RESUMEN
The aim of this study was to prepare molecularly imprinted polymers (MIPs) with ampicillin (AMP) and to evaluate the feasibility of these materials for being used as solid phase extraction sorbent for the selective preconcentration and determination of AMP in cow milk samples. MIPs were synthesized by bulk polymerization using methacrylic acid or methyl methacrylate as monomer and ethylene glycol dimethacrylate as cross-linker at different ratios. Characterization of the MIPs were carried out by Fourier-transform infrared spectrometry. The variables affecting the molecularly imprinted solid-phase extraction (MISPE) procedure were optimized. AMP recoveries were higher than 98%, and RSD less than 7%. A preconcentration factor of 20 was reached, which was sufficient to determine AMP at levels allowed by the EU (4µgkg-1) in cow milk. The selectivity of the AMP-MIP was evaluated in presence of other structurally related ß-lactam antibiotics (amoxicillin, oxacillin, penicillin G).
Asunto(s)
Ampicilina/análisis , Leche/química , Impresión Molecular/métodos , Polímeros/química , Amoxicilina/análisis , Animales , Glicol de Etileno/química , Estudios de Factibilidad , Metacrilatos/química , Oxacilina/análisis , Penicilina G/análisis , Reproducibilidad de los Resultados , beta-Lactamas/análisisRESUMEN
A series of molecularly imprinted polymers (MIPs) comprising reactionary sites which are complementary to macrolide antibiotic spiramycin (SPI) were synthetized by noncovalent bulk polymerization technique. MIPs were synthesized under different polymerization process and their recognition efficiency was evaluated in binding studies in comparison with non-imprinted polymers. The best MIP was morphologically characterized and equilibrium assays were carried out. The MIP was evaluated as a sorbent for extraction and preconcentration of SPI from aqueous and sheep milk samples, and an off-line MISPE method followed by high-performance liquid chromatography with UV diode-array detection was established. Good linearity were obtained for SPI in a range of 24-965µgkg-1 and the average recoveries at three spiked levels in milk samples were higher than 90% (RSD<5%). Limit of quantification was 24.1µgkg-1. Cross-reactivity studies from other macrolides with similar structure were tested. The optimum imprinted polymer showed a good selectivity and affinity for SPI, demonstrating the potential of the proposed MISPE for rapid, sensitive and effective sample pretreatment for selective determination of SPI in sheep milk samples.
Asunto(s)
Antibacterianos/análisis , Leche/química , Impresión Molecular/métodos , Polímeros/química , Espiramicina/análisis , Animales , Polímeros/síntesis química , OvinosRESUMEN
The paper describes a new and selective analytical sample treatment for quantitative extraction and preconcentration of erythromycin in presence of other macrolide antibiotics in sheep milk samples. The methodology is based on the use of a molecular imprinted polymer (MIP) employed as solid phase extraction sorbent (MISPE). The synthesized material by bulk polymerization using erythromycin (ERY) as template was evaluated as solid phase extraction sorbent, in a novel sample treatment technique that can be coupled to high-performance liquid chromatography with diode-array detector (HPLC-DAD). MIP selectivity was studied for other macrolide antibiotics with similar structures, such as tylosin (TYL), spiramycin (SPI), josamycin (JOS), roxithromycin (ROX) and ivermectin (IVER) getting recoveries for these interferents lower than 35%, for all cases except for ROX, which recoveries were around 85%. The variables affecting the molecularly imprinted solid-phase extraction (MISPE) procedure were optimized to select the best conditions of selectivity and sensitivity to determine ERY at concentration levels established by EU legislation in sheep milk. Under the selected experimental conditions, quantification limit was 24.1 µg kg(-1). Recoveries were higher than 98%, with RSDs between 0.7% and 2%. The proposed MISPE-HPLC method was validated and successfully applied to ERY analysis in sheep milk samples.
Asunto(s)
Residuos de Medicamentos/análisis , Eritromicina/análisis , Análisis de los Alimentos/métodos , Leche/química , Animales , Antibacterianos/análisis , Cromatografía Líquida de Alta Presión , Polímeros/química , Oveja Doméstica , Extracción en Fase SólidaRESUMEN
The presence of ß-lactam residues in foodstuffs constitutes a potential risk to the human health and undesirable effects on consumers, and nowadays these antibiotic residues are also recognised as an emerging environmental problem. In addition, these are of great concern to prestigious Manchego cheese processors (Central Spain denomination of origin) because they reduce the curdling of milk and cause improper cheese ripening, which consequently lead to an important loss of monetary income. This work describes the development of a sensitive and reliable method using liquid chromatography with UV-diode array detection (LC-DAD) for simultaneous determination of the ß-lactam antibiotics, ampicillin (AMP), benzylpenicillin (PEG), cephalexin (CFX), cefazolin (CFL), cefoperazone (CFP), cloxacillin (CLO), dicloxacillin (DCL), oxacillin (OXA) and phenoxymethylpenicillin (PEV), in Manchega ewe milk. The column, mobile phase, temperature and flow rate were optimised to provide the best resolution of these analytes. The extraction method of the antibiotic residues involves the deproteinisation of the milk sample using acetonitrile and centrifugation followed by a solid-phase extraction (SPE) clean-up. The recoveries for the studied ß-lactams ranged from 79% to 96% with relative standard deviations between 0.5% and 4.9%. The limits of quantification (LOQs) for all these compounds were in the range of 3.4-8.6µgkg(-1), which are lower than the maximum residue limits (MRLs) established by the European Union for the studied ß-lactams in milk, making the method suitable for performing routine analyses. The proposed multi-residue LC-UV-diode array detection (LC-DAD) method is a powerful and popular alternative for the determination and confirmation of antibiotic residues in small milk industries and is the first one capable of determining nine ß-lactam antibiotics in samples of Manchega ewe milk.
Asunto(s)
Antibacterianos/análisis , Cromatografía Líquida de Alta Presión/métodos , Contaminación de Alimentos/análisis , Leche/química , beta-Lactamas/análisis , Animales , Cromatografía Líquida de Alta Presión/instrumentaciónRESUMEN
This paper reports the synthesis and testing of a molecularly imprinted polymer membrane for digoxin analysis. Digoxin-specific bulk polymer was obtained by the UV initiated co-polymerisation of methacrylic acid and ethylene glycol dimethacrylate in acetonitrile as porogen. After extracting the template analyte, the ground polymer particles were mixed with plasticizer polyvinyl chloride to form a MIP membrane. A reference polymer membrane was prepared from the same mixture of monomers but with no template. The resultant membrane morphologies were examined by scanning electron microscopy. The imprinted membrane was tested as the recognition element in a digoxin-sensitive fluorescence sensor; sensor response was measured using standard solutions of digoxin at concentrations of up to 4x10(-3) mg L(-1). The detection limit was 3.17x10(-5) mg L(-1). Within- and between-day relative standard deviations RSD (n=5) were in the range 4.5-5.5% and 5.5-6.5% respectively for 0 and 1x10(-3) mg L(-1) digoxin concentrations. A selectivity study showed that compounds of similar structure to digoxin did not significantly interfere with detection for interferent concentrations at 10, 30 and 100 times higher than the digoxin concentration. This simply manufactured MIP membrane showed good recognition characteristics, a high affinity for digoxin, and provided satisfactory results in analyses of this analyte in human serum.
Asunto(s)
Técnicas de Química Analítica/instrumentación , Digoxina/sangre , Membranas Artificiales , Impresión Molecular , Fenómenos Ópticos , Polímeros/química , Adsorción , Calibración , Codeína/química , Digoxina/química , Fluorescencia , Heroína/química , Humanos , Sensibilidad y EspecificidadRESUMEN
This work describes the development of a competitive flow-through FIA assay for digoxin using a molecularly imprinted polymer (MIP) as the recognition phase. In previous work, a number of non-covalent imprinted polymers were synthesised by "bulk" polymerisation. The digoxin binding and elution characteristics of these MIPs were then evaluated to obtain a highly selective material for integration into a sensor. The optimum MIP was synthesised by photo-initiated polymerisation of a mixture containing digoxin, MAA, EDGMA and AIBN in acetonitrile. The bulk polymer was ground and sieved and the template removed by Soxhlet extraction in MeOH/ACN. The MIP was packed into a flow cell and placed in a spectrofluorimeter to integrate the reaction and detection systems. The physical and chemical variables involved in digoxin determination by the sensor (nature and concentration of solution, flow rates, etc.) were optimised. Binding with the non-imprinted polymer (NIP) was also analysed. The new fluorosensor showed high selectivity and sensitivity, a detection limit of 1.7x10(-2)microgl(-1), and high reproducibility (R.S.D. of 1.03% and 1.77% for concentrations of 1.0x10(-3) and 4.0x10(-3)mgl(-1), respectively). Selectivity was tested by determining the cross-reactivity of several compounds with structures analogous to digoxin. Under the assay conditions used, in which the potential interfering compounds were in concentrations 100 times higher than that of the analyte, no interference was recorded. The proposed fluorosensor was successfully used to determine digoxin concentration of human serum samples.
Asunto(s)
Análisis Químico de la Sangre/instrumentación , Digoxina/sangre , Análisis de Inyección de Flujo/instrumentación , Técnicas Analíticas Microfluídicas/instrumentación , Polímeros/química , Espectrometría de Fluorescencia/instrumentación , Diseño de Equipo , Análisis de Falla de Equipo , Espectrometría de Fluorescencia/métodos , Propiedades de SuperficieRESUMEN
A new rapid flow injection procedure for the simultaneous determination of nitrate, nitrite and ammonium in single flow injection analysis system is proposed. The procedure combines on-line reduction of nitrate to nitrite and oxidation of ammonium to nitrite with spectrophotometric detection of nitrite by using the Griess-Ilosvay reaction. The formed azo dye was measured at 543 nm. The influence of reagent concentration and manifold parameters were studied. Nitrite, nitrate and ammonium can be determined within the range of 0.02-1.60 microgmL(-1), 0.02-1.60 microgmL(-1) and 0.05-1.40 microgmL(-1), respectively. R.S.D. values (n=10) were 2.66; 1.41 and 3.58 for nitrate, nitrite and ammonium, respectively. This procedure allows the determination and speciation of inorganic nitrogen species in soils with a single injection in a simple way, and high sampling rate (18 h(-1)). Detection limits of 0.013, 0.046 and 0.047 microgmL(-1)were achieved for nitrate, nitrite and ammonium, respectively. In comparison with others methods, the proposed one is more simple, it uses as single chromogenic reagent less injection volume (250 mL in stead of 350 mL) and it has a higher sampling rate.
Asunto(s)
Análisis de Inyección de Flujo/instrumentación , Análisis de Inyección de Flujo/métodos , Nitratos/análisis , Nitritos/análisis , Compuestos de Amonio Cuaternario/análisis , Suelo/análisis , Espectrofotometría/métodos , Soluciones , Espectrofotometría/instrumentaciónRESUMEN
Oxazepam is the major metabolite screened in urine samples for the evidence of the use of benzodiazepine drugs. The methods currently used, however, are laborious and time consuming. This paper proposes an oxazepam detection method based on its hydrolysis and cyclization--a reaction catalysed by cerium (IV) in an ortho-phosphoric acid-containing medium--to form 2-chloro-9(10H)-acridinone, a strongly fluorescent molecule. The variables involved in the hydrolysis and cyclization stages were optimised. Oxazepam was detectable in the 5-900 ng mL(-1) range, with a detection limit of 4.15 ng mL(-1) for k=3. The method was successfully used for the determination of oxazepam in urine samples collected at different times after the oral administration of Valium and Tranxilium.
Asunto(s)
Clorazepato Dipotásico/metabolismo , Diazepam/metabolismo , Oxazepam/orina , Clorazepato Dipotásico/orina , Diazepam/orina , Humanos , Sensibilidad y Especificidad , Espectrometría de FluorescenciaRESUMEN
A rapid, simple and sensitive liquid chromatography-UV diode-array detection method was developed for the simultaneous determination of seven macrolides (erythromycin, oleandomycin, roxithromycin, josamycin, spiramycin, tylosin and ivermectin) in sheep's milk. The column, mobile phase, temperature and flow rate were optimised to provide the best resolution of these analytes. The extraction of the antibiotic residues involves the treatment of protein-free samples with a combination of concentrated sodium hydroxide and ethyl acetate. Necessary defatting is achieved by alkaline hydrolysis. The recovery of each antibiotic was between 55% and 77%, with relative standard deviations ranging from 1% to 6.5%. The limit of quantification was 72.4 microg/kg for ivermectin, 48.3 microg/kg for roxithromycin, and 24.1 microg/kg for erythromycin, oleandomycin, spiramycin, josamycin and tylosin. The procedure was successfully used in the multi-residue determination of these macrolides at levels below the maximum concentrations legally allowed in milk samples.