ABSTRACT A simple and fast spectrofluorimetric method for determination of ciprofloxacin based on its quenching effect on the fluorescence intensity of colloidal water soluble TGA caped, Mn doped ZnS quantum dots (QDs) has been described. The QDs having characteristic fluorescence spectra with maximum excitation at 315 nm followed by an emission peak at 632 nm were characterized using Energy Dispersive X-Ray and X-ray Diffraction techniques. The effect of various parameters such as concentration of QDs, time, pH, common excipients and metal ions on the quenching phenomenon was investigated. Fluorescence quenching was found to be maximum with 10 µg mL-1 of QDs at pH 8 and fluorescence intensity was observed to be constant upto 45 min. The Stern-Volmer calibration plot of F0/F as a function of ciprofloxacin concentration was found to be linear in the range of 0.5-10 µg mL-1 with r² = 0.993. Under optimal experimental conditions, the method was found to be interference free. The percent relative standard deviation of the proposed method, calculated against method blank, was found to be 1.10%. The limit of detection (LOD) and the limit of quantitation (LOQ) for ciprofloxacin (signal to noise ratio 3:1 for LOD and 10:1 for LOQ) were calculated to be 0.15 and 0.50 μg mL-1 respectively. Average percent recoveries (±SD) obtained for spiked commercial formulations; ciprol and ciproquine, and serum and urine samples were found to be in the range of 92.2±1.8% to 99.5±1.5%, 90.5±1.2% to 96.7±1.4% and 94.0±1.2% to 98.5±1.4% respectively. The data evidently proves the potential of the proposed sensor QDs in biological analysis.

A fast and sensitive method was developed for determination of glyphosate, using flow injection analysis. The analyte was converted to a photoactive product that shows maximum absorbance at 405 nm. Beer's law was obeyed over a range of 0.7-20μg mL-1. The limit of detection and quantification were found to be 0.20 ± 0.01 and 0.70 ± 0.02 μg mL-1 with a high sample throughput of 60 samples h-1. The investigation of interference effect shows that among the compounds studied, only aminomethyl phosphonic acid exhibits a signal enhancing effect when present in higher concentration ratio with the analyte and this can be assumed to be a limitation of the present method. The percentage recoveries and residue of glyphosate in wheat grains samples, were found in the range of 90.0 ± 0.6 % to 93.0 ± 0.6 % and 1.13 ± 0.009 μg g-1, respectively.

Propomos um método espectrofotométrico para a determinação do herbicida fenoxaprop-p-etil, usando injeção em fluxo.O fenoxaprop-p-etil foi convertido num ácido hidroxamico, na presença de hidroxilamina dihidrocloridrica em meio alcalino. O ácido hidroxâmico obtido reagiu com ferro(III) formando um complexo hidroxamato de ferro(III), vermelho. A absorbância do complexo foi medida a 500 nm em sistema de injeção em fluxo. O método apresenta linearidade entre 1,0-20,0 µg mL-1 com absortividade molar de 1,81 × 10(4) L mol-1 cm-1. O limite de detecção e o limite de quantificação encontrados foram 0,29 ± 0,1 µg mL-1 e 0,96 ± 0,1 µg mL-1 respectivamente. Médias similares de limite de detecção e limite de quantificação foram encontradas para a determinação de residuos, entre 0,35 -1 e 0,45 µg g-1 respectivamente para grãos de trigo, e 1,2 e 1,5 µg g-1 respectivamente para grãos de cevada. A velocidade de determinação foi de 90 amostras h-1. O método foi aplicado com sucesso em amostras de diferentes grãos.

A spectrophotometric method for determination of fenoxaprop-p-ethyl herbicide using flow injection system has been proposed. The fenoxaprop-p-ethyl was converted into hydroxamic acid in the presence of hydroxylamine hydrochloride in alkaline media. The hydroxamic acid produced was further reacted with iron(III) to form red color tris iron hydroxamate complex. The absorbance of the complex was measured at 500 nm using flow injection system. The method shows a linear range between 1.0-20.0 µg mL-1 with molar absorptivity of 1.81 × 10(4) L mol-1 cm-1. The limit of detection and limit of quantification were calculated and found to be 0.29 ± 0.1 µg mL-1 and 0.96 ± 0.1 µg mL-1 respectively. Similarly the average limit of detection and limit of quantification were calculated for residue determination and were found 0.35 and 0.45 µg g-1 respectively for wheat grains and 1.2 and 1.5 µg g-1 respectively for barley grains. The sample through put was 90 samples h-1. The method was successfully applied to different grain samples.