Rapid and sensitive on-line solid phase extraction-ultra high performance liquid chromatography-electrospray-tandem mass spectrometry analysis of pesticides in surface waters.

A simple, fast and sensitive method has been developed for the determination of 37 LC-amenable pesticides in surface water samples. On-line solid phase extraction (SPE) coupled to ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS. was employed for pre-concentration and analysis of all compounds in 16min. SPE parameters were evaluated in order to increase sample throughput and detectability. Thus, injected sample volume, sample loading flow, carryover effects and reusability of the cartridges employed were studied, observing that 70 extractions can be performed with the same cartridge. Validation parameters were performed and good linearity (R(2)>0.99 in all cases) and precision (interday relative standard deviation values were lower than 14%) were obtained. Limits of detection (LOD) and limits of quantification (LOQ) were lower than 6.0 and 18.0ngL(-1) applying an injection sample volume of 1.5mL, respectively, with exception of thifensulfuron methyl, whose limits were 10.0 and 33.0ngL(-1), respectively. On-line SPE recoveries were evaluated for three concentration levels (0.01, 0.03, 0.10 and 0.20µgL(-1)) and acceptable values were found. The on-line SPE method was also compared with off-line SPE. Matrix effects were observed for majority of compounds and standard addition method was selected for analysis of real water samples. Finally, surface water samples were analyzed and, in all cases, the pesticide concentrations were below than the allowable limit in water for human consumption.

Comparison of the predictive ability of several second-order multivariate methods in the simultaneous determination of two therapeutic drugs in human urine.

The aim of this paper is to study the applicability of second-order multivariate methods in the simultaneous determination of two therapeutic drugs in human urine samples. The studied drugs, irinotecan and thalidomide, are used in the treatment of malignant tumours. Irinotecan (CPT-11) is used to treat colon cancer; recent studies have shown the benefits of using thalidomide in combination with CPT-11 in the treatment of this disease. CPT-11 is highly fluorescent, but the native fluorescence of thalidomide is very weak. The second-order methods assayed were parallel factor analysis (PARAFAC), unfolded partial least-squares (U-PLS) and multidimensional partial least-squares (N-PLS), both combined with the residual bilinearization procedure (RBL). The excitation-emission matrices (EEMs) of the samples were recorded as analytical signal. The accuracy and precision of the algorithms were evaluated through the root mean square error of prediction (RMSEP) and the elliptical joint confidence region test (EJCR), obtaining better results with PARAFAC, which was successfully applied to the determination of thalidomide and CPT-11 in human urine samples, after a previous liquid-liquid extraction with chloroform.

Simultaneous determination of quinolones for veterinary use by high-performance liquid chromatography with electrochemical detection.

A selective method based on high-performance liquid chromatography with electrochemical detection (HPLC-ECD) has been developed to enable simultaneous determination of three fluoroquinolones (FQs), namely danofloxacin (DANO), difloxacin (DIFLO) and sarafloxacin (SARA). The fluoroquinolones are separated on a Novapack C-18 column and detected in a high sensitivity amperometric cell at a potential of +0.8 V. Solid-phase extraction was used for the extraction of the analytes in real samples. The range of concentration examined varied from 10 to 150 ng g(-1) for danofloxacin, from 25 to 100 ng g(-1) for sarafloxacin and from 50 to 315 ng g(-1) for difloxacin, respectively. The method presents detection limits under 10 ng g(-1) and recoveries around 90% for the three analytes have been obtained in the experiments with fortified samples. This HPLC-ECD approach can be useful in the routine analysis of antibacterial residues being less expensive and less complicated than other more powerful tools as hyphenated techniques.

Quantification of danofloxacin and difloxacin in chicken tissues in the presence of sarafloxacin as interference.

A new spectrofluorimetric method has been developed for the quantification of danofloxacin (DANO) and difloxacin (DIFLO), in the presence of the primary metabolite of difloxacin, with sarafloxacin (SARA) as interference, in chicken tissue samples. The method is based on second-order multivariate calibration, applying parallel factor analysis (PARAFAC), to the excitation-emission matrices (EEMs) of these compounds. High overlapping of the signals and influence of matrix effects were observed. To solve the problem, the standard addition method was used. Chemical variables were optimized. The measured EEMs of the analytes, as analytical signals, allowed their quantification in chicken tissue samples. Solid phase extraction was used for the extraction of the analytes in real samples. The range of concentration examined varied from 30 to 100 ng g(-1) for danofloxacin, and from 100 to 200 ng g(-1) for difloxacin. Both analytes can be analyzed individually, and the binary mixture can be resolved, with recoveries comprising between 88.7 and 106.6%.

Determination of anticarcinogenic and rescue therapy drugs in urine by photoinduced spectrofluorimetry using multivariate calibration: comparison of several second-order methods.

This paper shows the potential of excitation-emission fluorescence spectroscopy and several second-order methods, such as parallel factor analysis (PARAFAC), multiway partial least-squares (N-PLS) or bilinear least-squares (BLLS), as a multicalibration technique for the analysis of leucovorin (LV) and irinotecan (CPT-11). Although CPT-11 presents native fluorescence, leucovorin has little native fluorescence; however, under irradiation with short-wavelength UV light in the presence of traces of hydrogen peroxide, leucovorin was converted into a highly fluorescent compound. This reaction has been used for the sensitive and selective determination of both compounds. The convenience of analysing the total luminescence spectrum information when using multivariate calibration methods on fluorescence data is demonstrated. Direct determination of mixtures of both drugs in urine was accomplished on the basis of excitation-emission matrices (EEMs) and the three-way multivariate methods.

Spectrofluorimetric determination of irinotecan in the presence of oxidant agents and metal ions.

In this work four spectrofluorimetric methods for the determination of irinotecan (CPT-11) in human urine and pharmaceuticals have been developed. Initially, the fluorescent characteristics of irinotecan (CPT-11) have been studied in both acidic and basic media. Later, the fluorescence emission generated by the oxidation of CPT-11 with several agents was studied. A quenching of fluorescence could be observed in the presence of Ce(IV) and I(2)/I(-). Also, the reaction between several divalent and trivalent metal ions with CPT-11 was studied, and one method in presence of Fe(3+) was developed since it was the only metal ion that changes the fluorescence of the analyte. The proposed methods present limit of detection comprises between 0.46 and 2.57ngmL(-1). The spectrofluorimetric methods were applied to human urine. No pre-treatment of the sample was necessary, only a dilution 1:20 with water was made. No interference of the matrix was observed in the conditions used. Recoveries were comprises between 100.0 and 104.3%. Also, pharmaceuticals preparations were analyzed with recoveries between 106.7 and 119.7%. The proposed spectrofluorimetric methods were validated by RP-HPLC, obtaining that the oxidation with iodine is the best method to analyze urine samples, while than, the fluorimetric method developed at acidic pH value is the best for the analysis of pharmaceuticals.

Fluorescence of zirconium-naphthalene complexes: effect of ortho-naphthalene substitution.

The effect of the position of substituents on the formation of metal-naphthalene complexes has been investigated. Two positional isomers, 1-hydroxy-2-naphthoic acid (1H2NA) and 3-hydroxy-2-naphthoic acid (3H2NA), have been chosen. A comparative study of the luminescence behaviour of the two isomers in the presence of Zr(IV) has been performed. Interesting results were obtained. While 1-hydroxy-2-naphthoic acid is quenched in the presence of Zr(IV), 3-hydroxy-2-naphthoic acid produced high-fluorescence enhancement. Several pH studies were performed between pH 2.5 and 5.0 and the stoichiometries of the complexes were also established at the different pH values tested, by use of the Benesi-Hildebrand method. In addition, the formation constants have been calculated. Finally, quenching and lifetime studies were performed in an attempt to establish the type of quenching (static or dynamic) that is produced when a complex is formed between 1-hydroxy-2-naphthoic acid and zirconium metal ion.

Spectrofluorimetric determination of 3-hydroxy-2-naphthoic acid by use of its ternary complex with zirconium (IV) and beta-cyclodextrin: application to determination in river water.

A spectrofluorimetric method has been developed for the determination of 3-hydroxy-2-naphthoic acid (3H2NA) by formation of a ternary complex with zirconium (IV) and beta-cyclodextrin (beta-CD). It has been observed that the fluorescence intensity of 3H2NA is greatly enhanced when the ternary complex is formed and is accompanied with shifts in the excitation and emission wavelengths. The conditions for the formation of the ternary complex have been optimized and the stoichiometry has been calculated, resulting a 1:2:1 complex (3H2NA:Zr: beta-CD). The linear range was 20-2000 ng mL(-1) and the detection and quantification limits calculated were 17 and 58 ng mL(-1), respectively. The proposed method was applied to the determination of 3H2NA in river water. To eliminate interferences an off-line solid phase extraction (SPE) procedure using C18 cartridges was used. The extraction procedure was optimized and good recoveries were obtained (around 100%) with relative standard deviations (RSDs) of less than 5%.

Comparison of different fluorimetric signals for the simultaneous multivariate determination of tocopherols in vegetable oils.

This paper deals with the simultaneous determination of the quaternary mixture of tocopherols (alpha-, beta-, gamma-, and delta-T) performed using fluorimetric techniques and partial least squares (PLS-1) multivariate analysis. In this study, PLS-1 was applied to matrices made up of fluorescence excitation and emission spectra (EEM) and with fluorescence excitation, emission, and synchronous spectra (EESM) of tocopherols dissolved in hexane: diethyl ether (70:30 v/v). A calibration set of 55 samples based in a central composite plus a full factorial plus a fractionated factorial design was constructed. When synthetic samples were analyzed, recoveries around 100% were obtained and detection limits were calculated using EEM and EESM. For the analysis of the oils, the samples, diluted in hexane, were cleaned in silica cartridges and tocopherols were eluted with hexane: diethyl ether (90:10 v/v). The developed method was applied to different edible oils. The results are satisfactory for alpha-, beta-, and gamma-, but they are worse for delta-T.

Fluorescence of metal-ligand complexes of mono- and di-substituted naphthalene derivatives.

In this work, metal ion complexes for several naphthalene derivatives have been investigated. Different working pH values were chosen: 2.5 for complexes with Zr(IV), 4.0 for complexes with Fe(III), 5.0 for complexes with Al(III), and 7.5 for complexes with Cu(II). A stoichiometry of 1:1 for all complexes except two has been established by use of the Benesi-Hildebrand method and the stability constants have been calculated. All complexes between naphthalene derivatives and Cu(II) and Fe(III) show fluorescence quenching. In the case of Al(III), all complexes provided enhanced fluorescence. For Zr(IV), only the complex with 3-hydroxy-2-naphthoic acid provided enhanced fluorescence. The value of the stability constants as a function of the substituents of naphthalene derivatives has been analyzed. One can conclude that Cu(II) showed the largest binding affinity for the mono-substituted derivatives. However, Al(III) and Zr(IV) produced greater selectivity for the di-substituted derivatives. Iron(III) showed no specific binding with any of the naphthalene derivatives.

Complexation of antibacterial quinolonic acid and cinolonic derivatives with Zn(II) and Al(III): application to their determination in human urine.

Nalidixic acid, 7-hydroxymethylnalidixic acid, oxolinic acid, pipemidic acid and cinoxacine form complexes with zinc(II) in the presence of acetate buffer of pH 5.5 and oxolinic acid, pipemidic acid and cinoxacine form complexes with aluminium(III) in the presence of chloroacetate buffer of pH 3.0. In all cases, an enhancement of the fluorescence emission was observed. Fluorimetric studies on the spectral characteristics of the complexes were performed. A 1:1 stoichiometry for all the complexes was established. The association constants were calculated, by using the changes in the fluorescence of all antibacterials, that occurred when the complexes were formed. The fluorescence reactions were used to develop methods for the determination of all of the above compounds, showing a higher sensitivity than in the absence of the cationic ions. The methods were satisfactorily applied to the determination of these compounds in urine.

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

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.

Simultaneous fluorometric determination of nalidixic acid and 7-hydroxymethylnalidixic acid by partial least squares calibration.

The resolution of binary mixtures of nalidixic acid (NA) and 7-hydroxymethylnalidixic acid (OH-NA) has been accomplished by partial least squares (PLS) and principal component regression (PCR) multivariate calibration. The method of determination is based on the fluorescence emission of these compounds in the presence of gamma-cyclodextrin (gamma-CD). The formation of the inclusion compounds gives rise to an increase of the fluorescence emission compared to aqueous solution. The total luminescence information of the compounds has been used to optimize the spectral data set to perform the calibration. A comparison between the predictive ability of three multivariate calibration methods, PLS-1, PLS-2 and PCR, on three spectral data sets, excitation, emission and synchronous spectra has been performed. The PLS-1 method, applied to the emission spectra, has been selected as optimum. The proposed method has been applied to the simultaneous determination of NA and OH-NA in urine. Recovery values from urine samples containing (NA) and (OH-NA) range from 91 to 103% (mean 97%), and from 92 to 105% (mean 99%), respectively.

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.