Direct determination of salicylamide in serum by matrix isopotential synchronous fluorimetry

A method for the determination of salicylamide at concentrations between 25 and 350 ng ml(-1) by use of matrix isopotential synchronous fluorescence spectrometry (MISF) in combination with derivative techniques is proposed. The method allows the determination of compounds in samples with unknown background fluorescence without the need for tedious pre-separation. Synchronous scans are performed along a trajectory that connects points of identical intensity in a three-dimensional fluorescence spectrum. The unknown analytical signal of the serum is suppressed from the MISF spectrum, by calculating its first derivative at lambda(exc)=324 nm and lambda(em)=392 nm. In order to ensure maximum sensitivity and adequate selectivity, the experimental variables affecting the fluorescence intensity of the salicylamide band at lambda(exc)=328 nm and lambda(em)=418 nm were studied. Based on the results, the determination was performed in an aqueous medium at pH 12 that was adjusted with a sodium phosphate/hydrogen phosphate buffer. Calibration graphs were subjected to a comprehensive statistical analysis. The error propagation has been considered in order to calculate the detection limit by the criterium of Clayton.     

Spectrofluorimetric determination of cisatracurium and mivacurium in spiked human serum and pharmaceuticals

Spectrofluorimetric methods to determine cisatracurium and mivacurium are proposed and applied to the determination of both substances in human serum and to the determination of mivacurium in pharmaceuticals. The fluorimetric methods allow the determination of 5-500 ng ml(-1) of mivacurium in aqueous solutions and 5-500 ng ml(-1) of cisatracurium in water-acetonitrile solutions, both containing acetic acid-sodium acetate buffer (pH 5.5) with lambda(exc)=230 nm and lambda(em)=324 nm.     

Determination of urea using high-performance liquid chromatography with fluorescence detection after automated derivatisation with xanthydrol

A high-performance liquid chromatography (HPLC) method for the determination of urea that incorporates automated derivatisation with xanthydrol (9H-xanthen-9-ol) is described. Unlike the classic xanthydrol approach for the determination of urea, which involves the precipitation of dixanthylurea (N,N'-di-9H-xanthen-9-ylurea), the derivatisation procedure employed in this method produces N-9H-xanthen-9-ylurea, which remains in solution and can be quantified using fluorescence detection (lambda(ex)=213 nm; lambda(em)=308 nm) after chromatographic separation from interferences. The limit of detection for urea was 5 x 10(-8) M (0.003 mg L(-1)). This method was applied to the determination of urea in human and animal urine and in wine.     

Simultaneous determination of ethanol and glycerol in wines by a flow injection-pervaporation approach with in parallel photometric and fluorimetric detection

A simultaneous method for the determination of ethanol and glycerol in wines based on the coupling of pervaporation-chemical derivatisation-photometric detection for ethanol and biochemical derivatisation-fluorimetric detection for glycerol is proposed. After separation by pervaporation the ethanol is collected in a K(2)Cr(2)O(7) acceptor stream and the Cr(3+) formed is driven to the spectrophotometer and monitored at 600 nm. The determination of glycerol is based on its oxidation by oxidised beta-nicotinamide adenine dinucleotide (beta-NAD(+)) catalysed by glycerol dehydrogenase immobilised on controlled-pore glass, the reduced form of the coenzyme (NADH) being spectrofluorimetrically monitored (lambda(ex)=340 nm, lambda(em)=460 nm). The linear determination range is between 1-20% for ethanol and 2-8 g l(-1) for glycerol, with RSDs 3 and 2%, respectively. The method applied to red and white Spanish wines, compares well with the official methods for these analytes.     

Utility of oxidation-reduction reaction for the determination of ranitidine hydrochloride in pure form,in dosage forms and in the presence of its oxidative degradates

Three simple, accurate and sensitive colorimetric methods (A, B and C) for the determination of ranitidine HCl (RHCl) in bulk sample, in dosage forms and in the presence of its oxidative degradates are described. The first method A is based on the oxidation of the drug by N-bromosuccinimide (NBS) and determination of the unreacted NBS by measurement of the decrease in absorbance of amaranth dye (AM) at a suitable lambda(max)=520 nm. The methods B and C involve the addition of excess Ce(4+) and determination of the unreacted oxidant by decrease the red color of chromotrope 2R (C2R) at a suitable lambda(max)=528 nm for method B or decrease the orange pink color of rhodamine 6G (Rh6G) at a suitable lambda(max)=526 nm for method C. Regression analysis of Beer-Lambert plots showed good correlation in the concentration ranges 0.2-3.6, 0.1-2.8 and 0.1-2.6 microg ml(-1) for methods A, B and C, respectively. The apparent molar absorptivity. Sandell sensitivity, detection and quantitation limits were calculated. For more accurate results, Ringbom optimum concentration ranges were 0.3-3.4, 0.2-2.6 and 0.2-2.4 microg ml(-1) for methods A, B and C, respectively. Analyzing pure and dosage forms containing RHCl tested the validity of the proposed methods. The relative standard deviations were 相似文献   

Spectrophotometric methods for the determination of certain catecholamine derivatives in pharmaceutical preparations

Two simple, rapid and sensitive spectrophotometric methods for the determination of catecholamine derivatives (pyrocatechol, dopamine, levodopa and methyldopa) are developed. The first method involves the oxidation of o-dihydroxybenzene derivatives by N-bromosuccinimide followed by oxidative coupling with isoniazid leading to the formation of a red-coloured products of maximum absorbance (lambda(max)=480-490 nm). The second method is based on the formation of green to blue complex (lambda(max)=635-660 nm) between o- dihydroxybenzene derivatives and sodium nitroprusside in the presence of hydroxylamine hydrochloride. All measurements of the two procedures are carried out in an alkaline medium at room temperature. The two methods are successfully applied for the determination of dopamine hydrochloride, levodopa and methyldopa in injections and tablets of pharmaceutical preparation. The common excipients used as additives in pharmaceuticals do not interfere in the proposed methods. The reliability of these methods are established by parallel determination with the reported and official methods.     

Spectrofluorimetric kinetic determination of selenium (IV) by flow injection analysis in cationic micellar medium

A sensitive catalytic kinetic spectrofluorimetric method for determining ng ml(-1) of selenium by flow injection analysis has been developed. The method, based on the catalytic effect of Se (IV) on the reduction of resorufin by sulphide, in the presence of cetylpyridinium chloride, is monitored spectrofluorimetrically (lambda(ex)=480 nm; lambda(em)=583 nm). The linearity range of the calibration graph is dependent on the concentration of sulphide. The variables affecting the rate of the reaction were investigated. The method is simple, rapid, precise, sensitive, and widely applicable. The limit of detection is 1 ng ml(-1) Se (IV), and the calibration range is 5-1000 ng ml(-1). Sampling rate is 60 samples h(-1), and the relative standard deviation of 12 determinations of 100 ng ml(-1) Se was 0.76%. The determination of Se (IV) in the presence of Se (VI) and total selenium is described. The method was applied to the determination of Se in selenium tablets, and several synthetic samples.     

Reverse flow-injection manifold for spectrofluorimetric determination of aluminum in drinking water

A simple reverse flow-injection (rFIA) manifold for the direct determination of aluminum in drinking water is proposed. This rapid and sensitive method is based on the formation of an Al(3+) complex with salicylaldehyde picolinoylhydrazone (SAPH), which shows a maximum blue-green fluorescence (lambda(ex)=384 nm, lambda(em)= 468 nm) at pH 5.4. Operative conditions both for batch and rFIA procedures were investigated including reagent concentration, buffer solutions, injection loop, reacting coil and wavelengths used for the fluorimetric detection. The tolerance limits of foreign ions have been also evaluated, before and after the addition of masking agents. The reverse flow-injection procedure allows determination of Al(3+) at ppb level (LOD: 1.9 mug l(-1)) within a working range of 5-30 mug l(-1). The proposed method was successfully employed for the determination of Al(3+) in several commercial drinking, soft drinking (as certified reference material), and tap water samples.     

Inhibition-based determination of metrifonate in liquid and solid samples using the triple integration chemical hydrolysis-pervaporation-enzymic derivatisation

An innovative continuous flow approach consisting of the triple integration of chemical hydrolysis, analytical pervaporation and enzyme inhibition-based reaction for the determination of metrifonate is presented. The method is based on chemical degradation of the pesticide, a separation step consisting of analytical pervaporation of its volatile metabolite and inhibition action of this on the acetylcholinesterase catalysis. The subsequent derivatisation reaction is a two-step reaction involving choline oxidase (ChOD) and horseradish peroxidase (POD) with fluorimetric detection (lambda (ex )=310 nm and lambda (em )=415 nm ) of the dimer formed by the action of hydrogen peroxide. The efficiency of the inhibitory effect was increased using an open-closed flow system. Applied to liquid samples, the method has a linear determination range of 0.0025-0.15 g l(-1)(n=8, r=0.9993) with a precision, expressed as RSD, of 3.2-6.7% and a sampling frequency of 3 h(-1). When applied to solid samples the method shows a linear determination range of 0.0026-0.13 g kg(-1) (n=5, r(2)=0.9981, RSD 2.7-7.7%) and a sampling frequency of 2h(-1). The approach has been applied to the determination of metrifonate in natural water and spiked soil samples with recoveries ranging between 94.3 and 107.8% for liquid samples and between 86.5 and 99.6% for solid samples.     

High-performance thin-layer chromatographic determination of six major ginsenosides in Panax ginseng

A densitometric determination of six major ginsenosides in Panax ginseng, separated by high-performance thin-layer chromatography (HPTLC), was optimized. Simple extraction and clean-up methods of the target constituents and the development of standardized conditions of chromatoplates with a quaternary-solvents system allowed an efficient saponins recovery from the plant material and their selective separation. After exposure of the chromatograms to thionyl chloride vapors and further heating, stable reaction products of ginsenosides, which showed absorption maxima at lambda=275 nm as well as a fluorescence (lambda(excitation)=366 nm, lambda(emission)=400 nm), allowed the application of a sensitive and reproducible method for their simultaneous determination. The method was validated by spiking the ginseng extracts with pure standards.     

Trace determination of zinc in standard alloys, environmental and pharmaceutical samples by fourth derivative spectrophotometry using 1-2-(thiazolylazo)-2-naphthol as reagent and ammonium tetraphenylborate supported on naphthalene as adsorbent

A highly sensitive, selective, economical and rapid method for the trace determination of zinc using fourth derivative spectrophotometry has been proposed with 1-2-(thiazolylazo)-2-naphthol (TAN) as an analytical reagent and ammonium tetraphenylborate (ATPB)-naphthalene as an adsorbent. Zn-TAN is quantitatively retained on ATPB naphthalene in the pH range 6.5-9.5. The calibration plot is linear in the concentration range 0.02-1.4 mug ml(-1) Zn of DMF solution. The sensitivity of the method as determined from the slope of the calibration plot is 2.640 (d(4)A/dlambda(4))/(mug ml(-1)). Nine replicate determinations of 5.0 mug of zinc in 5 ml of DMF give a mean signal height of 2.660 (peak to peak height between lambda(1)=597 nm and lambda(2)=585 nm) with a relative standard deviation of 1.1%. The various conditions have been optimized and the developed method has been used for the determination of zinc in standard alloys, environmental and pharmaceutical samples.     

Kinetic model of energy transfer processes between low-coordinated ions on MgO by photoluminescence decay measurements.

Photoluminescence decay studies of emitting species on MgO nanocubes at room temperature provide evidence of three surface species characterized by an excitation and emission wavelength couple {lambda(exc);lambda(em)}. Species A corresponds to {lambda(exc)=240 nm; lambda(em)=380 nm}, whereas the couple {lambda(exc)=280 nm; lambda(em)=470 nm} is assigned to two species: B and B', the former is involved in energy transfer from excited state A* and the latter in direct emission from excited state B'*. A simple model for energy transfer from species A* to B is proposed. The numerical resolution of equations corresponding to this model is in good agreement with experimental data. This method quantifies the kinetics of intrinsic emission and energy transfer processes. Lifetime values indicate that phosphorescence is taking place, and species A, B and B' are identified as edge O(2-) (4 C), corner O(2-) (3 C) and kink O(2-) (3 C) oxide ions respectively.     

Flow injection analysis: Rayleigh light scattering technique for total protein determination

A novel flow injection analysis (FIA) method with Rayleigh light scattering (RLS) detection was developed for the determination of total protein concentrations. This method is based on the weak intensity of RLS of bromothymol blue (BB) (3',3"-dibromothymolsulfonephthalein) which can be enhanced by the addition of protein in weakly acidic solution. A common spectrofluorimeter was used as a detector. It was proved that the application of this method to quantify the total proteins in real samples by using bovine serum albumin was possible. The RLS signal was detected at lambda(ex)= lambda(em)=572 nm. The linear range was 7.0-70.0 microg mL(-1), the detection limit was 3.75 microg mL(-1), the reproducibility was 5.5% (n=7), and the sample throughput was 26 h(-1).     

Spectrophotometric determination of some antihistaminic drugs using 7,7,8,8-tetracyanoquinodimethane (TCNQ)

A simple and sensitive spectrophotometric method is suggested for analysis of 3 antihistaminic drugs, acrivastine (I), mequitazine (II), and dimethindene maleate (III). The method is based on reaction of the drugs with 7,7,8,8-tetracyanoquinodimethane (TCNQ) in acetonitrile to form highly stable colored products that are measured at 750, 766, and 844 nm for I and II, and 480 and 618 nm for III. Beer's law is obeyed in the ranges of 5-60 microg/mL for 1, 5-50 microg/mL for II, and 10-70 microg/mL for III. The optimum assay conditions and their applicability to the determination of the cited drugs in pharmaceutical formulations are described. The method is statistically analyzed as compared with the European Pharmacopoeia (2001) method for the analysis of dimethindene maleate and reference methods for acrivastine and mequitazine drugs revealing good accuracy and precision.     

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.     

Fluorescence quenching method for the determination of sodium carboxymethyl cellulose with acridine yellow or acridine orange

In near neutral to weak basic media, sodium carboxymethyl cellulose (NaCMC) will dissociate to become a macro polymeric anion, which can react with acridine yellow (AY) or acridine orange (AO) to form an ion-association complex resulting in fluorescence quenching of the acridine dyes. The maximum fluorescence quenching wavelength is 505 nm (lambda(ex)=440 nm) for AY system and 530 nm (lambda(ex)=493 nm) for AO system, respectively. The fluorescence quenching values (DeltaF) are directly proportional to the concentrations of NaCMC and the linear ranges are 20.0-4000 microg/L for AY system and 20.0-7000 microg/L for AO system, separately. This method has high sensitivity and the detection limits for NaCMC are 58.0 microg/L (AY system) and 157.2 microg/L (AO system). The effects of coexistent substance have been investigated, and the results show that this method has a relatively good selectivity. A fluorescence quenching method for the determination of NaCMC based on the ion-association reactions of CMC polymeric anion with a basic acridine dye was developed. The method is sensitive, simple and fast.     

Deprotonation and dimerization of maleimide in the triplet state: a laser flash photolysis study with optical and conductometric detection

The photochemistry of maleimide in aqueous solution is governed by the coexistence of up to three different triplet states, the keto triplet (lambda(max)=250, 330 nm, lambda(min)=290 nm, pK(a)=4.4+/-0.1, tau=5 micros), the deprotonated or enolate triplet (lambda(max)=360, 260 nm, lambda(min)=320 nm, shoulder at 370-380 nm) and a dimer triplet. This biradical is formed by the addition of the keto triplet to the double bond of a ground state maleimide in competition with electron transfer, (k( (3)MI+MI)=2.6 x 10(9) dm(3) mol(-1) s(-1)). Its spectrum is identical to that of the maleimide H-adduct radical (lambda(max)=370-380 (broad), 255 nm (narrow), lambda(min)=290 nm) and its lifetime is 110 ns. While protolysis is confined to maleimide and aqueous solutions, the dimer triplet is also found in acetonitrile. Dimer triplet formation is also observed with N-ethylmaleimide. Time-resolved conductometry and buffer experiments were used to characterise excited state protolysis. Multi-wavelength "global analysis" of the time profiles allowed the separation of the transient spectra and study of the kinetics of the monomer and dimer triplets. The cyclobutane dimer yield (determined by GC) is independent of maleimide concentration. This indicates that the dimer triplet does not contribute significantly to the initiation of free-radical polymerisation. Time-dependent Hartree-Fock calculations agree with the experimental data and further confirm the proposed mechanisms.     

Continuous flow system for the determination of trace boron in iron and steel utilizing in-line preconcentration/separation by Sephadex column coupled with fluorimetric detection

A simple, rapid and sensitive system for the determination of trace boron in iron and steels is presented, in which in-line separation/preconcentration of boron from iron matrix is directly coupled with fluorimetric detection in a continuous flow system. Boron was adsorbed on a small column packed with Sephadex G-25 gel, followed by elution with a small volume of dilute hydrochloric acid. The formation of boron complex with 1,8-dihydroxy-3,6-naphthalenedisulphonic acid in a continuous flow system was used for the sensitive determination of boron by fluorescence detection(lambda(ex)=314 nm and lambda(em)=355 nm). The present FIA system offers many advantages over existing methods, especially with respect to simplicity and sensitivity, permitting semi-automated determination of boron with a short analysis time (about 10 min), low limit of determination (0.1 ppm in steels) and good reproducibility (rsd<3% for 1-18 mug g(-1) boron in steels).The present FIA system can be readily applied to the steel samples.     

Fluorescence enhancement method for the determination of nucleic acids using cationic cyanine as a fluorescence probe

A fluorescence enhancement method with a cationic cyanine as a probe was developed for the determination of nucleic acids. Under the experimental conditions, the fluorescence enhancement of cyanine (lambda(ex)/lambda(em)= 524/591.5 nm) was observed in the presence of DNA. The calibration graphs were linear over the range of 0.01-15 microg mL(-1) for both calf thymus DNA (CT DNA) and fish sperm DNA (FS DNA). The limits of detection were 0.005 and 0.007 microg mL(-1) for CT DNA and FS DNA, respectively. The method was applied to the determination of DNA in synthetic and real samples and satisfactory results were obtained. A possible fluorescence enhancement mechanism was also studied.     

Liquid chromatographic method for the analysis of tocopherols in malt sprouts with supercritical fluid extraction.

A simple, specific and sensitive high-performance liquid chromatographic method has been developed for the determination of tocopherols in malt sprouts. A supercritical fluid extraction (SFE) procedure was used to isolate tocopherols from the vegetal matrix before quantitative analysis. The analytes were separated on a Zorbax reversed-phase column using methanol-water as mobile phase and quantified by measuring its fluorescence at lambda(em)=328 nm after excitation of the analytes at lambda(exc)=303 nm. The limits of detection for alpha-, gamma- and delta-tocopherols were 0.04, 0.05, and 0.05 microg/ml, respectively. The calibration graphs of the method were linear from 0.1 to 1.5, 0.2 to 2.5, and 0.2 to 2.0 microg/ml, for alpha-, gamma- and delta-tocopherols, respectively. This SFE and HPLC procedure is simple, precise and accurate for the determination of tocopherols in malt sprouts.