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P J Marriott

Publications and source records attributed to P J Marriott.

At least 19 recordsLinked to original sources
PubMed2006

Projection of multidimensional GC data into alternative dimensions-exploiting sample dimensionality and structured retention patterns.

Comprehensive multidimensional gas chromatography (GCxGC) is a powerful separation technique. One of the features of this technique is that it offers separations with more apparent structure than that offered by conventional one-dimensional GC (1-D GC). While some previous studies have alluded to this structure, and used structured retention patterns for some simple classifications, the topic of structured retention in GCxGC has not been studied in any great detail. Using the separation of fatty acid methyl esters (FAME) on both nonpolar/polar and polar/nonpolar column sets, the interaction between the separation dimensions and the sample dimensions is explored here. The GCxGC separation of a series of compounds is presented as a projection of the sample from sample space, a p-dimensional space with dimensions defined by the dimensionality of the sample, into separation space: for GCxGC, a two-dimensional plane passing through the sample space in an orientation defined by the separation conditions. Using this conceptual model and some a priori knowledge of the sample, it is shown how the image of the sample in the separation space can be used to construct an image of the sample in alternate dimensions, such as second dimension retention factor ((2)k) vs. chain length in the case of FAME. These projections into alternate dimensions should facilitate the interpretation of the complex patterns found within the GCxGC chromatogram for the identification and classification of compounds.

Journal Article↗
PubMed2006

Nest- and colony-mate recognition in polydomous colonies of meat ants (Iridomyrmex purpureus).

Workers of polydomous colonies of social insects must recognize not only colony-mates residing in the same nest but also those living in other nests. We investigated the impact of a decentralized colony structure on colony- and nestmate recognition in the polydomous Australian meat ant (Iridomyrmex purpureus). Field experiments showed that ants of colonies with many nests were less aggressive toward alien conspecifics than those of colonies with few nests. In addition, while meat ants were almost never aggressive toward nestmates, they were frequently aggressive when confronted with an individual from a different nest within the same colony. Our chemical analysis of the cuticular hydrocarbons of workers using a novel comprehensive two-dimensional gas chromatography technique that increases the number of quantifiable compounds revealed both colony- and nest-specific patterns. Combined, these data indicate an incomplete transfer of colony odor between the nests of polydomous meat ant colonies.

Aggression↗
PubMed2006

Comprehensive two-dimensional gas chromatography/mass spectrometric analysis of pepper volatiles.

The headspace compositions of 13 pepper and peppercorn samples of different species, colloquially also referred to as pepper, were analyzed, and more than 300 compounds were tentatively characterized by means of comprehensive two-dimensional gas chromatography in tandem with flame ionization detection, quadrupole mass spectrometric detection and time-of-flight mass spectrometric detection (GC x GC-FID, GC x GC/qMS and GC x GC/TOFMS, respectively). The analysis of volatile organic compounds (VOCs) was performed after solid-phase microextraction (SPME) using a 75-microm PDMS/DVB fibre. Fingerprint comparison between the three techniques permitted peaks to be assigned in the GC x GC-FID experiment based on the analogous MS analysis, taking into account retention shifts arising from method variations. When using GC x GC/TOFMS, about five times more peaks were identified than in GC x GC/qMS. Retention indices for all peaks were calculated in the bi-dimensional column set comprising of a 5% phenyl polysilphenylene-siloxane primary column and a polyethylene glycol second column. The spectra obtained by both mass detection techniques (qMS and TOFMS) give very similar results when spectral library searching was performed. The majority of the identified compounds eluted as pure components as a result of high-resolution GC x GC separations, which significantly reduces co-elution, and therefore increases the likelihood that pure spectra can be obtained. The differences between TOFMS and qMS (in fast scanning mode) spectra were generally small. Whilst spectral quality and relative ion ratios across a narrow peak (e.g. w(b) approximately 100-150 ms) do vary more for the fast peaks obtained in GC x GC/qMS operation, than with TOFMS, in general adequate spectral matching with the library can be achieved.

Gas Chromatography-Mass Spectrometry↗
PubMed2003

Application of comprehensive two-dimensional gas chromatography to drugs analysis in doping control.

Comprehensive two-dimensional gas chromatography (GC x GC) now occupies a niche within the GC technology regime. The technique is undeniably unique in the manner in which the experiment is conducted, the way results are presented and the interpretive opportunities offered. For the 1000th volume of this journal it is appropriate to expand upon these features, and review the progress made in GC x GC to date. Firstly, brief general comment is made on multidimensional procedures, and to review key aspects of GC x GC. The use of the targeted multidimensional GC method allows absolute retentions in the second dimension of a GC x GC experiment to be estimated, and also offers a novel way to obtain enhanced response for resolved solutes. Then, to illustrate the utility of the technique, the application of GC x GC to the screening of drugs and their metabolites in biological fluids is described using prolintane metabolites in canine urine as an example, with samples taken at four time intervals after administration. This example illustrates the first application of GC x GC in the field of forensic toxicology, an area traditionally dominated by GC-MS. Most drug compounds were found to be retained on the 0.8-m second column for a greater time than the modulation period (3 s) used for initial analysis, under the conditions described. Hence a 0.4-m D2 BPX50 (50% phenyl methyl polysilphenylene) column was then used throughout, with most compounds retained less than 4 s. For the standard drug mixture, three overlapping drugs on the first dimension column (BPX5) were subsequently baseline resolved on the BPX50 column. For prolintane administration samples, the parent drug and metabolites could be effectively resolved from background matrix peaks. Likewise a 23-drug spike standard in horse urine blank gave acceptable resolution of the drugs from matrix peaks.

Calibration↗
PubMed2001

Separation of chlorophenoxyacetic acids and chlorophenols by using capillary zone electrophoresis.

In this study, the choice of electrolyte systems for the separation and detection of a range of chlorophenoxyacetic acids and chlorophenols by means of capillary zone electrophoresis (CZE) is discussed. A series of acetate buffers over the buffering capacity pH range 4.03-5.5 were initially chosen for the separation. It was found that chlorophenoxyacetic acids could be separated at pH 4.03 and 4.5 but the most satisfactory separation of chlorophenols was obtained at pH 5.5. The factors affecting separation selectivity, including the addition of organic modifiers, was also studied. The use of 25% 2-butanol, 5% ethylene glycol and 10% acetonitrile as organic solvents resulted in the total separation of both classes of these compounds but poor peak shape of chlorophenols resulted and a number of chlorophenoxyacetic acids were not well separated. A borate-phosphate buffer gave improved peak shape of chlorophenols. Further improved separation of the components of the mixture was obtained by the addition of 2 mM fully methylated-beta-cyclodextrin to the 35 mM borate- 60 mM phosphate buffer at pH 6.5, maintaining good peak shape. In this case, separation of the two compound classes, chlorophenoxyacetic acids and chlorophenols, is achieved, with complete resolution of individual compounds in less than 5 min with high efficiency (of the order of 150,000 plates for the ca. 40 cm column). The method is applied to a commercial 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide mixture.

2,4-Dichlorophenoxyacetic Acid↗
PubMed2000

Time-resolved cryogenic modulation for targeted multidimensional capillary gas chromatography analysis.

Multidimensional gas chromatography (MDGC) is performed in a new manner, described in this paper. The method incorporates two directly coupled columns and employs a longitudinally modulated cryogenic trap located between the columns. No heartcutting process is used, but rather a method better termed selected zone compression pulsing is used. Compared with normal MDGC, where primary column effluent has to be temporarily diverted either to a monitor detector or to the second dimension column, the new procedure in its simplest mode passes all of the first column effluent to the second column. It is simply the times at which the modulation of the trap is performed that determines which target solutes will be selected for enhanced separation. This approach allows almost instantaneous separation of selected zones on the second column, and has the potential to significantly simplify the MDGC method. Since data are presented in a time-response format, and do not require transformation as previously described for comprehensive GC when using the longitudinal modulator, quantitation and report generation are essentially the same as in any GC method and data system. Advantages also include significant sensitivity improvement. By using cryofocussing, and benefiting from the zone compression effects along with fast GC conditions on the second dimension, new possibilities for MDGC can be realised. The method is demonstrated by using a mixture of semi-volatile aromatic hydrocarbons.

Chromatography, Gas↗
PubMed2000

Supercritical-fluid extraction of synthetic pyrethroids from wool.

A stepwise approach was used to develop a supercritical fluid extraction (SFE) method for analysis of synthetic pyrethroids (SPs) on a wool matrix, commencing with a simple inert matrix to examine the solubility of the pyrethroids in the extraction fluid CO(2) and then extended to the real wool matrix. Chemometric approaches were used to determine the SFE optimum conditions. It was found that pyrethroids were readily extractable from an inert matrix over a wide range of pressure (170-350 atm) and at low temperature (<90 degrees C). Subambient hexane efficiently trapped the compounds from the depressurised fluid. Excessively high pressure and temperature resulted in poor trapping, isomerisation and possibly degradation of some components. With spiked wool samples method modifications focused on reducing the coextraction of grease, a bulk matrix component of raw wool. By using alumina (containing 8% moisture) and operating the extraction at 50 degrees C, 200 atm for 60 min, sufficiently clean extracts of pyrethroids suitable for gas chromatography-electron-capture detection analysis were obtained. The recoveries of all SPs were satisfactory (78-101%) over the range of 0.5-5 microg/g levels of these compounds. The precision of the entire analysis procedure was comparable to the conventional Soxhlet extraction method. Detection limits of some commonly used SPs for sheep treatment were also evaluated. Comparable results relative to those achieved by solvent extraction for incurred wool samples were obtained with a recovery of 81-85%. The results, however, suffered high uncertainties (R.S.D. approximately 19-24%) due to the small amount of wool sample taken in each extraction and the suspected inhomogeneity of the wool. Different persistences of cypermethrin isomers in wool were observed.

Aluminum Oxide↗
PubMed2000

New operational modes for multidimensional and comprehensive gas chromatography by using cryogenic modulation.

Historically, hardware and method-related concerns have limited the use of multidimensional gas chromatography in the routine laboratory. This paper presents a new approach that offers the potential to significantly alter the manner in which multidimensional gas chromatography is conducted, based on the use of a modulated cryogenic trap which can be moved longitudinally along the column. Two columns are directly coupled, and no switching valves are used. It is demonstrated that a heartcut section can be cryofocused and zone-compressed, and then rapidly remobilized at the prevailing column oven temperature without any supplementary heating. A short second dimension column is used, giving fast second dimension analysis. This allows a large number of heartcuts to be programmed for any one analysis. The 'ultimate' manifestation of multidimensional gas chromatography is the comprehensive GC technique (GC X GC). This is now simply effected by performing very rapid heartcuts at intervals on the order of 1/5th of the peak width of primary dimension peaks, and requires that the second dimension be able to complete the analysis of each collected zone on a similar timeframe. This paper uses a semi-volatile aromatic mixture to demonstrate these selected operational modes, that can be achieved with the longitudinal modulation method. The flexibility that arises from this approach is shown by the ability to swap between selected whole-peak enhancement and comprehensive modes during the one analytical run. The increased sensitivity that follows from peak compression is a further advantage, which would be beneficial for trace analysis.

Chromatography, Gas↗
PubMed1998

Enantiomeric separation of propranolol and selected metabolites by using capillary electrophoresis with hydroxypropyl-beta-cyclodextrin as chiral selector.

A capillary electrophoresis (CE) investigation of the enantiomeric separation of propranolol and some of its metabolites using CE was undertaken. Resolution of the enantiomers was achieved using hydroxypropyl-beta-cyclodextrin (HP-beta-CD) as the chiral selector. Parameters found to influence separation include cyclodextrin concentration, potential, pH and organic solvent/additive. It was observed that 17 mM HP-beta-CD gave optimum separation over the concentration range used in this study, however different racemates appear to have best resolution at different CD concentration. The potential does not have a great effect on enantiomer resolution, but appears to cause relative metabolite migration times to alter such that separation is affected. Carrier pH affects both migration time, and enantiomer resolution and metabolite separation. Above pH 5 inferior results are obtained. This is the first report of enantiomeric resolution of propranolol metabolites using CE.

Carbohydrate Sequence↗
PubMed1984

Computerised gas chromatographic-mass spectrometric analysis of complex mixtures of alkyl porphyrins.

Computerised capillary gas chromatography-mass spectrometry (GC-MS) analysis of complex mixtures of alkyl porphyrins, as their bis-(trimethylsiloxy)silicon(IV) and bis(tert.-butyldimethylsiloxy)silicon(IV) derivatives, is described. The latter derivative is more suitable for routine GC-MS analysis. This computerised GC-MS approach, when applied to the alkyl porphyrins of two geological samples, a bitumen (Gilsonite, Eocene age, UT, U.S.A.) and a crude oil (Boscan, Cretaceous age, West Venezuela), has revealed the highly complex compositions of these fractions. Computer-aided data processing, using relative retention index (RRI) calculations, facilitated the classification of the chromatographic peaks according to structural type and membership of pseudo-homologous series. Computerised GC-MS is compared with, and contrasted to high-performance liquid chromatography as a means of petroporphyrin analysis.

Chemistry Techniques, Analytical↗
PubMed1981

Familial cutaneous amyloidosis with systemic manifestations in males.

We describe a family in which two males and seven females have brown pigmentation of the skin. In the females, the type and distribution of the pigmentation mimicked incontinentia pigmenti; in the males, the pattern was reticulate. The histological appearance was the same in both sexes with amyloid deposits in the papillary dermis, melanin in the basal layer, and slight hyperkeratosis. The females were otherwise normal. Both males had thrived poorly as infants but had survived. One had severe gastroenteritis with blood in the stools starting at the age of three weeks followed by seizures, hemiplegia, and developmental delay; the other had recurrent pneumonia throughout life, a urethral stricture, inguinal herniae, and near-blindness from amyloid deposition in the cornea. Five other males in the family had had severe illnesses. Two died of pneumonia by three months. One died at three months from colitis. Both remaining boys had colitis as infants, failed to thrive, and developed recurrent pneumonia from which one died at three years. We think all of these relatives had the same disease carried by a single gene with pleiotropic effects. The most likely form of inheritance is X-linked.

Adolescent↗
PubMed1976

Clobetasol propionate ointment compared with dithranol in Lassar's paste in the treatment of psoriasis.

The initial results on ten patients in a trial of clobetasol propionate (Dermovate) ointment compared with dithranol in Lassar's paste are described. The rates of clearing for each preparation in each patient were not noticeably different. Relapse was slower with clobetasol propionate in all but one patient for whom there was no preference. The results are highly significant (P less than 0-005).

Adolescent↗
PubMed1975

Angioma serpiginosum--familial incidence.

In this paper we present the first record of familial incidence in angioma serpiginosum observed in two families. The clinical and histological features are described.

Adult↗