Determination of dimetridazole, ronidazole and their common metabolite in poultry muscle and eggs by high performance liquid chromatography with UV detection and confirmatory analysis by atmospheric pressure chemical ionisation mass spectrometry.

A method was developed for the determination of the nitroimidazole compounds dimetridazole (DMZ) and ronidazole (RNZ) and their common metabolite, 2-hydroxymethyl-1-methyl-5-nitroimidazole (2-OH-M). Extracts obtained from a clean-up process using strong cation exchange (SCX) solid phase extraction (SPE) can be analysed either by high performance liquid chromatography with UV detection (HPLC-UV) or by high performance liquid chromatography with atmospheric pressure chemical ionisation mass spectrometry (HPLC-APCI-MS) as a confirmatory method. Up to 20 samples can be extracted in approximately 4 h. The HPLC-UV analysis had a limit of detection of 0.5 microgram kg-1. Validation in chicken muscle fortified at a concentration of 5 micrograms kg-1 gave recoveries of 75% DMZ, 77% RNZ and 81% 2-OH-M with RSDs of 16.4, 11.3 and 14.0%, respectively (n = 17). Validation in egg fortified at the same concentration gave recoveries of 77% DMZ, 80% RNZ and 80% 2-OH-M, with RSDs of 14.9, 22.0 and 18.2%, respectively (n = 18). The limit of detection of the HPLC-APCI-MS method was 0.1 microgram kg-1 for DMZ and RNZ and 0.5 microgram kg-1 for 2-OH-M. This method gave mean recoveries in fortified egg samples of 65% DMZ, 87% RNZ and 75% 2-OH-M with RSDs of 22, 11 and 14%, respectively (n = 10). The ratios of the peak areas of the molecular ion and a fragment ion were monitored as added confirmation of the presence of the analyte. Both the HPLC-UV screening procedure and the HPLC-APCI-MS confirmatory method have subsequently been used for the analysis of several hundred samples as part of UK surveillance programmes.

Survey of baked goods for propionic acid and propionates.

One hundred and thirty samples comprising bread (64), hamburger buns (33), pittas (16), cakes (9) and Christmas puddings (8) from various retail outlets in the UK, have been analysed for the preservative propionic acid. Only one sample of bread, two samples of hamburger buns and three samples of pitta contained propionic acid in excess of 1000 mg/kg (range 1110-2625 mg/kg). The three samples of pitta exceeded 2000 mg/kg of propionic acid, which is the maximum amount permitted for these products under a recently adopted European Union directive.

Characterization of the principal colouring components of annatto using high performance liquid chromatography with photodiode-array detection.

The principal colouring components of the natural food colouring material annatto, the 9'-cis- and all-trans- isomers of bixin and norbixin, have been prepared in pure form. A reverse-phase HPLC method utilizing photodiode-array detection has been developed to enable their chromatographic and spectroscopic characterization. One minor component, a di-cis-isomer of norbixin has also been identified and characterized.

A rapid capillary gas chromatographic method for the determination of propionic acid and propionates in bread and bread products.

A rapid method for the determination of propionic acid and propionates in bread and bread products is reported. The method employs solvent extraction, filtration and quantification by capillary gas chromatography using an internal standard. The limit of determination was 10 mg kg-1 propionic acid. The mean recovery rates for spiked bread samples were 108% at approximately 1,000 mg kg-1 (range of 106-110%, coefficient of variation 1.1%), 97% at approximately 2,000 mg kg-1 (range 96-98%, coefficient of variation 0.7%) and 98% at approximately 3,000 mg kg-1 (range of 97-100% and coefficient of variation of 1.1%). The method offers improved sensitivity, precision, chromatographic resolution and a wider sample analyte concentration range over a previously reported packed-column gas chromatographic method and has been applied to the analysis of bread, rolls, pitta breads and hamburger buns.