A. Espinosa Mansilla

A new spectrophotometric method for quantitative multicomponent analysis resolution of mixtures of salicylic and salicyluric acids

A new spectrophotometric method for resolving binary mixtures is proposed. The method is based on use of the first derivative of the ratios of spectra. The absorption spectrum of the mixture is obtained and the amplitudes at appropriate wavelengths are divided by the corresponding amplitudes in the absorption spectrum of a standard solution of one of the components, and the first derivative of the ratio spectrum is obtained. The concentration of the other component is then determined from a calibration graph. The method has been applied for resolving binary mixtures of salicylic and salicyluric acids. Calibration graphs for 2.6-52 ppm salicylic acid and for 2.1-42 ppm salicyluric acid were established by measuring the analytical signals at the maximum at 241.5 nm (for salicylic acid) and from the peak at 258 nm to the trough at 247 nm (for salicyluric acid) in the first derivative ratio spectra.

Derivative spectrophotometric determination of sulphonamides by the Bratton-Marshall reaction.

Abstract A modified method for the determination of sulphonamides, based on the Bratton-Marshall reaction with derivative spectrophotometry, is proposed. Diverse sulphonamides are determined with excellent precision by using first- to fourth-order derivative spectra. The method was applied for the determination of sulphonamides in urine, honey and pharmaceutical formulations without pretreatment of the samples.

Second-order multivariate calibration procedures applied to high-performance liquid chromatography coupled to fast-scanning fluorescence detection for the determination of fluoroquinolones

Different second-order multivariate calibration algorithms, namely parallel factor analysis (PARAFAC), N-dimensional partial least-squares (N-PLS) and multivariate curve resolution-alternating least-squares (MCR-ALS) have been compared for the analysis of four fluoroquinolones in aqueous solutions, including some human urine samples (additional four fluoroquinolones were simultaneously determined by univariate calibration). Data were measured in a short time with a chromatographic system operating in the isocratic mode. The detection system consisted of a fast-scanning spectrofluorimeter, which allows one to obtain second-order data matrices containing the fluorescence intensity as a function of retention time and emission wavelength. The developed approach enabled us to determine eight analytes, some of them with overlapped profiles, without the necessity of applying an elution gradient, and thus significantly reducing both the experimental time and complexity. The study was employed for the discussion of the scopes of the applied second-order chemometric tools. The quality of the proposed technique coupled to each of the evaluated algorithms was assessed on the basis of the figures of merit for the determination of fluoroquinolones in the analyzed water and urine samples. Univariate calibration of four analytes led to limits of detection in the range 20-40 ng mL(-1) and root mean square errors for the validation samples in the range 30-60 ng mL(-1) (corresponding to relative prediction errors of 3-8%). The ranges for second-order multivariate calibration (using PARAFAC and N-PLS) of the remaining four analytes were: limit of detection, 2-8 ng mL(-1), root mean square errors, 3-50 ng mL(-1) and relative prediction errors, 1-5%.

Analysis of Pteridines and Creatinine in Urine by HPLC with Serial Fluorimetric and Photometric Detectors

SummaryAlthough pteridines are excreted in the urine of normal healthy persons, levels of some of these compounds seem to be modified by several diseases. Creatinine is considered to be the best reference for study of the excretion of these markers in urine. A fast, very sensitive, and precise HPLC method with ultraviolet and fluorimetric detection has been established for the simultaneous determination of pterin-6-carboxylic (CAR), neopterin (NEO), xanthopterin (XAN), isoxanthopterin (ISO), biopterin (BIO), and creatinine (CREA) in urine. The influence of conditions such as mobile-phase composition and flow rate, have been studied. 0.015m Tris-HCl-10−3m NaCl buffer solution, pH 6.8, was selected as mobile phase. These five pteridine derivatives are well resolved in less than six minutes. CREA is determined by photometric detection at 230 nm and pteridines by fluorimetric detection at 444 nm, with excitation at 280 nm. The detection limits are below 25 pg for all pteridines and 0.30 ng for creatinine. The method has been applied to the determination of these compounds in urine. A non-clean-up concentration step is necessary before the separation. The urine sample is oxidized before HPLC injection. Values for the pteridine-to-creatinine ratios found for two groups of healthy persons (younger and older than 30 years) are reported.

Strategies for solving matrix effects in the analysis of sulfathiazole in honey samples using three-way photochemically induced fluorescence data.

A widely employed compound for honey treatment, sulfathiazole (ST), was determined in commercial honey samples, employing a combination of photochemically induced fluorescence excitation-emission matrices (EEMs) and chemometric processing of the recorded second-order data. Parallel Factor Analysis (PARAFAC) and Self-Weighted Alternating Trilinear Decomposition (SWATLD) methods were used for calibration. An appropriately designed calibration with a set of standards composed of 18 samples, coupled to the use of the second-order advantage offered by the applied chemometric techniques, allowed quantitation of sulfathiazole in spiked commercial honey samples. No previous separation or sample pretreatment steps were required. The results were compared with other calibration methods such as N-PLS and PLS-1 that produced good results on synthetic samples but not on the investigated commercial honey samples.

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.

Stopped-flow determination of dipyridamole in pharmaceutical preparations by micellar-stabilized room temperature phosphorescence

Abstract The stopped flow mixing technique has been used to study the kinetic determination of dipyridamole by means of micellar-stabilized room temperature phosphorescence (RTP). This mixing system diminishes the time required for the deoxygenation of the micellar medium by sodium sulfite. The phosphorescence enhancers thallium (I) nitrate, sodium dodecyl sulfate (SDS), and sodium sulfite were optimized to obtain maximum sensitivity and selectivity. A pH value of 10.6 was selected as adequate for phosphorescence development. The kinetic curve of dipyridamole phosphorescence was scanned at λ ex =303 nm and λ em =616 nm. Then, the intensity at 10 s, and the maximum slope of phosphorescence development, for an interval time of 1 s, were measured. Two determination approaches: intensity and rate methods, were proposed. The calibration graphs were linear for the concentration range from 50 to 400 ng ml −1 . The detection limits, according to Clayton et al., Anal. Chem. 59 (1987) 2506, were 21.5 and 37.5 ng ml −1 , for intensity and initial rate measurements, respectively. By applying the error propagation theory, the detection limits were 19.0 and 33.0 ng ml −1 , for intensity and initial rate measurements, respectively. Two commercial formulations (persantin and asasantin) were analyzed by both proposed methodologies. Adequate recovery values were obtained in both cases.

Second-Order Calibration of Excitation—Emission Matrix Fluorescence Spectra for the Determination of N-Phenylanthranilic Acid Derivatives

A spectrofluorimetric method has been developed for the quantitative determination of mefenamic, flufenamic, and meclofenamic acids in urine samples. The method is based on second-order data multivariate calibration (unfolded partial least squares (unfolded-PLS), multi-way PLS (N-PLS), parallel factor analysis (PARAFAC), self-weighted alternating trilinear decomposition (SWATLD), and bilinear least squares (BLLS)). The analytes were extracted from the urine samples in chloroform prior to the determination. The chloroform extraction was optimized for each analyte, studying the agitation time and the extraction pH, and the optimum values were 10 minutes and pH 3.5, respectively. The concentration ranges in chloroform solution of each of the analytes, used to construct the calibration matrix, were selected in the ranges from 0.15 to 0.8 μg mL−1 for flufenamic and meclofenamic acids and from 0.25 to 3.0 μg mL−1 for mefenamic acid. The combination of chloroform extraction and second-order calibration methods, using the excitation–emission matrices (EEMs) of the three analytes as analytical signals, allowed their simultaneous determination in human urine samples, in the range of approximately 80 mg L−1 to 250 mg L−1, with satisfactory results for all the assayed methods. Improved results over unfolded-PLS and N-PLS were found with PARAFAC, SWATLD, and BLLS, methods that exploit the second-order advantage.

Analytical properties of pyridine-2-aldehyde guanylhydrazone

The modified synthesis and analytical properties of pyridine-2-aldehyde guanylhydrazone are described for the first time. The solubility, spectral char.

A simple HPLC-ESI-MS method for the direct determination of ten pteridinic biomarkers in human urine.

Pteridines are important biomarkers metabolites related to several biochemical pathways such as activation of the cell-mediated immune system, biosynthesis of neurotransmitters, etc. The level of pteridinic compounds in urine is considered as an important clinic criterion. In this work, a new liquid chromatography-mass spectrometry (LC-MS) method is proposed to determine several pteridinic biomarkers in urine samples using 6-methylpterin as internal standard (I.S.). Matrix effect was evaluated and several dilutions of urine were tested in order to study the evolution of signal suppression. Sample preparation was limited to 10-fold dilution of the filtered urine followed by injection onto a reversed-phase column. The signal was recorded in selected ion monitoring mode. The lowest limit of detection was found for pterin (values ranged from 1.70 to 3.88 ng mL(-1)) whereas the highest limit was for xanthopterin (values ranged from 10.5 to 49.9 ng mL(-1)) for healthy volunteers between 17 and 51 years old.