Biomedical subjects

Robert A Shellie

Publications and source records attributed to Robert A Shellie.

6 recordsLinked to original sources

PubMed2006

Targeted multidimensional gas chromatography for the quantitative analysis of suspected allergens in fragrance products.

Two approaches are described and compared for the analysis of suspected allergens (SAs) in fragrance products, which are defined by the Scientific Committee of Cosmetics and Non-Food Products (SCCNFP). The first consists of a comprehensive two-dimensional gas chromatography (GC x GC) experiment using both a "conventional" non-polar/polar column combination and an "inverse" polar/non-polar column set. The second approach uses a targeted multidimensional gas chromatography (MDGC) system employing a Deans type pneumatic switch and a longitudinally modulated cryogenic system (LMCS). It was found that the conventional and inverse column sets complement each other well, providing identification of SAs present. Compounds well retained on the second dimension of one column set were the first to be eluted from the other. In some instances SAs co-eluting with matrix components on the second dimension for a given column set were clearly resolved on the other, although this has the disadvantage of requiring two analytical runs. Targeted MDGC with a non-polar/polar column set, successfully separated all SAs identified within a fragrance product. The instrument is set up in a similar fashion to a GC x GC system though with longer second dimension ((2)D) column, a cryogenic trap at the beginning of the second column, and a pneumatic switch coupling both columns. The data are easier to process than for a GC x GC experiment. The targeted MDGC method has the capacity to deliver far greater efficiency to targeted regions of a primary separation than a GC x GC experiment, whilst still maintaining overall run times similar to those of a conventional one-dimensional (1D) GC experiment. Cryogenic focussing at the beginning of the (2)D column delivers enhanced sensitivity, accurate (2)D retention times and narrow peak widths; these are responsible for an increased resolution obtained from the fast, relatively short (approximately 5 m) (2)D column. The two column set GC x GC analysis provided a quick and effective means to qualitatively determine the presence of six SAs in a commercially available air freshener, however all were not adequately resolved from matrix components. In contrast, quantitation was straightforward using the targeted MDGC method.

Allergens↗

PubMed2006

Comprehensive two-dimensional liquid chromatography.

Having nearly exhausted the possibilities for generating peak capacity through improvements in column technology, chromatographers are increasingly looking to alternative ways of maximising chromatographic separation. In recent years there has been increasing activity in the field of comprehensive multidimensional separations to meet analysis demands. Comprehensive two-dimensional liquid chromatography (LCxLC) approaches offer high peak capacity which leads to significantly improved analytical performance over single-column liquid chromatography. There are several closely related avenues available for achieving an LCxLC separation and this review pays special attention to the different valve-based interfaces that have been used to comprehensively couple the first and second dimension columns in LCxLC systems. A brief discussion of column choices for selected applications and the conditions employed is also presented.

Journal Article↗

PubMed2005

Towards high capacity latex-coated porous polymer monoliths as ion-exchange stationary phases.

The preparation of high capacity agglomerated monolithic ion-exchangers for capillary ion chromatography is described. Post-modification of reactive monoliths was investigated as an alternative to co-polymerisation of a suitable functional monomer with an overarching goal of increasing ion-exchange capacity. Direct sulfonation of poly styrene-co-divinyl benzene monoliths using concentrated sulfuric acid or chlorosulfonic acid was unsuccessful even for monoliths containing as low as 8% crosslinker. In contrast, chemical transformation of reactive monoliths containing glycidyl methacrylate was used to increase the ion-exchange capacity by up to more than thirty-fold with ion exchange capacities of 14-29 microequiv g(-1) achieved. Three different reactions were considered, including reaction with 4-hydroxybenenesulfonic acid under basic conditions; reaction with thiobenzoic acid followed by transformation to a reactive thiol and the subsequent oxidation to the sulfonic acid; and direct sulfonation with sodium sulfite. Of these, the reaction with sodium sulfite resulted in the most significant increase in the capacity and the best separation performance. In the isocratic mode separation efficiencies of over 13,500 plates m(-1) were observed (for iodate). The separation of seven inorganic anions was also demonstrated using a hydroxide gradient.

Chromatography, Ion Exchange↗

PubMed2005

Statistical methods for comparing comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry results: metabolomic analysis of mouse tissue extracts.

The potential for the utilization of GC x GC-time-of-flight (TOF) MS for high-resolution metabolomics studies is discussed, with the implementation of some statistical comparisons for biomarker detection. Metabolite profiles from NZO obese mice versus BL/6 control mice are compared and contrasted using a number of chromatogram comparison routines, including direct chromatogram comparisons, chromatogram subtraction and averaging routines, as well as a method for generating relative weighted peak surface difference chromatograms, and a more conventional Student's t-test statistical approach.

Animals↗

PubMed2004

Application of headspace solid-phase microextraction (HS-SPME) and comprehensive two-dimensional gas chromatography (GC x GC) for the chemical profiling of volatile oils in complex herbal mixtures.

The coupling of headspace solid-phase microextraction (HS-SPME) with comprehensive two-dimensional gas chromatography (GC x GC) was shown to be a powerful technique for the rapid sampling and analysis of volatile oils in complex herbal materials. When compared to one-dimensional (1-D) GC, the improved analytical capabilities of GC x GC in terms of increased detection sensitivity and separation power were demonstrated by using HS-SPME/GC x GC for the chemical profiling (fingerprinting) of essential/volatile oils contained in herbal materials of increasing analytical complexity. More than 20 marker compounds belonging to Panax quinquefolius (American ginseng) can be observed within the 2-D contour plots of ginseng itself, a mixture of ginseng and another important herb (P. quinquefolius/Radix angelicae sinensis), as well as a mixture of ginseng and three other herbs (P. quinquefolius /R. angelicae sinensis/R. astragali/R. rehmanniae preparata). Such analytical capabilities should be important towards the authentication and quality control of herbal products, which are receiving increasing attention as alternative medicines worldwide. In particular, the presence of Panax in the herb formulation could be readily identified through its specific peak pattern in the 2-D GC x GC plot.

Chromatography, Gas↗

PubMed2002

Retention time reproducibility in comprehensive two-dimensional gas chromatography using cryogenic modulation an intralaboratory study.

A survey was conducted to determine the reproducibility of retention times in both the first (D1) and second dimension (D2) axes of the two-dimensional separation space, in the comprehensive two-dimensional gas chromatographic analysis of an essential oil sample using cryogenic modulation. The retention times in the two dimensions for a number of individual components comprising hydrocarbon, alcohol, ester and ketone chemical classes in a Melaleuca alternifolia essential oil were recorded from replicate analyses using four separate column sets and two identical gas chromatographs. Run-to-run, day-to-day, instrument-to-instrument, and column set-to-column set reproducibility were demonstrated from the experimental design. A total of 60 GC x GC analyses were conducted. The longitudinally modulated cryogenic system produced reproducible modulation start times and consistent modulation phase profiles for individual components in all experiments, and retention time variations in both dimensions were negligible. The average run-to-run reproducibility of 43 components for six replicate injections was found to be 0.12% RSD in the first dimension, and 0.74% RSD in the second dimension. Day-to-day reproducibility showed statistically "significant" difference (F-test), but this was partly ascribable to the excellent within-day reproducibility that led to apparent day-to-day differences. Confidence in absolute retention times (hence component positions) in the two-dimensional separation space is critical to component identification.

Chromatography, Gas↗