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ABSTRACT: A second generation ionic liquid matrix (ILM), N,N-diisopropylethylammonium alpha-cyano-4-hydroxycinnamate (DEA-CHCA), was developed for the characterization of polar biodegradable polymers. It is compared with five solid matrices typically used for the characterization of these polymers and one other new ILM. It is shown that use of the ILM, DEA-CHCA, allows maximum signal with minimum laser intensity which minimizes polymer degradation. In these conditions, the DEA-CHCA ILM is able to assist in the ionization of analytes in an efficient but soft manner. These qualities produce spectra that allow an accurate and sensitive determination of the number average molecular weights, weight average m.w., and polydispersity index of labile polar polymers. With such polymers, many solid matrices produce spectra showing extensive polymer degradation leading to the underestimation of molecular weights. The distribution of intact analyte peaks obtained with the ILM DEA-CHCA allows for identification of the fine structure of complex copolymers. ILMs were much less susceptible to effects of extraction delay times on molecular weight determination than were solid matrices. The liquid nature of the matrix is an important reason for the outstanding results obtained for labile analyte polymers. No comparable results could be obtained with any known solid matrices or other ILMs. In many cases, the manufacturers' listed molecular weights and polydispersity measurements for biodegradable polymers are determined by size-exclusion chromatography and the data obtained by that method may differ considerably from the high-precision matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) results presented here.
Rapid Communications in Mass Spectrometry 10/2009; 23(21):3409-22. · 2.79 Impact Factor
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ABSTRACT: Second generation ionic liquid matrices are developed, examined, and tested. They have shown a wide mass detection range (<1000 Da to >270,000 Da) for proteins and peptides with greater S/N ratios than solid matrices. These ionic liquid matrices also exhibit the ability to effectively ionize proteins of large mass without disrupting noncovalent interactions between monomers. Both the anionic and cationic moieties have been varied systematically to find an ionic liquid matrix with the best physical properties, analyte signal intensity, and widest mass detection range. It was determined that both the proton affinity and pKa of the cation have a large effect on the ionic liquid matrices' ability to effectively ionize the analyte. The ionic liquid matrices can be used to detect polysaccharides with fewer degradation products than solid matrices. N,N-diisopropylethylammonium alpha-cyano-4-hydroxycinnamate and N-isopropyl-N-methyl-t-butylammonium alpha-cyano-4-hydroxycinnamate were the best matrices for proteins and peptides, while N,N-diisopropylethylammonium alpha-cyano-4-hydroxycinnamate and N,N-diisopropylethylammonium ferulate were the best matrices for carbohydrates.
Journal of the American Society for Mass Spectrometry 08/2009; 20(10):1790-800. · 4.00 Impact Factor
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ABSTRACT: A general method for detecting bisphosphonate drugs by ESI-MS and LC-ESI-MS as positive ions has been developed. Bisphosphonates can have multiple negative charges in solution. Tricationic ion-pairing reagents were paired with bisphosphonates to form a positively charged complex. It was clear that this facile pairing method worked. However, an appreciable presence of -1 bisphosphonate species were observed in positive mode ESI-MS (i.e. as the +2 complex with tricationic reagents). This led to an extended investigation on the use of dicationic pairing agents. The use of dicationic reagents improved the detection sensitivity for all of the bisphosphonates. Tandem mass spectrometry also improved the limits of detection for most of the bisphosphonates using both the tricationic and dicationic pairing reagents. A tricationic reagent also was used as an ion-pairing reagent in chromatography experiments. Thus the addition of a single reagent produced benefits in that it increased chromatographic retention and enhanced the ESI-MS detection of bisphosphonates.
Analytica chimica acta 03/2009; 633(2):232-7. · 4.31 Impact Factor
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ABSTRACT: We report a rapid and sensitive stochastic nanopore sensing method for the detection of monovalent cations and liquid explosive components and their sensitizers. The sensing element is a wild-type alpha-hemolysin protein pore with boromycin as a molecular adaptor, while a solution containing an ionic liquid was used as the background electrolyte. The analyte-boromycin complexes showed significantly different signatures. Specifically, their event mean dwell times and amplitudes were sufficiently distinct to permit the convenient differentiation and even simultaneous detection of liquid explosive components in aqueous environments. In addition, the results also demonstrate that the usage of specific ionic liquid salt solutions instead of NaCl or KCl solution as supporting electrolyte provides a useful means to greatly enhance the sensitivity of the nanopore for some analytes in stochastic sensing.
Analytical Chemistry 01/2009; 81(1):460-4. · 5.86 Impact Factor
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ABSTRACT: A rapid test of whether a laboratory sample contains any microorganisms is important and necessary for many areas of science and technology. Currently, most of the standard procedures for the detection of aerobic bacteria, anaerobic bacteria and fungi, require the preparation of microbial cultures in respective growth media, which are dramatically slow. Different approaches providing fast analysis such as CE are becoming more desired. To compensate for the natural electrophoretic heterogeneity of microbes, various buffer additives were examined to stack all bacteria and fungi in a sample plug into a single peak. This peak was removed from the molecular contaminants in the sample to prevent false positives. Both cationic surfactants and ionic liquids (IL) were investigated as run buffer additives and they are both widely applicable to different species of bacteria and fungi. Given that high concentrations of surfactants can potentially lyse cells, dicationic IL offer attractive auxiliary buffer additives for use in CE-based sterility tests. The analysis can be completed in 10 min, thus providing a great advantage over traditional direct inoculation methods that require several weeks to complete.
Electrophoresis 05/2008; 29(12):2587 - 2592. · 3.30 Impact Factor
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ABSTRACT: Dynamic solvation of the dye coumarin 153 is studied in a phosphonium ionic liquid: hexadecyltributylphosphonium bromide, [(C4)3C16P+][Br-]. It forms micelles in water, and the bulk also exists as a liquid under our experimental conditions. This system permits a comparison with an imidazolium ionic liquid studied earlier, which also formed micelles in water (J. Phys. Chem. A 2006, 110, 10725-10730). We conclude that our analysis of the comparable situation in a phosphonium liquid is not as definitive as we had proposed earlier, i.e., that the majority of the early-time solvation arises from the organic cation. Part of the difficulty in performing this analysis is most likely due to the amount of water that is associated with the micelle. In the course of this work, we have focused on the calculation of the solvation correlation function, C(t), and investigated how it depends upon the methods with which the "zero-time" spectrum is constructed.
The Journal of Physical Chemistry B 04/2008; 112(11):3390-6. · 3.70 Impact Factor
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ABSTRACT: Twenty-three different dications were investigated for their effectiveness in pairing with singly charged anions, thereby allowing the electrospray ionization mass spectrometry (ESI-MS) detection of anions as positively charged complexes. Nitrate, iodide, cyanate, monochloroacetate, benzenesulfonate, and perfluoro-octanoate were chosen as representative test anions as they differ in mass, size-to-charge ratio, chaotropic nature, and overall complexity. Detection limits were found using direct injection of the anion into a carrier liquid containing the dication. Detection limits are given for all six anions with each of the 23 dications. Each anion was easily detected at the ppb (microg/L) and often the ppt (ng/L) levels using certain dicationic reagents. The ability of dicationic reagents to pair with anions and produce ESI-MS signals varied tremendously. Indeed, only a few dications can be considered broadly useful and able to produce sensitive results. Liquid chromatography (LC)-ESI-MS also was investigated and used to show how varying the dicationic reagent produced significantly different peak intensities. Also, the use of tandem mass spectrometry can lead to even greater sensitivity when using imidazolium based dications.
Journal of the American Society for Mass Spectrometry 03/2008; 19(2):261-9. · 4.00 Impact Factor
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ABSTRACT: Fast GC separations of a broad range of analytes are demonstrated using a capillary column coated with a novel immobilized ionic liquid (IIL) stationary phase. Both completely cross-linked and partially cross-linked columns were evaluated, yielding approximately 1600 and approximately 2000 theoretical plates per meter, respectively. Enhanced separation is demonstrated using a dual-column ensemble comprised of an IIL column, a commercially coated Rtx-1 column, and a pneumatic valve connecting the inlet to the junction point between the two columns. Enhanced separation of 20 components, with two sets of co-eluting peaks is shown in approximately 150 s, while sacrificing only a length of time equivalent to the sum of the stop flow pulses, or about 15.5 s. A novel application of a band trajectory model that shows band position as a function of analysis time as analytes move through the column ensemble is employed to determine pulse application times. The model predicts component retention times within a few seconds. Another method of selectivity enhancement of the IIL stationary phase-coated columns is demonstrated using a differential mobility spectrometer (DMS) that provides a second dimension separation based on ion mobility in a high-frequency electrical field. The DMS is able to separate all but one set of co-eluting components from the IIL column. The separation of 13 components found in the headspace above U.S. currency is demonstrated using the IIL column in a dual-column ensemble as well as with the DMS.
Journal of Chromatography 01/2007; 1135(2):230-40. · 4.53 Impact Factor
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ABSTRACT: Dynamic solvation of the dye, coumarin 153, is compared in an ionic liquid that forms micelles in water against the bulk solvent. This provides the unprecedented opportunity of investigating the behavior of the ionic liquid in two globally different configurations. It is proposed that the imidazolium moiety is in both cases responsible for the majority of the solvation, which manifests itself in the first 100 ps. Exploiting the use of ionic liquids capable of accommodating specific structures thus provides a deeper insight into how solutes interact with these fascinating and interesting solvents (at least those that are imidazolium based) that are gaining ever increasing interest in the scientific community.
The Journal of Physical Chemistry A 10/2006; 110(37):10725-30. · 2.95 Impact Factor
