Correction for isotopic interferences between analyte and internal standard in quantitative mass spectrometry by a nonlinear calibration function.

Stable isotope-labeled internal standards are of great utility in providing accurate quantitation in mass spectrometry (MS). An implicit assumption has been that there is no "cross talk" between signals of the internal standard and the target analyte. In some cases, however, naturally occurring isotopes of the analyte do contribute to the signal of the internal standard.

A cellular model to mimic exhaled cigarette smokeinduced lung microvascular endothelial cell injury and death.

Tobacco smoke exhaled from smokers is a key component of secondhand smoke, contributing to lung alveolar wall destruction seen in chronic lung diseases. Although mainstream and sidestream tobacco smoke are cyto-toxic to lung cells, it is unclear whether exhaled smoke induces lung cell injury or even death. We sought to establish an in vitro model to examine the effects of exhaled smoke on lung cells.

Liquid chromatography tandem mass spectrometry for analysis of steroids in clinical laboratories.

Liquid chromatography tandem mass spectrometry is one of the most specific techniques available in clinical laboratories. In the past, immunoassays were the primary methodology for analysis of steroids in biological samples because they are rapid and easy to perform. However, these methods were shown to suffer from the lack of specificity for measuring many of the diagnostically important steroids.

Liquid chromatography-tandem mass spectrometry assay for androstenedione, dehydroepiandrosterone, and testosterone with pediatric and adult reference intervals.

Background: Measurement of serum androgens is important in adult, geriatric, pediatric endocrinology, and oncology patients. We developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for simultaneous measurement of androstenedione, dehydroepiandrosterone (DHEA), and testosterone in these patients.

Methods: We spiked 200 muL of serum or plasma with isotope-labeled internal standards and performed extraction with methyl t-butyl ether.

Quantitation of nicotine, its metabolites, and other related alkaloids in urine, serum, and plasma using LC-MS-MS.

We describe a method for the quantitative analysis of nicotine, cotinine, trans-3'-hydroxy cotinine, nornicotine, and anabasine in urine, serum, and plasma using liquid chromatography-tandem mass spectrometry. A mix of deuterium-labeled internal standards (IS) is added to a specimen aliquot. The aliquot is extracted using mixed-mode solid phase extraction and eluted into an autosampler vial for injection into an LC-MS-MS system.

High sensitivity measurement of estrone and estradiol in serum and plasma using LC-MS/MS.

Measurement of low concentrations of estrogens, encountered in pre-pubertal children, men, and postmenopausal women, is important for numerous clinical applications. We describe a method for high sensitivity analysis of estrogens that uses two-dimensional chromatographic separation and tandem mass spectrometry detection. Aliquots of serum or plasma samples are combined with stable isotope-labeled internal standard and estrogens are extracted with methyl t-butyl ether.

High-sensitivity tandem mass spectrometry assay for serum estrone and estradiol.

High-sensitivity measurement of serum estrogens is important in adult and pediatric endocrinology and oncology. We developed a high-sensitivity liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for simultaneous measurement of estrone (E1) and estradiol (E2). Aliquots of 200 muL of serum were spiked with internal standard, extracted, derivatized with dansyl chloride, and analyzed by LC-MS/MS using 2-dimensional chromatographic separation.

Choline in whole blood and plasma: sample preparation and stability.

Background: Choline is critical for a variety of biological functions and has been investigated as a biomarker for various pathological conditions including acute coronary syndrome.

Methods: A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was used to quantify choline in whole blood and plasma in freshly collected samples prepared with ultrafiltration or protein precipitation. We investigated the effects of preanalytical variables including types of anticoagulants and storage temperature and time.

Free thyroid hormones in serum by direct equilibrium dialysis and online solid-phase extraction--liquid chromatography/tandem mass spectrometry.

Background: Measurements of free thyroxine (FT4) and free triiodothyronine (FT3) are important for the diagnosis and monitoring of thyroid diseases. Considerable differences among methods limit their clinical utility, however, and accurate methods are needed for various clinical specimens. We describe a direct equilibrium dialysis (ED)-liquid chromatography (LC)/tandem mass spectrometry (MS/MS) method for FT4 and FT3.

New interface plate for microspray ionization mass spectrometry.

A new interface plate was employed in microspray ionization mass spectrometry (microESI-MS) to improve ion transmission from the sprayer into the sampling nozzle of the mass spectrometer at atmospheric pressure. Using a time-of-flight mass spectrometer (TOFMS), a fivefold increase in ion intensity and a sevenfold reduction in method detection limit were observed. The interface plate attenuated the dependence of the ion intensity on the sprayer position.

Superimposition of a magnetic field around an ion guide for electron ionization time-of-flight mass spectrometry.

A new electron ionization source was developed for orthogonal acceleration time-of-flight mass spectrometry (TOFMS) based on the superimposition of a magnetic field around a radio frequency-only (rf-only) ion guide. The cylindrically symmetric magnetic field compresses the electron beam from the electron source into a long narrow volume along the ion guide axis. The magnetic field also helps to maintain a narrow energy distribution of electrons that penetrate the full length of the ion guide despite the influence of the radial rf field.

Electron ionization in superimposed magnetic and radio frequency quadrupolar electric fields.

An improved design of a novel electron ionization source for orthogonal acceleration time-of-flight mass spectrometry is described, based on the superimposition of an axial magnetic field with cylindrical symmetry around a radio frequency-only quadrupole. A tubular permanent magnet was designed to generate the required strong magnetic field and field profile. An axial electric field along the ion guide for efficient ion extraction was introduced using segmented quadrupole rods.

Assessing analytical specificity in quantitative analysis using tandem mass spectrometry.

Objectives: The necessity of confirmation of compound identity in quantitative analysis is well recognized for methods utilizing single mass spectrometry detection but is not commonly addressed for applications utilizing multiple-stage mass spectrometry (MSn). For MSn detection, no commonly accepted rules for assessment of analytical specificity in quantitative analyses have been established to date.

Methods: To assure compound identity, we evaluated approaches based on monitoring multiple mass transitions of a target compound followed by comparison of the branching ratios of the mass transitions.

Mobility-based selective on-line preconcentration of proteins in capillary electrophoresis by controlling electroosmotic flow.

A simple method to perform selective on-line preconcentration of protein samples in capillary electrophoresis (CE) is described. The selectivity, based on protein electrophoretic mobility, was achieved by controlling electroosmotic flow (EOF). A short section of dialysis hollow fiber, serving as a porous joint, was connected between two lengths of fused silica capillary.

Incorporation of a venturi device in electrospray ionization.

Electrospray ionization has grown to be one of the most commonly used ionization techniques for mass spectrometry, and efforts continue to improve its performance. Typically, the sprayer tip must be very close to the entrance orifice of the mass spectrometer in order to maximize the conduction of ions from the sprayer into the mass spectrometer. However, because of space-charge repulsion, most ions never reach the sampling orifice.

Application of diaza-18-crown-6-capped beta-cyclodextrin bonded silica particles as chiral stationary phases for ultrahigh pressure capillary liquid chromatography.

Two bonded chiral stationary phases (CSPs), 8-aminoquinoline-2-ylmethyl- and 8-aminoquinoline-7-ylmethyl-diaza-18-crown-6-capped [3-(2-O-beta-cyclodextrin)-2-hydroxypropoxy]propylsilyl silica particles (non-porous, 1.5 microm), have been prepared and evaluated using capillary liquid chromatography at high pressures (> or = 8000 p.s.

Elevated-temperature ultrahigh-pressure liquid chromatography using very small polybutadiene-coated nonporous zirconia particles.

Capillary columns packed with small diameter particles typically lead to low permeability and long separation times in high-performance liquid chromatography. Ultrahigh pressures (>10,000 p.s.