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A method for the simultaneous determination of the isomers 3-hydroxybenzaldehyde and 4-hydroxybenzaldehyde in binary mixtures is proposed. The method is based on the use of the first derivative of the ratio spectra obtained by dividing the amplitudes, at appropriate wavelengths, of the absorption spectra of the mixtures by a standard of 4-hydroxybenzaldehyde for determining 3-hydroxybenzaldehyde and by a standard of 3-hydroxybenzaldehyde for determining 4-hydroxybenzaldehyde. The method compares favourably with other spectrophotometric methods.

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.

This manuscript reports the usefulness of the determination of sulphathiazole (ST) using photochemically induced fluorescence (RTPF) and RTPF coupling with first derivative (D 1 -RTPF), and the determination of sulphanilamide (SAN) by meaning first derivative of the emission spectrum. By irradiating 5 min, with intense UV radiation, sulphathiazole, in ethanol:water 20:80 (v/v) solutions at pH 4.5–5.0, show fluorescence emission at 342 nm ( λ ex = 251 nm). Under these conditions, a linear relation, fluorescence intensity–ST concentration, was found between 0.23 and 3.00 μg mL −1 of ST. The method was applied for determining ST in a pharmaceutical drug. ST was also determined in honey by using the D 1 -RTPF signal, applying the standard addition method, and measuring at 324.8 nm. Under the same experimental conditions of pH and solvent, a fluorimetric method for determining SAN in presence of ST is proposed. Calibration graphs for SAN determination were established using the amplitude of the first derivative of the emission spectrum measured at 324.4 nm, as the analytical signal. This method has been applied to determining SAN in a pharmaceutical formulation.

The fluorimetric characteristics of pipemidic acid (PIPE) have been investigated. It has been proven that the fluorescence emission band of pipemidic acid at 439 nm is significantly intensified in the presence of γ-cyclodextrin. The inclusional complexation between the antibacterial pipemidic acid and γ-cyclodextrin (γ-CD) has been studied. A 1:1 stoichiometry of the complex was established and its association constant was calculated by a nonlinear regression method, monitoring the changes in the fluorescence signal of pipemidic acid in the presence of γ-CD. According to the results obtained, a spectrofluorimetric method for the determination of PIPE has been proposed. The best limits of detection and quantification were obtained in presence of γ-CD, in acidic media. The dynamic range of the method was comprised between 0.18 and 1.40 μg/ml.

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 (g 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. # 2003 Elsevier Science B.V. All rights reserved.

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.

Binary mixtures of methotrexate (MTX) and leucovorin (LV) have been resolved by application of first-derivative spectrophotometry and partial least squares calibration (PLS-1). By measuring the first-derivative signals of MTX and LV at 354 and 300 nm, respectively, simultaneous determination was possible. The mean recoveries for urine samples were 91 and 96% for MTX and LV, respectively. Partial least squares (PLS-1) multivariate calibration has been applied to the determination of these compounds in serum and in urine without pretreatment of the samples. The absorption spectra of serum or urine samples spiked with methotrexate and/or leucovorin, were used to optimize the calibration matrixes by the PLS-1 method. The sensitivity and selectivity of the proposed procedures were calculated. Mean recoveries were 101 and 97% for MTX and LV, respectively, for serum samples, and 101 and 98% for MTX and LV, respectively, for urine samples.

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.

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.

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.

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.

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-4x10(-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 (lambda ex 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.

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.