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At least 613 records · Page 34Linked to original sources
PubMed2001

N-in-one determination of retention factors for drugs by immobilized artificial membrane chromatography coupled to atmospheric pressure chemical ionization mass spectrometry.

Immobilized artificial membrane (IAM) chromatography is widely used in drug discovery for ranking the absorption properties of drug candidates. In this work an IAM chromatography method using atmospheric pressure chemical ionization mass spectrometric detection (IAM/APCI-MS) was developed for the determination of log k(IAM) values for a mixture of compounds (9-in-one). Values were calculated from isocratic runs (0, 10, 20, 30, 35% acetonitrile) in both positive and negative modes. Good correlation (r(2) = 0.97) was achieved for n-in-one results obtained with ammonium acetate buffer and mass spectrometry, compared with the traditional method involving single compound analysis with phosphate buffered saline and an ultraviolet detector. A gradient elution method providing fast determination of relative log k(IAM) values in a single IAM/APCI-MS run was demonstrated for the same compounds.

Chromatography, High Pressure Liquid↗
PubMed1997

Determination of morphine and its 3- and 6-glucuronides, codeine, codeine-glucuronide and 6-monoacetylmorphine in body fluids by liquid chromatography atmospheric pressure chemical ionization mass spectrometry.

A selective assay of morphine-3-glucuronide (M3G), morphine-6-glucuronide (M6G), morphine, codeine, codeine-6-glucuronide (C6G) and 6-monoacetylmorphine (6-MAM) based on liquid chromatography atmospheric pressure chemical ionization mass spectrometry (LC-APCI-MS) is described. The drugs were extracted from serum, autopsy blood, urine, cerebrospinal fluid or vitreous humor using C18 solid-phase extraction cartridges and subjected to LC-APCI-MS analysis. The separation was performed on an ODS column in acetonitrile-50 mM ammonium formate buffer, pH 3.0 (5:95), using a flow-rate gradient from 0.6 to 1.1 ml/min (total analysis time was 17 min). The quantitative analysis was done using deuterated analogues of each compound. Selected-ion monitoring detection was applied: m/z 286 (for morphine, M3G-aglycone and M6G-aglycone), 289 (for morphine-d3, M3G-d3-aglycone and M6G-d3-aglycone), 300 (for codeine and C6G-aglycone), 303 (for C6G-d3-aglycone), 306 (for codeine-d6), 328 (for 6-MAM), 334 (for 6-MAM-d6), 462 (for M3G and M6G), 465 (for M3G-d3 and M6G-d3), 476 (for C6G) and 479 (for C6G-d3). The limits of quantitation were: 1 microg/l for morphine, 2 microg/l for 6-MAM, 5 microg/l for M3G, M6G and codeine and 200 microg/I for C6G. The recovery ranged from 85 to 98% for each analyte. The method appeared very selective and may be used for the routine determination of opiates in body fluids of heroin abusers and patients treated with opiates.

Analgesics, Opioid↗
PubMed2002

Development and evaluation of a nano-electrospray ionisation source for atmospheric pressure ion mobility spectrometry.

A nano-electrospray ionisation source has been designed and constructed for a high temperature ion mobility spectrometer. The drift cell was modified by replacement of the 63Ni atmospheric pressure chemical ionisation source with a tube lens/desolvation region and operated using commercial nano-electrospray capillaries. Ions were introduced into the drift region via a Bradbury-Nielson gate (pulse width 50 micros, repetition period 20 ms). A unidirectional flow of nitrogen was used as the drift gas at temperatures in the range 100-150 degrees C to aid desolvation. The performance of the nano-electrospray ion source has been demonstrated for analytes including crown ethers, amino acids and peptides. Reduced mobilities determined by nano-ESI were consistent with those reported using a 63Ni ion source.

Amino Acids↗
PubMed2003

Determination of alpha-tocopherol in infant foods by liquid chromatography combined with atmospheric pressure chemical ionisation mass spectrometry.

A novel, sensitive and specific method for the quantification of alpha-tocopherol in two infant foods (milk and cereals) using liquid chromatography on-line with positive atmospheric pressure chemical ionisation mass spectrometry detection (LC/APCI-MS) has been developed. The samples were first saponified in order to eliminate fats and to transform tocopherol esters into free tocopherol, followed up by a liquid-liquid extraction of the analyte in petroleum benzine/diisopropyl ether (75:25, v/v) prior to injection onto the LC system. For the quantification, deuterium-labelled tocopherol was used as internal standard and the samples were monitored in selected ion monitoring (SIM) mode. Calibration curves between 1-40 microg/mL of alpha-tocopherol showed a good linear correlation (r(2) = 0.99994), and the detection limit was determined to be 2.5 ng/mL. The within-day and between-day precision were determined for several dietetic infant formulae and certified reference samples, and found to be below 3.5%. The accuracy determined on a Nestlé reference sample (milk powder) was calculated to be 115.2 +/- 1.2%, which confirms the robustness of the proposed method. This study shows that single quadrupole LC/MS can be applied for the quantification of vitamins in food and the method offers better sensitivity and selectivity than traditional method such as LC-UV. This would simplify the preparation of the food samples and consequently enhance the vitamin analysis throughput in the food area.

Air Pressure↗
PubMed2006

Characterization of astaxanthin esters in Haematococcus pluvialis by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.

After first being analyzed by HPLC, 4 free carotenoids, 15 astaxanthin monoesters, 12 astaxanthin diesters, and 3 astacin monoesters in Haematococcus pluvialis were identified by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (LC-(APCI)MS). Identification of each compound was based on the characteristic fragment ions of the positive ion mode, negative ion mode, and MS(2). Astaxanthin esters were identified based on the loss of one or two fatty acids. In a positive ion mode, astaxanthin monoesters had characteristic fragment ions at m/z 597 [M+H-fatty acid](+) and m/z 579 and 561 that resulted from a continuous loss of water. The relative intensity of m/z 579 in MS(2) amounted to more than 80% of that of the molecular ion. In astaxanthin diesters, the intensity of m/z 561 occasionally was equal to that of m/z 579, but in general the former, amounting to 50 to 60% or more of the molecular ion, was stronger than the latter, which decreased to 20 to 30% of the molecular ion. In addition, a set of compounds with maximum absorbance at 400 nm, detected by high-performance liquid chromatography-diode array detector (HPLC-DAD), had strong characteristic fragment ions at m/z 871 and 593 in the positive ion mode MS(2). They were presumed to be linolenic acid or an isomer of omega-6-gamma-linolenic acid esters of astacin.

Chlorophyta↗
PubMed1998

Determination of flunitrazepam and its metabolites in blood by high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.

A selective assay of flunitrazepam (F) and its metabolites 7-aminoflunitrazepam (7-AF), N-desmethylflunitrazepam (N-DF) and 3-hydroxyflunitrazepam (3-OHF) with liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (LC-APCI-MS, positive ions) is described. The drugs were isolated from serum, blood or urine using a solid-phase extraction procedure previously applied to various drugs of abuse. F-d3 and 7-AF-d3 were used as internal standards. The drugs were separated on ODS column in acetonitrile-50 mM ammonium formate buffer, pH 3.0 (45:55, v/v). After analysis of mass spectra taken in full scan mode, a selected-ion monitoring detection was applied with following ions: m/z 284 (7-AF and F), 287 (7-AF-d3 and F-d3), 314 (F), 300 (N-DF and 3-OHF), 317 (F-d3), 330 (3-OHF). The limits of detection were: 0.2 microg/l for F and 7-AF, 1 microg/l for N-DF and 3-OHF. The method was linear in the range 1-500 microg/l, the recoveries ranged from 92 to 99%. The method was applied for determination of F and metabolites in clinical and forensic samples. LC-APCI-MS seems to be a method of choice for these compounds.

Anti-Anxiety Agents↗
PubMed2001

Atmospheric pressure ion trapping in a tandem FAIMS-FAIMS coupled to a TOFMS: studies with electrospray generated gramicidin S ions.

A tandem FAIMS-FAIMS system for ion trapping at room temperature and atmospheric pressure is described. The first FAIMS device consisted of a side-to-side configuration (sFAIMS) suitable for ion separation, whereas the second FAIMS device was appropriate for ion trapping (tFAIMS). Ions pre-selected by the sFAIMS entered the tFAIMS and were captured by virtual trapping fields at the hemispherical tip of the inner electrode. The use of the sFAIMS, with wider electrode diameters, and consequently better ion separation efficiency than the tFAIMS, lowered the number of background ions captured in the trapping region of tFAIMS, and thus reduced the space charge effects in the trap. This tandem device was coupled to a laboratory built time-of-flight mass spectrometer and was evaluated using the electrospray generated [M + 2H]2+ ion of gramicidin S. The half-time (t1/2) of the exponential decay of the ion cloud in tFAIMS, determined by monitoring the residual intensity of ions extracted from the ion trapping region of tFAIMS after various delay times, was about 2 s.

Algorithms↗
PubMedDate not supplied

Determination of triamcinolone acetonide in equine serum and urine by liquid chromatography-atmospheric pressure ionization mass spectrometry.

Urine and serum samples collected from four standard-bred mares after 30-mg intraarticular administrations of triamcinolone acetonide were analyzed using combined high-performance liquid chromatography-atmospheric pressure ionization mass spectrometry. Maximum triamcinolone acetonide concentrations of 32.3, 14.8, 24.3, and 29.4 ng/mL in the urine and 2.7, 1.9, 2.3, and 2.5 ng/mL in the serum samples were observed. The peak concentrations of the drug were detected approximately 22 h (urine) and 12 h (serum) after administration. The drug elimination profiles for both urine and serum are presented and discussed.

Animals↗
PubMed1999

In-source fragmentation of partially oxidized mono- and polycyclic aromatic hydrocarbons in atmospheric pressure chemical ionization mass spectrometry coupled to liquid chromatography

Partially oxidized derivatives of polycyclic aromatic hydrocarbons (PAHs) are known to be important environmental pollutants. For the identification of these substances in complex mixtures, e.g. atmospheric aerosol samples, liquid chromatography/mass spectrometry with atmospheric pressure chemical ionization (LC/APCI-MS) has been found to be a suitable analytical technique. In this study 31 derivatives of mono- and polycyclic aromatic hydrocarbons with up to five condensed aromatic rings carrying different functional groups (carboxyl, dicarboxylic anhydride, lactone, hydroxyl, and carbonyl) were characterized by LC/APCI-MS. Each substance was measured in positive and negative ion detection mode at four different fragmentor voltages (90 to 190 V). For the first time, the results show that characteristic and well-interpretable fragmentation patterns can be obtained for these classes of compounds by in-source collision-induced dissociation in a single quadrupole LC/APCI-MS system. For each class of compounds typical spectral features and optimum measurement conditions are reported, and fragmentation pathways are proposed. The study demonstrates the applicability of LC/APCI-MS for the determination of most of the investigated compounds at trace levels, and it provides a database for the identification of unknown partially oxidized aromatic hydrocarbons. Copyright 1999 John Wiley & Sons, Ltd.

Journal Article↗
PubMed2005

Boundary layer chemistry probed by in situ infrared spectroscopy during SiO2 deposition at atmospheric pressure from tetraethylorthosilicate and ozone.

The deposition of silicon dioxide films at 450 degrees C was studied in quasi real time by probing the thermally activated boundary layer region near the growing surface during atmospheric pressure chemical vapor deposition (APCVD). Potential tetraethylorthosilicate (TEOS)/O(3) reaction products have been investigated in an attempt to clarify the reaction mechanism leading to the observed silanol deposition intermediates and delineate the film formation process. The organic products formed during the TEOS/O(3) reaction are acetic acid, formic acid, formaldehyde, carbon monoxide, carbon dioxide, and water. Quantitative methods are developed using FT-IR (Fourier transform infrared) spectroscopy during ozonation of TEOS at elevated temperatures. The measurement of gaseous alcohols of silicon alkoxides by FT-IR is demonstrated by application of an in situ methodology that probes the high-temperature region within the CVD environment. Partial least squares (PLS) Beer's law absorption models are used in determining relative TEOS, ozone, and ethoxysilanol levels during the reaction. The reaction order in TEOS is measured at 1.65 +/- 0.02 over a 0.9 Torr pressure range. Similarly, the ratio of ethoxysilanol formed versus the amount of ozone consumed is ca. 1:3. A radical chain oxidative mechanism involving direct reaction of TEOS and ozone is proposed for formation of highly reactive silanol film growth intermediates.

Journal Article↗