Development of analytical methods for some penicillins in bovine milk by ion-paired chromatography and confirmation by thermospray mass spectrometry

Analytical methods for the determination of cloxacillin, ampicillin/hetacillin, and amoxicillin in bovine milk were developed. The methods involved ultrafiltration of milk diluted with methanol, acetonitrile, and water on a 10,000-dalton cut-off filter. Separation of penicillins from other milk components was accomplished by ion-paired chromatography using a microbore column. The penicillins were detected using ultraviolet photodiode array (UV-PDA) detection and confirmed by thermospray liquid chromatography-mass spectrometry (LC-MS). The thermospray spectra of these compounds exhibited [M + H]+ and [M + Na]+ ions along with several fragment ions. The limits of detection for these antibiotics were estimated to be 50 to 100 ppb for LC with UV-PDA detection and 100-200 ppb for thermospray LC-MS detection.     

Thermospray liquid chromatography/mass spectrometry of quaternary ammonium saltst

Various esters of choline and carnitine have been shown to undergo fragmentation dependent on both the structures of the molecules and the vapor and block temperatures when subjected to thermospray ionization mass spectrometry. The fragments observed vary with the structure of the ester portion and the backbone of the molecules, and are consistent with the compounds undergoing three types of reactions: (1) carbon—nitrogen bond cleavage to tertiary amines and alkyl compounds, (2) hydrolysis of the ester linkage, forming alcohols and organic acids, and (3) deacylation of the molecules to form acids and the corresponding quaternary alkene. The general applicability of the carbon—nitrogen bond cleavage mechanism was studied with other classes of quaternary compounds, but the sole products consistently detected for pyridinium, benzyldimethyldodecylammonium and tetraalkylammonium salts were amines. The fragments observed for the esters of choline and carnitine and also the anticholinergic 2,2-diphenyl-4-diisopropylaminobutyramide methiodide suggest that the mechanism of the thermospray fragmentation pathway is similar to that of the Hofmann elimination reaction.     

Acetic acid cluster ions for tuning and calibration in thermospray liquid chromotography/mass spectrometry

Combined liquid chromatography and mass spectrometry is frequently performed with the thermospray interface nowadays. With thermospray a special ion source has to be installed. Tuning and calibration of that special source is still a problem which has not been adequately solved, Reference compounds commonly used in conventional electron impact or chemical ionization mass spectrometry cannot be used in the thermospray source. Most of the solutions to this problem reported in the literature cause a rapid contamination of the ion source or may result in memory effects. In this paper the use of acetic acid ammonia cluster ions is proposed for tuning and calibration in thermospray. Abundant cluster ions can be observed over the mass range between m/z = 100 and 1000 when an eluent containing ammonium acetate and 0.5% acetic acid is used. Features of the mass spectra obtained in both filament-off, filament-on and discharge-on modes will be discussed.     

Application of thermospray liquid chromatography-mass spectrometry for the analysis of chloramphenicol and three related compounds

The thermospray (TS) liquid chromatographic-mass spectrometric analysis of the antibiotic chloramphenicol and three related compounds is presented. The three additional compounds are dehydrochloramphenicol, aminodehydrochloramphenicol, and nitrophenylaminopropanediol. Baseline separation of the four compounds is achieved. The TS mass spectrum of each of the four compounds includes a prominent [MH]+ ion plus some fragment ion peaks.     

Liquid chromatography-thermospray mass spectrometry of DNA adducts formed with mitomycin C, porfiromycin and thiotepa

High-performance liquid chromatography (HPLC) and thermospray mass spectrometry were combined for the analysis of DNA adducts formed from the interaction of the anticancer drugs mitomycin C, porfiromycin and thiotepa with calf thymus DNA. The adducts formed from reaction of mitomycin C and porfiromycin with DNA were separated from unmodified nucleosides by HPLC on a C18 column and identified by thermospray mass spectrometry. Thiotepa DNA adducts readily depurinated from DNA and were chromatographed and identified by thermospray liquid chromatography-mass spectrometry as the modified bases without the ribose moiety attached. The utility of thermospray mass spectrometry for the identification of microgram quantities of nucleoside adducts and depurinated base adducts of these anticancer drugs was demonstrated.     

New developments in thermospray sample introduction for atomic spectrometry

The status of thermospray sample introduction for analytical atomic spectrometry was last reviewed in 1992. In this review, we summarize developments in this field since that time, including investigations of aerosol generation processes, noise diagnosis and control with inductively coupled plasma-atomic emission or mass spectrometry (ICP-AES/MS), high flow thermospray, the use of dual-stage desolvation systems based on membrane dryers, and the utilization of thermospray with axially viewed ICP-AES. Since a major advantage of methods based on thermospray is improved limits of detection, the emphasis for applications of thermospray with ICP spectrometries remains focused on environmental sample types, particularly with ICP-MS. Relatedly, the use of thermospray as a means for the direct speciation of Se is also under development.     

Determination of nitroxynil residues in tissues using high-performance liquid chromatography-thermospray mass spectrometry

A method is described for the determination of nitroxynil residues in muscle, liver and kidney. The samples were extracted into diethyl ether and cleaned-up using a simple liquid-liquid extraction step. Any nitroxynil present was separated from interfering compounds by high-performance liquid chromatography and detected using thermospray mass spectrometry. The assay is specific and sensitive, with a detection limit of 2 ng g-1 in tissues.     

Application of a heated electrospray interface for on-line connection of the AAS detector with HPLC for detection of organotin and organolead compounds

A heated electrospray interface that affords high sensitivity and long-term signal stability for AAS detection of metal-containing analytes in organic or organic-water solvents after HPLC separation is described. The vitreous body of the electrospray interface is externally heated above the boiling point of the solvent and quartz furnace AAS is used for detection. Interface working conditions were optimized with a full experimental design for the detection of tin- (tetramethyl-, tetraethyl-, tetrabutyl-, and tetrapentyltin, tributyltin chloride, dibutyltin dichloride, and butyltin trichloride) and lead- (tetraethyl- and tetraphenyllead) containing compounds in the column eluate. The heated electrospray interface enables use of a wide range of flow rates - from 50 to 1000 micro L min(-1). The measurement sensitivity and detection limit achieved were compared with those obtained by use of the thermospray interface and post-column conversion of the organotin compounds to gaseous hydrides. The detection limits for the low-molecular weight species of the homologous series (2.8+/-0.1 ng (140+/-5 ng mL(-1)) for tetramethyltin and 3.1+/-0.2 ng (155+/-10 ng mL(-1)) for tetraethyltin) were obtained approximately one order of magnitude lower than those obtained by use of the thermospray interface. With this HPLC-ES-QFAAS system the tributyltin content of BCR reference material 477, mussel tissue, was analyzed. This system was also applied to analysis of tetraethyllead in gasoline samples.     

Thermospray liquid chromatography-mass spectrometry of corticosteroids.

A high-performance liquid chromatographic method was developed for thermospray mass spectrometric analysis of steroidal hormones. Using a Nova-Pak C18 reversed-phase column and isocratic elution with a solvent comprised of 25 mM ammonium formate in 30% acetonitrile, corticosteroids were separated within 10 min. This solvent also permitted ultraviolet absorbance detection down to 220 nm with low-nanogram sensitivity. The use of acetonitrile was favourable for thermospray mass spectrometric analysis because mass spectra were obtained with a pseudomolecular ion as the base peak. A combination of liquid chromatography, ultraviolet absorbance detection and thermospray mass spectrometry provided a sensitive and reliable method for unequivocal confirmation of the presence of steroidal drugs in equine urine.     

Use of a multi-tube Nafion® membrane dryer for desolvation with thermospray sample introduction to inductively coupled plasma-atomic emission spectrometry

A multi-tube Nafion^® membrane dryer used as a part of a desolvation system in conjunction with thermospray nebulization was optimized and characterized with inductively coupled plasma-atomic emission spectrometry (ICP-AES). Either argon or nitrogen could be used as the sweep gas, and optimum conditions were found to be at low temperature and low sweep gas flow rate. Analyte sensitivity was not significantly affected by placing the membrane between the plasma and the nebulizer, although about 20% of the analyte entering the dryer is lost within the dryer. A dual role of the membrane dryer was demonstrated. As a secondary step within the desolvation system, it enabled a high desolvation efficiency of 99.94% for aerosols from 1% (v/v) nitric acid. Plasma solvent load could be reduced to 0.9 mg min⁻¹ with a tap water cooled condenser combined with the membrane dryer, compared to 21 mg min⁻¹ with the normal chilled condenser desolvation system. Meanwhile, the membrane was also found to act as a pulse dampener, eliminating the plasma pulsation in the central channel caused by thermospray nebulization and thus improving the analytical performance of the system. The average relative standard deviations (RSD) with the optimized membrane/thermospray system were 0.83% and 0.60% for the background and analyte signals, respectively, which were reduced by a factor of 1.9 and 2.7 for the background and analyte signals, respectively, compared to thermospray without the membrane desolvation, and were essentially identical to those obtained with pneumatic nebulization sample introduction. The improvements in detection limits with the membrane/thermospray system were 1.2–3.0 times with an average factor of 1.8 compared to thermospray without the membrane dryer, and 18–68 times with an average factor of 39 compared to the standard pneumatic nebulization sample introduction system without a desolvation unit. The detection limits for Mn, Mg, Cr and Cd with the present thermospray/membrane system were comparable to those reported for pneumatic nebulization ICP mass spectrometry.     

Identification of RP-HPLC peaks of bisphenol F and of bisphenol F diglycidyl ether and its hydrolysis products by thermospray mass spectrometry and gas chromatography/mass spectrometry

Summary The need to determine the migration of toxic unreacted compounds in bisphenol diglycidyl ether epoxy resins prompted us to investigate the HPLC properties of bisphenol F diglycidyl ether and its hydrolysis products in the water-based food simulants 3% (w/v) acetic acid, distilled water and 15% (v/v) ethanol. Peaks were identified by reversed-phase HPLC thermospray mass spectrometry and gas chromatography/mass spectrometry.     

Thermospray liquid chromatographic-mass spectrometric method for the analysis of metribuzin and its metabolites

A thermospray liquid chromatographic-mass spectrometric (TSP LC-MS) method has been developed for the analysis of the herbicide metribuzin and its three major metabolites in plant tissue. Metribuzin and its metabolites exhibited widely varying sensitivities in positive-ion TSP, with metribuzin being the most sensitive and deaminated diketo metribuzin being the least sensitive. All four compounds of interest were detected in an extract of a soybean plant which had been treated with metribuzin.     

Polar organic compounds in the river Elbe — Development of optimized concentration methods using substance-specific detection techniques

Different methods for solid phase extraction (SPE) of polar, organic compounds found in Elbe water were compared. Mass-spectrometric detection (MS) after liquid chromatographic separation (LC) or flow injection analysis (FIA) and thermospray ionization (TSP) was used to assess the concentration behaviour as well as the detection techniques. A selected compound was identified using tandem mass spectrometry (MS/MS) carrying out mixture analysis.     

Positive-ion mass spectra and collision-induced dissociation of some 2,3-didehydro amino acids

The positive-ion mass spectra of a number of didehydro amino acids, ionized by electron impact and/or thermospray, and collision-induced dissociation spectra taken at collision energies of a few electron volts and keV have been performed on multiple quadrupole and reversed geometry sector instruments. Observed differences in the mass spectra and in the fragmentation patterns are explained in terms of different isomeric structures, different internal excitation energies and different ion transit times between the ion source and the collision cell. Molecular ions of unhydrated amino acids are efficiently formed both by electron impact and thermospray, whilst molecular ions of the hydrated compounds are formed more efficiently by the latter technique. The present investigation demonstrates that the use of different ionization techniques combined with mass spectrometry/mass spectrometry measurements at different collision energies yields a wealth of information relevant to structural characterization of this important class of molecules.     

Application of an HPLC-FTIR modified thermospray interface for analysis of dye samples.

Previously, we developed a reversed-phase HPLC method compatible to high performance liquid chromatography diffuse reflectance Fourier-transform infrared (HPLC-FTIR) thermospray interface for the analysis of dyes. Dye separation achieved with a mixed-mode (SCX-ODS) column using a small gradient (90 to 80% water with acetic acid) and pH 3.25; 10 to 20% acetonitrile was considered to be suitable for HPLC-FTIR. A constant-voltage setting for the thermospray temperature (227 degrees C) was successfully used for this gradient condition. The HPLC-separated components deposited as a series of concentrated spots on a moving tape were scanned by specially developed HPLC-FTIR software. Excellent repeatability of the thermospray deposition FTIR chromatograms and IR spectra was obtained. The interface-derived spectra of the separated components of formulated and purified reactive dyes were compared and differences in spectral features were observed.     

Characterization of aerosols generated by thermospray nebulization for atomic spectroscopy

The performance of an inductively coupled plasma (ICP) for atomic emission spectroscopy (AES) is strongly dependent upon the sample introduction system. The Thermospray Vaporizer has recently been shown to yield enhanced sensitivity compared to conventional pneumatic nebulizers when used as a sample introduction source for the ICP. This report is a study of the properties of the aerosols produced by the thermospray. Aerosol particle diameter distributions have been related to droplet size distribution and nebulization efficiencies as a function of the relevant variables of the nebulization system. The results help explain high emission intensities and lower detection limits achieved using the thermospray. The higher efficiencies with thermospray, compared to conventional pneumatic nebulization, also makes the thermospray a prime candidate for sample introduction into molecular gas ICPs.     

Liquid chromatography-mass spectrometry coupling and its application in pharmaceutical research

The advantages and technical problems related to the on-line connection of liquid chromatography and mass spectrometry are described, with special emphasis on applications in pharmaceutical chemistry. The most important characteristics of various interfaces, such as direct liquid introduction, Magic, continuous flow fast atom bombardment and thermospray, are discussed. Special applications to the study of thermally very labile compounds are considered.     

Studies on the complexation of polyols and carbohydrates with excess borate using thermospray mass spectrometry

Complex formation between different polyols, carbohydrates and borate was studied by thermospray mass spectrometry. The analytes were dissolved in 0.1 M ammonium borate buffer and introduced through a standard thermospray interface into a quadrupole mass spectrometer. The formation of various complexes which gave rise to relatively abundant ions in the thermospray spectra was observed. A correlation has been found between the relative intensities of these ions and the orientation of the hydroxyl groups involved in the complexation.     

Enhanced desolvation and improved deposition efficiency by modified thermospray for the coupling of HPLC and FT-IR.

A thermospray interface was modified for the on-line coupling of normal- and reversed-phase high-performance liquid chromatography (HPLC) and Fourier transform infrared (FTIR) spectrometry. An LC/FTIR assembly was used to evaporate the column effluents and the solutes were deposited as a series of individual spots on a stainless-steel moving belt, which continuously transferred the solutes into a diffuse reflectance accessory of FTIR, enabling the identification of deposited solutes by measuring the IR spectrum. A lowered desolvation temperature of reversed-phase HPLC eluents, a higher deposition efficiency, such as 69%, and a reduction of the thermospray capillary voltage were achieved by using a heated gas flow and a heating plate. The thermospray temperature and the distance between the tip of the thermospray tubing and the surface of the belt were shown to influence the area of deposition of spots. A variation of +/- 1 degrees C could be used for a sensitive and reproducible deposition of Irganox 565 with a relative standard deviation (RSD) of 1.8 to 2.5%. The UV and FTIR chromatograms gave similar features for the HPLC-separated constituents. The interface-derived IR spectra of the constituents showed excellent agreement of the spectral features with those of the standard FTIR spectra, and no thermal degradation was found to occur.     

Evaluation of the potential of thermospray liquid chromatography-mass spectrometry in neurochemistry

Optimized operating conditions previously developed for the determination of neuroactive indoleamines and metabolites were adapted to meet the requirements of thermospray liquid chromatography-mass spectrometry (LC-MS) in terms of the ammonium acetate buffer system needed in this technique. Mass spectra were obtained for nineteen indolic compounds in both the positive and negative ion modes. The positive thermospray mass spectra of indoles with a free primary amino group are characterized by the base peak at [M + H]+, whereas the alcohol and acid metabolites show the base peak at [M + NH4]+. In the negative mode only amino acids and acids give good mass spectra with base peaks at [M - H + ACOOH]-. Detection limits by selected ion monitoring were of the order of 50-100 pg SIM on-column, allowing the direct determination of endogenous serotonin in an extract from rat hypothalamus. Quantitation was performed by isotope dilution MS. In the same way 5-hydroxyindoleacetic, indoleacetic, indolepropionic and indolelactic acids in urine were directly determined in an ethyl acetate extract from acidified urine samples. Likewise, gamma-aminobutyric acid and tricyclic antidepressants gave detection limits of 10 pg whereas only nanogram sensitivity could be achieved with catecholamines.