F. Salinas López

Determination of fluoroquinolones in urine and serum by using high performance liquid chromatography and multiemission scan fluorimetric detection.

A high performance liquid chromatography (HPLC) method has been developed for the simultaneous determination of four fluoroquinolones. The studied compounds have been enoxacin (ENO), norfloxacin (NOR), ofloxacin (OFLO) and enrofloxacin (ENRO). An isocratic elution method, using a mixture of tetrahydrofuran (8%) and phosphate buffer (pH 3.00, 30.0mM, 92%) as mobile phase, has been developed. Fluorimetric detection, exciting at 277nm, and multiemission scan (407nm for ENO, 444nm for both NOR and ENRO and 490nm for OFLO) has been used. Detection limits of 500, 14.7, 25.2 and 15.0ngmL(-1) for ENO, NOR, OFLO and ENRO, respectively, have been obtained. The proposed method has been satisfactorily applied to analyze NOR, OFLO and ENRO in human urine and serum samples.

Determination of antitubercular drugs in urine and pharmaceuticals by LC using a gradient flow combined with programmed diode array photometric detection

The simultaneous determination of the antitubercular drugs rifampicin, pyrazinamide, isoniazid and the acetylisoniazid metabolite has been accomplished by LC, using a C-18 analytical column. The assayed drugs are usually administered together in the treatment of tuberculosis. Creatinine was also included in the chromatographic determination, in order to establish the curve of excretion of the drugs in urine. The chromatographic method uses a gradient flow in three steps, in conjunction with a programmed diode array photometric detection. In a 0.02 M potassium dihydrogen phosphate pH 7.0 buffer, a 5% (v/v) content of methanol for 1 min, a 8% (v/v) content of methanol for 3.4 min, and a 75% (v/v) content of methanol for 4 min were used. At 4.5 min, the wavelength value of detection was changed from 254 to 475 nm. Creatinine, acetylisoniazid, isoniazid and pyrazinamide were eluted in the first 4.5 min and rifampicin before 8 min. The method has been satisfactorily applied to the determination of the drugs in urine samples and in pharmaceuticals. The proposed LC method is simple, and a short time, less than 8 min is necessary for compounds elution.

Resolution of the Binary Mixture of Salicylaldehyde and 4-Hydroxybenzaldehyde by using First Derivative Ratio Spectra

Abstract A new spectrophotometric method for simultaneous determination of the isomers salicylaldehyde and 4-hydroxybenzaldehyde is proposed. Binary mixtures are resolved on the basis of the first derivative of the ratio spectra obtained by dividing the amplitude the salicylaldehyde absorption spectra by a standard spectrum of 4-hydroxybenzaldehyde for (determining salicylaldehyde) and vice versa for determining 4-hydroxybenzaldehyde - The method compares favorably with other spectrophotometric methods.

Determination of carbendazim, thiabendazole and fuberidazole using a net analyte signal-based method

The net analyte signal (NAS)-based method HLA/GO, modification of the original hybrid linear analysis (HLA) method, has been used to determine carbendazim, fuberidazole and thiabendazole in water samples. This approach was used after a solid-phase extraction (SPE) step, using the native fluorescence emission spectra of real samples, previously standardized by piecewise direct standardization (PDS). The results obtained show that the modification of HLA performs in a similar way that partial least-squares method (PLS-1). The NAS concept was also used to calculate multivariate analytical figures of merit such as limit of detection, selectivity, sensitivity and analytical sensitivity (gamma(-1)). With this purpose, blanks of methanol and ternary mixtures, with the target analyte at low concentration and the other two ranging according to the calibration matrix, were used, with different results. Detection limits calculated in the last way are more realistic and show the influence of the other components in the sample. Selectivity for carbendazim is higher than the corresponding values for fuberidazole and thiabendazole, whereas sensitivity, as well as the values obtained for their detection limits, are lower for carbendazim, followed by thiabendazole and fuberidazole. Results obtained by modification of HLA vary in the same way that the ones obtained by PLS-1.

Determination of triamterene and leucovorin in biological fluids by UV derivative-spectrophotometry and partial least-squares (PLS-1) calibration

The resolution of binary mixtures of triamterene (TAT) and leucovorin (LV) by application of first-derivative spectrophotometry and by application of Partial Least Squares calibration (PLS-1) was performed. Triamterene is determined in presence of leucovorin directly in the absorption spectra at 358 nm, and leucovorin is determined in the first-derivative spectra at 305.6 nm, zero-crossing of the triamterene. The mean recovery values in urine samples were 102 and 97% for TAT and LV, respectively. Partial Least Squares calibration (PLS-1) multivariate calibration of spectrophotometric data, have been applied to the determination of these compounds in serum and in urine without pretreatment of the samples. The absorption spectra of samples of serum or urine, spiked with triamterene and/or leucovorin, were used to perform the optimization of the calibration matrices by PLS-1 method. Mean recovery values were of 107 and 108% for TAT and LV in serum samples, and 98 and 91% for TAT and LV in urine samples.

Determination of the chemotherapeutic quinolonic and cinolonic derivatives in urine by high-performance liquid chromatography with ultraviolet and fluorescence detection in series☆

An HPLC method with ultraviolet and fluorimetric detection has been established for the separation and determination of six quinolonic and cinolonic antibiotics. A Nova-Pak C18 column (150 x 3.9 mm) and a Waters 486 UV and a Waters 470 fluorescence detector have been used. The influence of variables such as mobile-phase composition and flow-rate, has been studied. An acetonitrile-aqueous solution of oxalic acid 4x10(-4) M (28:72, v/v) has been selected as optimum. The wavelength for the photometric detection of the six antibiotics was 265 nm. For the fluorimetric detection two pairs of excitation/emission wavelengths, 260/360 or 270/440 nm, were selected for the determination of nalidixic acid, 7-hydroxymethylnalidixic acid and oxolinic acid, and for the determination of pipemidic acid and cinoxacin, respectively. The analytical parameters and detection and quantification limits of the method have been determined. The proposed method has been applied for the determination of the six compounds in urine, applying different procedures depending on their concentration, the results being very acceptable.

Comparison of different methods for the determination of several quinolonic and cinolonic antibiotics in trout muscle tissue by HPLC with fluorescence detection

Quinolonic and cinolonic derivatives are mainly used as antibacterials in fish-farms. In this paper we describe a careful revision of the treatment procedures of samples and a prodedure for the determination of residues of these compounds. Because of the complexity and duration of these procedures, several studies have been carried out and these have lead to a simpler and shorter method. Three approaches have been examined: lyophilization followed by extraction with chloroform, solid-liquid extraction with chloroform and solid-liquid extraction with sodium hydroxide solution, followed by liquid-liquid partition in chloroform. Some previous studies into the partition equilibrium are also included. As a result of our studies we propose a procedure with a lower number of steps than those previously described in the literature. This method has been applied to the analysis of nalidixic, 7-hydroxymethylnalidixic and oxolinic acids and cinoxacin in trout muscle. These analysis have been carried out using an HPLC system equipped with a C18 column and fluorimetric detection. The mobile phase was acetonitrile:oxalic acid. The recoveries obtained were: 70–97% for 7-hydroxymethylnalidixic acid, 75–78% for nalidixic acid, 71–95% for oxolinic acid and 72–85% for cinoxacin.

Kinetic-spectrophotometric determination of Cu(II) and pyridine by use of the aerial oxidation of dimedone bisguanylhydrazone

The synthesis and analytical properties of dimedone bisguanylhydrazone (DIBG) are described for the first time. DIBG is oxidized by aerial oxygen and the reaction is catalysed by copper(II). The catalytic effect of copper(II) is increased by the presence of pyridine. Kinetic methods are described for determining trace amounts of copper(II) and pyridine. The reaction is followed spectrophotometrically by measuring the rate of change of absorbance at 550 nm. The calibration graphs are linear in the range 0.6-9.5 mug for copper(II) and 0.2-8.8 mg for pyridine. The methods have been applied to the determination of copper in galena and of pyridine in piperidine and isoamyl alcohol. The kinetic parameters of the reaction have been determined.

Determination of piromidic acid residues in trout muscle tissue and in urine by liquid chromatography with post-column modification of pH and fluorimetric detection

Abstract A rapid high-performance liquid chromatographic method has been developed to determine piromidic acid in trout muscle tissue and in urine, in the presence of nalidixic, 7-hydroxymethylnalidixic, oxolinic and pipemidic acids and cinoxacin. A Nova-Pak C18 column was used with acetonitrile–4·10−4 M oxalic acid (40:60, v/v) as the mobile phase. A post-column change of pH was made with NaOH. Fluorimetric detection at 456 nm (λex 275 nm) was used. The instrumental detection limit was 5.91 ng/ml, based on height of peak. Pretreatment of the urine samples was not necessary and fish samples were extracted with sodium hydroxide solutions and cleaned by means of an extraction with chloroform. Detection limit was 147 ng/ml for urine and 5.91 ng/g for trout muscle. Good separation without interference from any other components was obtained. Recovery was better than 87% in urine and better than 72% in trout muscle tissue.

Spectrophotometric determination of manganese with 2-oximinocyclohexanone thiosemicarbazone

Abstract The 2-oximinocyclohexanone thiosemicarbazone forms, in basic medium, a violet complex with Mn(III) whose stoichiometry is 3:1 (reagent:Mn(III)). The molar absorptivity has a value of 3000 liters · mol−1 · cm−1. By means of the formation of this complex manganese can be determined between 9 and 400 μg with a relative error (95% confidence level) of 0.20%. The effect of foreign ions has been examined and the method has been applied to Mn(II) determination in Lincolnshire iron ore.