Louis Ramaley

Development of electrophoretic conditions for the characterization of protein glycoforms by capillary electrophoresis—electrospray mass spectrometry☆

A capillary electrophoresis (CE) method using acidic buffers and capillaries coated with Polybrene, a cationic polymer has been developed for the separation of glycoproteins and glycopeptides. Electrophoretic conditions have been optimized to provide resolution of individual glycoforms observed for different glycoprotein preparations. These conditions were found to be entirely compatible with the operation of electrospray mass spectrometry (ESMS), which facilitated the assignments of possible carbohydrate compositions of glycopeptides arising from digests of glycoproteins. By using operating conditions enhanced the formation of oxonium fragment ions prior to mass spectral analysis, selective identification of glycopeptides was achieved for complex samples such as those from proteolytic digests or chemical cleavages. Examples of applications are presented for ribonuclease B, ovalbumin, horseradish peroxidase, and a lectin from Erithrina corallodendron using both CE-ESMS and CE with ultraviolet detection (CE-UV).

Software for the calculation of isotope patterns in tandem mass spectrometry

Software, available at no cost on the Internet, is described which uses polynomial expansion algorithms to calculate the isotope patterns for precursor ion, neutral loss, and MSn product ion tandem mass spectra. Such information is useful for determining product ion and neutral loss composition, identification of analytes in complex samples, deconvolution of overlapping spectra, and correction of peak heights or areas in quantitative analysis. The effect of less than unit mass resolution on the isotope patterns is described and experimental examples of the use of the software are presented.

Quantitative Aspects of and Ionization Mechanisms in Positive-Ion Atmospheric Pressure Chemical Ionization Mass Spectrometry

The behavior in atmospheric pressure chemical ionization of selected model polycyclic aromatic compounds, pyrene, dibenzothiophene, carbazole, and fluorenone, was studied in the solvents acetonitrile, methanol, and toluene. Relative ionization efficiency and sensitivity were highest in toluene and lowest in methanol, a mixture of molecular ions and protonated molecules was observed in most instances, and interferences between analytes were detected at higher concentrations. Such interferences were assumed to be caused by a competition among analyte molecules for a limited number of reagent ions in the plasma. The presence of both molecular ions and protonated analyte molecules can be attributed to charge-transfer from solvent radical cations and proton transfer from protonated solvent molecules, respectively. The order of ionization efficiency could be explained by incorporating the effect of solvation in the ionization reactions. Thermodynamic data, both experimental and calculated theoretically, are presented to support the proposed ionization mechanisms. The analytical implications of the results are that using acetonitrile (compared with methanol) as solvent will provide better sensitivity with fewer interferences (at low concentrations), except for analytes having high gas-phase basicities.

Digital Laser Raman Spectrometer System with On-Line Computer Control of Data Acquisition and Reduction

An interface for coupling a laser Raman spectrometer employing photon counting detection to an on-line programmable calculator or minicomputer is described. The resulting system provides both background and spectral data in digital form that allows data manipulation to be easily performed. In addition online computer control allows the enhancement of the signal-to-noise ratio by signal averaging. The spectrum of gaseous N(2) and O(2) taken with the system illustrates the capability of the interface and computer when coupled with the spectrometer to make precise and sensitive measurements.

Atmospheric pressure ionization mass spectrometry techniques for the analysis of alkyl ethoxysulfate mixtures.

This paper compares two liquid introduction atmospheric pressure ionization techniques for the analysis of alkyl ethoxysulfate (AES) anionic surfactant mixtures by mass spectrometry, i. e., electrospray ionization (ESI) in both positive and negative ion modes and atmospheric pressure chemical ionization (APCI) in positive ion mode, using a triple quadrupole mass spectrometer. Two ions are observed in ESI(+) for each individual AES component, [M + Na]+ and a “desulfated” ion [M − SO3 + H]+, whereas only one ion, [M − Na]− is observed for each AES component in ESI(−). APCI(+) produces a protonated, “desulfated” ion of the form [M − NaSO3 + 2H]+ for each AES species in the mixture under low cone voltage (10 V) conditions. The mass spectral ion intensities of the individual AES components in either the series from ESI(+) or APCI(+) can be used to obtain an estimate of their relative concentrations in the mixture and of the average ethoxylate (EO) number of the sample. The precursor ions produced by either ESI(+) or ESI(−), when subjected to low-energy (50 eV) collision-induced dissociation, do not fragment to give ions that provide much structural information. The protonated, desulfated ions produced by APCI(+) form fragment ions which reveal structural information about the precursor ions, including alkyl chain length and EO number, under similar conditions. APCI(+) is less susceptible to matrix effects for quantitative work than ESI(+). Thus APCI(+) provides an additional tool for the analysis of anionic surfactants such as AES, especially in complex mixtures where tandem mass spectrometry is required for the identification of the individual components.

Autoranging in High Speed Data Acquisition Systems

ABSTRAC This paper is a presentation of various types of autoranging amplifiers and methods of incorporating them into fast digital data acquisition systems. The advantages and drawbacks of each type of autoranging method are examined. An example of fast autoranging using rapid scan square wave polarography is presented in which trace amounts of materials are detected in the presence of large amounts of other electroactive species.

Studying the Chemistry of Cationized Triacylglycerols Using Electrospray Ionization Mass Spectrometry and Density Functional Theory Computations

AbstractAnalysis of triacylglycerols (TAGs), found as complex mixtures in living organisms, is typically accomplished using liquid chromatography, often coupled to mass spectrometry. TAGs, weak bases not protonated using electrospray ionization, are usually ionized by adduct formation with a cation, including those present in the solvent (e.g., Na+). There are relatively few reports on the binding of TAGs with cations or on the mechanisms by which cationized TAGs fragment. This work examines binding efficiencies, determined by mass spectrometry and computations, for the complexation of TAGs to a range of cations (Na+, Li+, K+, Ag+, NH4+). While most cations bind to oxygen, Ag+ binding to unsaturation in the acid side chains is significant. The importance of dimer formation, [2TAG + M]+ was demonstrated using several different types of mass spectrometers. From breakdown curves, it became apparent that two or three acid side chains must be attached to glycerol for strong cationization. Possible mechanisms for fragmentation of lithiated TAGs were modeled by computations on tripropionylglycerol. Viable pathways were found for losses of neutral acids and lithium salts of acids from different positions on the glycerol moiety. Novel lactone structures were proposed for the loss of a neutral acid from one position of the glycerol moiety. These were studied further using triple-stage mass spectrometry (MS3). These lactones can account for all the major product ions in the MS3 spectra in both this work and the literature, which should allow for new insights into the challenging analytical methods needed for naturally occurring TAGs. Figureᅟ

Fragmentation pathways of some benzothiophene radical cations formed by atmospheric pressure chemical ionisation

Polycyclic aromatic sulfur-containing compounds (PASHs) are commonly found in fossil fuels and are of considerable importance in environmental studies. This work presents detailed studies on the fragmentation patterns of radical cations formed from four representative PASHs, benzo[b]thiophene, dibenzothiophene, 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene, using tandem atmospheric pressure chemical ionization mass spectrometry (APCI-MS/MS). Understanding these fragmentation patterns can be a useful aid in the analysis of PASHs employing APCI or electron ionization (EI-MS/MS), either alone or in conjunction with liquid or gas chromatography.

Digitally Controlled Potentiostat for Electrochemical Studies

ABSTRACT A potentiostat employing digital selection of sweep range, sweep rate, and cell current measurement time has been built for use in staircase voltammetry, square wave polarography and voltammetry, and tast polarography. The use of these techniques enables background current reduction and therefore provides high sensitivity. The method of cell potential generation and control allows very high measurement precision. The instrument can be operated either manually or under complete computer control.

Computer Controlled Sweep Generator For Electrochemical Studies

SUMMARY A computer programmable sweep generator for use in voltammetric electro chemical studies has been constructed from a reversible binary counter and a digital-to-analog converter. The generator produces staircase ramps, triangular waves, and sawtooth waves. The initial potential, upper potential limit, sweep direction, and resolution (step size and sweep rate) can be controlled by a 12-bit computer word. This generator is characterized by low drift, high sweep rate accuracy, high reproducibility of its various settings regardless of sweep rate, and ease with which it can be controlled by a computer. In combination with the proper clock and potentiostat, it can be used to implement closed-loop, on-line computer control of electrochemical measurements.