica thin-layer chromatography gave rise to two fractions, one of which contained predominantly butyric acid containing TAGs. Gel permeation chromatography (GPC) gave rise to 16 fractions, which were subsequently analysed using HPLC-APCI-MS. Twelve of the GPC fractions were also analysed by high-temperature GC-MS using a capillary column coated with a polarisable stationary phase. TAGs present in the fractions were correlated with those in the chromatogram of the whole milk fat through retention time comparison and the use of mass chromatograms. In total, 120 TAGs were identified.

Animals↗
PubMed2004

Multiple-stage mass spectrometric analysis of six pesticides in oranges by liquid chromatography-atmospheric pressure chemical ionization-ion trap mass spectrometry.

Six pesticides were determined by liquid chromatography (LC) with positive ion (PI) atmospheric pressure chemical ionization quadrupole ion-trap tandem mass spectrometry (APCI-MS-MS). Ion fragmentation was studied by MS, MS2 and MS3. Fragmentation of the pesticides produced ions formed by various losses from the side-chains and through heterocyclic ring opening, but without any common fragmentation pathway. Multiple reaction monitoring (MRM) of MS, MS2 and MS3 was used to identify and quantify the pesticides. The samples were extracted with ethyl acetate and dried over anhydrous sodium sulfate. Comparison of the three MS modes showed that MS3 is slightly less sensitive but much more selective. Recoveries from oranges were 72-94% at the limit of quantification (LOQ) level for all MS modes. The LOQs were 0.001-0.3 mg kg(-1) quantifying by means of the MS3 product ion. The method was used to analyse a number of orange samples. This is the first report on using MS3 product ions for quantification of pesticide residues.

Atmospheric Pressure↗
PubMed1984

Effect of reduced atmospheric pressure on patients with fluctuating hearing loss due to Ménière's disease.

Subjective symptomatic and objective audiologic effects of reduced atmospheric pressure on patients with confirmed fluctuating hearing loss due to Ménière's disease were statistically assessed on a prospective basis. The effect of hypobaric environments on absolute hearing thresholds was investigated in 10 normal subjects at 6,500 ft. Absolute hearing threshold levels obtained at altitude, after one hour altitude exposure, and on descent to normobaric conditions were compared with levels obtained prior to the hypobaric exposure. The results indicated slightly increasing sensitivity of the audiometer headphones with altitude and an insignificant difference in hearing threshold when comparing the differing experimental conditions. The Ménière's disease study group of 16 patients was followed symptomatically and audiologically for one year prehypobaric exposure and for one month post-treatment. The results in this group utilizing the same experimental protocol as with normal subjects indicated a mild deterioration of hearing in the lower frequencies (1,000, 2,000 Hz and calculating the Ménière's pure tone average) despite significant improvements in the vertigo and disability components of their disease.

Adolescent↗
PubMedDate not supplied

Use of the Microwave-Assisted Process in extraction of fat from meat, dairy, and egg products under atmospheric pressure conditions.

Fat from meat, dairy, and egg products was extracted by using Microwave-Assisted Process (MAP) technology under atmospheric pressure conditions. Fat content was determined gravimetrically after extraction with microwaves and organic solvents that are transparent to microwaves relative to the sample. (In situ hydrolysis was performed for dairy and egg products.) Fat from the food sample migrated completely to the extractant when samples were irradiated with focused microwave for a total of 3 min for meat products, 1 min for dairy products, and 4 min for egg products. Unlike current methods used for determining fat in meat products, the microwave-assisted method does not require a dry sample, because moisture in the sample (around 75%) enhances the efficiency of extraction. No preprocessing was required for meat samples other than homogenization, which is critical, as it is for other current methods. In addition to speed and ease of use, the features of this technology are low solvent consumption, low energy consumption, reproducibility, and recoveries similar to or even better than those of conventional extraction methods.

Atmospheric Pressure↗
PubMed1999

Simultaneous determination of residual tetracyclines in foods by high-performance liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry.

We established a method for precisely determining residual tetracycline antibiotics (TCs) in foods by atmospheric pressure chemical ionization liquid chromatography-tandem mass spectrometry (APCI LC-MS-MS) using selected reaction monitoring with an internal standard. By setting the nebulizer probe temperature to 475 degrees C, we were able to use a mobile phase containing oxalic acid without clogging problems at the APCI interface, since oxalic acid decomposes to carbon dioxide and water at high temperature. DMCTC was very effective as an internal standard for determining TCs in various foods. TCs were cleaned up using a Bond Elut ENV cartridge and analysed by APCI LC-MS-MS. The recovery of TCs from various foods including animal tissues, honey, milk, eggs, and fish fortified at levels of 0.05, 0.10, and 0.50 ppm averaged 60.1-88.9%, with an RSD of 1.2-8.7%. The detection limits were 0.001 ppm for OTC and TC, 0.004 ppm for CTC, and 0.002 ppm for DC. The present method was also successfully used to determine TCs in swine kidney samples that were previously found by microbiological assay.

Animals↗
PubMed2005

On-line capillary electrophoresis-mass spectrometry using dopant-assisted atmospheric pressure photoionization: setup and system performance.

The on-line coupling of capillary electrophoresis (CE) and mass spectrometry (MS) via atmospheric pressure photoionization (APPI) is demonstrated. To achieve CE-APPI-MS, an adapted coaxial sheath-flow interface was combined with an ion-trap mass spectrometer equipped with an APPI source originally designed for liquid chromatography-MS. Effective photoionization of test compounds was accomplished after optimization of several interface and MS parameters, and of the composition and flow rate of the sheath liquid. Further enhancement of the ionization efficiency could be achieved by adding a dopant, such as acetone or toluene, to the sheath liquid to aid indirect ionization. Acetone significantly increased the ionization of the polar test compounds by proton transfer, while toluene was more useful for the enhanced formation of molecular ions from nonpolar compounds. The effect of several common CE background electrolytes (BGEs) on the APPI-MS response of the analytes was also studied. It appeared that in contrast with electrospray ionization, nonvolatile BGEs do not cause suppression of analyte signals using APPI. Therefore, in CE-APPI-MS, a variety of buffers can be chosen, which obviously is a great advantage during method development. Remarkably, also sodium dodecyl sulfate (SDS) did not affect the photoionization of the test compounds, indicating a strong potential of APPI for the on-line coupling of micellar electrokinetic chromatography (MEKC) and MS.

Atmospheric Pressure↗
PubMed2002

Biocompatibility evaluation of ePTFE membrane modified with PEG in atmospheric pressure glow discharge.

ePTFE membranes were modified by poly(ethylene glycol) having a molecular weight of 600 (PEG-600) in atmospheric pressure glow discharge (APG) plasma treatment. ePTFE membranes were immersed in 1%, 3%, or 5% (w/v) PEG-600 in dehydrated ethanol. PEG-600-penetrated ePTFE membranes were dried in a vacuum to immediately remove ethanol, then treated with APG at 20 kHz and 60-70 W for 15 min and thoroughly washed with ethanol and water. PEG-600-modified ePTFE membranes were analyzed using contact angle measurement, Fourier transform infrared attenuated total reflectance (FTIR-ATR), and scanning electron microscopy (SEM). ePTFE membrane contact angles were reduced after PEG-600 plasma treatment. FTIR-ATR spectra showed an absorption band due to a PEG hydroxyl group (-OH). SEM showed that ePTFE fiber surfaces were uniformly immobilized with PEG-600 and retained their porous structure. A general biological evaluation of the PEG-modified ePTFE membranes showed no cytotoxicity on CHO-K1 cell lines and no hemolytic action. Albumin adsorption on the PEG-modified ePTFE membranes increased with increasing PEG-600 deposited on ePTFE membranes. Fibrinogen adsorption decreased with increasing PEG-600 deposited on ePTFE membranes. gamma-Globulin adsorption did not change before or after PEG plasma modification. 1% and 3% PEG-600 plasma-treated ePTFE only slightly increased platelet adhesion, but adhering platelets evidenced no pseudopod formation. 5% PEG-600-modified ePTFE showed relatively large numbers of platelet adhesion. We concluded that 3% PEG-600-modified ePTFE membrane had the best physical properties and biological compatibility, indicating 3% PEG-600-modified ePTFE membranes exhibit the potential for blood filter application.

Adsorption↗