Simultaneous determination of vitamin E homologs in chicken meat by liquid chromatography with fluorescence detection

A simple and reliable method for the simultaneous determination of all eight homologs of Vitamin E in chicken meat is described. All analytes, including the internal standard (alpha-tocopherol acetate), were eluted within 35 min and detected using their native fluorescence (295 nm excitation and 330 nm emission). Chromatography using hexane based eluent on a normal phase silica column included an initial column conditioning step to prevent irreversible adsorption of tocopherols and tocotrienols on silica. Lowest detectable levels of alpha-tocopherol, gamma-tocopherol, alpha-tocotrienol, beta-tocotrienol, gamma-tocotrienol and delta-tocotrienol were 0.73, 0.86, 1.0, 1.2, 1.7 and 1.3 ng, respectively.     

Rapid determination of succinylcholine in human plasma by high-performance liquid chromatography with fluorescence detection.

A high-performance liquid chromatographic method with fluorometric detection has been developed for the determination of succinylcholine in human plasma. Succinylcholine shows fluorescence at 282 nm with an excitation at 257 nm. The assay is sensitive, reproducible and linear for concentrations ranging from 100 ng/ml to 100 micrograms/ml of succinylcholine. In a pilot study the plasma concentration-time curve showed a triphasic elimination, with half-lives of 0.4, 1.2 and 8 min, respectively. In a clinical setting, drugs commonly administered during anaesthesia did not interfere with the assay. This method provides a simple and time-saving alternative to existing methods.     

Determination of pyrimethamine in animal tissue and egg by liquid chromatography with fluorescence detection

A sensitive and selective liquid chromatographic (LC) assay was developed to determine the concentration of pyrimethamine in animal tissue and egg by fluorescent derivative. Animal samples were extracted with acetonitrile, centrifuged, and purified by hexane. Fluorescent derivatization was performed by reacting pyrimethamine with chloroacetaldehyde and subjected to LC with fluorescence detection (excitation wavelength 300 nm, emission wavelength 420 nm). The limit of detection was 10 ng/g (10 ppb) and the standard calibration curve was linear in the range of 1-100 ppb (0.01-1 ng/10 microL). Recoveries from samples fortified at levels of 0.1 and 1 ppm (microg/g) were 61.0-77.4 and 65.5-81.2%, respectively. The method was applied to the monitoring of marketed samples. Pyrimethamine was not determined in any of the 70 samples: 20 swine muscle; 20 chicken muscle; 10 chicken liver; and 20 egg.     

Rapid determination of the neurotoxin lolitrem B in perennial ryegrass by high-performance liquid chromatography with fluorescence detection

A rapid, sensitive and quantitative method, based on high-performance liquid chromatography with fluorescence detection, is described for the determination of the neurotoxin lolitrem B in perennial ryegrass, in the ppm to sub-ppm range. The method, which requires a minimal clean-up step prior to chromatographic analysis, is suitable for the routine analysis of large numbers of ryegrass samples, and is currently being used in New Zealand to study the livestock disorder ryegrass staggers. The method is suitable for determining lolitrem B in the whole plant, the seed, and dissected plant components.     

Simultaneous determination of thiols and disulfides by high-performance liquid chromatography with fluorescence detection

The proposed simultaneous determination of thiols and disulfides requires 4- (aminosulfonyl)- 7-fluor-2,1,3,-benzoxadiazole (ABD-F) as the pre-column derivatization reagent for thiols and ammonium 7-fluoro-2,1,3,-benzoxadiazole-4-sulfonate (SBD-F) for disulfides followed by chromatography. The thiols and disulfides in solution are treated with ABD-F at 60°C for 5 min in pH 9.3 borate buffer containing 1 nM disodium-EDTA. After removal of excess of ABD-F with ethyl acetate, the remaining disulfides in the aqueous phase are treated with SBD-F at 60°C for 20 min in the presence of tri-n-butylphosphine, a reducing agent. The ABD-thiols and SBD-thiols thus produced are separated by reversed-phase chromatography and detected by fluorimetry (380- nm excitation, 510 - nm emission). SBD-cystein, SBD-homocystein, ABD-homocysteine, ABD-cysteine, SBD-glu- tathione, ABD-homocystein, SBD-N-acetylcystein, ABD-glutatione and ABD-N-acetylcysteine are well separated by linear gradient elution from 0.15 M H₃PO₄/CH₃CN (96:4) to 0.15 M H₃PO₄/CH₃CN (85:15) over 30 min followed by isocratic elution with 0.15 M H₃PO₄/CH₃CN (85:15) fro 10 min. The detection limits for the derivatives are in the range 0.09–0.9 pmol. When the method was applied to the determination of thiols and disulfides in rat tissues, cystein (0.75 μmol g^-1) and cystine (0.62 μmol g^-1) were obtained in kidney and reduced glutathione (1.4–3.4 μmol g^-1) was observed in liver, spleen, heart and testicle.     

Multiresidue determination of eleven quinolones in milk by liquid chromatography with fluorescence detection

A liquid chromatographic method with fluorescence detection was developed for simultaneous determination of norfloxacin, ofloxacin, ciprofloxacin, pefloxacin, lomefloxacin, danofloxacin, enrofloxacin, sarafloxacin, difloxacin, oxolinic acid, and flumequine in milk The samples were extracted with 10% trichloroacetic acid/acetonitrile (9 + 1, v/v) and cleaned by Strata-X reversed-phase solid-phase extraction cartridges. The 11 quinolones were separated on a reversed-phase C18 column (Hypersil BDS-C18) with mobile phase gradient elution and detected with fluorescence by means of a wavelength program. The recoveries for milk fortified with the 11 quinolones at 3 levels were 69-88% with acceptable relative standard deviations of <9% (intraday) and <14% (interday). The limits of detection were 23 microg/L for enrofloxacin, and 1-9 microg/L for the other 10 quinolones.     

Improved determination of sulpiride in plasma by ion-pair liquid chromatography with fluorescence detection

A specific and sensitive high-performance liquid chromatographic method for the measurement of sulpiride in plasma is described. The internal standard used was veralipride, a structurally related substituted benzamide. A fluorescence detector with maximum excitation at 300 nm and maximum emission at 365 nm was used for quantitation. After an alkaline extraction procedure, the benzamides were separated on a 5-micron ODS column using a large organic counter ion in the mobile phase. The detector response was linear from 10 to 1000 ng/ml and the detection limit was 10 ng/ml, which is sensitive enough for pharmacokinetic studies. The suitability of the method for the analysis of biological samples was tested by studying the variation with time of plasma concentrations of sulpiride in normal human volunteers after a single therapeutic 200-mg oral dose of three different formulations of sulpiride.     

Rapid determination of nitrite in foods in acidic conditions by high‐performance liquid chromatography with fluorescence detection

In this study, a simple, rapid, and sensitive method for the determination of nitrite (NO₂^?) in food samples by high‐performance liquid chromatography with fluorescence detection in acidic conditions had been developed. The derivatization of the nitrite with 2,3‐diaminonaphthalene was performed in acidic conditions to yield the highly fluorescent 2,3‐naphthotriazole, which was directly analyzed by high‐performance liquid chromatography with fluorescence detection without adjusting the solution to alkaline. The analysis column was reversed‐phase C₈ column. A constant flow rate of 1.0 mL/min was employed using water/acetonitrile as the mobile phase in isocratic mode (70:30, v/v). Fluorescence was monitored with excitation at 375 nm and emission at 415 nm. The standard calibration curves were linear for nitrite in different matrixes in the concentration range of 0–100 μg/L, and the correlation coefficients ranged from 0.9978 to 0.9998. The limits of detection and quantification were in the ranges of 0.012–0.060 and 0.040–0.20 mg/kg, respectively. The recoveries of nitrite from samples spiked at three different concentrations were 74.0–113.2%, and the relative standard deviations of the recovery results (n = 6) were 1.67–10.8%. The proposed method has good repeatability and is very sensitive and simple. It has been successfully used to determine nitrite in foods.     

Rapid determination of citrinin in corn by fluorescence liquid chromatography and enzyme immunoassay

A rapid assay procedure was developed for mycotoxin citrinin in corn using liquid-liquid extraction (LLE) cartridges. Ground corn was extracted with methylene chloride and 0.5 N phosphoric acid. The extract was added to an LLE cartridge containing a diatomaceous-earth adsorbant, previously impregnated with sodium bicarbonate solution. After aspiration to dryness, the cartridge was eluted with methanol-water (4 + 1), and aliquots were taken for quantitation by reversed-phase liquid chromatography with fluorescence detection. Recoveries of citrinin added to ground corn at 200-1600 ng/g ranged from 71.2 to 86.3%, with coefficients of variation between 4.1 and 10.6%. An indirect enzyme immunoassay was also evaluated, using sodium carbonate solution for extraction. Recoveries of citrinin added to ground corn at 200-2000 ng/g ranged from 53.2 to 67.2%, but the coefficients of variation varied between 18.4 and 51.5%. The LLE cartridge procedure offers the advantages of low solvent consumption and speed, and is amenable to automation.     

Quantitative determination of Closantel residues in milk by high-performance liquid chromatography with fluorescence detection.

A HPLC method with fluorescence detection for quantitative determination of Closantel residues in milk has been developed and validated. The proposed cleaning procedure with acetonitrile and acetone extraction, and solid-phase clean-up with Florisil enables concentrations of Closantel below 50 micrograms/l to be determined. The method was shown to be sufficient, precise, accurate, selective and rugged. The method was applied in the regular monitoring of Closantel residues in milk and of the pharmacokinetic behavior of Closantel in sheep.     

Simultaneous determination of airborne carbamates in workplace by high performance liquid chromatography with fluorescence detection

A high performance liquid chromatography with fluorescence (HPLC-F) detector was examined to simultaneous determination of airborne carbamates in the workplace of manufactory. The OVS-2 air sampling tube filled with glass fiber filter or quartz fiber and combined filter/XAD-2 were evaluated to collect nine commonly used carbamates (Carbofuran, Isoprocarb, Methomyl, Metolcarb, Thiodicarb, Carbaryl, Oxamyl, Methiocarb, and Prpoxur) from the air of manufactory in high humidity country. After being extracted with acetonitrile from sampling tubes, the carbamates were determined by high performance liquid chromatography with fluorescence detection posterior to on-line derivatization. The collection of carbamates and the recovery of extraction from glass wool fiber in several concentration levels, and from quartz filter were evaluated. The storage stability of carbamates was also tested. Results indicated that the HPLC-fluorescence method offers satisfactory resolution and sensitivity in carbamate analysis. With the glass fiber filter and combined filter/XAD-2, the Carbofuran, Isoprocarb, Methomyl, Metolcarb, and Thiodicarb were stable for a 28-day storage test, Carbaryl and Oxamyl for 14 days, and Methiocarb and Prpoxur for 7 days. All of these pesticides were with detection limit of 3 μg m⁻³. It is suited for environmental monitoring. The airborne carbamates in different areas of the manufactory were measured.     

Sensitive determination of josamycin and rokitamycin in plasma by high-performance liquid chromatography with fluorescence detection.

Rokitamycin and josamycin were successfully derivatized with dansylhydrazine in 20 min at 60 degrees C. Rokitamycin and josamycin levels were determined in plasma after ion-pair extraction into hexane-isoamyl alcohol with lauryl sulphate and precolumn derivatization. Resolution was obtained by liquid chromatography with fluorescence detection (352/537 nm) in 12 min. The limit of detection was 20 ng/ml macrolide starting from 1 ml of plasma, and linearity was demonstrated between 50 and 400 ng/ml. Inter-run coefficients of variation were 10.2% at 100 ng/ml and 9.1% at 300 ng/ml. The system was reliably used for pharmacokinetic studies in plasma.     

Rapid determination of glyphosate in cereal samples by means of pre-column derivatisation with 9-fluorenylmethyl chloroformate and coupled-column liquid chromatography with fluorescence detection

A rapid procedure for the determination of glyphosate in cereals has been developed. Convenient sample pretreatment is carried out by (i) a overnight standing extraction of 1.0 g homogenized sample with 20 ml of water, (ii) centrifugation of the samples, (iii) a passing of 2.5 ml of the clear layer through a 100 mg C18 solid-phase extraction cartridge and (iv) collection of the last 1.5 ml of the eluent into a calibrated tube. For the instrumental analysis, the efficient approach developed earlier for environmental water samples [J.V. Sancho, F. Hernández, F.J. LUpez, E.A. Hogendoorn, E. Dijkman, P. van Zoonen, J. Chromatogr. A, 737 (1996) 75] was successfully adopted for the determination of glyphosate in the obtained cereal extracts. The procedure includes a 15 min derivatisation step of the analyte with 9-fluorenylmethyl chloroformate and a 16 times dilution step prior to instrumental analysis employing coupled-column LC with fluorescence detection. The developed procedure has a sample throughput of more than 25 samples per day and a limit of quantification of 0.5 mg/kg. The method was validated by analyzing freshly spiked cereal samples and samples with aged residues at levels between 1.0 and 10 mg/kg. The overall recovery of the freshly spiked samples was 86% (n = 10) with a repeatability of 6.5% and a reproducibility of 9.5%. For samples with aged residues recoveries performed at different time intervals (range 80-150 days) did not differ significantly; the overall recovery (n = 10) was 74% with a repeatability and reproducibility of 14 and 20%, respectively.     

Trace determination of some phenolic growth-promoting hormones in meat by high-performance liquid chromatography with voltammetric detection

Summary The oxidative voltammetric behaviour of the growth-promoting hormones oestriol, 17-oestradiol, oestrone, diethylstilboestrol, dienoestrol and hexoestrol has been investigated at the glassy carbon electrode. The voltammetric responses obtained for these compounds in acid media were found to be the most suitable for analytical purposes. Based on this study, a sensitive, rapid and convenient method has been developed for their determination by high-performance liquid chromatography utilising voltammetric detection. This method could determine oestrone and hexoestrol down to 1–2 ng g^–1 and 17-oestradiol, diethylstilboestrol and dienoestrol down to 2–3 ng g^–1 in meat, but was unable to determine oestriol at this level due to the presence of co-extracted interferences.

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Spurenbestimmung einiger phenolischer wachstumsfördernder Hormone in Fleisch durch HPLC mit voltammetrischer Detektion

Zusammenfassung Das oxidative voltammetrische Verhalten der wachstumsfördernden Hormone Östriol, 17-Östradiol, Östron, Diethylstilböstrol, Dienöstrol und Hexöstrol wurde an der glasigen Kohlenstoffelektrode untersucht und als für analytische Zwecke sehr geeignet befunden. Ein schnelles und empfindliches Verfahren wurde ausgearbeitet, das auf HPLC-Trennung mit voltammetrischer Detektion beruht. Östron und Hexöstrol können bis herab zu 1–2 ng g^–1 und 17 -Östradiol, Diethylstilböstrol sowie Dienöstrol bis zu 2–3 ng g^–1 in Fleisch erfaßt werden. Östriol kann jedoch in diesem Konzentrationsbereich nicht bestimmt werden, da mitextrahierte Substanzen stören.

     

Multiresidue determination of fluoroquinolones in milk by column liquid chromatography with fluorescence and ultraviolet absorbance detection

Column liquid chromatography with fluorescence (FLD) and UV-diode array detection (UV-DAD) was used for the simultaneous determination of ciprofloxacin (CIPRO), enrofloxacin (ENRO), marbofloxacin (MARBO), danofloxacin (DANO) and sarafloxacin (SARA) residues in milk, using norfloxacin (NOR) as internal standard. Two solid-phase extraction (SPE) cartridges, were evaluated for sample clean-up and preconcentration, Strata X, based on a modified styrene-divinylbenzene polymer, and Strata Screen A, a mixed anion exchanger/C8 reversed-phase sorbent. The fluoroquinolones (FQs) were separated on a polar endcapped column (AQUA C18). The recoveries for raw milk spiked with the antibiotics at three concentrations close to the maximum residue limit (MRL), were 80-103% for ENRO, CIPRO and DANO, with relative standard deviations (R.S.D.) lower than 6.6%. SARA recoveries were 70% (R.S.D. = 7%) and values in the order of 95% (R.S.D. = 1.5%) were obtained for MARBO at the MRL level. The quantification limits ranged from 2.4 to l0 ng ml(-1) and are below the MRL established for these drugs by the European Union. The method was successfully applied to the analysis of ENRO and its metabolite CIPRO in an incurred milk sample.