Determination of epinephrine, norepinephrine, dopamine and L-dopa in pharmaceuticals by a photokinetic method.

A study of the photochemical reaction of the Rose Bengal (RB)-ethylenediaminetetraacetic acid system in the presence of epinephrine, norepinephrine, dopamine and L-dopa is presented. The rate of photoreduction of RB is dramatically retarded by small amounts of these catecholamines, which have an inhibitory effect on the excited state of RB, which is the activator of the process. Optimum conditions for the determination of catecholamines in the range of concentration between 5 x 10(-6) and 1 x 10(-4) mol dm-3 are described. The proposed method has been applied with excellent results to the determination of catecholamines in pharmaceuticals.     

Piezoelectric detection of ion pairs between sulphonate and catecholamines for flow injection analysis of pharmaceutical preparations

Fundamentals of ion-pair flow injection with piezoelectric detection were investigated experimentally and theoretically for the adsorption of dodecyl phenylsulfonate and interfacial ion-pair formation with epinephrine and l-dopa on silver electrode of quartz crystal microbalance. The influences of sulfonate concentration and operating parameters on the frequency response were demonstrated and provided the possibility for the discriminating determination of mixtures. The selected system of ion-pair flow injection with piezoelectric detection was applied to the determination of epinephrine and l-dopa. Calibration curves were linear in ranges 4.00-850 and 3.50-730 mug ml(-1), with detection limits of 1.22 and 1.05 mug ml(-1) and sampling frequencies of 120 samples h(-1), for epinephrine and l-dopa, respectively. The method has been satisfactorily applied to the determination of catecholamines in pharmaceutical preparations.     

Amperometric flow-injection method for the assay of l-ascorbic acid based on the photochemical reduction of Methylene Blue

Ascorbic acid (AA) is determined by amperometric detection based on the photochemical reduction of Methylene Blue (MB(+)) in 0.1 M phthalate buffer at pH 3.8. In this medium, MB(+) using flow-injection analysis. The carrier stream is 1 mM MB(+) is reduced quasi-reversibly at a glassy carbon electrode at -0.34 V vs. Ag/AgCl, while AA is oxidized irreversibly at about 0.3 V. The reactor is irradiated with a 500 W halogen lamp to facilitate the development of the photochemical reaction. A laboratory-built wall-jet electrode system was used. The Leucomethylene Blue formed in the reaction is detected at +0.050 V. At 2.2 ml min(-1) and using a sample loop of 43 mul, the method allows the determination of AA in the range 5.0-90.0 mug ml(-1), with a relative standard deviation of 1.3-4.8%, a detection limit of 1.9 mug ml(-1) and a sampling frequency of 45-50 h(-1).     

Simultaneous third-derivative spectrophotometric determination of copper and nickel in iron alloys and aluminium alloy

A method is proposed for the simultaneous determination of copper and nickel by third-derivative spectrophotometry based on the absorption spectra of their complexes with cyanide ion in the ultraviolet range. The method allows the determination of 0.55-5.8 mug/ml of copper and 0.55-6.8 mug/ml of nickel. The relative standard deviation for 11 determinations of 1.5 mul/ml of copper and nickel were 0.78 and 0.72%, respectively. The detection limits were 0.10,mug/ml for nickel and 0.13 mug/ml for copper. The method has been applied to direct determination of copper and nickel in iron alloys and an aluminium alloy without any separation.     

Flow injection spectrophotometric determination of lactic acid in skimmed milk based on a photochemical reaction

A spectrophotometric method for the determination of lactic acid in milk samples based on the use of a photochemical reaction carried out in a Flow Injection System is proposed. Determination is based on the reaction between lactic acid and Fe(III), which is reduced to Fe(II) in the presence of UV light, being the latter made to react with o-phenanthroline. The complex formed between Fe(II) and o-phenanthroline, Fe(o-phen)(3)(2+) (ferroin) is a coloured compound and it can be spectrophotometrically monitored at 512 nm. The method shows a linear range between 0.5 and 50 mug ml(-1) with a limit of detection of 0.16 mug ml(-1). The precision was +/-2.15 expressed as relative standard deviation (n=11) and the sample throughput of 30 samples h(-1). Also non-linear adjustments have been made and validated by ANOVA. The proposed method has been applied to the determination of lactic acid in both synthetic and milk samples.     

New spectrophotometric method for the determination of phenolic hormones

A new simple, selective and accurate spectrophotometric method is described for the determination of mono- and dihydric phenolic hormones (oestrogens and catecholamines) by nitration at 50 degrees and 100 degrees , respectively, for 10 min, followed by treatment with alkali. Coloured products with absorption maxima at 430, 385, 430, 380 and 380 nm, linearly proportional to the concentration of oestrone, oestradiol, ethinyloestradiol, adrenaline and noradrenaline, respectively, are obtained. Information is presented on the effect of nitration time, temperature, solvents, and alkali concentration. The method is satisfactorily applied to the determination of these hormones in the range 10-50mug ml in the final solution, of volume 10ml. The relative standard deviation is +/- 0.5% and no interferences are caused by non-phenolic hormones.     

Kinetic determination of selenium, based on inhibition of the Pd(II)-catalysed reaction between pyronine G and hypophosphite

A new kinetic method for determination of selenium is based on its inhibitory effect on the Pd(II)-catalysed reaction between Pyronine G and hypophosphite. Under the optimum experimental conditions (6 x 10(-5)M Pyronine G, 0.4M hypophosphite, 0.4 mug/ml Pd(II), pH 2.8, temperature 22.0 +/- 0.2 degrees ), Se can be determined in the concentration range 0.033-0.50 mug/ml. The method suffers from numerous interferences and is thus limited in application. It has been applied to the determination of selenium in spring waters and pharmaceutical preparations.     

Spectrophotometric determination of Diclofenac sodium with Methylene Blue

A sensitive spectrophotometric method was established for the determination of Diclofenac sodium (DS) with Methylene Blue (MB) as analytical reagent. It was found that DS reacts with an excess of MB in the pH range 9.2-9.4, to form a chloroform-extractable blue ion-association complex. Good agreement with Beer's law was found in the range of DS concentrations of 0.8-6.4 mug/ml with a detection limit of 0.37 mug/ml. The method was applied for the determination of DS in various tableted forms with a good precision.     

Analysis of plasma catecholamines by high-performance liquid chromatography with fluorescence detection: simple sample preparation for pre-column fluorescence derivatization

Analysis of plasma catecholamines (norepinephrine, epinephrine and dopamine) by high-performance liquid chromatography using 1,2-diphenylethylenediamine as a fluorescent reagent is described. We have developed an automatic catecholamine analyser, based on pre-column fluorescence derivatization and column switching. The analysis time for one assay was 15 min. The correlation coefficients of the linear regression equations were greater than 0.9996 in the range 10-10,000 pg/ml. The detection limit, at a signal-to-noise ratio of 3, was 2 pg/ml for dopamine. A new method of sample preparation for the pre-column fluorescence derivatization of plasma catecholamines was used. In order to protect the catecholamines from decomposition, an ion-pair complex between boric acid and the diol group in the catecholamine was formed at a weakly alkaline pH. The stabilities of plasma catecholamines were evaluated at several temperatures. After complex formation, the catecholamines were very stable at 17 degrees C for 8 h, and the coefficients of variation for norepinephrine, epinephrine and dopamine were 1.2, 4.2 and 9.3%, respectively.     

Simultaneous flow-injection determination of chlorpromazine and promethazine by photochemical reaction

Chlorpromazine and promethazine were simultaneously determined by irradiating flow-injection manifolds with ultraviolet light. The simultaneous determination was based on the difference in pH of the media where the photochemical conversion of each phenothiazine into a fluorescent product took place. The choice of the best flow-injection configuration and mathematical treatment for solving the mixtures are discussed. Chlorpromazine and promethazine can be simultaneously determined at the mug/ml level with r.s.d. values between 2 and 4% and sampling frequencies in the range 30-40/hr.     

Flow injection chemiluminescence determination of thiamine based on its enhancing effect on the luminol-hydrogen peroxide system

A new flow injection chemiluminescence (CL) method is proposed for the determination of thiamine, based upon its enhancing effect on the CL reaction of luminol with hydrogen peroxide in alkaline solution. The method allows the determination of thiamine within 0.05-8 mug ml(-1) range with a detection limit (3sigma) of 0.01 mug ml(-1). The relative standard deviation is 1.4% (n=11, 0.5 mug ml(-1) thiamine) and the sample throughput is about 90 samples h(-1). The method was successfully applied to the determination of thiamine in pharmaceutical preparations.     

Permanganate-based chemiluminescence analysis of cefadroxil monohydrate in pharmaceutical samples and biological fluids using flow injection

A chemiluminescent method using flow injection is described for the determination of cefadroxil monohydrate. The method is based on the chemiluminescence reaction of cefadroxil with potassium permanganate in sulphuric acid, sensitized by quinine. The proposed procedure allows the determination of cefadroxil over the concentration range 0.1-30 mug ml(-1) with a detection limit of 0.05 mug ml(-1) and a sample measurement frequency of 150 samples h(-1). The method was successfully applied to the determination of cefadroxil in pharmaceutical preparations and biological fluids.     

FI-on line photochemical reaction for direct chemiluminescence determination of photodegradated chloramphenicol

A new, simple, clean and selective flow injection strategy based on the tandem photochemical reaction-chemiluminescence detection was applied to the determination of chloramphenicol. The determination is based on the on-line photodegradation of the drug in a glycine buffer at pH 8.8 by using a photoreactor consisting of 697 cmx0.5 mm PTFE tubing helically coiled around an 8 W low-pressure mercury lamp. Photodegradated chloramphenicol is detected by direct chemiluminescence of resulting photo-fragments and their subsequent reaction with potassium permanganate in sulfuric acid medium as oxidant. The method allows the chemiluminescence determination of compounds which do not exhibit native chemiluminescence. The calibration graph was linear up to 14 mug ml(-1) chloramphenicol, the limit of detection was 30 ng ml(-1), the relative standard deviation was 2.4% for 7 mug ml(-1) of the drug and the sample throughput was 60 h(-1). Taking into account the importance of the medium of photodegradation on the mechanism of photodegradation a comparative study in terms of selective was performed for different chemical media employed in the procedure of photodegradation. The proposed method was applied to the determination of chloramphenicol in commercially available pharmaceutical formulations.     

Simultaneous determination of manganese and zinc in mixtures using first- and second-derivative spectrophotometry

A new direct spectrophotometric determination of manganese with 5,8-dihydroxy-1,4-naphthoquinone (naphthazarin,NAZA) is reported. Absorption maximum, molar absorptivity and Sandell's sensitivity of 1:2 (M:L) complex are 695 nm, 1.88x10(4) l mol(-1) cm(-1) and 2.92 ng cm(-2), respectively. A linear calibration graph is obtained up to a concentration of 7.2 mug ml(-1) of manganese. The optimum range for determination (Ringbom) is between 0.20 and 6.8 mug ml(-1). A rapid method for simultaneous determination of manganese and zinc in their mixture using derivative spectra is described. The range 0.28-5.6 mug ml(-1) manganese could be determined in the presence of 0.33-6.8 mug ml(-1) zinc and vice versa. The developed method was applied to the simultaneous spectrophotometric determination of manganese and zinc in some synthetic mixtures and was found to give satisfactory results.     

A new catalytic polarographic system for determination of trace amounts of tungsten

A new catalytic polarographic system for the determination of trace amounts of tungsten is described. It is found that the tungsten-2-mercaptobenzothiazole (MBT) complex yields a sensitive catalytic hydrogen wave at -1.10 V (vs. SCE) in strongly acidic medium. The peak height is a linear function of tungsten concentration over the range 0.004-1.4 mug/ml in 0.9M H(2)SO(4)-20 mg/ml NaCl-0.01 mug/ml MBT medium. The method can be applied for determination of trace amounts of tungsten in geochemical materials.     

Sensitive assay for catecholamines in pharmaceutical samples and blood plasma using flow injection chemiluminescence analysis.

A rapid and sensitive chemiluminescence (CL) method using flow injection analysis was described for the determination of three catecholamines: dopamine, adrenaline and dobutamine, based on their greatly enhancing effects on the CL reaction of luminol-potassium periodate in basic solutions. Under the optimized conditions, the calibration graphs relating the increase of CL intensity to the concentration of the analytes were linear. The present method allows for the determination of dopamine, adrenaline, and dobutamine over the range of 1.0 x 10(-10) - 1.0 x 10(-7) g/ml. The relative standard deviations for measurements (n=11) of dopamine, adrenaline and dobutamine were 2.9, 2.3 and 1.8% when the concentrations of three catecholamines were at 1.0 x 10(-9) g/ml, respectively. The detection limits of the method were 2.0 x 10(-11) g/ml dopamine, 1.0 x 10(-11) g/ml adrenaline and 4.0 x 10(-11) g/ml dobutamine. The method was successfully applied to the determination of three catecholamines in pharmaceutical samples and blood plasma.     

The separation of W(V) from HCl-KSCN medium on polyurethane foam sorbents for its spectrophotometric determination in steels and silicates

A simple procedure for selective sorption of tungsten is described. The method involves reduction of W(VI) to W(V) with tin(II) chloride (2%, w/v) at 8-9M hydrochloric acid, formation of the W(V)-SCN complex with 0.2M KSCN and its sorption on polyurethane foam within 20 min. The sorbed complex is then eluted with acidified acetone (1 ml of 1M hydrochloric acid and 8 ml of acetone) followed by addition of 1 ml of 0.1M KSCN to the eluent. The method has been applied to the spectrophotometric determination of tungsten in steels and silicates by measuring the absorbance of the eluted solution at 400 nm. Beer's law is obeyed for the range 0.1-12 mug W/ml. Other elements, e.g., Co(III) (50 mug/ml), Cu(II) (10 mug/ml), Ti(IV) (20 mug/ml), V(V) (10 mug/ml) and Mo(VI) (0.5 mug/ml) have no effect on the method. Interference of copper, up to 100 mug/ml has been eliminated by masking with thiourea and that due to molybdenum by prior separation with thioglycollic acid on PUF. The method has been verified with standard samples.     

Determination of catecholamines by ion chromatography coupled to acidic potassium permanganate chemiluminescence detection

A simple,fast,sensitive,highly selective and eco-friendly analytical method for the determination of catecholamines in human urine by ion chromatography（IC） with chemiluminescence（CL） detection was described in this paper.Using 12 mmol/L H₂SO₄ without any organic additive as eluent,three catecholamines including epinephrine（EP）,norepinephrine（NE） and dopamine（DA） were well separated on a cation-exchange column.The CL detection was based on the reaction of analytes with acidic potassium permanganate in the presence of formaldehyde as an enhancer.The absence of methanol and acetonitrile in eluent made the proposed method more sensitive and eco-friendly.Under the optimal conditions,the linear range of the proposed method was in the range of 0.02-0.5μg/mL.The limit of detection（LOD） was in the range of 0.6 and 5.1μg/L.The relative standard deviations （RSD） for 0.1μg/mL mixed standard solution were in the range of 0.8-1.9%（n = 11）.The method has been applied to the determination of catecholamines in human urine successfully.Excellent spiked recoveries were achieved for catecholamines ranged from 91.2%to 112.7%.     

Malachite green as a reagent for detection and spectrophotometric determination of chromium(VI)

A sensitive and inexpensive method of spectrophotometric determination of chromium(VI), based on the absorbance of its complex with malachite green and acetic acid at pH 2.5 is reported. The complex shows a molar absorptivity of 8 x 10(4) l.mole(-1) cm(-1) at 560 nm, using malachite green and acetic acid as reference solution. The effect of time, temperature, pH and reagent concentration is studied and optimum operating conditions are established. Beer's law is applicable in the concentration range 2.0-22.8 mug/ml chromium(VI). The resin beads act as a catalyst and as little as 1.6 mug of chromium(VI) is detected in the resin phase as compared to 4.1 mug in the solution phase. The standard deviation in the determinations is +/-0.40 mug/ml for a 10.35 mug/ml solution.     

Determination of clenbuterol in pharmaceutical preparations by reaction with o-phthalaldehyde using a flow-injection fluorimetric procedure

A new procedure for the determination of clenbuterol is proposed using flow-injection and fluorimetric detection. The method is based on the derivatization reaction of the primary amine group with o-phthalaldehyde in the presence of 2-mercaptoethanol. The calibration graph based on peak area was linear in the range 0.2-5 mug ml(-1) and the detection limit was 0.06 mug ml(-1). The method was validated using a reference spectrophotometric procedure and was applied to the determination of the drug in commercial pharmaceutical preparations.