Size-exclusion chromatography with on-line ultraviolet, proton nuclear magnetic resonance and mass spectrometric detection and on-line collection for off-line Fourier transform infrared spectroscopy

Multidimensional liquid chromatography for sample characterisation

While LC finds enormously widespread use in almost all areas of chemical science, the technique is limited as a means of identification because compounds do not elute with unique retention times. This limitation spurred the growth of hyphenated instrumental methods of analysis, such as LC-MS/MS, which because of the MS/ MS detection became a method of identification. However, techniques like LC-MS/ MS are specialised and require high initial purchase and running costs, inhibiting the more widespread growth of the technique. In an attempt to increase the separation power of LC, multi-dimensional LC was developed. This expanded the separation space and subsequently has allowed the development of methods with fingerprinting ability due to the lower probability of component overlap. The work in this study illustrates the application of 2-D LC as a means of chemical fingerprinting. We employed a sample base of various low molecular weight oligostyrenes and their diastereomers that represent a population of compounds whose selectivities in a one-dimensional separation are almost unity and hence essentially impossible to separate. Yet in a 2-D domain almost all individual components occupy unique 2-D retention times.

Spectrofluorimetric determination of phenyl-β-naphthylamine used as rubber antioxidant

Phenyl-beta-naphthylamine (PBN) used as rubber antioxidant was found to have native fluorescence. A spectrofluorimetric method for determination of PBN in multicomponent mixtures of polymer additives is described. The apparent excitation and fluorescence wavelengths used are 348 and 413.5 nm, respectively. Maximum fluorescence intensity is obtained by irradiating PBN dissolved in ethanol, at room temperature. The fluorescence varies linearly with the concentration of PBN in the range of 0.04-4 microg mL(-1). The accuracy and precision of the method are reported.

Gel permeation chromatography followed by pyrolysis–gas chromatography–mass spectrometry via a solvent-evaporative interface

The measurement of chemical composition as a function of molecular weight has always been a challenge for analytical chemists. In this paper, we present a unique way to combine gel permeation chromatography (GPC) with pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) for this purpose. A commercially available solvent-evaporative interface, originally designed for GPC-IR measurements, was used to deposit the eluent of GPC onto aluminum foil. Small strips of aluminum foil were cut and subjected to Py-GC-MS analysis. Compared with the GPC-IR measurements, the proposed technique offers the advantage of being able to distinguish between structurally similar monomers in a complex copolymer. As an example, a copolymer composed of four monomers was analyzed. The results clearly demonstrate that this technique can be applied to complex polymeric systems to yield information regarding chemical heterogeneity versus molecular weight.

Hyphenation and hypernation the practice and prospects of multiple hyphenation

In the past two decades, combining a chromatographic separation system on-line with a spectroscopic detector in order to obtain structural information on the analytes present in a sample has become the most important approach for the identification and/or confirmation of the identity of target and unknown chemical compounds. In most instances, such hyphenation can be accomplished by using commercially available equipment For most (trace-level) analytical problems encountered today, the combination of column liquid chromatography or capillary gas chromatography with a mass spectrometer (LC-MS and GC-MS, respectively) is the preferred approach. However, it is also true that additional and/or complementary information is, in quite a number of cases, urgently required. This can be provided by, for example, atomic emission, Fourier-transform infrared, diode-array UV-vis absorbance or fluorescence emission, or nuclear magnetic resonance spectrometry. In the present review, the various options are briefly discussed and a few relevant applications are quoted for each combination. Special attention is devoted to systems in which multiple hyphenation, or hypernation, is an integral part of the setup. As regards this topic, the relative merits of various combinations--which turn out to include a mass spectrometer as one of the detectors in essentially all cases--are discussed and the fundamental differences between GC- and LC-based systems are outlined. Finally, the practicability of more extensive hypernation in LC, viz. with up to four spectrometers, is discussed. It is demonstrated that, technically, such multiple hyphenation is possible and that, from a practical point of view, rewarding results can be obtained. In other words, further research in this area is certainly indicated. However, in the foreseeable future, using several separate conventional hyphenated systems will be the commonly implemented solution in most instances.

Attenuated total internal reflectance infrared microspectroscopy as a detection technique for high-performance liquid chromatography

The use of single reflection attenuated total internal reflection infrared microspectroscopy as a detector for high-performance liquid chromatography (HPLC) is demonstrated. The terminus of the HPLC column is placed at the focus of an ATR infrared microscope, allowing several advantages over other detection techniques. These include the following: (1) the reduction or elimination, or both, of detection cell dead volume, (2) the ability to interrogate a nearly pure aliquot of analyte, and (3) the ability to signal average spectra of the same aliquot (depending on its size) thereby improving the signal-to-noise ratio of the measurement and, concomitantly, the analytical characteristics of the method. Static measurements of succinylcholine chloride in water have shown a detection limit of 0.7 parts per thousand (ppt). Two-microliter injections of succinylcholine chloride in a 5-cm x 1-mm C-18 column with a flow rate of 60 microL/min have shown a detection limit of 1.9 ppt. This analytical concentration corresponds to a mass of 3.8 microg in the injection loop and a mass of 350 fg in the sampling volume. The potential of this detector for HPLC is demonstrated, and future improvements are also discussed.

HPLC analysis of ecdysteroids in plant extracts using superheated deuterium oxide with multiple on-line spectroscopic analysis (UV, IR, 1H NMR, and MS)

HPLC, using superheated D20 as the mobile phase, combined with on-line characterization via a combination of diode array UV, 1H NMR, FT-IR spectroscopy, and mass spectrometry has been used for the analysis of a standard of 20-hydroxyecdysone- and ecdysteroid-containing plant extracts. This combination of spectrometers enabled the on-flow collection of UV, 1H NMR, IR, and mass spectra not only for pure 20-hydroxyecdysone (100-400 microg on column) but also the major ecdysteroids present in crude extracts of Silene otites, Silene nutans, and Silene frivaldiskyana. The ecdysteroids unequivocally identified in these extracts included 20-hydroxyecdysone, polypodine B, and integristerone A.

Flow injection analysis with multiple on-line spectroscopic analysis (UV, IR, 1H-NMR and MS)

Studies on the capabilities of flow injection analysis (FIA) combined with on-line characterisation of model compounds via a combination of diode array UV, 1H-NMR, FT-IR spectroscopy and mass spectrometry are described. Using this combination of spectrometers enabled the on-flow collection of UV, 1H-NMR, IR and MS for a range of model compounds. Samples were introduced into the system as solutions in deuterium oxide in concentrations ranging from 1.4 to 8.4 mg ml(-1). A sample volume of 100 microl was used for FIA at a flow rate of 1 ml min(-1). From these studies a practical working quantity of ca. 140 microg/sample of analyte was determined which provided characteristic spectra.

Spectroscopic characterisation and identification of ecdysteroids using high-performance liquid chromatography combined with on-line UV--diode array, FT-infrared and 1H-nuclear magnetic resonance spectroscopy and time of flight mass spectrometry

A prototype multiply hyphenated reversed-phase HPLC system has been applied to the analysis of a mixture of pure ecdysteroids and an ecdysteroid-containing plant extract. Characterisation was achieved via a combination of diode array UV, 1H NMR, FT-IR spectroscopy and time of flight (TOF) mass spectrometry. This combination of spectrometers allowed the collection of UV, 1H NMR, IR and mass spectra for a mixture of pure standards enabling almost complete structural characterisation to be performed. The technique was then applied to a partially purified plant extract in which 20-hydroxyecdysone and polypodine B were identified despite incomplete chromatographic resolution and the presence of co-chromatographing interferents. The experimental difficulties in the use of such a systems for these analytes are described.

Directly coupled HPLC-NMR and HPLC-NMR-MS in pharmaceutical research and development

The methodology for the direct coupling of HPLC with NMR spectroscopy and the simultaneous double coupling of HPLC with NMR and mass spectrometry (MS) is described. Indications of the necessary technical developments to achieve this are given, and the applications of these new techniques to studies of pharmaceutical relevance are reviewed. These include studies of combinatorial chemistry libraries, synthetic chemical impurities, characterisation of drug mixtures, identification of natural products of possible pharmaceutical interest and identification of xenobiotic metabolites in human, animal and in vitro systems. In addition, HPLC-NMR has been used to investigate xenobiotic metabolite reactivity. Finally, the potential future directions of the techniques are discussed.

Multiple hyphenation of liquid chromatography with nuclear magnetic resonance spectroscopy, mass spectrometry and beyond

The advent of sensitive and reliable HPLC-NMR and HPLC-MS systems has revolutionised the identification of compounds eluting from chromatographic systems. More recently systems have been described wherein both NMR and MS are used together to provide an immensely powerful means of characterising compounds in chromatographic eluents. Here the construction and application of combined HPLC-NMR-MS systems to the analysis of mixtures of pharmaceuticals, drug metabolites in biological fluids and natural products in plant extracts is reviewed. In addition preliminary work with alternative systems such as HPLC-UV-NMR-FTIR-MS is highlighted and the prospects for such complex systems considered.

Reversed-phase high-performance liquid chromatography combined with on-line UV diode array, FT infrared, and 1H nuclear magnetic resonance spectroscopy and time-of-flight mass spectrometry: application to a mixture of nonsteroidal antiinflammatory drugs

A prototype multiply hyphenated system has been applied to the analysis of a mixture of nonsteroidal antiinflammatory drugs separated by reversed-phase HPLC. Characterization of the model NSAIDs was achieved via a combination of diode array UV, 1H NMR, FT-IR spectroscopy, and time-of-flight mass spectrometry. This combination of spectrometers allowed the collection of UV, 1H NMR, IR, and mass spectra together with atomic composition data enabling almost complete structural characterization to be performed.