A spectrophotometric flow injection system for streptomycin determination in veterinary samples.

In this work a spectrophotometric flow injection analysis system for streptomycin determination in veterinary samples, is being proposed. The method is based on streptomycin alkaline hydrolysis that forms guanidine, followed by the reaction with Fe(II). The colored product has absorption peak at 520 nm. To evaluate and optimize the system parameters, chemometrics tools, such as factorial design, Pareto chart and Doelhert design, were used. The veterinary samples are diluted in water and introduced in the FIA system, therefore no sample preparation is required. The optimized system presented: linear range of 60 up to 1000 mg L(-1), limit of detection of 18 mg L(-1) and sampling rate of 36 readings per hour. The precision was checked and the CV for veterinary sample readings were always less than 6.5%. The accuracy was studied by comparison with chromatographic method, thus, five samples of pharmaceutical veterinary were determined by HPLC and by the proposed method, and the results are in agreement (t-test, p=0.05).

Determinação de tetraciclinas em medicamentos veterinários utilizando análise por injeção em fluxo (FIA) / Determination of tetracyclines in veterinarian medicines by flow injection analysis (FIA)

Foi desenvolvido um método de análise por injeção em fluxo (FIA) com detector de fluorescência para determinação de oxitetraciclina (OTC), doxiciclina (DC) e tetraciclina (TC) em medicamentos veterinários. O sistema FIA foi otimizado com relação ao carregador (NaOH 2,5 10-3 mol L-1) e vazão (0,5 mL min-1). Os comprimentos de onda de excitação e emissão do detector foram 420 e 530 nm, respectivamente. O método foi validado mediante avaliação dos seguintes parâmetros: faixa linear (0,02 a 0,15 mg mL-1), linearidade r(OTC) 0,9975; r(DC) 0,9903; e r(TC) 0,9913; precisão intra- e inter-ensaio (RSD < 1,0 por cento e < 3,0 por cento, respectivamente), detectabilidade (120 ng), exatidão (98 a 104 por cento) e freqüência de amostragem (50 injeções h-1). Na determinação de tetraciclinas em preparações farmacêuticas, disponíveis no comércio, foi verificada variação de 90 a 104 por cento, na quantidade nominal de princípio ativo presente no medicamento

Evaluation of flow injection analysis for determination of urea in sheep's and cow's milk.

Difficulties in measuring the urea content in sheep's milk often occur with spectral photometry due to the high protein and fat concentrations of the milk. In this study an enzymatic flow procedure (QuickChem 8000 Ion Analyser, Lachat Instruments, Milwaukee, USA) to determine the urea content in ovine and bovine milk was evaluated. Urea content is determined by the Berthelot reaction after splitting it enzymatically with urease. The free ammonia diffuses through a teflon membrane into a stream of reagent solutions. Detection takes place by means of a reaction between the ammonium ions with hypochlorite and salicylate producing a green colour, which is measured spectrometrically in a flow meter at 660 nm. By using a diffusion cell chemical deproteinisation of milk is not necessary and capacity is high. The assessed procedure exhibited high accuracy and precision and reached a sample capacity of 55 samples an hour. Storage of the milk samples for several days as well as chemical preservation with bronopol had no effect on the measurement procedure. Due to the complexity of the apparatus and the costs associated therewith, the device proves less suitable for routine diagnostics but rather serves as a reference method for the measurement of urea concentration in milk.

Detection of glucose, galactose, and lactose in milk with a microdialysis-coupled flow injection amperometric sensor.

A microdialysis-coupled flow injection amperometric Sensor (microFIAS) was used to determine glucose, galactose, and lactose in milk. The sensor is based on enzyme-catalyzed reaction in combination with the three well-established analytical techniques, namely; microdialysis sampling, flow injection analysis (FIA), and amperometric detection. With the multianalyte sensor it was possible to detect glucose and galactose by sequential injection of their corresponding oxidase enzymes: glucose oxidase and galactose oxidase, while lactose was determined by injection of a mixture of beta-galactosidase and glucose oxidase enzymes. The sensor showed a linear response between 0.05 and 10 mM for glucose, between 0.1 and 20 mM for galactose and between 0.2 and 20 mM for lactose, respectively. The relative standard deviation values of the sensor measurements for glucose, galactose, and lactose were 3-4% (n = 3). The sensor measurements for lactose content in milk were compared with a standard method with an infrared spectrophotometer.