Biomedical subjects

P J Schoenmakers

Publications and source records attributed to P J Schoenmakers.

10 recordsLinked to original sources

PubMed2006

Experimental study on band dispersion in channels structured with micropillars.

The band dispersion in channels with an orderly pillar structure with a pressure-driven liquid flow was determined. Several channels with different geometries were etched in a silicon wafer and enclosed by a glass wafer. The microchannels obtained had the same depth, pillar disposition, and overall porosity, but different pillar diameters and channel widths. The broadening of narrow bands of a fluorescent sample solution flowing through the channels was measured using a fluorescence microscope. It was shown that the peak dispersion occurring in the channels can be much lower than in conventional packed columns, as a consequence of the higher degree of order of the solid structure. Reduced plate heights of approximately 0.2 could be obtained for (nonretained) bands. No correlation was found between the aspect ratio (the ratio of the channel width and the pillar diameter) and band dispersion. The geometrical construction of the sidewall region was shown to play a critical role for channel performance. A good agreement was found with predictions for the optimal sidewall geometry obtained previously with simulation studies.

Fluorescein↗

PubMed2005

Classification of highly similar crude oils using data sets from comprehensive two-dimensional gas chromatography and multivariate techniques.

Comprehensive two-dimensional gas chromatography (GCxGC) has proven to be an extremely powerful separation technique for the analysis of complex volatile mixtures. This separation power can be used to discriminate between highly similar samples. In this article we will describe the use of GCxGC for the discrimination of crude oils from different reservoirs within one oil field. These highly complex chromatograms contain about 6000 individual, quantified components. Unfortunately, small differences in most of these 6000 components characterize the difference between these reservoirs. For this reason, multivariate-analysis (MVA) techniques are required for finding chemical profiles describing the differences between the reservoirs. Unfortunately, such methods cannot discern between 'informative variables', or peaks describing differences between samples, and 'uninformative variables', or peaks not describing relevant differences. For this reason, variable selection techniques are required. A selection based on information between duplicate measurements was used. With this information, 292 peaks were used for building a discrimination model. Validation was performed using the ratio of the sum of distances between groups and the sum of distances within groups. This step resulted in the detection of an outlier, which could be traced to a production problem, which could be explained retrospectively.

Chromatography, Gas↗

PubMed2005

Comprehensive multi-dimensional chromatographic studies on the separation of saturated hydrocarbon ring structures in petrochemical samples.

Characterization of complex petrochemical samples has been a classical subject of comprehensive two-dimensional (2D) gas chromatography (GC x GC). Macroscopic properties of these samples can be described accurately by separation of compounds in classes of identical molecular functionality. Ring structures in the carbon backbone of these compounds, which can be divided in saturated and unsaturated, are amongst the foremost functionalities affecting samples properties. Unfortunately, GC x GC tuned for separation of both saturated and unsaturated ring structures is likely to result in convoluted chromatograms when a distribution of both molecular properties is present in the sample. An independent liquid chromatographic (LC) separation preceding GC x GC could be used to resolve the mixture based on unsaturated rings, allowing saturated rings to be resolved separately in the GC x GC separation. This three-dimensional separation (abbreviated LC-GC x GC) was performed after rigorous evaluation of LC as part of a multidimensional separation using LC x GC. Group-type separation was achieved using this separation for components with either saturated or unsaturated rings. Results of this separation were used to compare information obtained by GC x GC with LC-GC x GC.

Chromatography, Gas↗

PubMed2005

Comprehensive two-dimensional liquid chromatography with on-line Fourier-transform-infrared-spectroscopy detection for the characterization of copolymers.

The on-line coupling of comprehensive two-dimensional liquid chromatography (liquid chromatography x size-exclusion chromatography, LC x SEC) and infrared (IR) spectroscopy has been realized by means of an IR flow cell. The system has been assessed by the functional-group analysis of a series of styrene-methylacrylate (SMA) copolymers with varying styrene content. Ultraviolet (UV) detection was used as a detection technique to verify the detection with IR. The LC x SEC-IR functional-group contour plots (comprehensive chromatograms) obtained for styrene were in agreement with the contour plots constructed from the UV signal. In addition, contour plots can be obtained from non-UV-active groups. One such plot, for the carbonyl-stretching vibration of methylacrylate (MA), is shown. Selective detection of MA proved possible using flow cell IR detection. The combination of the contour plots for styrene and MA allowed a full characterization of the copolymer and it was revealed that the present series of SMA copolymers exhibited homogeneous chemical-composition distributions (CCDs). In addition, commercially available fast-SEC columns have been assessed in this study with respect to their potential to serve as second-dimension separation columns.

Acrylates↗

PubMed2004

Analysis of low-molar-mass materials in commercial rubber samples by Soxhlet and headspace extractions followed by GC-MS analysis.

Very tight regulations apply to materials used for pharmaceutical packaging and for administering drugs. In this paper, we describe a simple and reliable procedure involving both gas- and liquid-phase extraction steps followed by an analysis step to identify the low-molar-mass materials in commercial-rubber samples. Representative commercial rubbers, that could be used for pharmaceutical packaging, have been selected and cryogenically powdered. Headspace and Soxhlet extractions have been carried out and the key parameters are discussed. The obtained extracts have been analyzed by gas chromatography (GC)-mass spectrometry (MS). More than 100 compounds have been detected and identified. Headspace allowed to extract the more-volatile compounds, whereas Soxhlet extraction recovered less-volatile compounds, but induced a loss of the volatile ones. Thus, both extraction techniques are required to fully characterize the low-molar-mass compounds present in rubber.

Gas Chromatography-Mass Spectrometry↗

PubMed2003

Comparison of on-line flow-cell and off-line solvent-elimination interfaces for size-exclusion chromatography and Fourier-transform infrared spectroscopy in polymer analysis.

Two commercial liquid chromatography-Fourier-transform infrared spectroscopy interfaces (LC-FTIR), viz. a flow cell and a solvent-elimination interface have been assessed for use in size-exclusion chromatography (SEC) with respect to their chromatographic integrity (i.e. peak asymmetry, chromatographic resolution), quantitative and qualitative aspects. A polycarbonate/aliphatic polyester (PC/APE) blend and a polycarbonate-co-polydimethylsiloxane (PC-co-PDMS) copolymer were selected for the assessment. Both samples were successfully and selectively analyzed. The relatively large volume of the flow cell and the inherent deposition characteristics of the solvent-elimination interface led to a comparable decrease in the chromatographic resolution. The separation of oligomers was diminished in comparison with SEC-ultra-violet (UV). However, the peak asymmetry was not significantly affected by either interface. For both interfaces, a linear relationship was obtained for the FTIR response versus the injected concentration. The sensitivity was found to be higher for the solvent-elimination interface. For the current model compounds, the flow-cell interface detection limits are worse. However, the repeatability of flow-cell SEC-FTIR, evaluated by means of four SEC-FTIR analyses of polycarbonate, was considerably better than for solvent-elimination SEC-FTIR. This is probably due to the well-defined optical path length of the sample in the flow cell. By spectral subtraction, it was very well possible to obtain qualitative (functional group) information for compound identification also with flow-cell SEC-FTIR.

Chromatography, Gel↗

PubMed2003

Contribution of the polymer standards' polydispersity to the observed band broadening in size-exclusion chromatography.

The contribution of the polydispersity of polymer standards to the observed band broadening in size-exclusion chromatography was evaluated. Initially, theoretical predictions based on an equation by Knox et al. were found to overestimate this contribution, greatly due to the fact that the polydispersity values specified by the manufacturers are upper limits and therefore too high to be applied in this context. An improved estimate of the polydispersity values was obtained from the size-exclusion chromatography results and these new values were used to reassess the polydispersity contribution to band broadening. For two of three columns tested the best molar-mass-distribution parameters, i.e. those the least affected by extra-column and intra-column band broadening effects, can be obtained for polymers with a molar mass in the effective range of the given column and at rather low mobile-phase flow rates. At those conditions, for low-molar-mass polymers, the estimated polydispersity index values approach the theoretical ones derived from a Poisson distribution.

Chromatography, Gel↗

PubMed2002

Gas chromatographic methods for oil analysis.

In the past 50 years. gas chromatography (GC) has played a most important role in the analysis of oil. In this review, the early history is briefly reviewed; next developments in this highly relevant application area since about 1985 are highlighted. The main topic of interest are the introduction and decisive role of capillary GC, the use of selective detection techniques, the versatility of coupled-column techniques and, specifically, the additional power of comprehensive two-dimensional GC.

Chromatography, Gas↗

PubMed2002

Fourier transform infrared spectroscopy with a sample deposition interface as a quantitative detector in size-exclusion chromatography.

The use of a state-of-the-art commercial solvent-elimination interface for liquid chromatography-infrared spectroscopy is discussed from the perspective of quantitative analysis. The effect of eluent flow-rate is investigated with respect to the homogeneity of the deposit and the trace width along the deposition trace. Low flow-rates (50 microl/min or less) turn out to be favorable for obtaining a good trace and a high sensitivity. The trace width decreased from 2.20 to 1.13 mm when the flow-rate was reduced from 500 to 25 microl/min. Preservation of chromatographic detail during deposition was evaluated at different substrate moving speeds. The additional (extra-column) band broadening that is inherent to nebulizer-deposition interfaces, causes a loss in resolution in size-exclusion chromatography (SEC)-Fourier transform infrared (FTIR) spectroscopy in comparison with SEC-UV. The repeatability of the deposition is evaluated by SEC-FTIR analyses of polystyrene standards (peak molar-masses: 1250-2,950 000 g/mol) and the RSD is found to range from 3.2 to 5.8% in response and from 0.21 to 0.47% in retention time.

Chromatography, Gel↗

PubMed1999

Development of an on-line coupling of liquid-liquid extraction, normal-phase liquid chromatography and high-resolution gas chromatography producing an analytical marker for the prediction of mutagenicity and carcinogenicity of bitumen and bitumen fumes.

A fast and fully automated system for the determination of polycyclic aromatic compounds (PACs) is described. The system has been developed to produce an analytical 'marker', correlating chemical characteristics (including PAC analysis) with mutagenicity and carcinogenicity. The products of interest are bitumen fumes, bitumen and other (heavy or even residual) oil products, regardless of their boiling range. Dimethyl sulphoxide (DMSO) extractables obtained from a flow-injection analysis (FIA) system are introduced on-line in a normal-phase liquid chromatographic (NPLC) system. Here, the PACs are separated from the DMSO and possible co-extracted heavy residual species. The final step incorporates on-line gas chromatographic analysis of the three-to-six-ring PAC fraction, followed by flame-ionisation detection for quantification. It was demonstrated that data obtained from samples in the distillate lubrication-oil range correlate well with data obtained from the manual DMSO-extraction method standardised by the Institute of Petroleum as IP346.

Carcinogenicity Tests↗