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Philip Marriott

Publications and source records attributed to Philip Marriott.

At least 19 recordsLinked to original sources
PubMed2005

Orthogonality considerations in comprehensive two-dimensional gas chromatography.

This study explores separation orthogonality with respect to comprehensive two-dimensional gas chromatography (GC x GC) for a range of different column polarities in the first dimension (1D), with two second dimension (2D) column types. Systematic variation in the net polarity of the first dimension allows the effect of column phase relative polarity on analyte retention in both the first and second dimensions to be evaluated. First dimension polarity manipulation significantly affects elution temperature (T(e)) of the analytes. This alters the magnitude of retention on the second dimension, and the extent of utility of separation space. By use of retention factor/temperature data in single column experiments, along with 1D T(e) data, retention on the 2D column can be estimated. This allows the two-dimensional separation to be predicted, and compared with experimental data. Predicted GC x GC peak positions corresponded favourably with the experimentally derived chromatograms, yielding a simple approach for predicting two-dimensional separations, using unique column set combinations.

Chromatography, Gas↗
PubMed2005

Analysis of strawberry volatiles using comprehensive two-dimensional gas chromatography with headspace solid-phase microextraction.

The aims of the current study were to develop an enantioselective multi-dimensional gas chromatography (GC x GC) method for the examination of strawberry volatiles and to use this method to make comparisons between the volatile profiles of different cultivars and between fresh picked and post-harvest berries of the same cultivar. Strawberry volatiles were sampled using solid-phase microextraction (SPME), and the repeatability and reproducibility of this method was examined. Semi-quantitative analysis of the volatiles was conducted using the relatively new technique of comprehensive multi-dimensional gas chromatography, using enantioselective (chiral) columns for the differentiation of analyte enantiomers. Chiral GC x GC facilitated the detection of key enantiomers in strawberry flavour. The (-)-enantiomer of 2,5-dimethyl-4-hydroxy-(2H)-furan-3-one (DMHF) and the S-enantiomer of linalool were tentatively identified as the predominant forms in both the cultivars Selva and Adina. The compounds benzaldehyde and methyl hexanoate were shown to decrease in post-harvest berries, whilst DMHF and nerolidol increased upon storage.

Chromatography, Gas↗
PubMed2004

Comprehensive two-dimensional gas chromatography--quadrupole mass spectrometric analysis of drugs.

The use of comprehensive two-dimensional gas chromatography coupled to quadrupole mass spectrometry (GC x GC-qMS) for drug screening is investigated with 77 underivatised drug standards in methanolic solution. The GC x GC-qMS setup involved a reduced mass scan range of 42-235 u and minimum quadrupole sampling time to achieve quadrupole scanning frequency of 19.36 Hz. Only 26% of the drugs investigated gave fair-to-acceptable library matches with full mass scan range commercial libraries. The creation of a new "truncated" library based on the mass spectra of the drug standards in the applied mass scan range of 42-235 u extends the feasibility of the currently adopted GC x GC-qMS approach to higher molecular weight compounds and is investigated with blank blood spiked with drug standards. With the new library, 75% of the drugs yielded matches of at least 90%. The time-of-flight mass spectrometer (TOFMS) is expected to address the limitations of the present GC x GC-qMS setup and a brief comparison between GC x GC-qMS and GC x GC-TOFMS is also provided in this study.

Feasibility Studies↗
PubMed2004

Rapid sequential heart-cut multidimensional gas chromatographic analysis.

A method is described which allows the sequential fast analysis of heart-cuts taken during the first column elution of an essential oil sample in a multidimensional gas chromatography experiment. In this investigation, a relatively short, narrow bore capillary column is used in the second dimension, with fast cryogenic modulation permitting rapid delivery of cryofocussed heart-cuts into the second column of the multidimensional arrangement. In this implementation, the total analysis time on the second column is of the order of 30 s, which is less than the duration of the sampled heart-cuts (1 min), with peak theoretical efficiencies of about 7000 m(-1). Thus, the method should allow on-line heart-cutting of as many discrete heart-cuts as one may require from the first dimension chromatogram, and so two-dimensional separation can be achieved for almost the whole sample in one single analysis without the need for repeat injections or cycling of the oven temperature. The method is demonstrated by the transfer and rapid re-injection of 1 min heart-cuts taken from an initial separation stage of peppermint essential oil. The cryofocussing and fast analysis step is shown to increase signal response by up to 40-fold. Total peak capacity in the described system is measured to be of the order of 1800, with capacities of about 20-30 for each 30 s second dimension analysis. By increasing the frequency of sampling to remove excessive (unused) time to develop the 2D separation, it should be possible to achieve peak capacities of 5000 or more baseline resolved peaks.

Chromatography, Gas↗
PubMed2004

Analysis of roasted coffee bean volatiles by using comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry.

The volatile headspace from two coffee bean varieties, namely Arabica (Coffea arabica) and Robusta (Coffea canephora ex Froehner), were sampled by using solid-phase microextraction (SPME), and then analysed with comprehensive two-dimensional gas chromatography interfaced to a time-of-flight mass spectrometer (GC x GC-TOFMS). Two distinct column set combinations were investigated--an apolar-polar and polar-apolar configuration--and the separation achieved from each set was compared. Results were compared with a previous literature report for coffee analysed by GC x GC-FID, using an analogous polar-apolar column set combination, where authentic standards were used to confirm the position of the selected components in the 2D separation space. The present study provides independent mass spectral confirmation of component identity, and demonstrates that the relative, structured position of these components is comparable in the two experiments. Total ion current (TIC) chromatograms were processed using ChromaTOF automated data processing software. It was necessary to restrict the number of processed peaks to 1000 (S/N > 100), which required approximately 8 h for processing. Extracted ion chromatograms were generated using prominent fragment ions, and unique masses, to aid in analyte identification process, and was particularly useful in instances of component peak overlap, and for the identification of pyrazine analytes (e.g. 44, 88, 122 u). Semi-quantitative analysis was restricted to the 44 selcted components; however, the omission of peaks with S/N < 100, limiting the processed peaks to 1000, reduced the semi-quantitative application of the GC x GC-TOFMS method developed. Finally, results gained from GC x GC-TOFMS and GC x GC-qMS analyses were comparable with respect to spectral similarity assignments for the 44 target analytes.

Coffee↗
PubMed2004

Comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC x GC-TOFMS) for drug screening and confirmation.

Comprehensive two-dimensional gas chromatography (GC x GC) is applied to analysis of drug standard mixtures containing 78 drugs of interest in forensic samples. For this study, underivatised drugs were employed. While several of the drugs were not detected at the low concentrations employed in the samples, most could be satisfactorily assigned their first and second dimension retentions in the GC x GC retention plane. For this study, time-of-flight mass spectrometry (TOFMS) detection was used. The enhanced separation possible in GC x GC is demonstrated, and typical linearity and apparatus precision are shown for tramadol, diazepam, olanzapine and desipramine using selected qualifier ions. Mass spectral library search quality for the detection of drugs in a selection of authentic forensic cases, along with retention position in the 2D retention plane, is used to support positive identification of the presence of the drugs. The analysis of 'difficult' drugs paracetamol and phenytoin is shown to produce anomalous chromatographic peak shape in the 2D plane, whereas most drugs gave acceptable peak shapes. The GC x GC technique was applied to screening drugs in forensic samples, with either flame ionisation (FID) or TOFMS detection, and compared favourably with conventional single column GC-MS analysis when tested for diazepam in an authentic forensic study.

Forensic Medicine↗
PubMed2004

Molecular interconversion behaviour in comprehensive two-dimensional gas chromatography.

Comprehensive two-dimensional gas chromatography (GC x GC) is shown to provide information on dynamic molecular behaviour (interconversion), with the interconversion process occurring on both columns in the coupled-column experiment. The experiment requires suitable adjustment of both experimental conditions and relative dimensions of each of the columns. In this case, a longer column than normally employed in GC x GC allows sufficient retention duration on the second column, which permits the typical plateau-shape recognised for the interconversion process to be observed. The extent of interconversion depends on prevailing temperature, retention time, and the phase type. Polyethylene glycol-based phases were found to result in high interconversion kinetics, although terephthalic acid-terminated polyethylene glycol had a lesser extent of interconversion. Much less interconversion was seen for phenyl-methylpolysiloxane and cyclodextrin phases. This suggests that for the oximes, interconversion largely occurs in the stationary phase. Examples of different extents of interconversion in both dimensions are shown, including peak coalescence on the first column with little interconversion on the second column.

Chromatography, Gas↗
PubMed2004

Ultra-fast essential oil characterization by capillary GC on a 50 microm ID column.

A 5 m x 50 microm capillary column with 0.05 microm stationary phase film thickness, with a calculated efficiency of almost 20,000 plates per metre (under optimum conditions), was used for very fasthigh resolution GC analysis of lime essential oil. The total analysis time of this volatile essential oil was less than 90 s. Fast GC is shown to be appropriate for essential oil quality assurance analysis, and quantitative results of key components are comparable with those obtained by using conventional GC analysis. The fast GC analysis is approximately 33 times faster than the conventional GC method.

Chromatography, Gas↗
PubMed2004

Effects of pressure drop on absolute retention matching in comprehensive two-dimensional gas chromatography.

Comprehensive two-dimensional gas chromatography (GC x GC) analysis has the capability to resolve many more components of complex mixtures than traditional single column GC analysis. There is an increasing need to provide reliable identification of these separated components; time-of-flight mass spectrometry (TOFMS) is the most appropriate technology to achieve this task. Rather than require MS for all GC x GC separations, it is desirable to assign peak identities to specific peak positions in the GC x GC separation space, and this necessitates matching peak retentions in the two experiments - GC x GC-FID and GC x GC-TOFMS. The atmospheric vs. vacuum outlet conditions confound this task. It is shown here that by employing a supplementary gas supply, provided to a T-union between the column outlet and the MS interface, it is possible to generate 2D chromatograms for GC x GC-FID and GC x GC-TOFMS that are essentially exactly matched. There is no degradation in separation performance or efficiency in the second column in the system interfaced to the T-union. Since the GC x GC-FID experiment uses hydrogen for maximum efficiency, and GC x GC-TOFMS uses helium carrier, translation of (conditions/retentions) must account for the different viscosities of the carrier gases. Translation of conditions is based on well-known principles established in single column analysis. Tabulated data illustrate that retention reproducibility was of the order of better than 4 s for the average first dimension retention difference, and about 40 ms for the average second dimension retention difference when comparing GC x GC-FID and GC x GC-TOFMS results. This should provide considerable support for identification in routine GC x GC-FID analysis of specific sample types, once the peaks in 2D separation space have been assigned identities through GC x GC-TOFMS analysis.

Chromatography, Gas↗
PubMed2004

Comprehensive two-dimensional gas chromatography with flame ionization and time-of-flight mass spectrometry detection: qualitative and quantitative analysis of West Australian sandalwood oil.

The use of gas chromatography (GC)-mass spectrometry (MS), GC-time-of-flight MS (TOFMS), comprehensive two-dimensional GC (GCxGC)-flame ionization detection (FID), and GCxGC-TOFMS is discussed for the characterization of the eight important representative components, including Z-alpha-santalol, epi-alpha-bisabolol, Z-alpha-trans-bergamotol, epi-beta-santalol, Z-beta-santalol, E,E-farnesol, Z-nuciferol, and Z-lanceol, in the oil of west Australian sandalwood (Santalum spicatum). Single-column GC-MS lacks the resolving power to separate all of the listed components as pure peaks and allow precise analytical measurement of individual component abundances. With enhanced peak resolution capabilities in GCxGC, these components are sufficiently well resolved to be quantitated using flame ionization detection, following initial characterization of components by using GCxGC-TOFMS.

Gas Chromatography-Mass Spectrometry↗
PubMed2003

Pressurised liquid extraction--comprehensive two-dimensional gas chromatography for fast-screening of polycyclic aromatic hydrocarbons in soil.

Pressurised liquid extraction (PLE) was applied to the extraction of polycyclic aromatic hydrocarbons (PAHs) from contaminated soils from Husarviken in Stockholm, Sweden. The extraction step was followed by conventional gas chromatography (GC), comprehensive two-dimensional gas chromatography (GC x GC) (both with flame ionisation detection) and gas chromatography-quadrupole mass spectrometry (GC-MS) analysis. Qualitative and quantitative aspects of the results are considered. Qualitatively, results from all chromatographic analyses are in good agreement, and PLE provides a reliable extraction technique with all PAHs extracted in one extraction step; no carry over was observed. With respect to PAH quantification, some variability in results was noted, with better agreement in PAH concentrations for GC and GC x GC measurement, as compared to GC-MS. GC analysis compares favourably with GC x GC apart from the few exceptions where peaks are not fully resolved from other co-extracted analytes, which compromises GC-FID measurement. For example, acenaphthene shows a much higher concentration when measured by GC-FID, demonstrating the superior separating powers of GC x GC; the latter is the preferred technique if precise and accurate quantification of analytes are required. GC-MS results compare reasonably with GC x GC for low-molecular mass PAHs but not for high-molecular mass PAHs; results for GC-MS are consistently higher than those for GC x GC for high-molecular mass PAHs. Since PLE-GC x GC is proposed as a broad screening tool, the demand for precise quantification may be relaxed in the present situation. GC x GC has the added advantage of providing chemical structural information within the two-dimensional contour presentation. Reproducibilities for GC x GC results (peak area) and 2tR were acceptable with relative standard deviations (R.S.D.) of 8 and 1%, respectively (at the mg/kg level), and good repeatability within samples was achieved.

Chromatography, Gas↗
PubMed2003

Retention time reproducibility in comprehensive two-dimensional gas chromatography using cryogenic modulation. II. An interlaboratory study.

An interlaboratory survey was conducted to determine the reproducibility of retention times in both the first (1D) and second dimension (2D) axes of the two-dimensional separation space, using the longitudinal cryogenic modulation comprehensive two-dimensional gas chromatographic approach. Intralaboratory reproducibility has been demonstrated in part 1 of this investigation [J. Chromatogr. A 968 (2002) 161]. Confidence in absolute retention times (hence component positions) in the two-dimensional separation space is critical to component identification. Comparing data from four independent laboratories, five independent gas chromatographs, five independent LMCS units, and numerous operators has determined that the LMCS cryogenic modulation approach provides reliable comprehensive two-dimensional GC results.

Chromatography, Gas↗
PubMed2003

Targeted multidimensional gas chromatography using microswitching and cryogenic modulation.

A new method is described that allows fast target analysis in multidimensional gas chromatography by using a microswitching valve between two GC columns, with cryogenic trapping and rapid re-injection of trapped solutes in the second dimension. The essence of the procedure is that heart-cut fractions from the first column (1D) can be selectively transferred to column 2 (2D), where a moveable cryogenic trap first focuses the transferred solute(s) at the head of the second column and then permits their facile rapid analysis on 2D. Since 2D is a short narrow-bore column, which exhibits very fast analysis (on the order of a few seconds elution), peak responses (heights) are significantly enhanced (by up to 40-fold). Additionally, by using a 2D phase of a selectivity different from that used for 1D, it is possible to also separate components that are not resolved on the first column and to increase the resolution for other compounds. The heart-cut valve isolates the section(s) of solutes of interest from the first column separation, and this provides a considerable simplification to the chromatogram-in addition to the separation and sensitivity advantages. By using this method, multidimensional gas chromatography with multiple heart-cuts can be completed within the same time as the primary column separation. Since the described method permits non-heart-cut fractions to be transferred to a monitor detector, normal detection of these fractions is still permitted. By modulation of the cryotrap, it is also possible to achieve comprehensive two-dimensional gas chromatography for the heart-cut fractions; however, only those compounds passed to the second, separation column, which passes through the cryotrap, will be subjected to GC x GC analysis. The technique and the various modes of operation are described in this paper.

Journal Article↗
PubMed2003

Simulation of elution profiles for two-dimensional dynamic gas chromatographic experiments.

The interconversion of E and Z isomers of acetaldoxime 1 and butyraldoxime 2 have been investigated by comprehensive two-dimensional dynamic gas chromatography (DGCxDGC) and computer simulation. Time-resolved cryogenic modulation is capable of revealing the precise isomeric ratio as a fine structure under the dynamic elution profile, which is characterized in one-dimensional experiments by a plateau formation or peak coalescence caused by interconversion of the isomers during the separation process. The chromatographic theoretical plate model has been extended for the computer simulation of comprehensive two-dimensional dynamic chromatographic experiments. A novel program, ChromWin 2D, based on the new algorithm has been developed for computer simulation to evaluate and predict the elution profiles of DGCxDGC experiments. ChromWin 2D allows the determination of rate constants and barriers of isomerization, epimerization, and enantiomerization processes occurring during chromatographic separations. The Eyring activation parameters of the E/Z and Z/E isomerization barriers in the presence of the stationary phase BP21 (poly(ethylene glycol) terephthalate terminated) were determined by temperature-dependent experiments between 80 and 90 degrees C for 1 and 70 and 130 degrees C for 2. The thermodynamic Gibbs free energy of the E/Z equilibrium of the isomers has been determined from the time-resolved chromatograms by cryogenic modulation. The method described here constitutes a new and important tool for the determination of isomerization barriers, which are of great interest, for example, for the quantitative determination of derivatized aldehydes, such as dinitrophenylhydrazine derivatives, in trace analysis.

Journal Article↗
PubMed2003

Spherical coordinate representations of solvent composition for liquid chromatography method development using experimental design.

One of the major techniques used for the method development of ternary and quaternary high performance liquid chromatography (HPLC) systems has been to use mixture designs, often referred to as "Glajch's Triangle". This technique does not allow for the systematic and simultaneous optimization of other factors such as gradient time, pH and temperature that affect the quality of separations. An alternative approach is to use experimental designs. The condition, however, that the composition of all components of the mobile phase must total 100% presents a problem when trying to mathematically represent ranges of each mobile phase constituent of a ternary or quaternary system. A method is described here, based on spherical coordinate representations, that adheres to the constraints of the mobile phase composition and allows experimental designs, such as central composite and factorial designs, to be applied to the simultaneous optimization of the mobile phase composition. Other factors, in particular temperature and gradient time, can then be included in the design. As a result of applying these designs to the HPLC separation of phenols and corticosteroids, it was found necessary to include three-way interactions between experimental factors in the model. The significance of these interactions shows that they need to be considered in HPLC method development.

Adrenal Cortex Hormones↗