Quantitative Determination of Paralytic Shellfish Poisoning Toxins in Shellfish Using Prechromatographic Oxidation and Liquid Chromatography with Fluorescence Detection: Collaborative Study

A collaborative study was conducted for the determination of paralytic shellfish poisoning (PSP) toxins in shellfish. The method used liquid chromatography with fluorescence detection after prechromatographic oxidation of the toxins with hydrogen peroxide and periodate. The PSP toxins studied were saxitoxin (STX), neosaxitoxin (NEO), gonyautoxins 2 and 3 (GTX2,3; together), gonyautoxins 1 and 4 (GTX1,4; together), decarbamoyl saxitoxin (dcSTX), B-1 (GTX5), C-1 and C-2 (C1,2; together), and C-3 and C-4 (C3,4; together). B-2 (GTX6) toxin was also included, but for qualitative identification only. Mussels, both blank and naturally contaminated, were mixed and homogenized to provide a variety of PSP toxin mixtures and concentration levels. The same procedure was followed with clams, oysters, and scallops. Twenty-one test samples in total were sent to 21 collaborators who agreed to participate in the study. Results were obtained from 18 laboratories representing 14 different countries. It is recommended that the method be adopted First Action by AOAC INTERNATIONAL.

Proficiency studies on the determination of paralytic shellfish poisoning toxins in shellfish

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 method in the European Union is the mouse bioassay, but alternative methods including the liquid chromatography methodology are preferred for ethical reasons. Analyses of suspected shellfish batches revealed, however, unacceptable differences in results reported by a small group of Dutch laboratories all using liquid chromatography methods with precolumn derivatization, followed by fluorescence detection. Therefore, a series of proficiency studies were undertaken among these laboratories. In the first three studies, participants were more or less allowed their own choice of method execution details. This approach yielded unsatisfactory results. A fourth study was then initiated in which a standardized method was mandatory. Two types of test material were used in the fourth study: lyophilized Cardium tuberculatum material containing saxitoxin (STX) and decarbamoyl-saxitoxin (dc-STX), and lyophilized mussel material containing dc-STX. The latter material was investigated in an interlaboratory study involving 15 participants and was considered as the reference material. Among the four laboratories, coefficients of variation (ANOVA) for C. tuberculatum material were 10% (n = 11) and 9% (n = 12) for STX and dc-STX, respectively, and for the reference material was 8% (n = 12) for dc-STX. The joint efforts showed that variability in analysis results between laboratories that all apply more or less the same method can be drastically improved if the methodology is rigorously standardized.

Determination of 4-hexylresorcinol in shrimp by liquid chromatography with fluorescence detection

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 1.5-2.5 mg/kg was 81.6 +/- 0.8%. The relative standard deviation in the working range was 2.1%. Limits of quantitation and detection were 6.59 and 1.98 ng/mL extract, respectively, corresponding to 0.26 and 0.08 mg/kg in shrimp.

Liquid chromatographic determination of histamine in fish, sauerkraut, and wine: interlaboratory study

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 (pH 3.0)--acetonitrile (875 + 125, v/v) as mobile phase, histamine was measured fluorometrically (excitation, 340 nm; emission, 455 nm) in samples and standards after postcolumn derivatization with o-phthaldialdehyde (OPA). Fourteen samples (including 6 blind duplicates and 1 split level) containing histamine at about 10-400 mg/kg or mg/L were analyzed singly according to the proposed procedure by 11 laboratories. Results from one participant were excluded from statistical analysis. For all samples analyzed, repeatability relative standard deviations varied from 2.1 to 5.6%, and reproducibility relative standard deviations ranged from 2.2 to 7.1%. Averaged recoveries of histamine for this concentration range varied from 94 to 100%.

A terminating reagent for the peroxidase-labelled enzyme immunoassay

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.

Solvent-generated ion-exchange systems with anionic surfactants for rapid separations of amino acids

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 of amino acids can be influenced by changing the temperature, the nature of the hydrophobic support, the pH and the nature and concentration of the anionic detergent, organic constituent and counter ion in the eluent. In many instances this solvent-generated (dynamic) ion-exchange chromatography shows a greater selectivity than conventional ion-exchange systems towards amino acids. The results obtained so far indicate that a complete separation of the 19 protein amino acids by applying solvent gradients or/and multi-column system is possible within 30 min.