Rapid identification and semi-quantitative determination of polymer additives by desorption electrospray ionization/time-of-flight mass spectrometry

A fast and simple method for the direct qualitative and semi-quantitative determination of a set of four polymer additives in plastic samples by desorption electrospray ionization time-of-flight mass spectrometry (DESI-TOF-MS) is presented. After evaluation of crucial DESI parameters such as composition of spray solutions and spray voltages, a series of lab-made polypropylene samples containing Chimassorb 81 (2-hydroxy-4-n-octoxybenzophenone), Tinuvin 328 (2-(2-hydroxy-3, 5-ditert-pentylphenyl)-benzotriazole), Tinuvin 326 (2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-5-chloro benzotriazole), and Tinuvin 770 (bis(2,2,6,6,-tetramethyl-4-piperidyl)sebaceate) in concentrations between 0.02% and 0.2% were analyzed, resulting in calibration graphs with R ² better than 0.994. To demonstrate the applicability of the developed method for the investigation of real samples, liners for in-ground swimming pools and polypropylene granules were analyzed with respect to their content in the selected polymer additives. Two alternative methods, both well established in the fields of polymer additive analysis, namely HPLC with UV detection (after previous extraction) and thermodesorption gas chromatography/mass spectrometry have been employed for evaluation of the results from the DESI experiments.     

Rapid identification of environmental bacterial strains by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

In recent years, various mass spectrometry procedures have been developed for bacterial identification. The accuracy and speed with which data can be obtained by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) could make this a powerful tool for environmental monitoring. However, minor variations in the sample preparation can influence the mass spectra significantly. Therefore, the first objectives of this study were the adjustment and the optimization of experimental parameters allowing a rapid identification of whole bacterial cells without laborious sample preparation. The tested experimental parameters were matrix, extraction solvent, salt content, deposition method, culture medium and incubation time. This standardized protocol was applied to identify reference and environmental bacterial strains of Escherichia coli, Salmonella and Acinetobacter. The environmental bacterial strains were isolated from sewage sludge using an original microextraction procedure based on repeated sonications and enzymatic treatments. The bacterial identification was realized by the observation of the respective genus-, species- and strain-specific biomarkers. This bacterial taxonomy could be completed within one hour, with minimal sample preparation, provided that sufficient bacteria had been collected prior to MALDI-TOF analysis.     

Structural features of polyacylated anthocyanins using matrix-assisted laser desorption/ionization and electrospray ionization time-of-flight mass spectrometry

In our continuing studies to isolate water-soluble vacuolar pigments, we expect to elucidate more structural details using mass spectrometry (MS). Because of its sensitivity, only a small amount of pigment extracted from natural plants is required for MS measurement. Nuclear magnetic resonance is also a useful spectroscopic method for structural determination. In this study, two soft ionization techniques, electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI), on time-of-flight (TOF) mass spectrometers, were used to analyze five polyacylated anthocyanins with more than two aromatic acid molecules in the side chains. ESI is advantageous for the detection of individual molecular ions, while MALDI is essential for the detection of characteristic fragment ions originating from the anthocyanidin. Although 2,5-dihydroxybenzoic acid (DHBA) is an effective matrix in MALDI-TOFMS to obtain informative fragment ions of polyacylated anthocyanins, α-cyano-4-hydroxycinnamic acid (CHCA) is the preferred matrix for the identification of aglycones. In particular, in measurements of polyacylated anthocyanins with two acylated glycoside chains, fragment ions originating from anthocyanidin can only be observed in MALDI-TOFMS using CHCA as the matrix.     

Rapid characterization of polyalcohols by silylation and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

A matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry method for rapidly enumerating hydroxyl groups in analytes is described, and applied to some common polyalcohols (erythritol, mannitol and xylitol). Polyalcohols were derivatized with trimethylsilylimidazole (TMSI) either separately or as mixtures, and were analyzed, without chromatographic separation or purification. The mass spectra revealed consecutive peaks that are separated by 72 m/z units as a consequence of displacement of one hydroxyl hydrogen atom by one TMS group. The number of observed peaks was used to confirm the number of hydroxyl groups in each analyte.     

Rapid analysis of svoc in aerosols by desorption electrospray ionization mass spectrometry

Desorption electrospray ionization mass spectrometry (DESI-MS) was applied for the first time to the analysis of semivolatile organic compounds (SVOC) in atmospheric aerosols. We took polycyclic aromatic hydrocarbons (PAHs) as representatives of SVOCs. The DESI-MS conditions were optimized and the limit of detection for PAHs was about 10 pg with 5 s sampling time. PAHs from both laboratory-made biomass burning aerosols and ambient aerosols were selectively and rapidly analyzed without extraction or preconcentration. The observed PAH species and their relative ion intensities are discussed. This work demonstrates that DESI-MS is a promising method for rapid semiquantitative analysis of SVOC in atmospheric aerosols.     

Rapid analysis of controlled substances using desorption electrospray ionization mass spectrometry

The recently developed technique of desorption electrospray ionization (DESI) has been applied to the rapid analysis of controlled substances. Experiments have been performed using a commercial ThermoFinnigan LCQ Advantage MAX ion-trap mass spectrometer with limited modifications. Results from the ambient sampling of licit and illicit tablets demonstrate the ability of the DESI technique to detect the main active ingredient(s) or controlled substance(s), even in the presence of other higher-concentration components. Full-scan mass spectrometry data provide preliminary identification by molecular weight determination, while rapid analysis using the tandem mass spectrometry (MS/MS) mode provides fragmentation data which, when compared to the laboratory-generated ESI-MS/MS spectral library, provide structural information and final identification of the active ingredient(s). The consecutive analysis of tablets containing different active components indicates there is no cross-contamination or interference from tablet to tablet, demonstrating the reliability of the DESI technique for rapid sampling (one tablet/min or better). Active ingredients have been detected for tablets in which the active component represents less than 1% of the total tablet weight, demonstrating the sensitivity of the technique. The real-time sampling of cannabis plant material is also presented.     

Quantitative aspects in electrospray ionization ion trap and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of malto-oligosaccharides

Mass spectrometry is widely applied in carbohydrate analysis, but still quantitative evaluation of data is critical due to different ionization efficiencies of the constituents in a mixture. Different size and chemical structure of the analytes cause their uneven distribution in droplets (electrospray ionization, ESI) or matrix spots (matrix-assisted laser desorption/ionization, MALDI). In addition, instrumental parameters affect final ion yields. In order to study and optimize the latter, an equimolar mixture of malto-oligosaccharides (DP1-6) was analyzed using varying target masses for ESI as well as different matrices and laser power for MALDI. The sodium adducts and derivatives for positive ion mode (hydrazones with Girard's T Reagent, GT) and negative ion mode (reductively aminated with o-aminobenzoic acid, oABA) were studied. Negatively charged oABA-labeled malto-oligosaccharides turned out to be unsuitable for quantification of the malto-oligomeric composition. Best agreement was achieved when applying target masses in the range of the highest homolog in the mixture in electrospray ionization ion trap (ESI-IT) (1-2% deviation with GT label or as Na(+) adducts). Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) gave best results when the laser power was adjusted significantly over the desorption/ionization threshold (1% deviation with GT label). Both parameters show significant influence on the determined oligomeric composition. Consequently, estimation and even quantitative determination of amounts of oligosaccharides in a mixture can be achieved when the analytes are labeled and the proper instrumental parameters are used.     

Rapid identification of pesticides in human oral fluid for emergency management by thermal desorption electrospray ionization/mass spectrometry

Self‐poisoning with pesticides accounts for approximately one‐third of all suicides worldwide. To expedite rescue in the emergency department, it is essential to develop a point‐of‐care analytical method for rapid identification of ingested pesticides. In this study, five of the most common pesticides ingested by self‐poisoning patients in Taiwan were analyzed from oral fluid samples. Pesticide‐oral fluid mixtures were applied on a cotton swab and then transferred into methanol. A metallic probe was used to sample the methanol solution for subsequent thermal desorption‐electrospray ionization mass spectrometry analysis. Altogether, pesticide sampling, transfer, desorption, ionization, and detection took less than 1 min. The reproducibility of this method (n = 6) was shown in the observed low‐relative standard deviation (<7%) in the detection of pesticide in oral fluid. The detection limits of the pesticides in oral fluid obtained from four human subjects by thermal desorption‐electrospray ionization mass spectrometry were between 1–10 ppb with relative standard deviation 10.7%. Moreover, in this study, linear responses of five pesticides in oral fluid with concentrations between 1 ppb–1 ppm (R2 between 0.9938 and 0.9988) were observed. As the whole analytical process is extremely short, this technique allows for early non‐invasive point‐of‐care identification of pesticides in the oral fluid of self‐poisoning patients in the emergency room, providing important toxicological information for decision‐making during critical resuscitation. Copyright © 2016 John Wiley & Sons, Ltd.     

Application of an integrated matrix-assisted laser desorption/ionization time-of-flight, electrospray ionization mass spectrometry and tandem mass spectrometry approach to characterizing complex polyol mixtures

Polyols are being used in a wide range of industrial applications including surfactants and precursors for grafted polymers. The characterization of polyols is of significance in correlating compositions and structures with their properties. We illustrate two real world examples where traditional analytical methods including GPC and NMR failed to reveal compositional differences, but the combination of matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF), electrospray ionization mass spectrometry (ESI MS), and MS/MS can produce compositional information required for problem solving. The first example involves failure analysis of four ethylene oxide and propylene oxide (EO/PO) copolymer products. The results from the mass spectrometry analysis unequivocally demonstrate that one of the samples has a small variation in copolymer composition, leading to its abnormal activity. The second example is in the area of deformulation of complex polyol mixtures. Two samples displaying similar properties and activities were found to be two different polyol blends. One of the samples is a more cost-effective product. These examples demonstrate that MALDI, ESI MS, and MS/MS should be seriously considered as an integrated component of an overall polyol characterization program in product failure analysis and deformulation.     

Small molecule matrix-assisted laser desorption/ionization time-of-flight mass spectrometry using a polymer matrix

We have employed a light-absorbing electrically conductive polymer as a matrix to determine the molecular mass of small organic molecules using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. This method, which is in contrast to the usual MALDI strategy for matrix selection in which a small molecule matrix is used with a high molecular mass analyte, addresses the problem of matrix interference which limits the usefulness of MALDI-TOF for small molecule analysis. Use of negative ion mode offers advantages for this application. Using this approach, we have obtained clean molecular ion mass spectra of small organic molecules in the mass range 100-300 Da.     

Infrared laser-assisted desorption electrospray ionization mass spectrometry

We have used an infrared laser for desorption of material and ionization by interaction with electrosprayed solvent. Infrared laser-assisted desorption electrospray ionization (IR LADESI) mass spectrometry was used for the direct analysis of water-containing samples under ambient conditions. An ion trap mass spectrometer was modified to include a pulsed Er:YAG laser at 2.94 microm wavelength coupled into a germanium oxide optical fiber for desorption at atmospheric pressure and a nanoelectrospray source for ionization. Analytes in aqueous solution were placed on a stainless steel target and irradiated with the pulsed IR laser. Material desorbed and ablated from the target was ionized by a continuous stream of charged droplets from the electrosprayed solvent. Peptide and protein samples analyzed using this method yield mass spectra similar to those obtained by conventional electrospray. Blood and urine were analyzed without sample pretreatment to demonstrate the capability of IR LADESI for direct analysis of biological fluids. Pharmaceutical products were also directly analyzed. Finally, the role of water as a matrix in the IR LADESI process is discussed.     

Rapid determination of 5-hydroxymethylfurfural by DART ionization with time-of-flight mass spectrometry

DART (direct analysis in real time), a novel technique with wide potential for rapid screening analysis, coupled with high-resolution time-of-flight mass spectrometry (TOF-MS) has been used for quantitative analysis of 5-hydroxymethylfurfural (5-HMF), a typical temperature marker of food. The DART/TOF-MS method was optimised and validated. Quantification of 5-HMF was achieved by use of a stable isotope-labelled 5-HMF standard prepared from glucose. Formation of 5-HMF from saccharides, a potential source of overestimation of results, was evaluated. Forty-four real samples (honey and caramelised condensed sweetened milk) and 50 model samples of heated honey were analysed. The possibility of using DART for analysis of heated samples of honey was confirmed. HPLC and DART/TOF-MS methods for determination of 5-HMF were compared. The correlation equation between these methods was DART?=?1.0287HPLC?+?0.21340, R ²?=?0.9557. The DART/TOF-MS method has been proved to enable efficient and rapid determination of 5-HMF in a variety of food matrices, for example honey and caramel.     

Development of a dual-spray electrospray deposition system for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

A new method of matrix-assisted laser desorption/ionization (MALDI) sample preparation using a dual-spray electrospray deposition system is demonstrated and employed for the investigation of gas-phase cationization reactions in the MALDI plume. The dual-spray electrospray system is found to increase the homogeneity of the sample similarly to that of a conventional single-spray electrospray system. The dual-spray electrospray system allows for intimate mixing of separately prepared sample components and results in improved quantitative results. The development of this device also leads to the possibility of mixing sample components prepared in different solvents without the need to be concerned with solvent miscibility.     

High-throughput quantitative analysis by desorption electrospray ionization mass spectrometry

A newly developed high-throughput desorption electrospray ionization (DESI) source was characterized in terms of its performance in quantitative analysis. A 96-sample array, containing pharmaceuticals in various matrices, was analyzed in a single run with a total analysis time of 3 min. These solution-phase samples were examined from a hydrophobic PTFE ink printed on glass. The quantitative accuracy, precision, and limit of detection (LOD) were characterized. Chemical background-free samples of propranolol (PRN) with PRN-d₇ as internal standard (IS) and carbamazepine (CBZ) with CBZ-d₁₀ as IS were examined. So were two other sample sets consisting of PRN/PRN-d₇ at varying concentration in a biological milieu of 10% urine or porcine brain total lipid extract, total lipid concentration 250 ng/μL. The background-free samples, examined in a total analysis time of 1. 5 s/sample, showed good quantitative accuracy and precision, with a relative error (RE) and relative standard deviation (RSD) generally less than 3% and 5%, respectively. The samples in urine and the lipid extract required a longer analysis time (2. 5 s/sample) and showed RSD values of around 10% for the samples in urine and 4% for the lipid extract samples and RE values of less than 3% for both sets. The LOD for PRN and CBZ when analyzed without chemical background was 10 and 30 fmol, respectively. The LOD of PRN increased to 400 fmol analyzed in 10% urine, and 200 fmol when analyzed in the brain lipid extract.     

Intact skin analysis by desorption electrospray ionization mass spectrometry

In vivo skin analysis by Desorption Electrospray Ionization was characterized on healthy human volunteers by directing pneumatically assisted electrospray directly onto their fingertips. In order to eliminate the risk of electric shock, a high ohmic resistor was built into the system. Positive ion DESI-MS analysis yields low intensity spectra, while negative ion spectra feature a number of various biogenic carboxylic acids. Compounds of external origin and excreted molecules were found to have different analysis kinetics, with the exception of highly hydrophobic species. The difference was demonstrated in the case of nicotine and cotinine. Pharmacokinetic studies were performed using a rat animal model. The kinetics of the anesthetic ketamine was followed by DESI, and results were in agreement with off-line HPLC-MS blood analysis. Using a similar approach for N,N'-dimethylthiourea (DMTU), a novel method was developed for the real-time quantification of oxidative stress. DMTU was administered to the animals, and the ratio of the molecule and its oxidized form was monitored from the skin surface. The ratio was found to be highly sensitive to experimentally induced diabetes mellitus type I and angiotensin-induced chronic oxidative stress. It was concluded that the method has a number of potential applications in the fields of forensics, pharmacology and clinical chemistry.     

Characterization of fungal spores by laser desorption/ionization time-of-flight mass spectrometry

A considerable volume of research has now been completed on the application of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) to the analysis of bacteria; however, to date no definitive studies have been made using this technique on fungi. Preliminary studies on the application of the MALDI-MS methodology, previously developed for the analysis of bacteria, to the analysis of intact fungal spores are described here. MALDI-MS and electrospray mass spectrometry enable the high molecular weight analysis of proteins, glycoproteins, oligosaccharides and oligonucleotides. Using MALDI-MS with bacteria has demonstrated the ability to produce 'fingerprints' of the intact cells with the ions observed being associated with the proteinaceous components of the cell wall. This paper reports the adaptation of this technique to the direct analysis of fungal cells. The high percentage of carbohydrate in the fungal cell wall indicates that the ions observed in the mass spectrometric experiments may be of carbohydrate origin. Penicillium spp., Scytalidium dimidiatum and Trichophyton rubrum have been studied in this preliminary investigation and all show individually distinctive spectra which would appear to provide a profile of the cellular material with discrete peaks being observed over the mass range 2 to 13 kDa. The spectra obtained are reproducible within the method used but, as shown in our previous studies on bacteria, washing may selectively release components from the fungal cell wall.     

Multi-anode detection in electrospray ionization time-of-flight mass spectrometry

An electrospray ionization ion source coupled to a time-of-flight mass analyzer incorporating a multi-anode time-to-digital converter is described. High-speed data acquisition (kHz mass spectral acquisition) rates are achieved. The four-anode detector produces a significant increase in detection/counting efficiency over that for a single-anode detector. In this work a 2.5 times increase in detection efficiency is demonstrated. The multi-anode detector is also used as a diagnostic tool to optimize transmission of the ion optics.     

Structure determination of two conotoxins from Conus textile by a combination of matrix-assisted laser desorption/ionization time-of-flight and electrospray ionization mass spectrometry and biochemical methods

Two highly modified conotoxins from the mollusc Conus textile, epsilon-TxIX and Gla(1)-TxVI, were characterized by matrix-assisted laser desorption/ionization and electrospray mass spectrometry and also by electrospray ionization tandem and triple mass spectrometry in combination with enzymatic cleavage and chemical modification reactions. The mass spectrometric studies allowed the confirmation of the sequence determined by Edman degradation and assignment of unidentified amino acid residues, among which bromotryptophan residues and an O-glycosylated threonine residue were observed. Methyl esterification was found necessary for the site-specific assignment of the Gla residues in the peptides.