Liquid Chromatography-mass Spectrometry Interface Research Articles

Quantitative analysis of lactic acid oligomers from dimer to 15mer in poly(D,L-lactide) (PDLLA) polymers

Poly(D,L-lactide) (PDLLA) polymer is widely used in biomedical applications. To control the degradation of PDLLA, as well as to ensure effective quality control of the polymer raw material, it is essential to have analytical methods capable of analyzing the PDLLA oligomer species content quantitatively. In this study, liquid chromatography-mass spectrometry (LC-MS) based analytical methods were developed to quantitate oligomer species from dimer to 15mer (total of 14 analytes) in the PDLLA polymer resin. Negative electrospray ionization was employed as the LC-MS interface. For the lactic acid dimer and trimer analysis, a SIELC Primesep SB column was used for high performance liquid chromatography (HPLC) separation and selected reaction monitoring (SRM) was used as the acquisition mode. For other lactic acid oligomer (4mer to 15mer) analysis, a Phenomenex Synergi™ 4 µm Polar-RP column was used, and selected ion monitoring (SIM) was used as the acquisition mode. Both columns demonstrated good tolerability for samples with high polymer content which is critical for method development. Analytical parameters such as calibration, correlation, accuracy, and precision were evaluated. Quadratic functions best described the correlation between response and concentration for each oligomer analyte. Excellent accuracy and precision were demonstrated with both methods. The methods developed in this study can be used to evaluate the impact of manufacturing process on polymers and can also be a good reference for oligomer analysis method development of similar polymers.

Validated analytical strategy for the determination of polycyclic aromatic compounds in marine sediments by liquid chromatography coupled with diode-array detection and mass spectrometry

The aim of this work was to optimise and validate the experimental conditions for the analysis of 20 polycyclic aromatic compounds (PACs) [19 polycyclic aromatic hydrocarbons (PAHs) and dibenzothiophene as polycyclic aromatic sulphur heterocycle (PASH)] in marine sediments by reversed-phase high-performance liquid chromatography (LC) coupled to photodiode array detection (DAD) and to mass spectrometry (MS). The LC–MS interface used was atmospheric pressure chemical ionization (APCI) in the positive ion mode. The operational parameters of the APCI interface and MS detection, such as organic modifier, fragmentation voltage, gain, vaporizer temperature, corona current, capillary voltage, drying gas (N 2) and nebulizer pressure, were studied. The sediments were subjected to microwave-assisted solvent extraction (MAE) and clean-up by solid-phase extraction (SPE). The relevance of the selected PACs lies in the fact that 16 PACs are classified by the US Environmental Protection Agency as priority pollutants; 17 PACs are detected in the Prestige oil spill; and 8 PACs are included in the priority substance list of the EU water policy. Recoveries from 47% to 102% were obtained for SRM 1944 certified reference sediment. The limits of quantitation were lower than 100 ng g −1 dry weight for most PACs, and good precision was achieved.

Liquid chromatography—mass spectrometry with on-line solid-phase extraction by a restricted-access C 18 precolumn for direct plasma and urine injection

In this paper, the on-line coupling of solid-phase extraction, based on a restricted-access support with liquid chromatography—mass spectrometry (LC-MS), for the analysis of biological samples is described. The system was tested with cortisol and prednisolone for plasma analysis and arachidonic acid for urine analysis. A precolumn packed with a 25-μm C 18 alkyl-diol support is used for direct plasma or urine injection. Using column-switching techniques, the analytes enriched on the precolumn are eluted to the analytical column without transfer loss. An on-line heart-cut technique was employed and only the analyte-containing fraction eluting from the LC column is directed to the MS to protect the LC-MS interface and ion-source from contamination. The whole system is operated in a parallel mode, that is, sample pre-treatment and LC-MS analysis are performed simultaneously to provide the shortest possible analysis time. The only off-line sample pre-treatment step required was centrifugation to remove particulate matter. With the fully automated system, total analysis times of 5 and 9.5 min were achieved for cortisol in serum and arachidonic acid in urine, respectively. Cortisol and related compounds were quantitatively recovered from plasma with a detection limit for prednisolone (direct injection of 100 μl on restricted-access precolumn) of 2 ng/ml.

Analysis of lignan constituents from Schisandra chinensis by liquid chromatography-electrospray mass spectrometry

An electrospray high-performance liquid chromatography-mass spectrometry interface coupled with a photodiode-array detector has been applied successfully to the identification of a number of lignan constituents from an ethanol extract of the fruits of Schisandra chinensis Baill. A total of fifteen peaks were identified, six of them unambiguously identified as schisandrin (1), schisantherin A (19), schisantherin B (20), schisanhenol (4), deoxyschisandrin (3) and γ-schisandrin (11), based on their abundant [M+H] +, [M+Na] + ions, UV spectra and retention times, compared with those data of reference compounds. Another nine peaks were tentatively identified, based on their intense [M+H] + and [M+Na] + ions and UV spectra.

Is particle beam an up-to-date LC-MS interface? State of the art and perspectives.

The particle beam liquid chromatography-mass spectrometry interface, developed more than ten years ago, has withstood the assault of several new soft ionization-based interfaces, and it is still largely used worldwide. The particle beam has widened the possibility for many HPLC-amenable compounds to be ionized under electron ionization conditions without any appreciable thermal degradation. This feature is not of secondary importance in several "small" molecules applications, where the analytes can be easily identified and their spectra matched with those collected in literature. The task of separating any solute from a liquid mobile phase is carried out very efficiently by the particle beam interface, and the only real limitation is found at the moment of the solute vaporization in the ion source; therefore, the principle of particle formation for sample transfer into a mass spectrometer could be extended profitably to other ionization techniques. © 1997 John Wiley & Sons, Inc.

Electrospray Liquid Chromatography-Mass Spectrometry of Carotenoids

The first method for electrospray liquid chromatography-mass spectrometry (LC-MS) of carotenoids is reported, which uses a C 30 reversed-phase HPLC column and a gradient solvent system containing methanol/methyl tert-butyl ether/ammonium acetate at a flow rate of 1.0 mL/min. The entire HPLC column effluent passes through a photodiode array absorbance detector and then into the electrospray LC-MS interface without solvent splitting. In this way, maximum sensitivity is achieved for both the photodiode array detector, which records the UV/vis spectra of each carotenoid, and the mass spectrometer, which measures the molecular ions of each carotenoid. Molecular ions, M .+ , without evidence of any fragmentation, were observed in the electrospray mass spectra of both xanthophylls and carotenes. In order to enhance the formation of molecular ions, solution-phase carotenoid oxidation was carried out by means of postcolumn addition of a halogenated solvent to the HPLC effluent Several different halogenated solvents were evaluated, including chloroform, 2,2,3,3,4,4,4-heptafluoro-1-butanol, 2,2,3,3,4,4,4-heptafluorobutyric acid, 1,1,1,3,3,3-hexafluoro-2-propanol, and trifluoroacetic acid. Among these halogenated solvents, 2,2,3,3,4,4,4-heptafluoro-1-butanol at a concentration of 0.1% (v/v) was found to produce the best combination of carotenoid molecular ion abundance and reproducibility. The limits of detection for lutein and β-carotene were between 1 and 2 pmol each, which was 100-fold lower than the detection limit of the photodiode array detector signal.

Optimization of the Hewlett-Packard particle-beam liquid chromatography-mass spectrometry interface by statistical experimental design

Optimization of both sensitivity and ionization softness for the Hewlett-Packard particle-beam liquid chromatography-mass spectrometry interface has been achieved by using a statistical experimental design with response surface modeling. Conditions for both optimized sensitivity and ionization softness were found to occur at 55-lb/in.(2) nebulizer flow, 35°C desolvation chamber temperature with approximately 45% organic modifier in the presence of 0.02-F ammonium acetate and a liquid chromatography flow rate of 0.2 mL/min.

Analysis of coumarins by micro high-performance liquid chromatography—mass spectrometry with a particle beam interface

Coumarins are a large group of compounds that are naturally present in plant tissues and that exhibit a wide range of pharmacological properties. Analytical methods based on chromatographic techniques and conventional detectors are inadequate to accurately analyze coumarins in complex matrices such as plant extracts. In this article a new method based on a modified particle beam liquid chromatography-mass spectrometry interface is described. The method allows specific and accurate determination of several coumarins in biological matrices. An application regarding the analysis of 18 coumarins in the extract of Smyrnium perfoliatum L. is also reported.

Simple direct liquid introduction system usable as an interface for liquid chromatography-mass spectrometry on quadrupole and magnetic-sector mass spectrometers

A simple and inexpensive direct liquid introduction system that can be used for tandem mass spectral analysis and for interfacing liquid chromatography on quadrupole and magnetic-sector mass spectrometers is described. The interface consists of a transfer fused-silica capillary that is introduced directly into the chemical ionization source of the mass spectrometer through the conventional gas chromatography-mass spectrometry interface, replacing the capillary column. The coupling uses no desolvation chamber and the transfer capillary is heated over the whole length of the interface. Experiments on the effect of interface temperature and flow-rate demonstrate that the system is extremely stable under optimal operating conditions, which are similar on different spectrometers. The chemical ionization plasma generated by the mobile phase under typical operation consists mainly of protonated monomers, and its composition is similar on different spectrometers, as shown by the comparison of spectra obtained. The system can be used with a series of mobile phases, and the ionization features that they produce are comparable. The system is stable, reproducible and allows picogram range sensitivity to be achieved in mass spectrometric, tandem mass spectrometric or liquid chromatographic-mass spectrometric experiments.

Use of non-volatile ion-pairing agents for liquid chromatographic-mass spectrometric analyses with a moving-belt interface

Micro-membrane suppressor systems were employed to allow non-volatile ion-pairing agents to be used with combined liquid chromatography-mass spectrometry (LC-MS). This enabled the technique to be used with reversed-phase gradient chromatography for the determination of both anionic and cationic species from a range of compounds. The membrane suppressors remove the ion-pairing agent by counter-current flow regeneration. The determination of cationic species is demonstrated with the use of pyridinium and imidazolium iodides. Hexanesulphonic acid was used as the chromatographic ion-pairing agent and tetrabutylammonium hydroxide as the regenerant. The determination of anionic species is demonstrated with carboxylic and sulphonic acids, which were chromatographed as the tetrabutylammonium hydroxide ion pair using sulphuric acid as the regenerant. The system described has been used successfully with a moving-belt interface, enabling spectra to be acquired in both electron impact (EI) and chemical ionization (CI) modes, with a magnetic sector instrument. The system is in essence compatible with any LC-MS interface, although some modification may be required if the interface generates a significant back-pressure, e.g., thermospray.

On-line capillary zone electrophoresis-ion spray tandem mass spectrometry for the determination of dynorphins

Capillary zone electrophoresis-mass spectrometry and capillary zone electrophoresis-tandem mass spectrometry with ionization at atmospheric pressure are demonstrated as being feasible for the separation and determination of small peptides such as dynorphins (1–6, 1–7, 1–8, 1–9) and leucine enkephalin at low picomole levels by full-scan mass spectrometry and tandem mass spectrometry and at the low femtomole range under selected ion monitoring conditions. Ion evaporation resulting from the ion spray liquid chromatography-mass spectrometry interface exhibits primarily molecular weight information as singly and multiply charged ions and is shown to be a sensitive and mild ionization method for peptides. The full-scan daughter ion mass spectrum of leucine enkephalin is shown to contain fragment ions consistent with the sequence of the peptide. Parent ion scanning in the tandem mass spectrometry mode is a promising technique for the screening of related peptides.

Direct electrically heated spray device for a moving belt liquid chromatography—mass spectrometry interface

A direct electrically heated capillary spray device for the deposition of liquid chromatographic eluents onto a moving belt interface for liquid chromatographymass spectrometry (LC—MS) has been constructed. This system shows significant advantages over hot propellant gas driven or cartridge heated sprayers, especially when eluents with high water content and high flow-rates are used. Various parameters have been examined to achieve optimum conditions with respect to capillary wall temperature, peak variance and analyte yield during deposition. Reversed-phase high-performance liquid chromatographic separations with standard bore columns (4.6 mm I.D.) demonstrate the enhanced possibilities of the moving belt interface for on-line high-performance LC—MS.

Continuous-flow fast atom bombardment mass spectrometry

The continuous-flow fast atom bombardment probe performs equally well with or without a high-performance liquid chromatography column producing clean spectra containing little or no background noise. Its function as a liquid chromatography-mass spectrometry interface for labile and involatile samples has been illustrated with reference to dansylated amino acids. The versatility of the new probe has been exemplified by on-line enzymatic peptide sequencing.

Liquid chromatographic-mass spectrometric analysis of 2-nitrofluorene and its derivatives

Liquid chromatography-mass spectrometry (LC-MS) with a nebuliser and a moving belt was used to characterise 2-nitrofluorene, its metabolites and related compounds. In total, 13 different compounds were analysed. The LC-MS interface did not affect the chromatographic performance achieved by high performance liquid chromatography (HPLC). The method allowed determination of the positions of the hydroxyl groups in different hydroxylated 2-acetylaminofluorene derivatives. The LC-MS procedure generated acceptable mass spectra with as small amounts of substance as 65 ng. The dose-response curves from the HPLC-detector and the ion-source in the LC-MS were parallel and linear.

Generation of hydroxyeicosatetraenoic acids by human inflammatory cells: analysis by thermospray liquid chromatography-mass spectrometry

Arachidonic acid was converted to a series of hydroxyeicostatraenoic acids (HETEs) by mixed human inflammatory cells following stimulation with the calcium ionophore A23187. HETEs were purified by a simple one-step extraction procedure followed by HPLC. The HPLC was coupled to a Finnigan quadrupole mass spectrometer using the now commercially available thermospray liquid chromatography-mass spectrometry interface. The HPLC eluant was monitored ‘on line’ by the mass spectrometer. Soft ionisation occurs, generating intense molecular ion species in the negative ion mode ((M − H −: m/ z 319) for each of the isomeric HETEs. The (M + H + − H 2O) ion at m/ z 303 is the major species in the positive ion spectra of HETEs. Mass spectra wer obtained on-line post-HPLC for HETEs formed by the human cells, and the HPLC-MS profile compared with that obtained from standards; species corresponding to the 11-, 9- and 5-HETEs were observed.

Design and construction of an interface for direct liquid introduction coupling of a microbore high-performance liquid chromatograph to a quadrupole mass spectrometer

Recently various efforts have been made to transfer the compounds separated by high-performance liquid chromatography into the ion source of a mass spectrometer. One development in such interfacing is the on-line direct liquid introduction of the column effluent. In this paper we describe the design and construction of a splitless micro-high-performance liquid chromatography-mass spectrometry interface which allows the unrestricted flow of the eluent and jet-formation directly into the ion volume of a quadrupole mass spectrometer. The use of a water-cooling, laser-punctured orifice or diaphragm at the probe tip was not necessary in our experiments. The desolvation of the mobile liquid phase in the transline, an open glass capillary, is controlled only by the selected parameters for ion source temperature, the flow-rate of the chromatographic pump and by the high vacuum of the mass spectrometer. Tests on different transline materials have been carried out and the results are discussed; applications and mass spectra obtained by this procedure are presented.

Performance of a moving belt liquid chromatography-mass spectrometry interface

Performance of a moving belt liquid chromatography-mass spectrometry interface

Liquid chromatography mass spectrometry in the pharmaceutical industry: Objectives and needs

The role of liquid chromatography-mass spectrometry (LC-MS) in the analysis of drugs is discussed. The main fields of application are thermally labile compounds, compounds with low volatility and compounds with rather high molecular weights, all of which are not generally suitable for analysis by combined gas chromatography-mass spectrometry. The objectives, needs, limitations and abilities of LC-MS for the analysis of by-products, degradation products, traces of drug substances for pharmacokinetic studies and metabolites in complex matrices are presented. The LC-MS coupling is discussed as a sophisticated LC detector for sensitive and selective quantitative determinations or as an on-line sample-introduction system for the mass spectrometer to obtain structural information for identification or structural elucidation. LC-MS combined with a flow-switching technique can be used for the analysis of mixtures containing large amounts of components which otherwise would be detrimental to the LC-MS technique. With flow-injection techniques the LC-MS interface is used as a sample-introduction system with possibilities for sample preparation, sample clean-up and chemical derivatization.

Studies of combined liquid chromatography-mass spectrometry with a moving-belt interface

The advantages and limitations of a moving-belt interface for liquid chromatography-mass spectrometry are discussed using examples of combined liquid chromatography-mass spectrometry of natural coumarins, alkaloids, rotenoids, sugars, nucleosides, peptides and pesticides and drugs and their metabolites. Preliminary data obtained using a micro high-performance liquid chromatograph interfaced to the moving belt are reported.