The measurement of nicotine in human plasma by high-performance liquid chromatography-electrospray-tandem mass spectrometry

The authors describe a reverse-phase high-performance liquid chromatography-electrospray-tandem mass spectrometry method for the measurement of nicotine in human plasma. Samples (500 muL) with added deuterium-labeled d(3)-nicotine as an internal standard (IS) were treated with a 2-step process of ether extraction (6 mL) followed by back-extraction into 0.1% formic acid (50 muL). Chromatography was performed on a phenyl Novapak column with a mobile phase consisting of 50% 10 mM ammonium fortriate (pH 3.3) and acetonitrile (50:50, vol/vol). A flow rate of 0.2 mL/min resulted in a total analysis time of 5 minutes per sample. Mass spectrometric detection was by selected reactant monitoring (nicotine m/z 163.2 --> 130.2; IS m/z 166.2 --> 87.2). The assay was linear from 0.5 to 100 mug/L (r > 0.993, n = 9). The accuracy and imprecision of the method for quality control sampleswere 87.5% to 113% and < 10.2%, respectively. Interday accuracy and imprecision at the limit of quantification (0.5 mug/L) was 113% and 7.2% (n = 4). The process efficiency for nicotine in plasma was > 75%. The method described has good process efficiency, stabilized nicotine, avoided concentration steps, and most importantly minimized potential contamination. Further, we have established that water-based standards and controls are interchangeable with plasma-based samples. This method was used successfully to measure the pharmacokinetic profiles of subjects involved in the development of an aerosol inhalation drug delivery system.

Enhancing the ratio of molecular ions to non-covalent compounds in the electrospray interface of LC-MS in quantitative analysis

A common problem encountered during the development of MS methods for the quantitation of small organic molecules by LGMS is the formation of non-covalently bound species or adducts in the electrospray interface. Often the population of the molecular ion is insignificant compared to those of all other forms of the analyte produced in the electrospray, making it difficult to obtain the sensitivity required for accurate quantitation. We have investigated the effects of the following variables: orifice potential, nebulizer gas flow, temperature, solvent composition and the sample pH on the relative distributions of ions of the types MH+, MNa+, MNH+, and 2MNa(+), where M represents a 4 small organic molecule: BAY 11-7082 ((E)-3-[4-methylphenylsulfonyl]-2-propenenitrile). Orifice potential, solvent composition and the sample pH had the greatest influence on the relative distributions of these ions, making these parameters the most useful for optimizing methods for the quantitation of small molecules.

Simultaneous determination of morphine, oxycodone, morphine-3-glucuronide, and noroxycodone concentrations in rat serum by high performance liquid chromatography-electrospray ionization-tandem mass spectrometry

An assay using high performance liquid chromatography (HPLC)-electrospray ionization-tandem mass spectrometry (ESI-MS-MS) was developed for simultaneously determining concentrations of morphine, oxycodone, morphine-3-glucuronide, and noroxycodone, in 50 mul samples of rat serum. Deuterated (d(3)) analogues of each compound were used as internal standards. Samples were treated with acetonitrile to precipitate plasma proteins: acetonitrile was removed from the supernatant by centrifugal evaporation before analysis. Limits of quantitation (ng/ml) and their between-day accuracy and precision (%deviation and %CV) were-morphine, 3.8 (4.3% and 7.6%); morphine-3-glucuronide, 5.0 (4.5% and 2.9%); oxycodone, 4.5 (0.4% and 9.3%); noroxycodone, 5.0 (8.5% and 4.6%). (C) 2004 Elsevier B.V. All rights reserved.

Matrix effects: The Achilles heel of quantitative high-performance liquid chromatography-electrospray-tandem mass spectrometry

High-performance liquid chromatography coupled by an electrospray ion source to a tandem mass spectrometer (HPLC-EST-MS/ MS) is the current analytical method of choice for quantitation of analytes in biological matrices. With HPLC-ESI-MS/MS having the characteristics of high selectivity, sensitivity, and throughput, this technology is being increasingly used in the clinical laboratory. An important issue to be addressed in method development, validation, and routine use of HPLC-ESI-MS/MS is matrix effects. Matrix effects are the alteration of ionization efficiency by the presence of coeluting substances. These effects are unseen in the chromatograrn but have deleterious impact on methods accuracy and sensitivity. The two common ways to assess matrix effects are either by the postextraction addition method or the postcolumn infusion method. To remove or minimize matrix effects, modification to the sample extraction methodology and improved chromatographic separation must be performed. These two parameters are linked together and form the basis of developing a successful and robust quantitative HPLC-EST-MS/MS method. Due to the heterogenous nature of the population being studied, the variability of a method must be assessed in samples taken from a variety of subjects. In this paper, the major aspects of matrix effects are discussed with an approach to address matrix effects during method validation proposed. (c) 2004 The Canadian Society of Clinical Chemists. All rights reserved.

Performance of five different electrospray ionisation sources in conjunction with rapid monolithic column liquid chromatography and fast MS/MS scanning

The performances of five different ESI sources coupled to a polystyrene-divinylbenzene monolithic column were compared in a series of LC-ESI-MS/MS analyses of Escherichia coli outer membrane proteins. The sources selected for comparison included two different modifications of the standard electrospray source, a commercial low-flow sprayer, a stainless steel nanospray needle and a coated glass Picotip. Respective performances were judged on sensitivity and the number and reproducibility of significant protein identifications obtained through the analysis of multiple identical samples. Data quality varied between that of a ground silica capillary, with 160 total protein identifications, the lowest number of high quality peptide hits obtained (3012), and generally peaks of lower intensity; and a stainless steel nanospray needle, which resulted in increased precursor ion abundance, the highest-quality peptide fragmentation spectra (5414) and greatest number of total protein identifications (259) exhibiting the highest MASCOT scores (average increase in score of 27.5% per identified protein). The data presented show that, despite increased variability in comparative ion intensity, the stainless steel nanospray needle provides the highest overall sensitivity. However, the resulting data were less reproducible in terms of proteins identified in complex mixtures -- arguably due to an increased number of high intensity precursor ion candidates.

Identification of oxidized phospholipids by electrospray ionization mass spectrometry and LC-MS using a QQLIT instrument

Phospholipids are complex and varied biomolecules that are susceptible to lipid peroxidation after attack by free radicals or electrophilic oxidants and can yield a large number of different oxidation products. There are many available methods for detecting phospholipid oxidation products, but also various limitations and problems. Electrospray ionization mass spectrometry allows the simultaneous but specific analysis of multiple species with good sensitivity and has a further advantage that it can be coupled to liquid chromatography for separation of oxidation products. Here, we explain the principles of oxidized phospholipid analysis by electrospray mass spectrometry and describe fragmentation routines for surveying the structural properties of the analytes, in particular precursor ion and neutral loss scanning. These allow targeted detection of phospholipid headgroups and identification of phospholipids containing hydroperoxides and chlorine, as well as the detection of some individual oxidation products by their specific fragmentation patterns. We describe instrument protocols for carrying out these survey routines on a QTrap5500 mass spectrometer and also for interfacing with reverse-phase liquid chromatography. The article highlights critical aspects of the analysis as well as some limitations of the methodology.

Studies of phospholipid oxidation by electrospray mass spectrometry: from analysis in cells to biological effects

The oxidation of lipids is important in many pathological conditions and lipid peroxidation products such as 4-hydroxynonenal (HNE) and other aldehydes are commonly measured as biomarkers of oxidative stress. However, it is often useful to complement this with analysis of the original oxidized phospholipid. Electrospray mass spectrometry (ESMS) provides an informative method for detecting oxidative alterations to phospholipids, and has been used to investigate oxidative damage to cells, and low-density lipoprotein, as well as for the analysis of oxidized phosphatidylcholines present in atherosclerotic plaque material. There is increasing evidence that intact oxidized phospholipids have biological effects; in particular, oxidation products of 1-palmitoyl-2-arachidonoyl-sn-glycerophosphocholine (PAPC) have been found to cause inflammatory responses, which could be potentially important in the progression of atherosclerosis. The effects of chlorohydrin derivatives of lipids have been much less studied, but it is clear that free fatty acid chlorohydrins and phosphatidylcholine chlorohydrins are toxic to cells at concentrations above 10 micromolar, a range comparable to that of HNE and oxidized PAPC. There is some evidence that chlorohydrins have biological effects that may be relevant to atherosclerosis, but further work is needed to elucidate their pro-inflammatory properties, and to understand the mechanisms and balance of biological effects that could result from oxidation of complex mixtures of lipids in a pathophysiological situation.

Detection of phospholipid oxidation in oxidatively stressed cells by reversed-phase HPLC coupled with positive-ionization electrospray MS

Measurement of lipid peroxidation is a commonly used method of detecting oxidative damage to biological tissues, but the most frequently used methods, including MS, measure breakdown products and are therefore indirect. We have coupled reversed-phase HPLC with positive-ionization electrospray MS (LC-MS) to provide a method for separating and detecting intact oxidized phospholipids in oxidatively stressed mammalian cells without extensive sample preparation. The elution profile of phospholipid hydroperoxides and chlorohydrins was first characterized using individual phospholipids or a defined phospholipid mixture as a model system. The facility of detection of the oxidized species in complex mixtures was greatly improved compared with direct-injection MS analysis, as they eluted earlier than the native lipids, owing to the decrease in hydrophobicity. In U937 and HL60 cells treated in vitro with t-butylhydroperoxide plus Fe2+, lipid oxidation could not be observed by direct injection, but LC-MS allowed the detection of monohydroperoxides of palmitoyl-linoleoyl and stearoyl-linoleoyl phosphatidylcholines. The levels of hydroperoxides observed in U937 cells were found to depend on the duration and severity of the oxidative stress. In cells treated with HOCl, chlorohydrins of palmitoyloleoyl phosphatidylcholine were observed by LC-MS. The method was able to detect very small amounts of oxidized lipids compared with the levels of native lipids present. The membrane-lipid profiles of these cells were found to be quite resistant to damage until high concentrations of oxidants were used. This is the first report of direct detection by LC-MS of intact oxidized phospholipids induced in cultured cells subjected to oxidative stress.