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In JoVE (1)
Other Publications (10)
- European Journal of Mass Spectrometry (Chichester, England)
- Rapid Communications in Mass Spectrometry : RCM
- Journal of the American Society for Mass Spectrometry
- Journal of the American Society for Mass Spectrometry
- Analytical Chemistry
- Analytical Chemistry
- Rapid Communications in Mass Spectrometry : RCM
- Rapid Communications in Mass Spectrometry : RCM
- Analytica Chimica Acta
- Journal of the American Society for Mass Spectrometry
Articles by Kevin Owens in JoVE
JoVE General
Optimization of the Ugi Reaction Using Parallel Synthesis and Automated Liquid Handling
1Department of Chemistry, Drexel University, 2Mettler-Toledo, 3Chemspider
The Ugi reaction has proved to be a convenient way to quickly create diverse libraries of compounds. It involves the reaction of an amine, an aldehyde, a carboxylic acid and an isonitrile typically in methanol at room temperature. In this video, we utilize a 48-slot Mettler-Toledo MiniBlock equipped with filtration tubes and a Mettler-Toledo MiniMapper automated liquid handler was used to deliver the reagents and solvent. The parameters of interest were the concentration, the solvent composition and the excess of some of the reagents.
Other articles by Kevin Owens on PubMed
Atmospheric Pressure Matrix-assisted Laser Desorption/ionisation Ion Trap Mass Spectrometry of Synthetic Polymers: a Comparison with Vacuum Matrix-assisted Laser Desorption/ionisation Time-of-flight Mass Spectrometry
Atmospheric pressure matrix-assisted laser desorption/ionisation quadrupole ion trap (AP-MALDI/QIT) mass spectrometry has been investigated for the analysis of polyethylene glycol (PEG 1500) and a hyperbranched polymer (polyglycidol) in the presence of alkali-metal salts. Mass spectra of PEG 1500 obtained at atmospheric pressure showed dimetallated matrix/analyte adducts, in addition to the expected alkali-metal/PEG ions, for all matrix/alkali-metal salt combinations. The relative intensities of the desorbed ions were dependent on the matrix, the alkali-metal salt added to aid cationisation and the ion trap interface conditions [capillary temperature, in-source collisionally-induced dissociation (CID)]. These data indicate that the adducts are rapidly stabilised by collisional cooling enabling them to be transferred into the ion trap. Experiments using identical sample preparation conditions were carried out on a vacuum MALDI time-of-flight (ToF) mass spectrometer. In all cases, vacuum MALDI-ToF spectra showed only alkali-metal/PEG ions and no matrix/analyte adducts. The tandem mass spectrometry (MS/MS) capability of the ion trap has been demonstrated for a lithiated polyglycol yielding a rich fragment-ion spectrum. Analysis of the hyperbranched polymer polyglycidol by AP-MALDI/QIT reveals the characteristic ion series for these polymers as also observed under vacuum MALDI-ToF conditions.
Optimization of Matrix-assisted Laser Desorption/ionization Time-of-flight Collision-induced Dissociation Using Poly(ethylene Glycol)
Details of the optimization of the collision-induced dissociation (CID) process, using a collision cell on a matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometer, are described using poly(ethylene glycol) 1000 (PEG 1000) as a model analyte. The effects of collision gas identity (helium, air, and argon), as well as collision gas pressure, on the resulting MS/MS data were investigated. With PEG 1000, helium was found to give the best results with respect to signal-to-noise (S/N) ratio. The optimum pressure for each gas was found to be in the range where the precursor ion signal was attenuated to approximately 30-50% for helium and 40-60% for argon. The effect of cation choice (Li, Na, and K) on the CID of PEG was also studied. CID spectra were produced for each, but PEG cationized with lithium was found to produce the spectra with the highest S/N ratio. The MALDI-TOF CID spectra that were generated for PEG were compared with the high-energy and low-energy MS/MS spectra obtained from a sector mass spectrometer and from a triple quadrupole mass spectrometer, respectively. The results observed for PEG confirm that CID on a MALDI-TOF mass spectrometer is a high-energy MS/MS technique.
Investigations of Electrospray Sample Deposition for Polymer MALDI Mass Spectrometry
In the interest of a more thorough understanding of the relationship between sample deposition technique and the quality of data obtained using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, details of the electrospray (ES) process of sample deposition are investigated using a number of techniques. Sample morphology was observed with scanning electron microscopy (SEM) and atomic force microscopy (AFM), while matrix-enhanced secondary ion mass spectrometry (MESIMS) monitored surface coverage. Electrospray deposition reduces the analyte segregation that can occur during traditional dried droplet deposition for MALDI. We attribute statistically significant improvements in the reproducibility of signal intensity and MALDI average molecular mass measurements to the ES sample deposition technique.
Improved PSD and CID on a MALDI TOFMS
The influence of several instrument-operating parameters on the product-ion resolution and mass accuracy in matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) post-source decay (PSD) and collision-induced dissociation (CID) experiments is reported. Voltages commonly applied to the reflectron for PSD and CID experiments were found to be non-ideal; optimization of these voltages resulted in better resolution across each segment of the measured PSD spectrum. Mass resolution, calculated as M/DeltaM (FWHM) for the product-ion peaks, was as high as 2500. Additionally, precursor-ion selection and segment mass range setup were each found to have dramatic influences on product-ion mass accuracy. An understanding of the influence of these variables aided in the interpretation of (a-NH3) and (b - NH3) ions observed in the PSD/CID spectra of a number of peptides. In addition, product ions resulting from coincidence peaks in the precursor-ion selection window were found to be a general problem. With the improvements to resolution and optimization of these mass accuracy variables, the mass accuracy of product ions from MALDI TOF PSD and CID experiments was tested with several reference materials, including the peptides Substance P, bradykinin, angiotensin I, and angiotensin II and the synthetic polymers poly(methyl methacrylate) and polystyrene. The absolute error (Da) for each test material was, on average, below 0.1 Da, demonstrating a significant improvement in mass accuracy using the improved operational parameters and an extension of the use of poly(ethylene glycol) (PEG) as a mass calibrant for the PSD/CID spectra.
Exploring the Importance of the Relative Solubility of Matrix and Analyte in MALDI Sample Preparation Using HPLC
New insight into the role of solubility in the sample preparation process for MALDI MS is reported. Reversed-phase gradient HPLC conditions were developed that enable the analysis of a broad range of analyte polarities with a single method. This HPLC method was used to establish a relative polarity scale for a series of 15 MALDI matrix materials, a set of example peptides, and a series of model polymer materials with a broad range of polarity. Examples of each polymer type within the range of 6000-10,000 were analyzed with six matrixes that cover a broad range of polarity using MALDI TOFMS. With regard to polymer signal-to-noise ratio, the matrix and polymer combinations that had a close match of HPLC retention time produced the best MALDI spectra. Conversely, the matrix and polymer combinations that have a large difference in HPLC retention time produced poor MALDI spectra. The results suggest that there is a relationship between polarity (solubility) and effective MALDI sample preparation. The relative HPLC retention time of an unknown polymer can serve as a starting point for predicting the matrix (or range of matrixes) that would be most effective.
Importance of Solubility in the Sample Preparation of Poly(ethylene Terephthalate) for MALDI TOFMS
The role of solubility in the sample preparation process for matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is demonstrated for oligomeric and medium molar mass poly(ethylene terephthalate) (PET). For low molar mass oligomers (PET-1), minor discrimination effects were observed when the sample was not completely in solution. MALDI spectra of medium molar mass PET, representative of the entire molar mass distribution, were obtained only when a good solvent for PET was used, such as 1,1,1,3,3,3-hexafluoro-2-propanol (commonly referred to as HFIP), as the sample preparation solvent and dithranol as the matrix. The azeotropic composition of 70:30 CH(2)Cl(2)/HFIP better solubilizes the more nonpolar matrixes, which enables more latitude in selecting sample preparation conditions than pure HFIP. Segregation effects were observed when the azeotrope mixture was diluted with tetrahydrofuran, resulting in large molar mass distribution discrimination effects in the MALDI spectra. Dilution with CH(2)Cl(2) resulted in a significant decrease in the overall signal intensity for the entire polymer distribution. With each attempt to dilute the azeotrope, the sample after solvent evaporation was visibly heterogeneous, which resulted in shot-to-shot variability. Both examples demonstrate the importance of constant solvent composition during solvent evaporation. The compatibility of matrix and polymer was explored using relative HPLC retention times. Consistent with previous work in our laboratories, it was found that the matrix/polymer combination that has the closest match of retention time resulted in the best MALDI signal intensity.
A Study of Gas-phase Cationization in Matrix-assisted Laser Desorption/ionization Time-of-flight Mass Spectrometry
A specially constructed split sample probe was used to unequivocally demonstrate that gas-phase cationization occurs within the desorption plume during a matrix-assisted laser desorption/ionization experiment. Two separate samples were prepared for analysis: on side A, a mixture of poly(ethylene glycol) (PEG) 1500 analyte and 2,5-dihydroxybenzoic acid (DHB) matrix, and on side B a mixture of DHB matrix and lithium hydroxide (LiOH), the cationization reagent. Analysis of the data showed that when the ionization laser was focused on the split (so that both sides were illuminated), Li(+)-cationized PEG peaks were observed. Since the PEG analyte did not come into contact with Li(+) in either the solution or solid phase, the only possibility for the observed cationization was a reaction in the gas phase. Due to the difficulty in completely removing the adventitious cations (Na(+) and K(+)) present in DHB and on sample surfaces, gas-phase cationization could not be demonstrated to be either the only or most important mechanism operating in the MALDI experiment.
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.
Optimization of a Modified Aerospray Deposition Device for the Preparation of Samples for Quantitative Analysis by MALDI-TOFMS
A modified aerospray apparatus was used to prepare a thin layer sample of matrix and analyte for quantitative analysis by MALDI-TOFMS. The apparatus consists of a set of coaxial tubing; the liquid sample is forced by a syringe pump through the inner capillary and it is nebulized by a flow of gas through the outer capillary. The small droplets of sample exiting the device are deposited onto a rotating plate, which serves as the sample surface for a time-of-flight mass spectrometer. An optimization was carried out after initial experiments with the device resulted in poorer than expected reproducibility of analyte signal. A two-level plus center point factorial experiment was performed investigating several factors, including the inner capillary internal diameter, gas pressure, liquid flow, spray distance, and time. After optimization the within-sample reproducibility of the analyte signal improved 3-fold, while the sample-to-sample reproducibility improved 4.5-fold.
Development of a Combined Standard Additions/internal Standards Method to Quantify Residual PEG in Ethoxylated Surfactants by MALDI TOFMS
Measuring the residual polyethylene glycol (PEG) in polyethylene oxide (PEO)-based surfactants is important to fully understanding the performance of these materials. Traditional methods of quantitating PEG in PEO-based surfactants can be time-consuming and struggle with low amounts or overlapping molecular mass distributions. This paper describes a matrix-assisted laser desorption/ionization (MALDI) mass spectrometry method developed to quantitate residual PEG in a series of ethoxylated surfactants. The technique addresses the difficulties faced in doing quantitative MALDI experiments by utilizing both internal standard and standard additions protocols. The method produces excellent straight line standard addition plots, and the quantitative results are verified using both a constructed standard and an independent traditional chromatographic separation.
