Klaas M Jonker

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Shellfish from oyster farms in the Netherlands and imported from other European countries were examined for viral contamination. A method that allows sequence matching between noroviruses from human cases and shellfish was used. The samples of shellfish (n = 42) were analyzed using a semi-nested RT-PCR that had been optimized for detection of norovirus in(More)
Two liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods were developed for the determination of streptomycin (STR) and its derivative dihydrostreptomycin (DHSTR) in milk and honey. These aminoglycoside antibiotics are used as veterinary drugs. In the EU, the presence of dihydro- and streptomycin residues in honey is forbidden, the maximum(More)
A method was developed to determine 4-hexylresorcinol in shrimp meat. The procedure is based on extraction of test portions with methanol followed by liquid chromatographic analysis of the extracts, using a reversed-phase column and fluorimetric detection (excitation: 280 nm, and emission: 310 nm). The confidence interval of the recovery in working range of(More)
The retention behaviour of amino acids in phase systems consisting of a hydrophobic solid support as the stationary phase and water-organic solvent mixtures containing a small amount of an anionic detergent as the mobile phase was investigated. Such phase systems are found to behave like conventional ion-exchange systems. The degree and order of retention(More)
One of the most convenient methods for the identification of animal species in processed meat products is the examination of DNA sequences. Real-time polymerase chain reaction (qPCR) techniques are particularly suitable because even small fragments of DNA formed during heat processing of the meat can be amplified and identified. A real-time PCR method has(More)
An interlaboratory study of the liquid chromatographic (LC) determination of histamine in fish, sauerkraut, and wine was conducted. Diminuted and homogenized samples were suspended in water followed by clarification of extracts with perchloric acid, filtration, and dilution with water. After LC separation on a reversed-phase C18 column with phosphate buffer(More)
Addition of a low concentration of sodium azide completely stops colour development in a peroxidase-labelled enzyme immunoassay using 2,2'-azino-di(3-ethylbenzthiazoline sulphonic acid-6) as substrate. Whereas high concentrations of azide cause a decrease in the colour intensity, the low concentrations used here have no significant affect on the colour.
Paralytic shellfish poisoning toxins are produced by dinoflagellates. Shellfish filtering these unicellular algae will accumulate the toxins and pose a health risk when consumed by man. In the European Union, paralytic shellfish poisoning toxins in bivalve molluscs are regulated at a maximum content of 80 microg/100 g (91/492/EEC). The current reference(More)
A liquid chromatography-tandem mass spectrometry method has been developed for the determination of residues of alkylbenzyldimethylammonium, didecyldimethylammonium, didodecyldimethylammonium, and benzyldodecylhydroxyethylammonium compounds in various food matrixes. These quaternary ammonium compounds (QAs) are used in the food industry as disinfectants.(More)
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