Synchronous fluorimetric determination of salicylic acid and diflunisal in human serum using partial least-squares calibration

The simultaneous determination of salicylic acid and diflunisal in human serum has been accomplished by synchronous fluorimetry, in combination with partial least-squares multivariate calibration. The total luminescence information of the analytes has been used to optimize the spectral data set for the calibration, by analysis of the three-dimensional excitation-emission matrices. The synchronous spectrum, maintaining a constant difference of Deltalambda = 128 nm between the emission and excitation wavelengths, has been selected as optimum to perform the determination. The method is based on the fluorescence of these compounds in chloroform containing 1% (v/v) acetic acid. Serum samples are treated with trichloroacetic acid to remove the proteins, and both analytes are extracted into chloroform-1% (v/v) acetic acid prior to the determination. For concentrations ranging from 60-240 mug ml(-1) of each drug, analytical recoveries range from 96% to 103% for salicylic acid and from 97% to 105% for diflunisal.     

Simultaneous determination of aluminium and beryllium by first-derivative synchronous solid-phase spectrofluorimetry

A method for the simultaneous determination of aluminium and beryllium in mixtures by first-deravative synchronous solid-phase spectrofluorimetry has been developed. Aluminium and beryllium reacted with morin to give fluorescent complexes, which were fixed on a dextran-type resin. The fluoresnce of the resin, packed in a 1-mm silica cell, was measured directly with a solid-surface attachment. The constant wavelength difference chosen to optimize the determination was Deltalambda = lambda(em) = 75 nm. Aluminium was measured at lambda(em)lambda = 445/520 nm and beryllium at lambda(em)lambda(em) = 430/505 nm. The range of application is between 0.5 and 5.0 ng/ml for both aluminium and beryllium. The accuracy and precision of the method are reported. The method has been successfully applied to the determination of aluminium and beryllium in synthetic mixtures and natural waters.     

Second-derivative synchronous fluorescence spectroscopy for the simultaneous determination of cinnarizine and nicergoline in pharmaceutical preparations

A rapid, simple, and highly sensitive second-derivative synchronous fluorometric method has been developed for the simultaneous analysis of binary mixtures of cinnarizine (CN) and nicergoline (NIC). The method is based upon measurement of the native fluorescence of these drugs at constant wavelength difference (Deltalambda) = 80 nm in aqueous methanol (50%, v/v). The different experimental parameters affecting the native fluorescence of the studied drugs were carefully studied and optimized. The fluorescence-concentration plots were rectilinear over the range of 0.025-1.5 and 0.25-5.5 microg/mL for CN and NIC, respectively, with lower detection limits of 0.58 and 0.82 ng/mL and quantitation limits of 1.93 and 2.73 ng/mL for CN and NIC, respectively. The proposed method was successfully applied for the determination of the studied compounds in synthetic mixtures and in commercial tablets. The results obtained were in good agreement with those obtained with reference methods. The high sensitivity attained by the proposed method allowed the determination of CN in real and spiked human plasma. The mean recovery in the case of spiked human plasma [number of trials (n) = 3] was 102.82 +/- 2.17%, while that in real human plasma (n = 3) was 105.25 +/- 2.05.     

Selective and stability-indicating methods for the simultaneous determination of mexiletine hydrochloride and/or its related substance: 2,6-dimethylphenol

Four simple, rapid, sensitive, and selective analytical procedures were developed for determination of mexiletine hydrochloride (MX) and/or its related substance: 2,6-dimethylphenol (DMP). The latter is a synthetic impurity for which a maximum pharmacopeial limit is defined. The first method depends on derivative-ratio spectrophotometry, for which the first-derivative signals of the ratio spectra at 259 nm (Deltalambda = 3 nm) are selected for the determination of MX. The second method is based on the spectrofluorometric measurement of MX in alkaline solution in the presence of 15 mM sodium dodecyl sulfate micellar medium at 292 nm (lambdaEx 260 nm). The third method is based on liquid chromatographic (LC) separation of MX and DMP on an RP-C8 column with a mobile phase consisting of 50 mM Na2HPO4-acetonitrile (60 + 40, adjusted to pH 2.4), and quantification of the analytes is achieved with UV detection at 212 nm based on peak area. The fourth method uses the coupling reaction of DMP with 2,6-dibromo-quinone-4-chlorimide (DBQC) in borate buffer to form an intensely colored product that was spectrophotometrically measured using first-derivative amplitudes at 670 nm (Deltalambda = 6 nm) for the determination of DMP. Different variables affecting each method were carefully investigated and optimized. The reliability and analytical performance of the proposed methods, including linearity, range, precision, accuracy, and detection and quantitation limits, were statistically validated. The first 3 methods were successfully applied for the stability-indicating determination of MX in laboratory-prepared mixtures with DMP, as well as for the determination of MX in capsules. Also, the LC and the DBQC spectrophotometric methods permitted the selective determination of DMP in the presence of a large excess of the parent drug at or near the pharmacopeial limit (0.1-1%).     

Synchronous fluorescence determination of human serum albumin with methyl blue as a fluorescence probe

A new synchronous fluorescence scan analysis was developed for the determination of HSA with high sensitivity with a triphenylmethane acid dye methyl blue as a fluorescence probe. When Deltalambda=140 nm, the synchronous fluorescence peak of methyl blue is located at 323 nm and the synchronous fluorescence intensity of the methyl blue is significantly increased in the presence of trace HSA due to the complex formed between methyl blue and HSA at pH 4.1. Under optimal conditions, the calibration graphs are linear over the range 0.03-266.0 and 266.0-665.0 microg mL(-1) for human serum albumin (HSA). Limit of determination were 0.03 microg mL(-1) for HSA. In the detection of HSA in human serum samples, this method gave values close the clinical data got from hospital.     

The use of synchronous luminescence spectroscopy in qualitative analysis of aromatic fraction of hard coal thermolysis products

The synchronous luminescence method was used in qualitative analysis of aromatic fraction of low-temperature tar from hard coal. The spectra obtained by this method are simpler than spectra obtained with the use of conventional emission luminescence method. The synchronous luminescence analysis requires the selection of respective Deltalambda parameter values. This parameter is a constant difference between position of excitation and emission monochromators during measurement. From literature, the Deltalambda parameter value of 23 nm was first used here. The characteristic emission ranges of spectra obtained indicated (by comparison with spectra of standards) degree of condensation of aromatic compounds present in investigated mixtures. It was also possible to identify some individual compounds. However, this identification could be more effective with the use of the respective value of Deltalambda parameter for each particular component of the mixture. This manner of analysis was used here, e.g. for investigating aromatic fraction containing phenanthrene (identified previously by gas chromatography method) among other compounds. The spectrum recorded at Deltalambda value characteristic for phenanthrene (53nm) presents a rather simple shape with a maximum at 346 nm attributed to phenanthrene after standard and literature data.     

A flow-through fluorimetric sensing device for determination of alpha- and beta-naphthol mixtures using a partial least-squares multivariate calibration approach

A single flow-through optosensor spectrofluorimetric system is proposed for the resolution of mixtures of alpha- and beta-naphthol at mug l(-1) levels using a partial least-squares (PLS) calibration approach. The sensor was developed in conjunction with a monochannel flow-injection analysis system with fluorimetric detection using Sephadex QAE A-25 resin as an active sorbent substrate in the flow cell and the second derivative of the native synchronous fluorescence spectra of analytes as analytical signal. In the manifold, the solutions of naphthol (at pH 10.0) were injected in a carrier stream of KCl (0.15 M)/NaOH (10(-2) M). Because of the strong spectral overlap, the mixture could not be resolved by conventional spectrofluorimetry. The non-additive behaviour of the fluorescence signals revealed an interaction in the system, which was not found by working in the solution only (without the sorbent support). This interaction, probably due to the environment of the analytes on the solid phase, made impossible their simultaneous determination. So, the use of synchronous fluorescence spectroscopy or even its derivative signal could not resolve satisfactorily the mixture. The simultaneous determination of both naphthol has been carried out by recording the signal of the second-derivative synchronous fluorescence (Deltalambda=170 nm) spectra between 200 and 450 nm and a PLS multivariate calibration treatment. The optimum number of factors was selected by using the cross-validation method. After validating the proposed method, it was applied to the determination of these compounds in natural waters with different amounts of each chemical.     

Preparation and application of cysteine-capped ZnS nanoparticles as fluorescence probe in the determination of nucleic acids

Cysteine-capped ZnS nanometer-sized fluorescent particles were produced by a colloidal aqueous synthesis. The functionalized nanoparticles are water-soluble and suitable for biological application. A synchronous fluorescence method has been developed for the rapid determination of DNA with functionalized nano-ZnS as a fluorescence probe, based on the synchronous fluorescence enhancement of cysteine-capped nano-ZnS in the presence of DNA. When Deltalambda =190 nm, maximum synchronous fluorescence is produced at 267 nm at pH 5.12. Under optimum conditions, the synchronous fluorescence intensity is proportional to the concentration of nucleic acids in the range 0.1-1.2 microg ml(-1) for calf thymus DNA, 0.1-0.6 microg ml(-1) for fish sperm DNA. The corresponding detection limit is 32.9 ng ml(-1) for calf thymus DNA and 24.6 ng ml(-1) for fish sperm DNA. This method is simple, inexpensive, rapid and sensitive. The recovery and relative standard deviation are satisfactory.     

A fluoride-selective PCT chemosensor based on formation of a static pyrene excimer

[reaction: see text] Calixarene-based fluorescent chemosensor 1 with two fluorogenic pyrene units conjugated to amide groups as guest recognition sites is synthesized. Complexation of F(-) by 1 causes a red shift of its absorption band to 400 nm (Deltalambda = 54 nm) and a blue shift of the excimer emission to 470 nm (Deltalambda = 12 nm) together with enhanced fluorescence intensity. The blue-shifted excimer emission is attributed to a pyrene dimer formed in the ground state, a so-called static excimer.     

Fluorimetric determination of salsalate in urine, serum and pharmaceutical preparations

A method for the determination of salsalate at concentrations between 0.10 and 1.00 mug ml(-1) by means of fluorescence spectrometry technique is proposed. Salsalate, lightly soluble in water, is totally extracted into chloroform. In this organic phase, the drug shows low fluorescence but when an alkaline medium is provided, salsalate undergoes a substantial increase of the fluorescent intensity. Thus, the determination is performed in a chloroformic medium, where pyrrolidine chloroformic solution is added to give the basic character. The fluorescence measurements to quantify salsalate are carried out in its fluorescent band centered at lambda(ex)=299 nm and lambda(em)=410 nm. The method was successfully applied to the determination of salsalate in authentic pharmaceutical preparations, urine and serum. Samples of these latter two matrices, urine and serum, are extracted into chloroform, using in the aqueous phase a pH 4.8, provided by adding acetic acid/sodium acetate buffer solution. Owing to matrix interference, the method of standard additions was used to determine salsalate in the serum. The sensitivity and repeatability achieved with the proposed method are adequate for the determination of salsalate in these matrices.     

Simultaneous quantitative resolution of atorvastatin calcium and fenofibrate in pharmaceutical preparation by using derivative ratio spectrophotometry and chemometric calibrations.

In the present work, five different spectrophotometric techniques for simultaneous determination of formulations containing atorvastatin calcium (ATOR) and fenofibrate (FENO) in various combinations are described. In ratio spectra derivative spectrophotometry, analytical signals were measured at wavelengths corresponding to either maximums or minimums for both drugs in first derivative spectra of ratio spectra obtained by using either spectrum as divisor. For the remaining four methods using chemometric techniques, namely, classical least squares (CLS), inverse least squares (ILS), principal component regression (PCR) and partial least squares (PLS), the calibrations were constructed by using the absorption data matrix corresponding to the concentration data matrix, with measurements in the range of 231 - 310 nm (Deltalambda = 1 nm) in their zero-order spectra. The linearity range was found to be 4 - 22 and 2 - 20 microg/ml for ATOR and FENO, respectively. The validity of the proposed methods was successfully assessed for analyses of both drugs in laboratory-prepared mixtures and in commercial tablet formulations.     

Spectrophotometric determination of some dithiocarbamates

A procedure has been developed for the determination of six dithiocarbamates [sodium dimethyldithiocarbamate (dibam), sodium diethyldithiocarbamate (NaDDC), tetramethylthiuram disulphide (thiram), zinc dimethyldithiocarbamate (ziram), sodium N-methylpiperazinecarbodithioate and potassium morpholine-4-carbodithioate] in microgram quantities by converting them into selenium dithiocarbamate complexes, which are then extracted into chloroform and measured at 430 nm against a reagent blank. The method is sensitive and can be used for the determination of dithiocarbamates in commercial samples and synthetic mixtures.     

In vivo monitoring the changes of interstitial pH and FAD/NADH ratio by fluorescence spectroscopy in healing skin wounds

The aim of our study was to evaluate the changes of interstitial pH and flavin adenine dinucleotide (FAD)/reduced nicotinamide adenine dinucleotide (NADH) ratio in healing skin wounds using fluorescence spectroscopy in Sprague Dawley rats. In the experiment, excisional and incisional models of wound healing were used. The florescein as the pH-sensitive probe using excitation spectra (lambda(Em) = 535 nm) was used for the measurement of pH changes, and synchronous fluorescence spectra (Deltalambda = 60 nm) for the monitoring of FAD/NADH ratio changes were measured from the surfaces of healing wounds. Increase of interstitial pH and FAD/NADH ratio was recorded during the time interval from the 15th to the 65th minute after surgery. The decrease of pH between the 48th and the 72nd hour after surgery as well as the increase of FAD/NADH ratio between the 72nd and the 96th hour of wound healing were recorded. The results indicate that the use of fluorescence spectroscopy may be considered as a valuable tool for noninvasive in vivo monitoring of selected redox parameters in the early phases of wound healing.     

Resolution of mixtures of three nonsteroidal anti-inflammatory drugs by fluorescence using partial least squares multivariate calibration with previous wavelength selection by Kohonen artificial neural networks

A spectrofluorometric method for the quantitative determination of flufenamic, mefenamic and meclofenamic acids in mixtures has been developed by recording emission fluorescence spectra between 370 and 550 nm with an excitation wavelength of 352 nm. The excitation–emission spectra of these compounds are deeply overlapped which does not allow their direct determination without previous separation. The proposed method applies partial least squares (PLS) multivariate calibration to the resolution of this mixture using a set of wavelengths previously selected by Kohonen artificial neural networks (K-ANN). The linear calibration graphs used to construct the calibration matrix were selected in the ranges from 0.25 to 1.00 μg ml⁻¹ for flufenamic and meclofenamic acids, and from 1.00 to 4.00 μg ml⁻¹ for mefenamic acid. A cross-validation procedure was used to select the number of factors. The selected calibration model has been applied to the determination of these compounds in synthetic mixtures and pharmaceutical formulations.     

Simultaneous determination of codeine and pyridoxine in pharmaceutical preparations by first-derivative spectrofluorimetry

A method for the simultaneous determination of codeine and pyridoxine was developed, based on the measurement of their native fluorescence signals, by using first-derivative spectrofluorimetry to resolve the mixture. Codeine was measured at lambda(em) = 309 nm, and pyridoxine was measured at lambda(em) = 450 nm. Instrumental parameters were optimized, and the emission spectra were recorded between 275 and 475 nm, at lambda(ex) = 255 nm and excitation and emission slit widths of 2.5 and 10 nm, respectively. Systematic studies on the influence of species usually present along with the analytes (such as caffeine, ascorbic acid, paracetamol, and thiamine) were also performed. The calibration graphs were linear over the ranges of 0.5-7.0 and 0.1-1.0 microg/mL for codeine and pyridoxine, respectively, and the relative standard deviations (n = 10) were about 3%. The method was successfully applied to the determination of codeine and pyridoxine in solutions of synthetic mixtures and in synthetic and semisynthetic pharmaceutical formulations.     

Fluorescence investigation of isochlorotetracycline: ground-state and excited-state acid-base equilibria

The fluorescence emission from isochlorotetracycline is shown to be associated with the hydroxyphthalide portion of the molecule. Neutral, anionic, zwitterionic and cationic forms of the fluorophore are proposed to account for the fluorescent behaviour in aqueous and organic media of different acidities. In strongly acidic aqueous solution intermolecular photoautomerism is observed, while in chloroform intramolecular phototautomerism occurs. In aqueous solution an excited-state pK_a of 3.3 was observed for the fluorophore. From a study of the pH vs. fluorescence profile with excitation at 350 nm, the ground-state microscopic dissociation constants for isochlorotetracycline hydrochloride were calculated. The optimum conditions for the fluorimetric determination of isochlorotetracycline are an alkaline medium (pH > 10) with κ_ex = 350 nm and κ_em = 415 nm.     

Identification of polycyclic aromatic hydrocarbons (PAHs) in suspended particulate matter by synchronous fluorescence spectroscopic technique

The synchronous fluorescence (SF) technique has been used in the identification of polycyclic aromatic hydrocarbons (PAHs) from air particulate sample in an urban environment of Delhi, Jawaharlal Nehru University. Suspended particulate matter samples of 24h duration were collected on glass fiber filter papers. PAHs were extracted from the filter papers using dichloromethane (DCM)+hexane with ultrasonication method. Qualitative measurements of the polycyclic aromatic hydrocarbons (PAHs) were carried out using the SF technique at various wavelength intervals (Deltalambda). Due to the difference in chemical structure, each PAH gives specific characteristic spectrum for each Deltalambda. Following PAHs were detected in our measurement: benz(a)anthracene (BaA), pyrene (Pyr), chrysene (Chry), fluoranthene (Flan), phenanthrene (Phen), and benz(ghi)perylene (BghiP). This is in agreement with our earlier work for determination of these PAHs using gas chromatography (GC). The seasonal variation of the PAHs was found to be maximum in winter and minimum during the monsoon.     

Extractive photometric simultaneous determination of iron(II) and copper(II) with syn-phenyl-alpha-pyridyl ketoxime and analysis of ferrites

A rapid method of simultaneous spectrophotometric determination of up to 4 ppm of iron(II) and 20 ppm of copper(II) in a mixture by chloroform extraction of the syn-phenyl-alpha-pyridyl ketoxime complexes at pH 10.0, is developed. Measurements are made at 550 and 475 nm. Two simultaneous equations are solved to obtain the concentrations of the two ions. Analysis of five synthetic mixtures in triplicate gave relative standard deviations of 0.7% for Fe(II) and 1.1% for Cu(II).     

Arsenazo III and its analogues-VI( *) Some new photometric reagents for palladium

Colour reactions of palladium with 2,7-bisazo derivatives of chromotropic acid, containing the o,o'-dihydroxyazo group, are characterized by high sensitivity ( = 60-82 x 10(2)) and good contrast (Deltalambda = 70-80 nm) and permit determination of palladium over a wide range of acidity (from pH 5 to 4N sulphuric acid). Many other metals, including the other platinum metals, do not interfere when present in up to 100-fold amounts.     

HPLC-fluorescence determination of equilin and equilenin in postmenopausal women's urine

A high-performance liquid chromatographic (HPLC) method with fluorescence detection (lambda(ex) = 280 nm; lambda(em) = 410 and 312 nm) in combination with a post-column on-line photochemical derivatization is described for the determination of equilin and equilenin in urine from normal postmenopausal women after therapy with conjugated oestrogens. The column effluents were subjected on-line to UV irradiation (254 nm) and the photo-induced modifications were useful for the identification of the analytes. The conjugated (sulphate and glucuronide) forms were analysed after enzymatic or chemical hydrolysis and extracted with chloroform. Solid-phase extraction using strong anion-exchange sorbent was applied to the analysis of unconjugated oestrogen fraction to obtain a practical and reliable sample clean-up. The HPLC separations were achieved using ODS columns with a mobile phase consisting of 0.05 M triethylamine phosphate buffer (pH 4.0)-acetonitrile (64:36, v/v) at a flow rate of 1.0 mL/min. The method was accurate and reproducible; for the equilin and equilenin separation isocratic conditions were satisfactory, allowing a sensitive detection in urine samples with a detection limit of about 50 fmol for equilin (lambda(ex) = 280 nm; lambda(em) = 312 nm, after photoderivatization) and 10 fmol for equilenin (lambda(ex) = 280 nm; lambda(em) = 410 nm).