Abstract A convenient and accurate method is presented for the determination of sorbic, dehydroacetic, and propionic acids in cheese by liquid chromatography and gas chromatography. The volatile acids are separated from cheese by steam distillation. Sorbic and dehydroacetic acids are determined by liquid chromatography using a reverse phase column and a mobile phase mixture (30 + 70) of methanol and 0.02M phosphate buffer, pH 7.2, containing 0.005M tetrabutyl ammonium. The effluent is monitored at 235 nm. After the distillate is acidified with formic acid, propionic acid is determined by gas chromatography with a flame ionization detector using a Porapak QS column. Average recoveries of sorbic, dehydroacetic, and propionic acids ranged from 92.3 to 99.5%. By this method, the acids could be determined without using organic solvent during extraction and cleanup.

An analytical system for the simultaneous determination of residual oxytetracycline, tetracycline, chlortetracycline, doxycycline, methacycline, demethylchlortetracycline and minocycline in honey has been established by a combination of simple thin-layer chromatographic (TLC) and precise high-performance liquid chromatographic (HPLC) methods. In this system, screening by TLC can detect tetracyclines (TCs) at a level of 0.1 ppm in honey without the need for special equipment, and the quantitative method by HPLC can determine TCs with good recovery (83.7–99.6%) and coefficient variation (0.9–4.3%).

ABSTRACTDuplicate portions of daily meals consumed by 21 housewives were collected for 3 consecutive days at Nagoya‐city and Asuke‐cho in Japan. The 24 h duplicate meals were analyzed for chloroform. Thirty grams of samples, 170 mL of water, 1 mL of phosphoric acid, and 0.5 g of ascorbic acid were mixed in a distillation flask which was heated under nitrogen gas flow. The purged chloroform was trapped in n‐pentane cooled at 0° C. The pentane solution was analyzed to by electron capture gas chromatography. Confirmation of chloroform was carried out by GC‐MS.The concentration of chloroform in each of the 24‐h duplicate meals were in the range of 1.7 to 45.8 ppb and the average concentration was 13.7± 9.6 ppb.Daily dietary intake of chloroform by housewives were in the range of 7.5 to 51.9 μg and the mean intake was 26.4 ± 11.8 μg.

Analytical methods for eight tetracyclines (TCs) were established using silica gel high-performance thin-layer chromatography (HPTLC), reversed-phase thin-layer chromatography (RP-TLC) and high-performance liquid chromatography (HPLC). Good separations of eight TCs were obtained using chloroform-methanol-5% disodium ethylenediaminetetraacetate solution (65:20:5) (lower layer) and methanol acetonitrile 0.5 M oxalic acid solution (1:1:4) (pH 3.0) on silica gel HPTLC and C8 TLC plates, respectively. A combination of HPTLC and RP-TLC made possible the identification of the eight TCs. Each calibration graph was linear between 0.1 and 1.0 microgram using UV densitometry except for rolitetracycline. For detection reagents, the diazonium salts including Fast Violet B gave variously coloured spots with the eight TCs and good sensitivities were obtained except with minocycline. In HPLC, the simultaneous analysis of the eight TCs on a C8 column was possible using methanol-acetonitrile-0.01 M oxalic acid solution (1:1.5:7) adjusted to pH 3.0 as the mobile phase. A linear relationship was obtained between 1.0 and 10 ng using the usual sample preparation except for rolitetracycline. The direct determination of rolitetracycline was possible using tetrahydrofuran, dimethyl sulphoxide and the mobile phase as solvents for preparation of the sample. For the determination of residual rolitetracycline, it was effective to measure the amount of rolitetracycline as tetracycline by HPLC, HPTLC and RP-TLC after conversion of rolitetracycline to tetracycline by incubating for 5 min in methanol at 50 degrees C.

A simple, rapid and precise analytical method for tetracycline (TC) residues in the liver of slaughtered animals has been established. The recoveries of oxytetracycline (OTC), TC, chlortetracycline (CTC) and doxycycline (DC) from beef liver spiked at the level of 1.0 ppm were 87.7, 87.5, 79.6 and 67.5% with coefficients of variations of 1.01–2.87%. Detection limits in beef liver were 0.05 and 0.1 ppm for OTC and TC and for CTC and DC, respectively. It is also possible to apply this method to the analysis of residual TCs in various foods with the same recovery, accuracy and detection limits as in the case of beef liver.

A clean-up method for the removal of organochlorine interference prior to the determination of chlordane by gas chromatography was studied. Chlordane, polychlorinated biphenyls and organochlorine pesticides were treated with a cold mixture (5 ml) of concentrated sulphuric acid and fuming nitric acid (1 + 1 V/V) at 0 °C for 15 min. The product was mixed with cold water (100 ml) and submitted to continuous distillation (cyclic steam extraction) for 90 min to extract chlordane into 3 ml of heptane. The extract was cleaned up by reduction with iron in acetic acid and the chlordane was determined by gas chromatography with electron capture detection. The acid treatment removed polychlorinated biphenyls and organochlorine pesticides, which gave peaks overlapping those of chlordane. The method was applied to the determination of chlordane in human blood. The blood sample was haemolysed with water and extracted with acetone-hexane (1 + 9 V/V), and the extract was treated by the above method. The recovery of chlordane added to human blood was above 88%.

Semi-quantitative screening methods for tetracyclines using detection on silica gel high-performance thin-layer chromatographic (HPTLC) and reversed-phase (RP) TLC plates are described. Good results with respect to the background and detection limits were obtained using detection with 1% Fast Violet B Salt solution followed by heating on the silica gel HPTLC plate and with 0.5% Fast Violet B Salt solution and pyridine without heating on the RP-TLC plate. The above detection method and UV densitometry using the silica gel HPTLC plate were compared with respect to recovery from spiked samples after Sep-Pak C18 extraction. For the measurement of impurities in tetracycline drugs, both methods were compared using the RP-TLC plate and similar results were obtained.

An isocratic high-performance liquid chromatographic method for the determination of tetracyclines is described using a mobile phase containing oxalic acid and C8- and C18-modified silica gel columns. For good separations of tetracyclines, oxalic acid concentrations of above 0.01 and 0.2 M respectively for parent tetracyclines (group I) and impurities in tetracycline (group II) are required. The optimum pH of the aqueous oxalic acids solution in the mobile phase is 2.0. The combinations of the C8-modified silica gel column with methanol-acetonitrile-0.01 M aqueous oxalic acid solution pH 2.0 (1:1.5:5) and the C18-modified silica gel column with methanol-acetonitrile-0.2 M aqueous oxalic acid solution pH 2.0(1:1:3.5) gave satisfactory results for groups I and II, respectively.

The common tetracyclines (TCs) in fish tissues which are used in agriculture, tetracycline, oxytetracycline, and chlortetracycline, are analysed using an ODS-cartridge extraction device, and high performance thin layer chromatography (HPTLC) followed by densitometry. Fish tissue is blended in 0.1 M disodium ethylenediaminetetraacetate (di-Na EDTA)-McIlvaine buffer (pH 4.0) and centrifuged. The supernatant is adsorbed on the pretreated ODS-cartridge with 0.2 M di-Na EDTA aqueous solution, the cartrige is washed with water, and TCs are eluted with ethanol. The concentrated residue is spotted on a silica gel HPTLC plate predeveloped with saturated di-Na EDTA aqueous solution. The plate is then developed with chloroform-methanol-5% di-Na EDTA aqueous solution (65 : 20 : 5, lower layer). The amounts of TCs present on the developed plate are determined by ultraviolet absorption densitometry. Recoveries of TCs from fish samples fortified at level of 1 ppm are 60.2-78.6%.

A technique for determination of tetracyclines using silica gel high-performance thin-layer chromatography followed by densitometry is established. A predevelopment with saturated disodium ethylenediaminetetraacetate aqueous solution and the complementary use of three solvent systems enable a reliable identification. Direct determination using densitometry without further treatment with any reagents is of high sensitivity and reproducibility. A change of measurement wavelength enables the determination of overlapping spots.