Nel H. Velthorst

Flow injection determination of hydrogen peroxide by means of a solid-state-peroxyoxalate chemiluminescence reactor

Abstract A solid-state reactor for detection of hydrogen peroxide in aqueous samples by peroxyoxalate chemiluminescence is described. Bis(2,4,6-trichlorophenyl)oxalate in solid form is packed into a bed reactor, which eliminates mixing problems and facilitates the instrumental development. Perylene is added as a sensitizer to a water/acetonitrile (20:80) carrier stream into which the samples (200–600 μl) are injected. Detection limits of 6 × 10 −9 M H 2 O 2 (0.2 μg l −1 ) are obtained with both a commercial and a home-made luminescence detector. Calibration graphs are linear up to 10 −5 M. The r.s.d. for 2 × 10 −7 M (6.7 μg −1 ) hydrogen peroxide ( n = 10) is 2.8%. Sample throughput is ca. 120 h −1 .

A solid-state chemiluminescence detector for hydrogen peroxide based on an immobilized luminophore : Application to Rain Water

Abstract The construction and functioning of a chemiluminescence detector for hydrogen peroxide is described. It is based on peroxyoxalate chemiluminescence and consists of a two-bed reactor packed with solid trichlorophenyloxalate (TCPO) and 3-aminofluoranthene immobilized on controlled pore glass beads. Optimal conditions (pH, solvent, TCPO purity) for flow-independent operation are discussed. Samples can be injected into a moving stream or directly into the monitor with a syringe so as to provide a manually operated field monitor. The detection limit is 1.5 × 10−8 M, and calibration graphs are linear over six orders of magnitude. The r.s.d. for the manual monitoring mode is ±3% for 17 μg l−1 hydrogen peroxide. A sample throughput of 100 h−1 is possible in the flow injection mode, and 40 samples h−1 for manual injection.

Pyrene metabolites in the hepatopancreas and gut of the isopod Porcellio scaber, a new biomarker for polycyclic aromatic hydrocarbon exposure in terrestrial ecosystems

The object of this study was to investigate the formation of pyrene metabolites by the isopod Porcellio scaber as a possible tool in the environmental risk assessment of polycyclic aromatic hydrocarbon (PAH) exposure in terrestrial ecosystems. The formation of pyrene metabolites was studied after either pulse exposure to a single high dose, or prolonged exposure (14 d) to a lower dosage. Exposure studies were carried out with unlabeled or radiolabeled pyrene, ion pair chromatography was used for analysis, and reference conjugates were synthesized. We also measured pyrene metabolites in field—exposed animals, to explore their use as biomarkers of PAH exposure. Analysis of the hepatopancreas and gut of single isopods revealed the formation of five products, one of which was 1-hydroxypyrene. Four of the remaining products were identified as phase II metabolites of 1- hydroxypyrene, with UV absorption and fluorescence characteristics similar to that of pyrene. One metabolite was identified as pyrene−1-glucoside, which is in accordance with high rates of glucosidation, reported for these isopods. Another conjugate was identified as pyrene−1-sulfate. None of the metabolites coeluted with a pyrene−1-glucuronide reference obtained from fish bile. A fifth metabolite detected by on—line scintillation detection did not exhibit any absorption at 340 nm, possibly because one of the aromatic rings of pyrene had lost its aromatic character. Although pyrene is not known for its toxicity, it usually co—occurs with other PAHs that are transformed into toxic products. Investigating the metabolism of pyrene can provide information with regard to the biotransformation capacity of invertebrate species and uptake and elimination kinetics. Because pyrene is one of the most predominant PAHs in the environment, analysis of its metabolites provides an extra tool for the environmental risk assessment of ecosystems with regard to PAH exposure, bioavailability, and biotransformation.

Solid-state peroxyoxalate chemiluminescence detection of hydrogen peroxide generated in a post-column reaction

Abstract Solid-state chemiluminescence detection was used for the first time in conjunction with high-performance liquid chromatography (HPLC) and compared with liquid-phase chemiluminescence detection. The separation and detection of quinones commonly used in the wood pulping industry served as a model system. Hydrogen peroxide was produced by the eluting quinones in a post-column photochemical reaction. The reaction is photocatalytic in that up to 100 H 2 O 2 molecules are produced for each analyte molecule. The H 2 O 2 was subsequently detected using peroxyoxalate energy transfer chemiluminescence. The two additional reagents, a suitable fluorophor and an oxalate ester, may be introduced by means of post-column reagent pumps. It is shown that one pump may be eliminated by chemically bonding the fluorophor, 3-aminofluoranthene in these experiments, to glass beads or silica gel at a small cost in sensitivity and peak width. Use of an oxalate ester (bis-2,4,6-trichlorophenyl oxalate) in the solid state allowed the elimination of the remaining post-column pump at an additional cost in sensitivity and resolution. In this ultra-simple solid-state system using no post-column reagent pumps, detection limits were typically less than 5 pmol on-column, or about five times poorer than the best results obtained with a three-pump liquid phase system. The role of base catalysis of the chemiluminescence was also explored. As shown earlier for flow injection analysis, although addition of a catalyst enhances the detection sensitivity, the signal-to-noise ratio is only slightly improved; however, the catalyst does improve the precision and, as a buffer, reduces the susceptibility of the technique to interference from pH changes.

Pyrene metabolites in the hepatopancreas and gut of the isopod porcellio scaber, a new biomarker for polycyclic aromatic hydrocarbon exposure in terrestrial ecosystems: Pyrene metabolites in the isopod Porcellio scaber

The object of this study was to investigate the formation of pyrene metabolites by the isopod Porcellio scaber as a possible tool in the environmental risk assessment of polycyclic aromatic hydrocarbon (PAH) exposure in terrestrial ecosystems. The formation of pyrene metabolites was studied after either pulse exposure to a single high dose, or prolonged exposure (14 d) to a lower dosage. Exposure studies were carried out with unlabeled or radiolabeled pyrene, ion pair chromatography was used for analysis, and reference conjugates were synthesized. We also measured pyrene metabolites in field-exposed animals, to explore their use as biomarkers of PAH exposure. Analysis of the hepatopancreas and gut of single isopods revealed the formation of five products, one of which was 1-hydroxypyrene. Four of the remaining products were identified as phase II metabolites of 1- hydroxypyrene, with UV absorption and fluorescence characteristics similar to that of pyrene. One metabolite was identified as pyrene-1-glucoside, which is in accordance with high rates of glucosidation, reported for these isopods. Another conjugate was identified as pyrene-1-sulfate. None of the metabolites coeluted with a pyrene-1-glucuronide reference obtained from fish bile. A fifth metabolite detected by on-line scintillation detection did not exhibit any absorption at 340 nm, possibly because one of the aromatic rings of pyrene had lost its aromatic character. Although pyrene is not known for its toxicity, it usually co-occurs with other PAHs that are transformed into toxic products. Investigating the metabolism of pyrene can provide information with regard to the biotransformation capacity of invertebrate species and uptake and elimination kinetics. Because pyrene is one of the most predominant PAHs in the environment, analysis of its metabolites provides an extra tool for the environmental risk assessment of ecosystems with regard to PAH exposure, bioavailability, and biotransformation.

Forward-scattering degenerate four-wave mixing for sensitive absorption detection in microseparation systems coupling to micro-column liquid chromatography

Abstract The feasibility of forward-scattering degenerate four-wave mixing (F-D4WM) for detection in micro-column (internal diameter 0.3 mm) liquid chromatography (micro-LC) is studied, using the separation of 1-amino-9,10-anthraquinone (I-AAQ) and 2-amino-9,10-anthraquinone (II-AAQ) as a model system and utilizing the 514 nm line of an argon-ion laser. Though the F-D4WM signal can be detected on a virtually dark background, in practice background reduction is of utmost importance. Background reduction by means of a mechanical chopper and a scanning confocal Fabry–Perot interferometer (CFP) are compared both experimentally and theoretically. Using the CFP set-up, an injected concentration limit of detection of 3·10−8 M could be achieved for I-AAQ (molar absorptivity of 2·103 M−1 cm−1 at 514 nm), which is roughly two decades more favourable than obtained when using the mechanical chopper. In comparison to conventional absorption detection in micro-LC at 514 nm, the gain is also about two decades. In view of the fact that the present F-D4WM set-up still suffers from significant band broadening caused by the detector cell, further improvement seems possible.

Detection of Oxidase Generated Hydrogenperoxide by a Solid State Peroxyoxalate Chemiluminescence Detector

Abstract The compatability of a solid state peroxyoxalate chemiluminescence detector for hydrogen peroxide with an immobilized oxidase reactor is investigated. As a model system glucose oxidase immobilized by electrostatic forces on an ion-exchanger or chemically bonded to glass beads were chosen. The former support is less suitable for immobilization of oxydases due to strong retention of hydrogenperoxide on the ion exchanger. The relatively little flow dependence of these systems renders them suitable for low-cost manual sample injection monitors as well as in a flow injection analyses (FIA) mode with low-cost pumping systems. The system was operated with 80% acetonitrile water solutions. A detection limit of 8 × 10−7M of glucose was achieved in directly injected samples. Enzymes more sensitive to organic solvents can be operated with pure water and adjustment for optimal chemiluminescence condition is achieved with a make-up flow prior to detection. A detection limit of 5 × 10−8M glucose is achieved un...

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.

HPLC detection of choline and acetylcholine in serum and urine by an immobilized enzyme reactor followed by chemiluminescence detection.

A method using HPLC has been developed for the detection of choline (Ch) and acetylcholine (ACh) using an immobilized enzyme reactor which converts Ch and ACh into hydrogen peroxide and betaïne. The formed H(2)O(2) is quantified by means of a solid-state peroxyoxalate chemiluminescence detector based on an immobilized fluorophore and addition of oxalate from a solid bed. The conditions necessary for chemiluminescence detection are obtained by using a make-up flow of acetonitrile after the enzyme reactor. Precipitation problems due to the poor solubility of salts in the final acetonitrile-water mixture are circumvented by adding a crown ether to the make-up flow. The reproducibility of the method was calculated to be 3.4-3.7% RSD. Detection limits are in the sub-picomole range and a linear range of at least three orders of magnitude is found. Measurements in urine and serum reveal no matrix effects.

Quenched peroxyoxalate chemiluminescence detection in aqueous liquid chromatographic separations

Abstract Several analytes, such as bromide, iodide, sulphite, nitrite, substituted anilines and organosulphur compounds cause quenching of peroxyoxalate chemiluminescence. This phenomenon, quenched peroxyoxalate chemiluminescence, can be used as a method of detection for liquid chromatography. The potential of quenched chemiluminescence is discussed, with special attention give to its compatibility with aqueous separation systems. An immobilized fluorophore, 3-aminofluoranthene on controlled pore glass, is packed in the detector cell. Liquid-state studies show that the influence of both the nature and concentration of the fluorophore is small, which indicates a more complicated mechanism of the chemiluminescence reaction than previously assumed. It is shown that bis(2-nitrophenyl)oxalat is a more suitable oxalate for quenched chemiluminescence detection than bis(2,4,6-trichlorophenyl) oxalate. This is demostrated for ion-chromatography of bromide and iodide and the aqueous reversed-phase separation of organosulphur compounds. Detection limits in the low nanogram and sub-nanogram region are reported for the above compounds. When an electronic inverter was used, calibration curves were linear over a concentration range of 2–3 decades. The method is quite selective and can be applied to relatively complex matrices without sample pretreatment.