HPLC-MS investigations of acidic contaminants in ammunition wastes using volatile ion-pairing reagents (VIP-LC-MS)

In order to hyphenate ion pairing chromatography and MS detection we used several types of formates as volatile ion pairing reagents (IPRs) instead of common tetraalkylammonium salts, as these salts tend to precipitate in the ion source. The formates were prepared by mixing formic acid with the corresponding amine. Both tributyl- and trihexylammonium formate proved to be valuable IPRs for the separation of acidic compounds like nitrobenzoic acids, nitrobenzenesulfonic acids and nitrated phenols. Due to the weaker retention of the ion-pairs with trialkylammonium formates compared with tetraalkylammonium compounds, either less organic modifier or a higher concentration of the IPR had to be used. With negative atmospheric pressure chemical ionization mass spectrometry and electrospray ionization mass spectrometry it was possible to unambiguously identify several acidic oxidation products of 2,4,6-trinitrotoluene (TNT) in ammunition wastewater and soil extracts. 2-amino-4,6-dinitrobenzoic acid was often found to be the main metabolite of TNT in such water samples.     

Determination of saccharides in fruit juices by capillary electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

A fast method for the detection of cheap sweeteners is presented. Detecting the adulteration of foods rich in carbohydrates is complicated by the presence of variety of commercial sweeteners that are designed to match exactly the major carbohydrate profiles of these foods. Electrophoretic and mass spectrometric assays for the determination of fruit juice authenticity were developed. Capillary zone electrophoresis with indirect detection was employed to detect adulteration of juices demonstrated by the ratio of the concentrations of major low molecular mass saccharides (glucose, fructose and sucrose). Traces of oligosaccharides, which are not present in the sugar profiles of citrus fruits but are present in inexpensive sweeteners, were evaluated as the other group of target compounds. The fast determination of oligomeric starch hydrolysates in a complex matrix was tested by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) and applied to orange juice. MALDI-TOFMS was shown to be a suitable method for the identification of adulteration of fruit juices by starch hydrolysates. The effects of the presence of salts and low molecular mass saccharides on the detection of oligosaccharides by MALDI-TOFMS were studied. Low molecular mass saccharides and organic acids decrease the detectability of oligosaccharides by MALDI-TOFMS, but the concentration of maltooligosaccharides present in juices sweetened with starch hydrolysates is high enough to be detected with good sensitivity.     

Analysis of various organic and organometallic compounds using nanostructure-assisted laser desorption/ionization time-of-flight mass spectrometry (NALDI-TOFMS)

Nanostructure-assisted laser desorption/ionization time-of-flight mass spectrometry (NALDI-TOFMS) has been developed recently as a matrix-free/surface-assisted alternative to matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). The NALDI surface of silicon nanowires is already very effective for the analysis of small to medium sized, polar organic molecules in positive ion mode. The current study examined this technology for the analysis of several nonpolar organic, organometallic, and ionic compounds in positive ion mode, as well as a fluorinated compound and various acids in negative ion mode. NALDI data are compared and contrasted with MALDI data for the same compounds, and the higher sensitivity of NALDI is highlighted by the successful characterization of two porphyrins for a sample amount of 10 amol per spot.     

Enhanced detection of sulfo-peptides as onium salts in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

A new two-component system, consisting of a matrix and an onium salt as comatrix, is described for detection of sulfo-peptides in the positive mode by matrix-assisted desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). Binary iodonium salts were superior to quaternary phosphonium salts in terms of suppression of desulfation and salt formation with the carboxyl group. Of the iodonium salts examined, bis(4-tert-butylphenyl)iodonium (BTI) hexafluorophosphate and bromide were most effective in giving intensive molecular ion signals in the form of [M(BTI)+BTI](+). The conditions optimized for O-sulfated tyrosine-containing peptides could be applicable for O-sulfated serine- and threonine-containing peptides. In the case of a phospho-peptide, a molecular ion appeared more intensively as a proton adduct than as a BTI adduct.     

Tetraalkylammonium halides as chemical standards for positive electrospray ionization with ion mobility spectrometry/mass spectrometry

Chemical standards for positive ion mode electrospray ionization ion mobility spectrometry/mass spectrometry (ESI(+)-IMS/MS) are suggested. The low clustering tendency of tetraalkylammonium halides makes them ideal chemical standards for ESI(+)-IMS/MS. A homologous series of these compounds forms a useful external standard for instrument testing and resolution calibration of an IMS instrument. Selected homologues or a mixture of tetraalkylammonium halides can be used as mobility standards in the analytical runs. Absolute and relative reduced mobilities were calculated for C2--C8, C10 and C12 tetraalkylammonium halides. Absolute reduced mobilities in nitrogen were 1.88, 1.56, 1.33, 1.15, 1.02, 0.92, 0.84, 0.73, and 0.67 cm2 V(-1) s(-1), for C2--C8, C10 and C12 tetraalkylammonium halides, respectively. Relative reduced mobilities (relative to 2,6-di-tert-butylpyridine) for the same compounds were 1.20, 1.00, 0.855, 0.743, 0.658, 0.59, 0.54, 0.47, and 0.43, respectively.     

Analysis of some commercial polysorbate formulations using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Analyses of polysorbate formulations (Tween 20, Tween 40, Tween 60, and Tween 80) by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) reveal a complex mixture of oligomers that include polyethylene glycols, polyethylene glycol esters, isosorbide polyethoxylates, sorbitan polyethoxylates, polysorbate monoesters, polysorbate diesters, and sorbitol polyethoxylate esters. The MALDI-TOF mass spectra for these formulations show the presence of sodiated molecules in which the major signals are attributed to the presence of polyethylene glycols, isosorbide polyethoxylates, and sorbitan polyethoxylates. Additionally, the complexity of the spectra was correlated to the constituent fatty acid moieties in the polysorbate formulations. Thus Tween 20 showed the presence of polysorbate monolaurates, polysorbate monomyristates, and polysorbate monopalmitates. Tween 40 contained polysorbate mono- and dipalmitates. Tween 60 contained polysorbate monopalmitates and polysorbate monostearates. For the Tween 80, mass assignment for polysorbate monooleates and polysorbate dioleates was equivocal, because both of these oligomeric series have the same molecular weight as the sorbitan polyethoxylates, and thus the Tween 80 MALDI-TOF spectrum appeared to be the least complicated of the four commercial polysorbate formulations.     

Identification of proteins by combination of size-exclusion chromatography with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and comparison of some desalting procedures for both intact proteins and their tryptic digests

Separation of a protein mixture by size-exclusion chromatography (SEC) was combined with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). Identification of proteins in the collected fractions was performed both as intact proteins by MALDI-TOFMS and using peptide mass fingerprinting (PMF) after their digestion with trypsin. The presence of salts mostly disturbs the MALDI-TOFMS signal and, therefore, proper purification or desalting procedures must be employed. Four desalting procedures (desalting column packed with Sephadex G-100, on-target washing, centrifugal filter devices and ZipTip C(18)) for purification of fractions of proteins separated by SEC and their tryptic digests prior to determination of their exact molecular masses by MALDI-TOFMS were compared. In the case of intact proteins, the experiments showed that the best desalting procedures are the use of ZipTip C(18) pipette tips and Ultrafree CL centrifugal filter devices. The peptide digests can be purified by using ZipTip C(18) pipette tips or on-target washing when both of these procedures provide similar results. On-target washing can be used as a simple procedure to improve the mass spectra of salt-containing samples. Analyses of the droplets collected after the on-target washing show losses of sample and matrix caused by dissolution of these compounds during this procedure. Further, it was found that protein identification based on PMF is more sensitive than analyses of intact proteins and that multiple on-target washing is very advantageous for analyses of peptide mixtures with a high content of salts.     

Sample preparation for high throughput accurate mass analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

An automated sample preparation for high throughput accurate mass determinations by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) has been developed. Sample preparation was performed with an automated workstation and automated mass analyses were performed with a commercial MALDI-TOF mass spectrometer. The method was tested with a 41-sample library. MALDI-TOFMS was found to give the needed sensitivity, accurate mass measurement, and soft ionization necessary for structure confirmation, even of mixtures. A mass accuracy of 5 ppm or less was obtained in over 80% of known compound measurements. A mass accuracy better than 10 ppm was obtained for all measurements of known compounds. Analyses of parallel synthesis products resulted in 77% of the measurements with a mass accuracy of 5 ppm or better.     

Forensic identification of explosive oxidizers by electrospray ionization mass spectrometry

The mass spectrometry of a group of inorganic oxidizers was studied using the electrospray ionization technique. It was found that a series of cluster ions were predominant in both positive- and negative-ion mode, allowing for the characterization of the investigated oxidizers. The identity of the recorded cluster ions was further confirmed by using some isotopically labeled compounds and tandem mass spectrometry with collision-induced dissociation. The use of electrospray ionization mass spectrometry for positive identification of major oxidizer components in explosive formulations was demonstrated by three samples of forensic interest.     

Determination of cationic surfactants in pharmaceutical disinfectants using a new sensitive potentiometric sensor

A new sensitive potentiometric surfactant sensor was prepared based on a highly lipophilic 1,3-didecyl-2-methyl-imidazolium cation and a tetraphenylborate antagonist ion. This sensor was used as a sensing material and incorporated into the plasticized PVC-membrane. The sensor responded fast and showed a Nernstian response for investigated surfactant cations: cetylpyridinium chloride (CPC), hexadecyltrimethylammonium bromide (CTAB) and Hyamine with slope 59.8, 58.6 and 56.8 mV/decade, respectively. The sensor served as an end-point detector in ion-pair surfactant potentiometric titrations using sodium tetraphenylborate as titrant. Several technical grade cationic surfactants and a few commercial disinfectant products were also titrated, and the results were compared with those obtained from a two-phase standard titration method. The sensor showed satisfactory analytical performances within a pH range of 2-11, and exhibited excellent selectivity performance for CPC compared to all of the organic and inorganic cations investigated. The influence of the nonionic surfactants on the shape of titration curves was negligible if the mass ratio of ethoxylated nonionic surfactants and cationic surfactants (EONS:CS) was not greater than 5.     

Trace detection of inorganic oxidants using desorption electrospray ionization (DESI) mass spectrometry

Desorption electrospray ionization (DESI), an established ambient ionization method in mass spectrometry (MS) for the analysis of organic compounds, is applied here to trace detection of inorganic salts, including inorganic oxidants. In-situ surface analysis of targeted compounds, including nitrogen-, halogen- and sulfur-salts, down to sub-nanogram levels, was performed using DESI-MS. Successful experiments were carried out in both the negative and the positive ion modes; simple anions and cations as well as small cluster ions were observed. Various surfaces are examined and surface porosity effects were briefly explored. Absolute detection limits on porous polytetrafluoroethylene (PTFE) of 120 pg (surface concentration 0.07 ng mm⁻²) and 50 pg (surface concentration 0.03 ng mm⁻²), were achieved for sodium chlorate and sodium perchlorate, respectively. The compounds of interest were examined in the presence of a hydrocarbon mixture to assess matrix effects: only a two- or three-fold decrease in the target ion intensity was observed. Commercial fireworks were analyzed to determine perchlorate salts in complex mixtures. This work demonstrates the potential applicability of ambient ionization mass spectrometry to forensic investigations involving improvised explosives.      

The use of nonpolar matrices for matrix-assisted laser desorption/ionization mass spectrometric analysis of high boiling crude oil fractions

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) with nonpolar matrices has been investigated for its applicability to the characterization of atmospheric resid crude oil fractions. The data obtained by use of nonpolar matrices was compared with that from polar matrices as well as from direct LDI-MS and field ionization mass spectrometry. Nonpolar matrices, such as anthracene or 9-cyanoanthracene, yield only a single radical molecular cation upon LDI. Thus, no interfering matrix-related ions are present during the MALDI-TOFMS analysis of the crude oil sample. Nonpolar matrices yield molecular mass distributions from linear mode MALDI-TOFMS that are comparable to distributions found with LDI-MS. An advantage of nonpolar matrices is the increased production of analyte ions, which allows reflectron mode MALDI-TOFMS to be performed. Nonpolar matrices are also shown to be less sensitive to solvent and sample preparation conditions than conventional polar matrices. These results suggest that nonpolar matrices may be favorable alternatives to more traditional polar or acidic matrices commonly used in the MALDI mass spectral characterization of crude oil related samples.     

Investigation into accurate mass capability of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, with respect to radical ion species

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) has been shown to be an effective technique for the characterization of organometallic, coordination, and highly conjugated compounds. The preferred matrix is 2-[(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enylidene]malononitrile (DCTB), with radical ions observed. However, MALDI-TOFMS is generally not favored for accurate mass measurement. A specific method had to be developed for such compounds to assure the quality of our accurate mass results. Therefore, in this preliminary study, two methods of data acquisition, and both even-electron (EE+) ion and odd-electron (OE+.) radical ion mass calibration standards, have been investigated to establish the basic measurement technique. The benefit of this technique is demonstrated for a copper compound for which ions were observed by MALDI, but not by electrospray (ESI) or liquid secondary ion mass spectrometry (LSIMS); a mean mass accuracy error of -1.2 ppm was obtained.     

Even-electron ions: a systematic study of the neutral species lost in the dissociation of quasi-molecular ions

The collision-induced dissociations of the even-electron [M + H](+) and/or [M - H](-) ions of 121 model compounds (mainly small aromatic compounds with one to three functional groups) ionized by electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) have been studied using an ion trap instrument, and the results are compared with the literature data. While some functional groups (such as COOH, COOCH(3), SO(3)H in the negative ion mode, or NO(2) in both the positive and negative ion modes) generally promote the loss of neutrals that are characteristic as well as specific, other functional groups (such as COOH in the positive ion mode) give rise to the loss of neutrals that are characteristic, but not specific. Finally, functional groups such as OH and NH(2) in aromatic compounds do not lead to the loss of a neutral that reflects the presence of these substituents. In general, the dissociation of [M + H](+) and [M - H](-) ions generated from aliphatic compounds or compounds containing an aliphatic moiety obeys the even-electron rule (loss of a molecule), but deviations from this rule (loss of a radical) are sometimes observed for aromatic compounds, in particular for nitroaromatic compounds. Thermochemical data and ab initio calculations at the CBS-QB3 level of theory provide an explanation for these exceptions. When comparing the dissociation behaviour of the even-electron [M + H](+) and/or [M - H](-) ions (generated by ESI or APCI) with that of the corresponding odd-electron [M](+) ions (generated by electron ionization, EI), three cases may be distinguished: (1) the dissociation of the two ionic species differs completely; (2) the dissociation involves the loss of a common neutral, yielding product ions differing in mass by one Da, or (3) the dissociations lead to a common product ion.     

A study of common discovery dosing formulation components and their potential for causing time-dependent matrix effects in high-performance liquid chromatography tandem mass spectrometry assays

Hydroxyproyl-beta-cyclodextran (HPBCD), methyl cellulose (MC), Tween 80 and PEG400 are commonly used in dosing formulations in pharmacokinetic (PK) studies during the early drug discovery stage. A series of studies was designed to evaluate the potential matrix effects of these dosing vehicles when the samples are assayed by high-performance liquid chromatography combined with tandem mass spectrometry (HPLC/MS/MS). These dosing vehicles were dosed into the rats via either an intravenous (IV) or an oral route (PO) and plasma samples were collected for a 24-h post-dose period. Five test compounds with CLog P values ranging from 0.9 to 5.4 were spiked into the collected rat plasma. After protein precipitation, these samples were analyzed using a generic fast-gradient HPLC/MS/MS method. Three popular mass spectrometers (Thermo-Finnigan Quantum with ESI and APCI, AB-Sciex API 3000 with ESI and APCI, and Waters-Micromass Quattro Ultima with ESI) were used to test these plasma samples. Results indicated that there was no observed matrix effect for all five compounds when 20% HPBCD or 0.4% MC was used as the vehicle in either the IV or the PO route, respectively. In addition, 0.1% Tween 80 dosed either IV or PO caused significant ion suppression (50-80%, compared to results obtained from plasma samples free from vehicles) for compounds that eluted at the beginning of the chromatogram. Also, PEG400 when used in an oral formulation caused significant ion suppression (30-50%) for early eluting compounds. These matrix effects were not only ionization mode (ESI or APCI) dependent, but also source design (Thermo-Finnigan, AB-Sciex or Waters-Micromass) dependent. Overall, the APCI mode proved to be less vulnerable to matrix effects than the ESI mode. Some possible mechanisms of these matrix effects are proposed and simple strategies to avoid these matrix effects are discussed.     

N-Alkylnicotinium halides: A class of cationic matrix additives for enhancing the sensitivity in negative ion Fast-Atom bombardment mass spectrometry of polyanionic analytes

The addition of some surfactants to the fast-atom bombardment (FAB) matrix previously has been demonstrated to enhance analyte signals in fast-atom bombardment mass spectrometry. In particular, cationic surfactants appear to enhance the negative ion FAB detectability of analytes that exist as anionic species in the matrix solution. It has been proposed that the charged surfactant concentrates the oppositely charged analyte near the surface, which results in larger signals for the analyte. Cationic surfactants that contain a fixed positive charge and an additional basic site were prepared with different hydrophobic moieties and were evaluated for their effectiveness as FAB matrix additives. The compound N-octylnico-tinium bromide (ONBr) is shown to improve greatly the analyte-related signals in negative ion fast-atom bombardment mass spectrometry for a variety of polyanionic analytes, relative to other surfactants (e.g., cetylpyridinium salts). This surfactant not only enhances detectability, but also simplifies the pseudomolecular ion region of the resulting spectra by reducing or eliminating metal cation adduct peaks. The simple mechanism of enhancement via surface activity is evaluated, and alternative mechanisms are considered. It is clearly shown that ONBr, as a FAB matrix additive, will allow mass spectrometry to be used for the analysis of anionic compounds that normally exhibit very low responses.     

On-line characterization of gaseous and particulate organic analytes using atmospheric pressure chemical ionization mass spectrometry

A modified atmospheric pressure chemical ionization ion source is applied for direct analysis of volatile or low volatile organic compounds in air. The method is based on the direct introduction of the analytes in the gas phase and/or particle phase into the ion source of a commercial ion-trap mass spectrometer. Two methods are employed for the production of primary ions at atmospheric pressure, photoionization and corona discharge. It is shown that in the presence of a dopant, photoionization can be a highly efficient ionization method also for real-time analysis with detection limits for selected analytes in the lower ppt-range. Using corona discharge for the production of primary ions, which is instrumentally easier since no additional chemicals have to be added to the sample flow, we demonstrate the analytical potential of on-line atmospheric pressure chemical ionization mass spectrometry for reaction monitoring experiments. To do so, an atmospherically relevant gas phase reaction is carried out in a 500 l reaction chamber and gaseous and particulate compounds are monitored in the positive and negative ion mode of the mass spectrometer.     

Formation and emission of tetraalkylammonium salt molecular ions sputtered from a gelatin matrix

A gelatin matrix was simultaneously doped with nine equimolar, homologous, tetraalkylammonium salts ranging in mass from 210 to 700 Da. Bombardment of the sample with kiloelectronvolt ions resulted in a nonidentical distribution of relative cation intensities with a maximum at m/z 242 for samples with a total salt concentration of 0.004 g of salt/g of gelatin. A rapid increase in relative intensities with increasing mass is observed for the low mass salts and is believed to be linked to changes in the ionization efficiencies. The changes in ionization efficiencies are likely related to decreasing coulombic attractive forces between the organic cation and the counterion. Disappearance cross-sections, determined from decay curves, indicate that sputter-induced damage increases with increasing mass of the cation. Fragment-to-intact cation ratios also suggest that damage accumulates fastest in the heaviest salts. These observations indicate that desorption yields of the organic salts in a gelatin matrix decrease with increasing mass. In addition, suppression of lower mass tetraalkylammonium salt intact cation intensities was observed for salt-in-gelatin concentrations greater than 10⁻³ g/g.     

Rapid identification of stress-related fingerprint from whole bacterial cells of <Emphasis Type="Italic">Bifidobacterium lactis</Emphasis> using matrix assisted laser desorption/ionization mass spectrometry

Whole cells of Bifidobacterium lactis were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). Characteristic and reproducible mass spectra were obtained in the mass range from 6 to 19 kDa. After several days of bacterial cell storage at 4 degrees C (D0, D2, and D6), only minor signal differences were observed. Under identical and reproducible conditions, fourteen relevant diagnostic ions were identified. Moreover, control- and stress-related fingerprints were rapidly obtained using MALDI-TOFMS by comparison of protein patterns obtained from non-stressed (control) versus stressed cells (addition of bile salts during growth). After quantitative validation of the MALDI-MS data by a statistical approach, two and eight signals were assigned as control- and stress-specific ions, respectively. This work provides the evidence that MALDI-TOFMS can be used for the identification of stress-related fingerprint of B. lactis bacterial cells and could have a high potential for the assessment of the physiological status of the cells.     

Impurity profiling of acetylspiramycin by liquid chromatography–ion trap mass spectrometry

Investigation of acetylspiramycin (ASPM) and its related substances was carried out using a reversed-phase liquid chromatography/tandem mass spectrometry method. The identification of impurities in the ASPM complex was performed with a quadrupole ion trap mass spectrometer, with an electrospray ionization (ESI) source in the positive ion mode which provides MSⁿ capability. A total of 83 compounds were characterized in commercial samples, among which 31 impurities that had never been reported and 31 partially characterized impurities were deduced using the collision-induced dissociation (CID) spectra of major ASPM components as templates. Most of the major impurities arise from the starting materials and the synthesis process. This work provides very useful information for quality control of ASPM and evaluation of its synthesis process.