Search

Complex samples can be challenging, and there are many caveats that need to be considered to mitigate matrix effects. Matrix interferences can be detrimental to analysis, and the contents of [...]

The 'State-of-the-Art in Capillary Liquid Chromatography' panel discussion at the 43rd International Symposium on Capillary Chromatography (ISCC 2019) in Fort Worth, Texas, was a thoughtful dialogue on current challenges and [...]

In the scientific publication process, studies lacking appropriate validation and quality control are regularly rejected during peer review. Similarly, in forensics, measurements that have not been supported by widely accepted [...]

The lack of proper method validation has important implications in blood alcohol concentration (BAC) determinations. We examine this issue, addressing the importance of gas chromatography (GC) for BAC determination, why certain validation procedures are important, and why accreditation bodies need to step up their game., Over the past several years, we have consulted in a variety of litigation surrounding various patent, environmental, and forensics cases. What we have learned is that laboratory accreditation is not [...]

In the past, I have openly lamented the seeming lack of National Science Foundation (NSF) support for research into fundamental separation science. This past fall, I was heartened to receive [...]

Those working in a technical field are always trying to innovate and increase operational efficiency to produce the most value out of any given project. This requires making data-driven decisions [...]

Schug: When did you first discover chromatography and why did you remain in this field? Lindner: Between 1969 and 1972, I carried out my PhD research in chemistry at the [...]

Some might consider gas chromatography (GC) a mature technique. However, several substantial advances in GC technology in the past few years have proven that there is still room for innovation. [...]

Those of you in the analytical science community are likely familiar with the concept of method validation. If you have developed a new quantitative method, it is almost impossible to [...]

The past year has been a remarkable ride for the oil and gas industry, and for the entire energy sector in general. Extreme volatility in commodity pricing, an oil contango, [...]

In April 2020, on the heels of the pandemic shutdown, the price of crude oil fell to a negative value for the first time ever, sending ripples through an oil [...]

Kevin Schug: Who introduced you to gas chromatography (GC)? Harold McNair: Dr. A.J.P. Martin, Dr. Steve Dal Nogare, and Professor A.I.M. Keulemans. You could not have wished for a better [...]

A review of recent research related to the coupling of ambient ionization mass spectrometry (MS) with various separation techniques is presented. Ambient ionization, referring to a mode of atmospheric pressure [...]

A review of recent research related to the coupling of ambient ionization mass spectrometry (MS) with various separation techniques is presented. Ambient ionization, referring to a mode of atmospheric pressure [...]

Recently, we have shown that dilute multivalent cationic reagents can be paired with analyte anions in ESI-MS, thereby allowing them to be detected in the positive mode at very low limits of detection. However, there can be differences in the efficiency of this technique depending on the nature of the cationic pairing agent and the anion being analyzed. In this study, three dicationic ion-pairing agents and four singly charged anionic species were examined in a series of experiments to elucidate the mechanism of action that allows for such sensitive detection and the profound differences in the selectivity of this ion-pairing method. The binding constants for the dication/anion complexes were determined by NMR and ESIMS. The results indicated that the binding of these species is greatly enhanced as they move from the solution phase to the gas phase. Furthermore, surface tension measurements for the complexes were performed. This test revealed that, as the dication pairs with the anion, it creates a surface-active species within the ESI droplet. This is determined to be one of the major factors that leads to the overall sensitivity enhancement. This has led to a better understanding of how this ion-pairing technique produces unprecedented limits of detection for anions and why there are selectivity differences in pairing agents of different structures. 10.1021/ac102115w

Negati e-ionization mode electrospray ionization-mass spectrometry (ESI-MS) analysis of antimony(III)-tartrate in frequently used solvent systems, ACN/[H.sub.2]O and MeOH/ [H.sub.2]O, revealed that the antimony(III)-tartrate dianion associates to solvent reaction products generated by radical formation and their subsequent recombination during the negative-mode electrospray process. A systematic increase and decrease in negative spray capillary voltage (SCV) from normal operational voltage ranges of a conventional quadrupole ion trap instrument during these analyses showed initially unobserved adduct ions to correspondingly increase and diminish in relative ion intensity. The identity of the adducted species, including products such as [H.sub.2][O.sub.2], NCC[H.sub.2]C[H.sub.2]CN, and C[H.sub.2][(OH).sub.2], were confirmed by performing similar experiments with deuterated and nondeuterated solvent mixtures. Relative intensity dependence of these adducted ions was monitored as the volume composition of each solvent system was changed. It was clearly observed that the relative intensity of {[[Sb.sub.2]-[tar.sub.2]][[H-O-O-H]}.sup.2-] and [{[[Sb.sub.2][tar.sub.2]][NC-C[H.sub.2] C[H.sub.2]-CN]}.sup.2-] adduct ions increased with the volume percent of [H.sub.2]O and C[H.sub.3]CN, respectively. Similarly, an increase in volume percent of C[H.sub.3]OH increased the relative intensity of [{[[Sb.sub.2][tar.sub.2]][H-O-C[H.sub.2]-O-H]}.sup.2] adducted ions. On the basis of this evidence, it was proposed that homolytic cleavage of C-H bonds for C[H.sub.3]CN and C[H.sub.3]OH molecules, and O-H bonds for [H.sub.2]O molecules, produces a series of radicals during negative-ionization mode ESI, and subsequent self-recombination or cross-recombination of these radicals then occurs to form the neutral solvent products, which are observed in the mass spectra as [[Sb.sub.2]-[tar.sub.2]]-adducted ionic species. These findings provide new insight into processes, which are relevant to understanding the mechanism of electrospray ionization, a widely used technique. 10.1021/ac1003344

Comprehensive chromatography, microscale separations, sample preparation, and the latest supporting technologies, oh my! When we say that the 43rd International Symposium on Capillary Chromatography (ISCC) and the 16th GCxGC Symposium [...]

None of the current biodegradable polymers can function as both implant materials and fluorescent imaging probes. The objective of this study was to develop aliphatic biodegradable photoluminescent polymers (BPLPs) and their associated cross-linked variants (CBPLPs) for biomedical applications. BPLPs are degradable oligomers synthesized from biocompatible monomers including citric acid, aliphatic diols, and various amino acids via a convenient and cost-effective polycondensation reaction. BPLPs can be further cross-linked into elastomeric cross-linked polymers, CBPLPs. We have shown representatively that BPLP-cysteine (BPLP-Cys) and BPLP-serine (BPLP-Ser) offer advantages over the traditional fluorescent organic dyes and quantum dots because of their preliminarily demonstrated cytocompatibility in vitro, minimal chronic inflammatory responses in vivo, controlled degradability and high quantum yields (up to 62.33%), tunable fluorescence emission (up to 725 nm), and photostability. The tensile strength of CBPLP-Cys film ranged from 3.25 [+ or -] 0.13 MPa to 6.5 [+ or -] 0.8 MPa and the initial Modulus was in a range of 3.34 [+ or -] 0.15 MPa to 7.02 [+ or -] 1.40 MPa. Elastic CBPLP-Cys could be elongated up to 240 [+ or -] 36%. The compressive modulus of BPLP-Cys (0.6) (1:1:0.60D:CA:Cys) porous scaffold was 39.60 [+ or -] 5.90 KPa confirming the soft nature of the scaffolds. BPLPs also possess great processability for micro/nanofabrication. We demonstrate the feasibility of using BPLP-Ser nanoparticles ('biodegradable quantum dots') for in vitro cellular labeling and noninvasive in vivo imaging of tissue engineering scaffolds. The development of BPLPs and CBPLPs represents a new direction in developing fluorescent biomaterials and could impact tissue engineering, drug delivery, bioimaging. bioimaging | elastomers | photoluminescence | tissue engineering

We describe a novel optical sensor for the simultaneous measurement of atmospheric nitrogen dioxide (N[O.sub.2]), ozone ([O.sub.3]), and relative humidity (RH). A transparent backing thin layer silica gel chromatographic plate impregnated with 8-amino-1-naphthol-5-sulfonic acid (ANS) is used as the collection/sensor element. The plate transmittance is probed by three discrete light emitting diodes (LEDs) centered, respectively, at 442, 525, and 850 nm. The transmission of the plate changes reversibly across visible to NIR wavelengths as the RH around the plate changes; this is the basis for a limited-resolution RH sensor. The ANS on the plate reacts to form brown and pink colored products, respectively, when it reacts with N[O.sub.2] and [O.sub.3]. The sample air impinges on the plate via an entrance nozzle. The LEDs are alternately turned on in a preprogrammed manner and the light is brought to the impregnated face of the plate by a three-legged fiber optic. The transmitted light is detected on the obverse side of the plate. The 850 nm signal provides the RH value and optionally serves as the reference measurement for the other two wavelengths; the N[O.sub.2] and [O.sub.3] reaction products do not absorb at this wavelength. The absorbance at 442 and 525 nm, thus referenced against 850 nm, are used to obtain N[O.sub.2] and [O.sub.3] concentrations from a pair of simultaneous equations. For a sampling period of 5 min, the limits of detection (LOD) based on 3 times the standard deviation of blank responses were 0.64 and 0.42 ppbv for N[O.sub.2] and [O.sub.3], respectively. Data obtained with collocated commercial instruments ([O.sub.3] induced chemiluminescence analyzer for N[O.sub.2] and UV-absorption for [O.sub.3]) show good agreement. Overall, this provides a viable affordable approach for inexpensive measurement of atmospheric N[O.sub.2] and [O.sub.3].

With recent growth in fields such as life sciences and supramolecular chemistry, there has been an ever increasing need for high-throughput methods that would permit determination of binding affinities for noncovalent complexes of various host--guest systems. These are traditionally measured by titration experiments where concentration-dependent signals of species participating in solution-based binding equilibria are monitored by methods such as UV--vis spectrophotometry, calorimetry, or nuclear magnetic resonance spectrometry. Here we present a new titration technique that unifies and allows chromatographic separation of guests with determination of dissociation constants by electrospray mass spectrometry in a multiplexed format. A theoretical model has been derived that describes the complex formation for the guests eluted from a chromatographic column when hosts are admixed postcolumn. The model takes possible competition equilibria into account; i.e., it can deal with unresolved peaks of guests with the possible addition of multiple hosts in one experiment. This on-line workflow makes determination of binding affinities for large libraries of compounds possible. The potential of the method is demonstrated on the determination of dissociation constants for complexes of [beta]- and [gamma]-cyclodextrins with nonsteroidal antiinflammatory drugs ibuprofen, naproxen, and flurbiprofen.

A new method for determination of dissociation constants ([K.sub.d]) using on-line titration by electrospray ionization mass spectrometry is presented. Unlike in common titration experiments, where a set of discrete solutions with a fixed concentration of host and increasing concentration of guest is measured, here a continuous Gaussian concentration profile of guest, formed by band-broadening dispersion during passage through a long tubing, is utilized. An equation allowing access to dissociation constant values from experimental data fit to a 1:1 binding model was derived and incorporated into an in-house-written computer program for automated data processing. The new method is demonstrated for noncovalent complexes of cinchona alkaloid carbamate chiral selectors with N-dinitrobenzoylleucine enantiomers and a series of cyclodextrins with sulfonated azo dyes.

Development of chiral selectors (SOs) is important both for understanding chiral molecular recognition processes and for their use in the separation of chiral species (selectands). Their evaluation by chromatographic procedures (e.g., as chiral stationary phase) can, however, be time-consuming. In this respect, electrospray ionization-MS (ESI-MS) is tested here as a possible alternative for screening enantioselective binding by SOs. The set of well-characterized cinchona alkaloid SOs are investigated with respect to their enantioselective binding to a set of model enantiomers, dinitrobenzoyl-(R)- and dinitrobenzoyl-(S)-leucine. MS-based enantioselectivity values from normalized gas-phase ion abundances for the diastereomeric complexes are compared empirically to chromatographic (HPLC) enantioselectivity results and shown to be consistent. Investigations into the fundamentals of measuring unbiased enantioselectivity values in the limit of dilute solution by correlation between experimental and modeled theoretical data are shown. Titration experiments are used to extract binding constants and are compared with published calorimetric (ITC) data. Results show that while the magnitude of binding affinities determined for various diastereomeric complexes is attenuated, the relative ranking and stereochemical preference in binding are consistently reproduced. This work represents a fundamental study of solution- versus gas-phase correlation for enantioselective systems by ESI-MS and indicates that, although not all questions and assumptions can be clearly engaged, for these enthalpically driven binding systems, the relative degree of binding affinity and selectivity is preserved.

y initial inclination was to write about something other than the current status of life, given the threats of coronavirus. However, after a month extension to the 'shelter in place' [...]

Last fall, I attended the 16th International Interdisciplinary Meeting on Bioanalysis (CECE 2019) in Gdansk, Poland. I was absolutely delighted both by the city and the scientific quality of the [...]

We have been working to develop the use of liquid chromatography-triple quadrupole-mass spectrometry (LC-MS/MS) for quantification of intact proteins from biological fluids (1). The idea is to essentially mimic a [...]

Vacuum ultraviolet absorption spectroscopy detection for gas chromatography (GC-VUV) was introduced in 2014 (1,2). The first generation of GC-VUV features a detector that simultaneously measures a full wavelength range of [...]

Review of work pertaining to noncovalent binding interactions involving primarily the cationic guanidinium group and the anionic sulfonate and phosphonate groups is presented. Noncovalent binding interactions are used in spectroscopic, biomimetic, molecular interaction modeling, and bioinformatics tools among others, that are greatly varied and used in a wide variety of fields.

Electrospray ionization (ESI) is the most commonly used source for ion generation when high performance liquid chromatography is coupled to mass spectrometry detection (HPLC-ESI-MS). High and moderately polar and ionic [...]

The 23rd International Symposium on Chiral Discrimination (Chirality 2011) was held in Liverpool, UK, this past July. This conference, which rotates each year between Europe, the United States, and Asia, [...]

Once you have found the right capillary (sprayer) voltage for a particular application using electrospray ionization, this voltage can then be equally applied for most separations. True or false? Schug: [...]