Aqueous High-performance Liquid Chromatography Research Articles

Automated, Transferable, and Ethanol-Free Radiosynthesis of [11C]Butanol.

Cerebral blood flow and blood-brain barrier permeability assessment are crucial hemodynamic parameters to measure under neurological conditions. In conjunction with positron emission tomography (PET), oxygen-15-labeled water has emerged as a gold standard for measuring cerebral perfusion; however, at higher flow rates, [15O]water extraction becomes nonlinear. In such a scenario, freely diffusible [11C]butanol can provide a truer estimate. Radiosyntheses of [11C]butanol reported to date are protracted, are not automated, or require ethanol in the final formulation. By using a flow-based, captive solvent approach on a commercially available radiosynthesizer, we automated and reduced the synthesis time to 28 min. Forgoing cartridge-based purification for an aqueous high-performance liquid chromatography method, we obtained high purity [11C]butanol in ethanol-free phosphate buffered saline in sufficient yields for clinical PET studies. We here report our expedited, automated, and ethanol-free radiosynthesis of [11C]butanol along with preliminary imaging of a porcine subject.

In‐source collision‐induced dissociation (IS‐CID): Applications, issues and structure elucidation with single‐stage mass analyzers

A discussion of the definition, advantages, and issues with the formation of ions in the transition region between an electrospray ionization (ESI) source and the ion optics of a mass analyzer is presented. The various types of ions formed in the so-called in-source collision-induced dissociation (IS-CID) process are illustrated. Applications of IS-CID with single-stage mass analyzers, such as structure elucidation and quantitation, are demonstrated. The discussion is illustrated by examples of the in-source fragmentation of ginkgolides, which are marker compounds found only in Ginkgo biloba. Supercritical fluid chromatography (SFC) with non-aqueous eluents was used to achieve a fast resolution of the ginkgolides without the hydrolysis reactions possible with aqueous high-performance liquid chromatography (HPLC) eluents. In-source ion generation occurs at relatively high pressures (ca. 1-3torr) compared to the low pressure normally observed in collision chambers of tandem mass spectrometry (MS/MS). As a result, the fragmentation process is complex and often generates ions other than the fragments observed with classic CID or the same ions at different intensities. The objective of the current tutorial is to illustrate the conditions under which single-stage, quadrupole or time-of-flight mass analyzers with electrospray or in-air (direct analysis in real time; DART) ionization can be used for quantitation and structure elucidation in a manner similar to that observed with MS/MS. While the low m/z (≤ [M±H]± ) ions formed in-source often duplicate the ions observed in MS/MS systems, it is the focus of this discussion to illustrate the utility of in-source generated fragment ions that may not be observed or observed at different intensities than in the collision cells of MS/MS instruments.

An Aqueous High-Performance Liquid Chromatographic Procedure for the Determination of 5-Hydroxymethylfurfural in Honey and Other Sugar-containing Materials

ABSTRACT: A new, all aqueous high-performance liquid chromatography (HPLC) procedure for the determination of 5-hydroxymethylfurfural (HMF) in honey and other sugar-containing materials was developed without harmful chemicals. The method involved dilution of the sample in water and the analysis of the diluent using an HPLC system equipped with an absorbance detector and a 30-mm sulfonated poly(styrene-divinylbenzene) cation exchange column. Water was used as the mobile phase at a high flow rate of 2.00 mL/min Using this high flow rate in conjunction with a column heater set at 55°C, HMF eluted in less than 4 min. Overall precision was less than 1% relative standard deviation, recovery of HMF from spiked samples was approximately 99%, and there were no interferences from similar compounds such as 2-furfural and 5-methylfurfural. Several sugar-containing materials were analyzed by this method where the results compared well with the classic Winkler spectrophotometric procedure, but not as well with a commonly used reverse-phase HPLC technique. In addition, several consumer products were also analyzed for their HMF content.

A Glow Discharge−Conductivity Detector for Carbohydrates in Aqueous Chromatography

A new glow discharge-conductivity detector is shown to respond to low nanomolar and femtomole quantities of carbohydrates in aqueous high-performance liquid chromatography. Its sensitivity is comparable to those of the most sensitive detection methods available for carbohydrate analysis. The atmospheric pressure argon glow discharge is sustained between two metallic electrodes and is operated at the output of a liquid chromatography system. The glow discharge induces oxidation in the eluting carbohydrates, forming acid(s) in amounts proportional to carbohydrate concentration. The relative acid concentration is monitored with a conductivity detector placed downstream from the discharge region. A detailed description of the detector and the parameters that control sensitivity is presented. The formation of hydrogen peroxide, hydronium ion, and UV-absorbing species in aqueous flowing glucose solutions is also studied using the glow discharge-conductivity detector. A comparison between these products and the products formed under similar conditions using high-energy radiation is discussed.

Preparation and characterization of monodisperse oligo(ethylene glycol) dimethacrylate polymer beads for aqueous high-performance liquid chromatography

Abstract Three types of oligo(ethylene glycol) dimethacrylate were polymerized by seed polymerization. The gel beads so prepared had a narrow size distribution and were macroporous. The columns packed with gel beads were suitable for aqueous size-exclusion chromatography for polysaccharides, proteins and other hydrophilic polymers. The hydrophilicity of the gel beads was almost equal to that of 2-hydroxyethyl methacrylate-ethylene dimethacrylate copolymer beads which are usually used for aqueous size-exclusion chromatography.

Determination of N-Nitroso Compounds by High-Performance Liquid Chromatography with Postcolumn Reaction and a Thermal Energy Analyzer

Carcinogenic nonvolatile N-nitroso compounds have been difficult to determine in foods and other consumer products because of the incompatibility of aqueous high-performance liquid chromatography (HPLC) mobile phases with the thermal energy analyzer (TEA), a sensitive and selective detector for N-nitroso compounds. A postcolumn technique has been developed that permits the use of aqueous mobile phases with an interfaced liquid chromatograph/TEA. This system was linear from 3.5 to 900 ng of N-nitrosoproline injected. Coefficients of variation of 3.0 and 5.1%, respectively, were obtained when N-nitrosoproline and N-nitrosotrimethylurea were repeatedly injected at the 80- to 90-ng level. Mixtures of volatile and nonvolatile N-nitroso compounds as well as N-nitrosodipeptides were separated and quantitated by HPLC/TEA with a water/acetonitrile gradient.

Degradation of ketoses during aqueous high-performance liquid chromatography on lead-form cation-exchange resins

A variety of sugars were found to be subject to degradation during aqueous chromatography at 60°C on lead-form, divinylbenzene—cross—linked sulfonated polystyrene resins. This phenomenon results in only minor interference with the analysis of 2-hexuloses, but presents serious problems in the analysis of 2-pentuloses and prohibitive problems in the analysis of trioses at 60°C. No such problems were encountered during the chromatography of these sugars on the calcium form of the resin under the same conditions. The calcium-form resin is, therefore, the packing material of choice for analysis of 2-pentuloses and trioses, and is to be preferred in the analysis of samples containing 2-hexuloses, unless overriding considerations of selectivity call for use of the lead-form column.

Noble, diatomic and aliphatic gas analysis by aqueous high-performance liquid chromatography

Dissolved non-polar gases (five noble, three diatomic, and four unbranched aliphatic hydrocarbon gases) were resolved by aqueous high-performance liquid chromatography using an ion-moderated partition chromatography column (Bio-Rad HPX-87P) originally designed for monosaccharide analysis. The dissolved-gas peaks, which were detected and quantitated by high-sensitivity refractive-index detection, are eluted at 25°C in the order Ne, He, N 2, H 2, O 2, Ar, CH 4, Kr, Xe, C 2H 6, C 3H 8, n-C 4H 10. Based on the general elution order, and on the temperature dependences (4–72°C) of elution times for the individual gases, a mixed chromatographic mechanism is proposed, in which separation of the gases results from a mixture of size-exclusion, ion-ion-induced dipole, and classical hydrophobic effects, plus a second type of “hydrophobic” effect involving binding of the clathrate hydrate cages surrounding non-polar solutes to similar cages formed around hydrocarbon portions of the column packing material.