Spectrophotometric determination of acyclovir and ribavirin in their dosage forms

Two simple, accurate, and reliable spectrophotometric methods have been developed for the determination of 2 antiviral drugs, acyclovir (ACV) and ribavirin (RBV), in their pharmaceutical formulations. These methods are based on oxidation of the 2 drugs with either cerium (IV) ammonium sulfate (Method A) or potassium persulfate (Method B). The products of oxidation in both methods are coupled with 3-methylbenzothiazolin 2-one hydrazone, producing a deep blue color with a maximum absorption wavelength at 630 nm. In Method A, the absorbance-concentration plots were linear over the ranges of 5-50 and 10-60 microg/mL with detection limits of 0.18 microg/mL (8 x 10(-7) M) and 0.63 microg/mL (2.58 x 10(-6) M) for ACV and RBV, respectively. In Method B, the ranges were 5-45 and 20-50 microg/mL with detection limits of 0.11 microg/mL (4.88 x 10(-7) M) and 1.40 microg/mL (5.73 x 10(-6) M) for the 2 drugs, respectively. The molar absorptivities were 4.1 x 10(3) and 3.65 x 10(3) L/mol/cm in Method A and 5.03 x 10(3) and 3.97 x 10(3) L/mol/cm in Method B for the 2 drugs, respectively. The proposed methods were applied successfully for the determination of the 2 drugs in their pharmaceutical formulations. The percentage recoveries +/- standard deviation were 99.57 +/- 0.86 and 100.82 +/- 0.46 for ACV; 99.41 +/- 1.08 and 100.35 +/- 1.03 for RBV. The results obtained were compared statistically with those given by official methods and showed no significant differences regarding accuracy and precision.     

Spectrophotometric determination of some drugs for osteoporosis

Three simple, accurate and sensitive spectrophotometric methods are developed for the determination of some new drugs for the treatment of osteoporosis: risedronate sodium (I), alendronate sodium (II) and etidronate disodium (III). The first method is based on the measurement of difference in absorbance (Delta A) of risedronate sodium in 0.01 mol l(-1) hydrochloric and 0.1 mol l(-1) sodium hydroxide at 262 nm. Beer's law is obeyed over a concentration range of 15-150 microg ml(-1) with mean recovery 99.75+/-1.22 and molar absorptivity (epsilon) 1.891 x 10(3). The second method is based on the reaction of the primary amino group of (II) with ninhydrin reagent in methanolic medium in the presence of 0.05 mol l(-1) sodium bicarbonate. The colored product is measured at 568 nm, and the linearity range is found to be 3.75-45 microg ml(-1) with mean recovery 99.77+/-0.73 and epsilon 9.425 x 10(3). The third method is based on oxidation of the three mentioned drugs with ceric (IV) sulphate in 0.5 mol l(-1) sulphuric acid at room temperature and subsequent measurement of the excess unreacted cerium (IV) sulphate at 320 nm. The method obeyed Beer's law over a concentration range of 2-24 microg ml(-1) for the three drugs with mean recovery 99.79+/-1.16, 99.73+/-1.38 and 99.86+/-1.13 and epsilon 14.427 x 10(3), 13.813 x 10(3) and 14.000 x 10(3) for drugs I, II, III respectively. The proposed methods were successfully applied for the determination of the studied drugs in bulk powder and in pharmaceutical formulations. The results were found to agree statistically with those obtained the reported methods. Furthermore, the methods were validated according to USP regulations and also assessed by applying the standard addition technique.     

Spectrofluorimetric determination of vigabatrin and gabapentin in dosage forms and spiked plasma samples through derivatization with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole

A highly sensitive and specific method is proposed for the determination of vigabatrin (I) and gabapentin (II) in their dosage forms and spiked human plasma. The method is based on coupling the drugs with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole in borate buffer at pH 7.1 and measuring the resulting fluorescence at 532 nm after excitation at 465 nm. The fluorescence intensity was a linear function of the concentration of the drugs over the ranges of 1.3-6.5 and 1.7-8.5 microg/mL for I and II, respectively. Minimum detectability values were 0.54 microg/mL (4.2 x 10(-6)M) and 0.97 microg/mL (5.7 x 10(-6)M) for I and II, respectively, under the described conditions. The proposed method was successfully applied to the determination of the 2 drugs in their dosage forms, and the percent recoveries +/- standard deviation (SD) were 104.53 +/- 1.2 and 100.00 +/- 1.32 of the label claim for I and II, respectively. The method was further applied to the determination of vigabatrin in spiked plasma samples. The percent recovery +/- SD was 101.58 +/- 2.68. Interference from endogenous alpha-amino acids was overcome through selective complexation with freshly prepared Cu(OH)2. The interference likely to be encountered from co-administered drugs, such as carbamazepine, cimetidine, clonazepam, clopazam, phenobarbital, valproic acid, and lamotrigine, was also studied. A reaction pathway is suggested.     

Stability-indicating methods for determination of pyritinol dihydrochloride in the presence of its precursor and degradation product by derivative spectrophotometry

A first-derivative spectrophotometric (1D) method and a derivative-ratio zero-crossing spectrophotometric (1DD) method were used to determine pyritinol dihydrochloride (I) in the presence of its precursor (II) and its degradation product (III) with 0.1N hydrochloric acid as a solvent. Linear relationships were obtained in the ranges of 6-22 microg/mL for the (1D) method and 6-20 microg/mL for the (1DD) method. By applying the proposed methods, it was possible to determine pyritinol dihydrochloride in its pure powdered form with an accuracy of 100.36 +/- 1.497% (n = 9) for the (1D) method and an accuracy of 99.92 +/- 1.172% (n = 8) for the (1DD) method. Laboratory-prepared mixtures containing different ratios of (I), (II), and (III) were analyzed, and the proposed methods were valid for concentrations of < or = 10% (II) and < or = 50% (III). The proposed methods were validated and found to be suitable as stability-indicating assay methods for pyritinol in pharmaceutical formulations.     

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.     

Determination of nifuroxazide and drotaverine hydrochloride in pharmaceutical preparations by three independent analytical methods

Three new, different, simple, sensitive, and accurate methods were developed for quantitative determination of nifuroxazide (I) and drotaverine hydrochloride (II) in a binary mixture. The first method was spectrophotometry, which allowed determination of I in the presence of II using a zero-order spectrum with an analytically useful maximum at 364.5 nm that obeyed Beer's law over a concentration range of 2-10 microg/mL with mean percentage recovery of 100.08 +/- 0.61. Determination of II in presence of I was obtained by second derivative spectrophotometry at 243.6 nm, which obeyed Beer's law over a concentration range of 2-10 microg/mL with mean recovery of 99.82 +/- 1.46%. The second method was spectrodensitometry, with which both drugs were separated on a silica gel plate using chloroform-acetone-methanol-glacial acetic acid (6 + 3 + 0.9 + 0.1) as the mobile phase and ultraviolet (UV) detection at 365 nm over a concentration range of 0.2-1 microg/band for both drugs, with mean recoveries of 99.99 +/- 0.15 and 100.00 +/- 0.34% for I and II, respectively. The third method was reversed-phase liquid chromatography using acetonitrile-water (40 + 60, v/v; adjusted to pH 2.55 with orthophosphoric acid) as the mobile phase and pentoxifylline as the internal standard at a flow rate of 1 mU/min with UV detection at 285 nm at ambient temperature over a concentration range of 2-10 microg/mL for both drugs, with mean recoveries of 100.24 +/- 1.51 and 100.08 +/- 0.78% for I and II, respectively. The proposed methods were checked using laboratory-prepared mixtures and were successfully applied for the analysis of pharmaceutical formulations containing the above drugs with no interference from other dosage form additives. The validity of the suggested procedures was further assessed by applying the standard addition technique which was found to be satisfactory, and the percentage recoveries obtained were in accordance with those given by the EVA Pharma reference spectrophotometric method.     

Smart stability-indicating spectrophotometric methods for determination of binary mixtures without prior separation

Ratio subtraction and isosbestic point methods are 2 innovating spectrophotometric methods used to determine vincamine in the presence of its acid degradation product and a mixture of cinnarizine (CN) and nicergoline (NIC). Linear correlations were obtained in the concentration range from 8-40 microg/mL for vincamine (I), 6-22 microg/mL for CN (II), and 6-36 microg/mL for NIC (III), with mean accuracies 99.72 +/- 0.917% for I, 99.91 +/- 0.703% for II, and 99.58 +/- 0.847 and 99.83 +/- 1.039% for III. The ratio subtraction method was utilized for the analysis of laboratory-prepared mixtures containing different ratios of vincamine and its degradation product, and it was valid in the presence of up to 80% degradation product. CN and NIC in synthetic mixtures were analyzed by the 2 proposed methods with the total content of the mixture determined at their respective isosbestic points of 270.2 and 235.8 nm, and the content of CN was determined by the ratio subtraction method. The proposed method was validated and found to be suitable as a stability-indicating assay method for vincamine in pharmaceutical formulations. The standard addition technique was applied to validate the results and to ensure the specificity of the proposed methods.     

Voltammetric determination of benazepril and ramipril in dosage forms and biological fluids through nitrosation

A simple and highly sensitive voltammetric method was developed for the determination of benazepril (I) and ramipril (II). The compounds were treated with nitrous acid, and the cathodic current produced by the resulting nitroso derivatives was measured. The voltammetric behavior was studied by adopting direct current (DCt), differential pulse (DPP), and alternating current (ACt) polarography. Both compounds produced well-defined, diffusion-controlled cathodic waves over the whole pH range in Britton-Robinson buffers (BRb). At pH 3 and 5, the values of diffusion-current constants (Id), were 5.90 +/- 0.40 and 6.66 +/- 0.61 for I and II, respectively. The current concentration plots for I were rectilinear over the range of 1.5-40 and 0.1-30 microg/mL in the DCt and DPP modes, respectively; for II, the range was 2-30 and 0.1-20 microg/mL in the DCt and DPP modes, respectively. The minimum detectabilities (S/N = 2) were 0.015 microg/mL (about 3.25 x 10(-8)M) and 0.012 microg/mL (about 2.88 x 10(-8)M) for I and II, respectively, adopting the DPP mode. Results obtained for the proposed method when applied to the determination of both compounds in dosage forms were in good agreement with those obtained using reference methods. Hydrochlorthiazide, which is frequently co-formulated with these drugs, did not interfere with the assay. The method was also applied to the determination of benazepril in spiked human urine and plasma. The percentage recoveries adopting the DPP mode were 96.2 +/- 1.21 and 95.7 +/- 1.61, respectively.     

Capillary gas chromatographic analysis of pyrrolidinedithiocarbamate metal chelates

Pyrrolidinedithiocarbamate (PDTC) chelates of Zn(II), Cu(II), Ni(II), Co(III), Fe(III), Mn(II), Cr(III), and VO(II) were analysed by capillary GC on a DB-1701 column (30 m x 0.25 mm id) with flame ionisation detection (FID). Linear calibrations were attained within "1-30 microg/mL" for Ni(II), Fe(III), Mn(II), Cr(III), Cu(II), and VO(II), and within "2-50 microg/mL" for Co(III) and Zn(II). The limits of detection were in the "150-500 ng/mL" range, corresponding to 15-50 pg amounts reaching the FID system. The optimised method was applied to the determination of Cu(II) and Ni(II) in coins, and that of Zn(II), Cu(II), Ni(II), Fe(III), Mn(II), Cr(III), and VO(II) in pharmaceutical preparations with relative standard deviations within 1.1-5.2%. The results obtained are in good agreement with sewage water samples and the declared values for the pharmaceutical formulations, or with the results of AAS of metal contents in coins, pharmaceutical preparations, and sewage water samples.     

Chemometric methods for the simultaneous determination of some water-soluble vitamins

Two spectrophotometric methods, derivative and multivariate methods, were applied for the determination of binary, ternary, and quaternary mixtures of the water-soluble vitamins thiamine HCI (I), pyridoxine HCI (II), riboflavin (III), and cyanocobalamin (IV). The first method is divided into first derivative and first derivative of ratio spectra methods, and the second into classical least squares and principal components regression methods. Both methods are based on spectrophotometric measurements of the studied vitamins in 0.1 M HCl solution in the range of 200-500 nm for all components. The linear calibration curves were obtained from 2.5-90 microg/mL, and the correlation coefficients ranged from 0.9991 to 0.9999. These methods were applied for the analysis of the following mixtures: (I) and (II); (I), (II), and (III); (I), (II), and (IV); and (I), (II), (III), and (IV). The described methods were successfully applied for the determination of vitamin combinations in synthetic mixtures and dosage forms from different manufacturers. The recovery ranged from 96.1 +/- 1.2 to 101.2 +/- 1.0% for derivative methods and 97.0 +/- 0.5 to 101.9 +/- 1.3% for multivariate methods. The results of the developed methods were compared with those of reported methods, and gave good accuracy and precision.     

Spectrophotometric, spectrofluorometric and HPLC determination of desloratadine in dosage forms and human plasma

Four sensitive, simple and specific methods were developed for the determination of desloratadine (DSL), a new antihistaminic drug in pharmaceutical preparations and biological fluids. Methods I and II are based on coupling DSL with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) in borate buffer of pH 7.6 where a yellow colored reaction product was obtained and measured spectrophotometrically at 485 nm (Method I). The same product could be measured spectrofluorometrically at 538 nm after excitation at 480 nm (Method II). Methods III and IV, on the other hand, involved derivatization of DSL with 2,4-dinitrofluorobenzene (DNFB) in borate buffer of pH 9.0 producing a yellow colored product that absorbs maximally at 375 nm (Method III). The same derivative was determined after separation adopting HPLC (Method IV). The separation was performed on a column packed with cyanopropyl bonded stationary phase equilibrated with a mobile phase composed of acetonitrile-water (60 : 40, v/v) at a flow rate of 1.0 ml min(-1) with UV detection at 375 nm. The calibration curves were linear over the concentration ranges of 0.5-6, 0.02-0.4, 1-10 and 1-30 microg ml(-1) for Methods I, II, III and IV, respectively. The lower detection limits (LOD) were 0.112, 0.004, 0.172 and 0.290 microg ml(-1), respectively, for the four methods. The limits of quantification (LOQ) were 0.340, 0.012, 0.522 and 0.890 microg ml(-1) for Methods I, II, III and IV, respectively. The proposed methods were applied to the determination of desloratadine in its tablets and the results were in agreement with those obtained using a reference method. Furthermore, the spectrofluorometric method (Method II) was extended to the in-vitro determination of the drug in spiked human plasma, with a mean percentage recovery (n=4) of 99.7+/-3.54. Interference arising from endogenous amino acids has been overcome using solid phase extraction. The proposed methods are highly specific for determination of DSL in the presence of the parent drug loratadine. A proposal for the reaction pathways is postulated.     

Kinetic spectrophotometric determination of ethamsylate in dosage forms

A simple and sensitive kinetic method has been developed for the determination of ethamsylate (ESL) in its pharmaceutical preparations. The method is based upon oxidation of ESL with 3-methyl-2-benzothiazolinone hydrazone hydrochloride in presence of cerium (IV) ammonium sulfate at room temperature for 20 min. The absorbance of the reaction product is measured at 514 nm. The absorbance-concentration plot was rectilinear over the range of 4-30 microg/mL (r = 0.9999). The lower detection limit was 0.267 microl/mL (9.110 x 10(-6) M) and the lower quantitation limit was 0.808 microg/mL. The different experimental parameters affecting the development and stability of the reaction product were studied and optimized. The proposed method was applied to the determination of ESL in formulations, and the results obtained were in good agreement with those obtained using a reference method. The proposed method was also used for the in vitro detection of ESL in spiked human plasma at its therapeutic concentration level.     

Spectrofluorometric determination of verapamil hydrochloride in pharmaceutical preparations and human plasma using organized media: application to stability studies

A highly sensitive spectrofluorometric method was developed for the determination of verapamil hydrochloride (VP HCl) in pharmaceutical formulations and biological fluids. The proposed method is based on investigation of the fluorescence spectral behavior of VP HCl in micellar systems, such as sodium dodecyl sulfate (SDS) and beta-cyclodextrin (beta-CD). In aqueous solutions of borate buffer of pH 9 and 8.5, VP HCI was well incorporated into SDS and beta-CD, respectively, with enhancement of its native fluorescence. The fluorescence was measured at 318 nm after excitation at 231 nm. The fluorescence intensity enhancements were 183 and 107% in SDS and in beta-CD, respectively. The fluorescence-concentration plots were rectilinear over the range of 0.02-0.2 and 0.02-0.25 microg/mL, with lower detection limits of 5.58 x 10(-3) and 3.62 x 10(-3) microg/mL in SDS and beta-CD, respectively. The method was successfully applied to the analysis of commercial tablets and the results were in good agreement with those obtained with the official method. The method was further applied to the determination of VP HCl in real and spiked human plasma. The mean % recoveries in the case of spiked human plasma (n=4) was 92.59 +/- 3.11 and 88.35 +/- 2.55 using SDS and beta-CD, respectively, while that in real human plasma (n=3) was 90.17 +/- 6.93 and 89.17 +/- 6.50 using SDS and beta-CD, respectively. The application of the method was extended to the stability studies of VP HCl after exposure to ultraviolet radiation and upon oxidation with hydrogen peroxide.     

Spectrofluorometric determination of fluvoxamine in dosage forms, spiked plasma, and real human plasma by derivatization with fluorescamine

A sensitive, simple, and selective spectrofluorometric method was developed for the determination of fluvoxamine (FXM) in pharmaceutical formulations and biological fluids. The method is based upon the reaction between the drug and fluorescamine in borate buffer of pH 8.0 to yield a highly fluorescent derivative that is measured at 481 nm after excitation at 383 nm. The different experimental parameters affecting the development and stability of the reaction product were carefully studied and optimized. The method was applied for the determination of the drug over the concentration range of 0.1-1.1 microg/mL with a detection limit of 0.01 microg/mL (2 x 10(-8) M). The proposed method was successfully applied to the analysis of commercial tablets. The results obtained were in good agreement with those obtained using a reported spectrophotometric method. The method was applied for the determination of FXM in spiked human plasma with recovery (n=4) of 97.32 +/- 1.23%, while that in real human plasma (n=3) was 90.79 +/- 2.73%. A proposal for the reaction pathway is presented.     

New methods for determination of cinnarizine in mixture with piracetam by spectrodensitometry, spectrophotometry, and liquid chromatography

Four new methods were developed and validated for the determination of cinnarizine HCl in its binary mixture with piracetam in pure and pharmaceutical preparations. The first one was a densitometric analysis that provides a simple and rapid method for the separation and quantification of cinnarizine HCI. The method depends on the quantitative densitometric evaluation of thin-layer chromatograms of cinnarizine HCI at 252 nm over concentration range of 1-6 microg/spot, with a mean accuracy of 100.05 +/- 0.91%. The second method was determination of the drug using a colorimetric method that utilizes the reaction of 3-methyl-benzothiazolin-2-one in the presence of FeCl3 as an oxidant. The green color of the resulting product was measured at 630 nm over concentration range 10-40 microg/mL, with a mean accuracy of 100.10 +/- 1.13%. The third method was a direct spectrophotometric determination of cinnarizine HCI at 252 nm over the concentration range 7-20 microg/mL, while piracetam was determined by derivative ratio spectrophotometry at 221.6 nm over concentration range 5-30 microg/mL, with a mean accuracy of 100.14 +/- 0.79 and 100.26 +/- 1.24% for cinnarizine HCI and piracetam, respectively. The last method was a liquid chromatography analysis of both cinnarizine HCI and piracetam, depending on quantitative evaluation of chromatograms of cinnarizine HCI and piracetam at 252 and 212 nm, respectively, over the concentration range 10-200 microg/mL for cinnarizine HCI and 20-500 microg/mL for piracetam, with a mean accuracy of 100.03 +/- 0.89 and 100.40 +/- 0.94% for cinnarizine HCI and piracetam, respectively. The proposed procedures were checked using laboratory-prepared mixtures and successfully applied for the analysis of their pharmaceutical preparations. The validity of the proposed procedures was further assessed by applying the standard addition technique. Recoveries were quantitative, and the results obtained agreed with those obtained by other reported methods.     

Spectrophotometric determination of olanzapine by its oxidation with N-bromosuccinimide and cerium(IV)sulfate.

Three simple spectrophotometric methods have been described for the assay of olanzapine in its pure and pharmaceutical formulations. The direct method (A) is based on the drug oxidation with excess of N-bromosuccinimide in acidic medium and the two indirect methods (B and C) are based on the oxidation of the drug with excess of N-bromosuccinimide and cerium(IV)sulfate, followed by the reaction of the unconsumed oxidants with celestine blue. The calibration graphs were linear over the range 10 - 120 microg mL(-1) (method A), 0.5 - 6.0 microg mL(-1) (method B) and 0.6 - 3.0 microg mL(-1) (method C). After validation, the proposed methods were successfully applied to assay of olanzapine in its commercial tablets with mean percentage recoveries of 101.23 +/- 0.10, 96 +/- 0.10 and 94 +/- 0.04%. The mechanism of olanzapine oxidation with N-bromosuccinimide was also proposed.     

Estimation of trace amounts of chromium(III) in multi-vitamin with multi-mineral formulations.

Two new specific, selective, simple and inexpensive spectroscopic methods for estimating a trace amount of chromium (Cr3+) from a multi-vitamin with multi-mineral pharmaceutical formulations were developed. The proposed methods are based on the conversion of Cr3+ to Cr6+ either by oxidation with a nitric acid-perchloric acid mixture (method I) or by fusion with an excess amount of sodium carbonate (method II), followed by the complexation of Cr6+ with 1,5-diphenylcarbazide (DPC) in a mineral acidic solution of pH 1.0 +/- 0.5. The pink-colored complex was estimated at 544 nm. Both methods were found to be linear in the range of 0.1 - 0.8 microg/ml with a limit of detection in the range of 0.0123 - 0.0157 microg/ml and a limit of quantitation in the range of 0.0419 - 0.0525 microg/ml. Method I was found to be suitable for estimating Cr3+ species in various formulations, like tablets, capsules and syrups, while method II was found to be suitable for tablets and capsules. Satisfactory recovery from spiked samples of standard Cr3+ suggests no interference of any excipients and diverse ions present in the formulations. The developed methods were compared with AAS by ANOVA, and no significant difference was observed.     

Utility of NBD-Cl for the spectrophotometric determination of some skeletal muscle relaxant and antihistaminic drugs

A simple, accurate, precise and sensitive colorimetric method for the determination of some skeletal muscle relaxant drugs, namely orphenadrine citrate (I), baclofen (II), antihistaminic drugs as acrivastine (III) and fexofenadine hydrochloride (IV) is described. This method is based on the formation of charge transfer complex with 4-chloro-7-nitro-2,1,3-benzoxadiazole (NBD-Cl) in non-aqueous medium. The orange color products were measured at 472, 465, 475 and 469 nm for drugs I, II, III and IV, respectively. The optimization of various experimental conditions was described. Beer's Law was obeyed in the range (2.5-17.5), (5-70), (2.5-25) and (10-50)microg/ml for drugs I, II, III and IV, respectively. The molar absorptivity (epsilon), sandell sensitivity, detection((LOD)) and quantitation limits((LOQ)) are calculated. The procedure was favorably applied for determination of certain pharmaceutical dosage forms containing the studied drugs. The obtained results were compared with the official and reported methods. There were no significant differences between proposed, reported and the official methods.     

Diformylhydrazine as analytical reagent for spectrophotometric determination of iron(II) and iron(III)

The bidentate ligand diformylhydrazine (OHC-HN-NH-CHO), DFH, combines with iron(II) and iron(III) in alkaline media in the pH range 7.3-9.3 to form an intensely colored red-purple iron(III) complex with an absorption maximum at 470 nm. Beer's law is obeyed for iron concentrations from 0.25 to 13 microg mL(-1). The molar absorptivity was in the range 0.3258x10(4)-0.3351x10(4) L mol(-1) cm(-1) and Sandell's sensitivity was found to be 0.0168 microg cm(-2). The method has been applied to the determination of iron in industrial waste, ground water, and pharmaceutical samples.     

New plastic membrane and carbon paste ion selective electrodes for the determination of triprolidine.

Triprolidine (Trip) ion selective electrodes of three types: the conventional polymer membrane (I), graphite coated electrode (II) and carbon paste electrode (III), have been prepared, based on the ion pair of triprolidine hydrochloride with sodium tetraphenylborate. The electrodes exhibit a linear response with a mean calibration graph slope of 56.12, 55.00 and 54.32 mV decade(-1) at 25 degrees C for I, II and III, respectively, within the concentration ranges 1.96 x 10(-5) - 1.00 x 10(-2) M for I and 3.84 x 10(-5) - 1.00 x 10(-2) M for II and III. The detection limits are 1.13+/-0.13 x 10(-5), 1.70+/-0.06 x 10(-5) and 1.78+/-0.05 x 10(-5) M for the three electrodes, respectively. The change of pH within the ranges 4.85 - 8.75 and 4.70 - 8.50 for I and III, respectively, did not affect the electrode performance. The standard electrode potentials were determined at different temperatures and were used to calculate the isothermal coefficient of the electrode. The electrodes showed a very good selectivity for Trip with respect to a large number of inorganic cations and compounds. The standard addition method was applied to the determination of TripCl in pure solution, pharmaceutical preparations, and urine samples.