Biomedical subjects

C Gooijer

Publications and source records attributed to C Gooijer.

At least 19 recordsLinked to original sources

PubMed2006

Cavity ring-down spectroscopy for detection in liquid chromatography: extension to tunable sources and ultraviolet wavelengths.

In earlier studies, it was demonstrated that the sensitivity of absorbance detection in liquid chromatography (LC) can be improved significantly by using cavity ring-down spectroscopy (CRDS). Thus far, CRDS experiments have been performed using visible laser light at fixed standard wavelengths, such as 532 nm. However, since by far most compounds of analytical interest absorb in the ultraviolet (UV), it is of utmost importance to develop UV-CRDS. In this study, as a first step towards the deep-UV region, LC separations with CRDS detection (using a previously described liquid-only cavity flow cell) at 457 and 355 nm are reported for standard mixtures of dyes and nitro-polyaromatic hydrocarbons (nitro-PAHs), respectively. For the measurements in the blue range a home-built optical parametric oscillator (OPO) system, tunable between 425 and 478 nm, was used, achieving a baseline noise of 2.7 x 10(-6) A.U. at 457 nm, improving upon the sensitivity of conventional absorbance detection (typically around 10(-4) A.U.). An enhancement of the sensitivity can be seen at 355 nm as well, but the improvement of the baseline noise (1.3 x 10(-5) A.U.) is much less pronounced. The sensitivity at 355 nm is limited by the quality of the UV-CRDS mirrors that are currently available: whereas the ring-down times as obtained at 457 nm are around 70-80 ns for the eluent, they are only 20-25 ns at 355 nm. Critical laser characteristics for LC-CRDS measurements, such as pulse length and mode structure, are given and prospects for going to shorter wavelengths are discussed.

Journal Article↗

PubMed2005

Interfacing capillary electrophoresis and surface-enhanced resonance Raman spectroscopy for the determination of dye compounds.

The at-line coupling of capillary electrophoresis (CE) and surface-enhanced resonance Raman spectroscopy (SERRS) was optimized for the separation and subsequent spectroscopic identification of charged analytes (dye compounds). Raman spectra were recorded following deposition of the electropherogram onto a moving substrate. To this end a new interface was developed using a stainless steel needle as a (grounded) cathode. The outlet end of the CE capillary was inserted into this metal needle; CE buffer touching the needle tip served as the electrical connection for the CE separation. A translation table was used to move the TLC plate at a constant speed during the deposition. The distance between the tip of the fused silica column and the TLC plate was kept as small as possible in order to establish a constant bridge-flow, while avoiding direct contact. The dyes Basic Red 9 (BR9), Acid Orange 7 (AO7) and Food Yellow 3 (FY3) were used as test compounds. After CE separation in a 20 mM borate buffer at pH 10, after deposition, concentrated silver colloid was added to each analyte spot, followed by irradiation with 514.5 nm light from an argon ion laser to record the SERRS signal using a Raman microscope. Different types of silver colloids were tested: Lee-Meisel type (citrate), borate, and gold-coated silver. BR9 (positively charged) gave much more intense SERRS spectra than the two negatively charged dyes. For BR9 and AO7 the citrate-coated Lee-Meisel colloid yielded the most intense SERRS spectra. The CE-SERRS system was used to separate and detect the negatively charged dyes. Silver colloid and nitric acid (to improve adsorption) were added post-deposition. Even though their chemical structures are very similar, AO7 and FY3 could be readily distinguished based on their SERRS spectra. The limits of detection (S/N = 3) of the CE-SERRS system ranged from 6.7 x 10(-5) M (2.6 x 10(-12) mol injected) for FY3 down to 1.8 x 10(-6) M (7.0 x 10(-14) mol injected) for BR9.

Journal Article↗

PubMed2005

Miniaturized cavity ring-down detection in a liquid flow cell.

A novel method for applying cavity ring-down spectroscopy in the liquid phase, compatible with LC analyses, is presented. The core of the setup is a home-built cavity ring-down flow cell (cell volume 12 microL) that is constructed using a silicon rubber spacer, which is clamped leak-tight between two high-reflectivity mirrors. The mirrors are in direct contact with the liquid flow, which provides for a small path length and short ring-down times. Inside the cavity there are no windows, reflection losses, or Brewster angles to be considered. Due to the small size of the presented cavity geometry, the setup can be implemented in conventional-size LC apparatuses. With a flow injection setup, a detection limit of 2.5 nM was obtained for Crystal Violet in ethanol, and the linear dynamic range of the system is at least 2 orders of magnitude. The method has the potential to become a powerful alternative for commercial LC UV/visible absorbance detectors.

Journal Article↗

PubMed2004

Temperature dependence of the melittin folding equilibrium studied by means of fluorescence excitation spectra.

The temperature dependence of fluorescence excitation spectra is investigated. This gives information on melittin folding equilibrium complementary to that obtained from fluorescence emission studies. A fit of the excitation spectra of melittin with three Gaussian functions gives good results. It suggests that in melittin a reversal of La and Lb electronic states of tryptophane takes place. The separate La and Lb bands exhibit a temperature dependence of the width and maximum.

Melitten↗

PubMed2002

Sub-second liquid chromatographic separations by means of shear-driven chromatography.

Utilizing the concept of shear-driven chromatography, we have been able to realize reversed-phase LC separations in flat rectangular nano-channels coated with a C8 monolayer and being as thin as 100 nm. At this scale, the separation kinetics are strongly enhanced, as is witnessed by the extremely short time (< 0.1 s) needed to separate a mixture of coumarin dyes. The observed plate numbers are still relatively small, because the experiments were conducted in ultra-short columns (< or = 1 mm) and under injection band width-limiting conditions.

Chromatography, Liquid↗

PubMed2002

Laser-based non-fluorescence detection techniques for liquid separation systems.

Over the last two decades, the possibility to use lasers for detection purposes in column liquid chromatography (LC) and capillary electrophoresis (CE) received much attention in the analytical chemistry literature. Most attention has been devoted to laser-induced fluorescence. The present review covers developments on non-fluorescence techniques for LC and CE. The techniques considered are thermal lens spectrometry, photoacoustic detection, refractive index detection including refractive index backscattering, Raman spectroscopy and degenerate four-wave mixing (a special mode of transientholographic spectroscopy). The paper starts with an outline of the characteristics of lasers; it ends with an overall evaluation and a discussion of the perspectives of the techniques dealt with.

Lasers↗

PubMed2001

Detection of nonderivatized peptides in capillary electrophoresis using quenched phosphorescence.

A capillary electrophoresis detection technique for (small) peptides is presented, i.e. quenched phosphorescence, a method that is generally applicable and does not require chemical derivatization. For this purpose, a novel phosphorophore, 1-bromo-4-naphthalenesulfonic acid (BrNS), was synthesized. BrNS has sufficient water solubility and provides strong phosphorescence at room temperature over a wide pH range. The detection is based on the dynamic quenching of the BrNS phosphorescence background signal by electron transfer from the amino group of the peptides at pH 9.5-10. For the di- and tripeptides Val-Tyr-Val, Val-Gly-Gly, Ala-Ser, Gly-Asn, Gly-Ala, and Gly-Tyr, detection limits in the range of 5-20 microg/L were obtained. The novel technique is even a good alternative for the (limited) group of peptides containing tyrosine and, thus, exhibiting native fluorescence as well as strong UV absorption: using Gly-Tyr, Val-Tyr-Val, methionine enkephalin, and human angiotensin II as test compounds, quenched phosphorescence detection was found to compare favorably with absorption detection at 190- and 266-nm laser-induced fluorescence detection, as performed with a recently developed, small-size, quadrupled Nd:YAG laser.

Angiotensin II↗

PubMed2001

On-line identification method in column liquid chromatography: UV resonance Raman spectroscopy.

Ultraviolet resonance Raman spectroscopy (RRS) is presented as a novel identification tool for conventional-size column liquid chromatography (LC). The on-line coupling was made using a standard Z-shaped flow cell. A continuous-wave frequency-doubled argon ion laser operating at a wavelength of 244 nm was used for excitation. "On-the-fly" resonance Raman spectra of four model compounds, fluorene, phenanthrene, fluoranthene, and pyrene, were recorded after a standard acetonitrile/water reversed-phase LC separation. When applying a large-volume-injection procedure (32 mL), detection limits were at the nanogram per milliliter level. The results indicate that UV-RRS gives detailed spectral information at an appropriate sensitivity level so that coupling with LC becomes feasible.

Journal Article↗

PubMed2001

Liquid-core waveguide technology for coupling column liquid chromatography and Raman spectroscopy.

The on-line coupling of liquid chromatography (LC) and Raman spectroscopy (RS) via an entirely plastic liquid-core waveguide (LCW) was optimized in terms of excitation wavelength of the laser, especially in relation to the fluorescence background, and the length of the LCW. Excitation at 632.8 nm (He-Ne laser) was found to be a good compromise between a wavelength long enough to strongly reduce the fluorescence background and, on the other hand, short enough to avoid (re)-absorption of laser light and Raman signals by H2O in LCWs of considerable length. This conclusion is supported by a theoretical discussion on the optimization of LCW lengths as function of the excitation wavelength for H2O and 2H2O. When using the He-Ne laser the optimum length is approximately 50 cm for H2O; this corresponds to a detection cell volume of 19 microl for an LCW of 220 microm I.D., which is fully compatible with conventional-size LC. The influence of an organic modifier, usually necessary for reversed-phase LC, on the free spectral window was evaluated. The potential applicability of LC-LCW-RS was shown for a mixture of adenosine 5'-monophosphate (AMP), guanosine 5'-monophosphate (GMP) and uridine 5'-monophosphate (UMP), utilizing an aqueous eluent without the addition of a modifier. Improved detectability was achieved by using the stopped-flow mode and applying a large-volume-injection procedure (injection volume: 200 microl). Under these conditions, the limit of identification for AMP, GMP and UMP was in the 0.1-0.5-mg/ml range.

Adenosine Monophosphate↗

PubMed2001

Laser-induced fluorescence detection at 266 nm in capillary electrophoresis. Polycyclic aromatic hydrocarbon metabolites in biota.

The separation of five phenolic polycyclic aromatic hydrocarbon metabolites (hydroxy-PAHs) has been performed by cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC) using a 30 mM borate buffer (pH 9.0) containing 60 mM sodium dodecyl sulfate and varying concentrations of gamma-cyclodextrin (gamma-CD). A concentration of 12.5 mM gamma-CD was found to provide a baseline separation of the five hydroxy-PAHs. We applied conventional fluorescence and laser-induced fluorescence (LIF) detection, using a new, small-size, quadrupled Nd-YAG laser emitting at 266 nm. The best limits of detection, in the low ng/ml range, were achieved using LIF detection. For all analytes, linearity was observed up to ca. 100 ng/ml. As an application, conjugated pyrene metabolites in hepatopancreas samples from the terrestrial isopods Oniscus asellus and Porcellio scaber were separated and detected. Finally, flatfish bile samples from individuals exposed to polluted sediment or crude oil, which were part of an interlaboratory study, were analyzed by CD-MEKC with conventional fluorescence and LIF detection to determine the 1-hydroxypyrene concentrations.

Animals↗

PubMed2001

Applicability of surface-enhanced resonance Raman scattering for the direct discrimination of ballpoint pen inks.

In situ surface-enhanced resonance Raman spectroscopy (SERRS) with excitation at 685 nm is suitable for the direct discrimination of blue and black ballpoint pen inks on paper. For black inks, shorter excitation wavelengths can also be used. For blue inks, SERRS at 514.5 and 457.9 nm does not provide adequate discriminative power. At these excitation wavelengths, the SERRS signals of the Methyl Violet derivatives present in inks easily dominate the overall spectrum because of resonance enhancement and preferential interaction with silver sol particles. At 685 nm, this problem is not encountered as the Methyl Violet derivatives do not show resonance enhancement, while other components may still exhibit resonance. Thirteen blue and thirteen black ink lines were examined. For the blue and black inks, on the basis of the 685 nm SERR spectra, eight and six groups of spectra, respectively, could be distinguished. This discrimination largely agrees with information from thin layer chromatography (TLC) experiments, although some differences in group compositions are found. The in situ SERR spectra show good repeatability with regard to the Raman frequencies, band shapes and relative intensities of the spectral bands. However, absolute intensities cannot be used for discrimination purposes.

Journal Article↗

PubMed2000

Surface-enhanced resonance Raman spectroscopy as an identification tool in column liquid chromatography.

The compatibility of ion-pair reversed-phase column liquid chromatography and surface-enhanced resonance Raman spectroscopy (SERRS) for separation and identification of anionic dyes has been investigated, with emphasis on the at-line coupling via a thin-layer chromatography (TLC) plate. SERR spectra using silver sols were recorded both for aqueous solutions and for samples deposited on aluminum oxide and silica TLC plates at 514.5- and 457.9-nm laser excitation. For some dyes, the shorter wavelength was needed to diminish the fluorescence background. For aqueous solutions and for samples deposited on aluminum oxide, clear SERR spectra were obtained upon addition of poly(L-lysine); for the silica plates, the addition of nitric acid was required. Upon drying the plates, the SERRS signals decreased in intensity; simply adding a drop of water could largely restore them. At-line coupling of LC and SERRS was successfully achieved when using silica, but not aluminum oxide, plates. The application of a gradient, a high water content, and the presence of ion-pair reagents needed for the separation did not adversely affect the deposition and the recording of SERR spectra. The identification limits were 10-20 ng of deposited material, depending on the dye selected, which corresponded to injected concentrations of 5-10 microg mL(-1).

Journal Article↗

PubMed2000

Quenched phosphorescence, a new detection method in capillary electrophoresis.

The applicability of quenched phosphorescence as a detection mode in capillary electrophoresis (CE) was explored for a number of analyte classes and buffer systems. The detection method is based on the quenching of biacetyl phosphorescence (biacetyl is a constituent of the CE buffer) by the analytes via various mechanisms (energy transfer, electron transfer and, possibly, hydrogen donation) and gives rise to negative peaks in the electropherograms. A number of buffers in the pH range 4.7-11.5, frequently used in CE, were tested for their compatibility with this detection mode. Borate, succinate, malonate, acetate, and phosphate buffers (pH 4.7-8.5) could be used without any problems. With a pH of ca. 8.5 or higher the baseline declined with time, while at a pH higher than 9.5 no signal at all was obtained. Obviously, the noise on the phosphorescence signal (i.e., the baseline) determines the ultimate analyte detection limits (LODs). The baseline signal-to-noise ratio, usually denoted as the dynamic reserve (DR), was enhanced ca. 25-fold compared to direct biacetyl excitation by sensitization of the biacetyl phosphorescence by 1,5-naphthalenedisulfonic acid, and by application of a total emission mirror (TEM). A concentration of 1 x 10(-3) M 1,5-naphthalenedisulfonic acid was found to be optimal. For the buffer systems considered, the DR was typically ca. 300-600 under optimized conditions (noise defined as 1 x sigma). Investigated analytes include naphthalenesulfonic acids (NS), nitrophenols, hydroxybenzoic acids, amino acids, and dithiocarbamates (DTCs.). For most of these, the LODs were in the 10(-7)-10(-8) M range, which is significantly lower than with direct or indirect absorption detection.

Amino Acids↗

PubMed1999

Liquid chromatography-Fourier-transform infrared spectrometry.

Over the past years the coupling of liquid chromatography (LC) and Fourier-transform infrared spectrometry (FT-IR) has been pursued primarily to achieve specific detection and/or identification of sample constituents. Two approaches can be discerned in the combination of LC and FT-IR. The first and simpler approach is to use a flow cell through which the effluent from the LC column is passed while the IR spectra are continuously recorded. The second approach involves elimination of the LC solvent prior to IR detection using an interface which evaporates the eluent and deposits the analytes onto a substrate. This paper provides a general overview of flow-cell based IR detection and briefly discusses early solvent-elimination interfaces for LC-FT-IR. A more comprehensive description is given of interface systems which use spraying to induce rapid eluent evaporation, and which basically represent the state-of-the-art in LC-FT-IR. Finally, the interface systems suitable for reversed-phase LC are summarized and the perspectives of LC-FT-IR are discussed. The overview indicates that flow-cell LC-FT-IR has rather poor detection limits but can be useful for the specific and quantitative detection of major constituents of mixtures. Solvent-elimination techniques, on the other hand, provide much better sensitivity and enhanced spectral quality which is essential when unambiguous identification of low-level constituents is required.

Chromatography, Liquid↗

PubMed1999

On-line dialysis-SPE-CE of acidic drugs in biological samples.

A fully automated method is presented for the determination of acidic drugs in urine and serum using on-line dialysis-solid-phase extraction (SPE)-capillary electrophoresis (CE) with UV detection. With non-steroidal anti-inflammatory drugs (NSAIDs) as test compounds, detection limits in the biological samples were 0.05-1.0 microgram ml-1. Calibration plots were linear over two orders of magnitude and the within-day and between-day repeatability were better than 10%. The CE capillary and SPE column were used for over 500 analyses; the dialysis membrane was replaced after 250 analyses. A general protocol for dialysis-SPE-CE which can be used for amphoteric and acidic drugs was devised. The present results show that this protocol has general validity and can be recommended for future work on other classes of drugs.

Acids↗

PubMed1998

At-line solid-phase extraction for capillary electrophoresis: application to negatively charged solutes.

The analysis of complex biological samples with capillary electrophoresis (CE) requires proper sample pretreatment. In this paper the applicability of solid-phase extraction (SPE) coupled at-line with CE is studied, by using a laboratory-made interface. A fresh (disposable) SPE cartridge is used for each sample to prevent carry-over effects. The sample handling procedure is performed parallel with the analysis of the previous sample, to improve sample throughput. Using this set-up, negatively charged test compounds (some non-steroid anti-inflammatory drugs) can be determined in serum and urine. The method is linear over at least two decades and detection limits are around 40 microg/l. A single capillary, flushed only once a week with a sodium hydroxide solution, was used without problems for the analysis of ca. 900 samples during 1 year. The robustness of the system was very good: no blocking of loop, interface or capillary was found during this period. Furthermore, the system was successfully used for overnight runs.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1998

Determination of phenprocoumon in plasma and urine using at-line solid-phase extraction-capillary electrophoresis.

The use of capillary electrophoresis (CE) for the analysis of biological samples is rather problematic because of the large number of interferences present in the matrix. One of the possibilities to solve such problems is to couple solid-phase extraction (SPE) at-line with CE, a technique developed in our laboratory. In this study at-line SPE-CE is performed for the determination of the anticoagulant phenprocoumon in biological fluids. Plasma samples are injected after the addition of 1 vol.% of formic acid to release the drug from binding proteins, while urine samples can be directly injected. The procedure is linear between 0.2 and 30 microg ml(-1) with a correlation coefficient, r2, of 0.9996. The detection limit in plasma is 0.1 microg ml(-1), which is fully adequate in view of the concentrations, that have to be dealt with in practice. The phenprocoumon concentration in a plasma sample of a patient treated with the anticoagulant was 3.8 microg ml(-1).

Electrophoresis, Capillary↗

PubMed1998

Analyte identification in capillary electrophoretic separation techniques.

A review on applications of on-line hyphenation in capillary electrophoresis and capillary electrochromatography for the identification of migrating analytes is presented. There is an urgent need for unambiguous analyte identification by combining spectral information and observed migration times, because the parameters influencing the migration times and separation efficiencies in these separation techniques are not easily controlled, especially when real samples containing unknown interferences have to be analyzed. The spectrometric techniques covered here are ultraviolet and visible radiation (UV/Vis) absorption, fluorescence including fluorescence line-narrowing spectroscopy, Raman spectroscopy, nuclear magnetic resonance and mass spectrometry. Attention is essentially confined to literature reports in which the extra information provided by the detector is really used for identification purposes, especially in real-life samples, while the interfacing as such and analyte detectabilities in standard solutions are only briefly discussed. This article covers an extensive fraction of the literature published on this topic until the beginning of 1998.

Electrophoresis, Capillary↗