Unreacted Oxidant Research Articles

Colorimetric Assay of Cimetidine in the Presence of Its Oxidative Degradates

Three simple, accurate, and sensitive colorimetric methods for the determination of cimetidine (Cim) in pure form, in dosage forms, and in the presence of its oxidative degradates were developed. These methods are indirect, involve the addition of excess oxidant [N-bromosuccinimide (NBS) for method A; cerric sulfate [Ce(SO4)2] for methods B and C] of known concentration in acid medium to Cim, and the determination of the unreacted oxidant by measurement of the decrease in absorbance of amaranth dye for method A, chromotrope 2R for method B, and rhodamine 6G, for method C at a suitable maximum wavelength, lambda max: 520, 528, and 525 nm, for the 3 methods, respectively. Regression analysis of the Beer plots showed good correlation in the concentration ranges of 0.2-4.4 microg/mL for method A, and 0.2-3.4 microg/mL for methods B and C. The apparent molar absorptivity, Sandell sensitivity, and detection and quantitation limits were evaluated. The stoichiometric ratio between the drug (Cim) and the oxidant (NBS or Ce4+) was estimated. The validity of the proposed methods was tested by analyzing pure and dosage forms containing Cim with relative standard deviation < or = 1.18. The proposed methods could successfully determine the studied drug with varying excess of its oxidative degradation products, with recovery between 99.2 and 101.8, 100.2 and 102.8, and 99.8 and 102.0% for methods A-C, respectively.

Spectrophotometric Determination of Pantoprazole Sodium in Pharmaceuticals Using N-Bromosuccinimide, Methyl Orange and Indigo Carmine as Reagents

Two sensitive spectrophotometric methods are presented for the assay of pantoprazole sodium sesqui hydrate (PNT) in bulk drug and in formulations using N-bromosuccinimide (NBS) and two dyes, methyl orange and indigo carmine, as reagents. The methods involve the addition of a known excess of NBS to PNT in acid medium, followed by determination of unreacted oxidant by reacting with a fixed amount of either methyl orange and measuring the absorbance at 520 nm (method A) or indigo carmine and measuring the absorbance at 610 nm (method B). In both methods, the amount of NBS reacted corresponds to the amount of PNT and the measured absorbance is found to increase linearly with the concentration of PNT which is corroborated by the correlation coefficients of 0.9959 and 0.9985 for method A and method B, respectively. The systems obey Beer's law for 0.1 - 2.0 mu g mL(-1) and 0.5 - 6.0 mu g mL(-1) for method A and method B, respectively. The limits of detection and quantification are also reported for both methods. Intra-day and inter-day precision,. and accuracy of the methods have been evaluated The methods were successfully applied to the assay of PNT in tablet preparations and the results were statistically compared with those of the reference method by applying Student's t-test and F-test. No interference was observed from the common tablet excipients. The accuracy of the methods was further ascertained by performing recovery studies via standard-addition method.

Gas-Phase, Bulk Production of Metal Oxide Nanowires and Nanoparticles Using a Microwave Plasma Jet Reactor

We report gas-phase production of metal oxide nanowires (NWs) and nanoparticles (NPs) using direct oxidation of micron-size metal particles in a high-throughput, atmospheric pressure microwave plasma jet reactor. We demonstrate the concept with production of SnO2, ZnO, TiO2, and Al2O3 NWs. The results suggest that the NW production primarily depends upon the starting metal particle size, microwave power, and the gas-phase composition. The resulting NW powders could be separated from the unreacted metal and metal oxide NPs by sonication in 1-methoxy 2-propanol followed by gravity sedimentation. The experiments conducted using higher microwave powers resulted in spherical, unagglomerated, metal oxide NPs. The results obtained using various metal oxides suggest that the mechanism of NW nucleation and growth in the gas phase is similar to that observed in experiments with metal particles supported on substrates. A simplified analysis suggests that the metal powders melt in the plasma primarily with the heat g...

Indirect spectrophotometric determination of thiocyanate by the ion-starch reaction

We have proposed a technique for indirect determination of thiocyanate including its oxidation by iodate in the sulfate medium followed by photometric detection of an unreacted oxidant after addition to the reaction mixture of a surplus of iodide and starch. The detection limit constitutes 0.15 μg of thiocyanate in 10 cm3 of the solution.

Cerimetric determination of simvastatin in pharmaceuticals based on redox and complex formation reactions

Two sensitive spectrophotometric methods are described for the determination of simvastatin (SMT) in bulk drug and in tablets. The methods are based on the oxidation of SMT by a measured excess of cerium (IV) in acid medium followed by determination of unreacted oxidant by two different reaction schemes. In one procedure (method A), the residual cerium (IV) is reacted with a fixed concentration of ferroin and the increase in absorbance is measured at 510 nm. The second approach (method B) involves the reduction of the unreacted cerium (IV) with a fixed quantity of iron (II), and the resulting iron (III) is complexed with thiocyanate and the absorbance measured at 470 nm. In both methods, the amount of cerium (IV) reacted corresponds to SMT concentration. The experimental conditions for both methods were optimized. In method A, the absorbance is found to increase linearly with SMT concentration (r = 0.9995) whereas in method B, the same decreased (r = -0.9943). The systems obey Beer’s law for 0.6-7.5 and 0.5-5.0 μg mL-1 for method A and method B, respectively.

Sensitive and validated spectrophotometric methods for the determination of pantoprazole sodium in pharmaceuticals using N-bromosuccinimide based on redox and complexation reactions

Two simple, sensitive and rapid methods are described for the determination pantoprazole sodium sesqui hydrate (PNT) in bulk drug and in formulations using N-bromosuccinimide (NBS) as the oxidimetric reagent. The methods involve the addition of a known excess of NBS to PNT in HCl medium followed by estimation of the unreacted oxidant by two reaction schemes involving the use of iron(II) and thiocyanate (method A) or tiron (method B). In both methods, the absorbance is found to decrease linearly with PNT concentration. Beer’s law is obeyed over the ranges 0.25-3.5 and 1-15 µg mL-1 for method A and method B, respectively. The calculated molar absorptivity values are 1.4 × 105 and 2.5 × 104 L mol-1cm-1 for method A and method B, respectively. The limit of detection (LOD) and quantification (LOQ) are also reported for both methods. The RSD values for intra-day and inter-day precision studies were less than 2.5 and 3.0 %, respectively. Both the methods were applied to the determination of PNT in dosage forms and the results were satisfactory, and were comparable with those obtained by the reference method. The accuracy and reliability of the proposed methods were further ascertained by recoveries studies, and the recoveries of the spiked drug ranged between 98.5 and 102.5 %. KEY WORDS: Pantoprazole sodium, Determination, N-bromosuccinimide, Complexation reactions, Pharmaceuticals Bull. Chem. Soc. Ethiop. 2008, 22(1), 135-141.

Spectrophotometric determination of some phenothiazine drugs using chloramine-T-iodine-starch

A simple, accurate, and sensitive spectrophotometric method for the determination of promethazine hydrochloride (PMH), prochlorperazine maleate (PCPM), trifluoperazine hydrochloride (TFPH), trimeperazine tartrate (TMT), fluphenazine dihydrochloride (FH), and trifluopromazine hydrochloride (TPH) is described. The method is based on the oxidation of the studied drugs by a known excess of chloramine-T in a hydrochloric acid medium and subsequent determination of the unreacted oxidant by interacting it with iodide in the same acid medium. Liberated iodine subsequently reacts with starch to form a stable starch-iodine complex. The reacted oxidant corresponds to the drug content. The colored complex exhibits a maximum absorption at 590 nm. The apparent molar absorptivity and Sandell sensitivity values are in the range 4.07 × 104 − 1.18 × 105 L/mol cm and 45.00−95.00 ng/cm2, respectively. The proposed method has been applied to the assay of phenothiazine drugs in pure and dosage forms. The reliability of the analysis was established using parallel determination by the reference method.

Effect of Gallium Oxide on Phase Assemblage in Apatite and Whitlockite Hosts for Waste Immobilization

AbstractTo immobilize halide and actinide ions present in specific ILW waste a process has been developed that uses mineral phases as the host material. The mechanism of substitution of gallium into these phases will have a large effect on the phase assemblage. This will inevitably affect the total amount of halide that can be immobilized in to total phase mixture.The full simulated waste stream composition containing varying concentrations (1–40 wt.%) of gallium oxide was studied. Also nominal compositions for gallium doped fluorapatites (Ca10-1.5xGax)F2(PO4)6 (x = 0, 0.25, 0.5, 0.75, 1.0) and gallium doped whitlockites Ca9Gay(PO4)6+y (x = 0.2, 0.4, 0.6, 0.8, 1.0) were prepared at 750–1050 °C.These were studied by powder x-ray diffraction (XRD) to determine the phase assemblage and solid solution limits of gallium in the apatite and whitlockite phases. It was found that a complete solid solution was formed between whitlockite, Ca3(PO4)2, and Ca9Gay(PO4)6+y. In the nominal apatite compositions it was found that gallium did not substitute into the apatite structure but was instead partitioned over Ca9Gay(PO4)6+y, gallium phosphate, and unreacted gallium oxide. At higher temperatures gallium suppressed the formation of the apatite phase and was largely partitioned into the Ca9Gay(PO4)6+y phase whereas at lower temperature the majority was present as unreacted Ga2O3. In the full DCHP compositions it was found that gallium is likely to be partitioned over a number of phases including apatite, cationdoped whitlockite and gallium phosphate.

Cerimetric determination of simvastatin in pharmaceuticals based on redox and complex formation reactions

Two sensitive spectrophotometric methods are described for the determination of simvastatin (SMT) in bulk drug and in tablets. The methods are based on the oxidation of SMT by a measured excess of cerium (IV) in acid medium followed by determination of unreacted oxidant by two different reaction schemes. In one procedure (method A), the residual cerium (IV) is reacted with a fixed concentration of fer- roin and the increase in absorbance is measured at 510 nm. The second approach (method B) involves the reduction of the unreacted cerium (IV) with a fixed quantity of iron (II), and the resulting iron (III) is com- plexed with thiocyanate and the absorbance measured at 470 nm. In both methods, the amount of cerium (IV) reacted corresponds to SMT concentration. The experimental conditions for both methods were opti- mized. In method A, the absorbance is found to increase linearly with SMT concentration (r = 0.9995) whereas in method B, the same decreased (r = -0.9943). The systems obey Beer's law for 0.6-7.5 and 0.5- 5.0 µg mL-1 for method A and method B, respectively. The calculated molar absorptivity values are 2.7 X 104 and 1.06 X 105 Lmol-1 cm-1, respectively; and the corresponding sandel sensitivity values are 0.0153 and 0.0039µg cm-2, respectively. The limit of detection (LOD) and quantification (LOQ) are reported for both methods. Intra-day and inter-day precision, and accuracy of the methods were established as per the current ICH guidelines. The methods were successfully applied to the determination of SMT in tablets and the results were statistically compared with those of the reference method by applying the Student's t-test and F-test. No interference was observed from the common excipients added to tablets. The accuracy and validity of the methods were further ascertained by performing recovery experiments via standard addition procedure.

Use of chloramine-T and two dyes in the sensitive determination of stavudine in pharmaceuticals

Three new methods are described for the assay of stavudine (STV) in bulk drug and in dosage forms using chloramine-T (CAT) and two dyes, methyl orange and indigocarmine, as reagents. Titrimetry involves treating STV with a measured excess of CAT in hydrochloric acid medium, and after the oxidation of STV is judged to be complete, the unreacted oxidant is determined iodometrically. Spectrophotometric methods entail the addition of a known excess of CAT to STV in hydrochloric acid medium followed by determination of residual oxidant by reacting with a fixed amount of either methyl orange and measuring the absorbance at 520 nm (Method A) or indigo carmine and measuring the absorbance at 610 nm (Method B). In all the methods, the amount of CAT reacted corresponds to the amount of STV. In titrimetric method, the reaction follows 1:1 stoichiometry (STV: CAT), and is applicable over the range 1.5-10 mg of STV. In spectrophotometric methods, the absorbance is found to increase linearly with concentration of STV. The systems obey Beer's law for 0.2-2.0 and 1.0-10.0 mg/mL for method A and method B, respectively. The apparent molar absorptivities are calculated to be 5.7x10(4) and 1.5x10(4) L/mol/cm for method A and method B, respectively, and the corresponding Sandell sensitivity values are 0.004 and 0.015 µg/cm². The limits of detection and quantification are reported for both methods. Intra-day and inter-day precision and accuracy of the developed methods were evaluated as per the current ICH guidelines. The methods were successfully applied to the assay of STV in tablet and capsule formulations and the results were compared with those of a reference method by applying Student's t-test and F-test. No interference was observed from common tablet adjuvants. The accuracy and reliability of the methods were further ascertained by performing recovery experiments via standard-addition method.

A Sensitive Spectrophotometric Determination of Ritodrine, Pentazocine, Isoxsuprine Hydrochlorides and Amoxicillin in Pure and Pharmaceutical Samples

A simple, accurate and highly sensitive spectrophotometric method for the determination of ritodrine hydrochloride (RTH), pentazocine hydrochloride (PZH), isoxsuprine hydrochloride (ISH) and amoxicillin (AMX) is described. The method is based on the oxidation of the studied drugs by a known excess of chloramine – T (CAT) in hydrochloric acid medium and subsequent determination of the unreacted oxidant by reacting it with iodide in the same acid medium liberates iodine, which subsequently react with starch to form a stable starch‐iodine complex. The reacted oxidant corresponds to the drug content. The coloured complex exhibits a maximum absorption at 590 nm. The apparent molar absorptivity values and Sandell’s sensitivity values are in the range 6.96x104 ‐ 1.43x105 L mol–1 cm–1 and 2.45‐4.30 ng cm–2, respectively. The method was successfully applied to the studied drugs in their dosage forms. The results are reproducible within ±1% and compare favorably with those of official methods of British Pharmacopoeia and the United States Pharmacopoeia.

A New Spectrophotometric Method for Hydrogen Sulphide Through Electrolytically Generated Mn(III) With O‐Tolidine

A simple, sensitive and economical spectrophotometric method for the determination of hydrogen sulphide is developed. The method is based on a redox reaction in that Mn(III) generated electrolytically is taken in excess, which is oxidizing a known but a less quantity of hydrogen sulphide and the unreacted oxidant will oxidize further o‐tolidine to produce an orange yellow quinonediimine absorbing cation (λ max. 455 nm). Therefore, in principle, the decrease in color intensity of the absorbing system is proportional to the concentration of hydrogen sulphide. The stoichiometry between Mn(III) and o‐tolidine and stability constant of the complex were determined by Job′s continuous method, the corresponding values were found to be 2:1 and 1.42X105 Lmol-1. The system was obeying Lambert‐Beer′s law in the range 0.2‐1.4 μg mL-1 of hydrogen sulphide. Molar absorptivity, correlation coefficient and Sandell′s sensitivity values were also calculated and found to be 4.2062X103 L mol-1 cm-1, 0.999 and 0.0012 μg cm-2 respectively. The method was employed for the determination of hydrogen sulphide in water samples. The results obtained were reproducible with acceptable standard deviation 0.01‐0.068 and relative standard deviation, less than 3.21%. For a comparison, hydrogen sulphide present in water samples were also determined separately following the methylene blue official method. The results of the proposed method compare well with the official method.

Quantitation of ranitidine in pharmaceuticals by titrimetry and spectrophotometry using potassium dichromate as the oxidimetric reagent

Four new methods are described for the determination of ranitidine hydrochloride (RNH) in bulk drug and in formulations employing titrimetric and spectrophotometric techniques and using potassium dichromate as the oxidimetric reagent. In titrimetry (method A), RNH is treated with a measured excess of dichromate in acid medium, and the unreacted oxidant is back titrated with iron(II) ammonium sulfate. The three spectrophotometric methods are also based on the oxidation of RNH by a known excess of dichromate under acidic conditions followed by the determination of surplus oxidant by three different reaction schemes. In one procedure (method B), the residual dichromate is treated with diphenylcarbazide and the absorbance measured at 540 nm. Calculated amount of iron(II) is added to residual dichromate and the resulting iron(III) is complexed with thiocyanate and measured at 470 nm (method C). Method D involves reduction of unreacted dichromate by a calculated amount of iron(II) and estimation of residual iron(II) as its orthophenanthroline complex after raising the pH, and measuring the absorbance at 510 nm. In all the methods, the amount of dichromate reacted corresponds to the drug content. The experimental conditions are optimized. The titrimetric procedure is applicable over 5–10 mg range. In spectrophotometric methods, Beer’s law is obeyed in the ranges 5–50, 5–80, and 10–100 µg ml−1 for method B, method C, and method D, respectively. The methods were validated for accuracy, precision and recovery. The proposed methods were applied to the analysis of RNH in the tablet and the injection forms, and the results were in agreement with those obtained by the reference method.

Rapid titrimetric and spectrophotometric methods for salbutamol sulphate in pharmaceuticals using N-bromosuccinimide

One titrimetric and two spectrophotometric methods which are simple, sensitive and rapid are described for the assay of salbutamol sulphate (SBS) in bulk drug and in tablet dosage forms using N-bromosuccinimide (NBS) and two dyes, rhodamine-B and methylene blue, as reagents. In titrimetry, aqueous solution of salbutamol sulphate is treated with a measured excess of NBS in acetic acid medium and after the oxidation of SBS is complete, the unreacted oxidant is determined iodometrically. Spectrophotometric methods entail addition of a known excess of NBS in acid medium followed by the determination of residual oxidant by reacting with a fixed amount of either rhodamine B and measuring the absorbance at 555 nm (method A) or methylene blue and measuring the absorbance at 665 nm (method B). In all methods, the amount of NBS reacting corresponds to the amount of SBS content. Titrimetric method is applicable over 1.74 x 10(-4) - 8.68 x 10(-4) mol L(-1) range and the reaction stoichiometry is found to be 1:6 (SBS:NBS). In spectrophotometric methods, the absorbance is found to increase linearly with the concentration of SBS, which is corroborated by the correlation of coefficients of 0.9993 and 0.9988 for method A and method B, respectively. The systems obey Beer's law for 0.25-1.75 microg mL(-1) (method A) and 0.5-5.0 microg mL(-1) (method B). The calculated apparent molar absorptivity values were found to be 2.10 x 10(5) and 6.16 x 10(4) L mol(-1) cm(-1), for method A and method B, respectively. The limits of detection and quantification are also reported for both spectrophotometric methods. Intra-day and inter-day precision and accuracy for the developed methods were evaluated. The methods were successfully applied to the assay of SBS in tablet and capsule formulations and the results were statistically compared with those of a reference method. No interference was observed from common tablet adjuvants. The accuracy and reliability of the methods were further ascertained by recovery experiments via the standard-addition technique.

Indirect spectrophotometric determination of gentamicin and vancomycin antibiotics based on their oxidation by potassium permanganate

Abstract Four simple, accurate, sensitive and economical procedures (A–D) for the estimation of gentamicin sulphate and vancomycin hydrochloride, both in pure form and in pharmaceutical formulations have been developed. The methods are based on the oxidation of the studied drugs by a known excess of potassium permanganate in sulphuric acid medium and subsequent determination of unreacted oxidant by reacting it with amaranth dye (method A), acid orange II (method B), indigocarmine (method C) and methylene blue (method D), in the same acid medium at a suitable λmax=521, 485, 610 and 664 nm, respectively. The reacted oxidant corresponds to the drug content. Regression analysis of Beer-Lambert plots showed good correlations in the concentration ranges 4–8, 3–8, 4–9 and 5–9 µg ml−1 with gentamicin and 4–8, 1.5–4, 1.5–4 and 3.5–5.5 µg ml−1 with vancomycin for methods A, B, C, and D, respectively. The molar absorptivity, sandell sensitivity, detection and quantification limits were calculated. The stoichiometric ratios for the cited drugs were studied. The optimum reaction conditions and other analytical parameters were evaluated. The influence of the substance commonly employed as excipients with these drugs were studied. The proposed methods were applied to the determination of these drugs in pharmaceutical formulations. The results have demonstrated that the methods are equally accurate and reproducible as the official methods.

Titrimetric and Spectrophotometric Determination of Metaprolol tartrate in Pharmaceuticals Using N‐Bromosuccinimide

One titrimetric and two spectrophotometric methods are presented for the assay of metaprolol tartrate (MPT) in bulk drug and in tablets. The methods employ N‐bromosuccinimide (NBS) as the oxidimetric reagent and two dyes, methyl orange and indigo carmine as spectrophotometric reagents. In titrimetry, an acidified solution of MPT is treated with a known excess amount of NBS and after a definite time, the unreacted oxidant is determined by iodometric back titration. Spectrophotometry involves adding a measured excess of NBS to MPT in acid medium followed by determination of residual NBS by reacting with a fixed amount of either methyl orange and measuring the absorbance at 520 nm (Method A) or indigo carmine and measuring the absorbance at 610 nm (Method B). In all the methods, the amount of NBS reacted corresponds to the amount of MPT. Reaction conditions have been optimized. Titrimetry allows the determination of 1 ‐ 12 mg of MPT and the calculations are based on a 1: 4 (MPT: NBS) reaction stoichiometry. In spectrophotometry, the measured absorbance is found to increase linearly with the concentration of MPT serving as basis for quantitation. The systems obey Beer’s law for 0.5 ‐ 4.0 μg mL-1 and 1.25 ‐ 10.0 μg mL-1 for method A and method B, respectively. The apparent absorptivities are calculated to 1.07 × 105 be and 4.22 × 104 L mol cm-1 for method A and method B, respectively. The methods developed were applied to the assay of MPT in commercial tablet formulations, and the results were compared statistically with those of a reference method. The accuracy and reliability of the methods were further ascertained by performing recovery tests via standard‐addition method.

Sensitive spectrophotometric determination of lansoprazole in pharmaceuticals using ceric ammonium sulphate based on redox and complex formation reactions

Two simple sensitive and cost-effective spectrophotometric methods are described forthe determination of lansoprazole (LPZ) in bulk drug and in capsules using ceric ammoniumsulphate (CAS), iron (II), orthophenanthroline and thiocyanate as reagents. In both methods, anacidic solution of lansoprazole is treated with a measured excess of CAS followed by thedetermination of unreacted oxidant by two procedures involving different reaction schemes. Thefirst method involves the reduction of residual oxidant by a known amount of iron(II), and theunreacted iron(II) is complexed with orthophenanthroline at a raised pH, and the absorbance of theresulting complex measured at 510 nm (method A). In the second method, the unreacted CAS isreduced by excess of iron (II), and the resulting iron (III) is complexed with thiocyanate in the acidmedium and the absorbance of the complex measured at 470 nm (method B). In both methods, theamount CAS reacted corresponds to the amount of LPZ. In method A, the absorbance is found toincrease linearly with the concentration of LPZ where as in method B a linear decrease inabsorbance occurs.

Colorimetric microdetermination of captopril in pure form and in pharmaceutical formulations

A simple, rapid, accurate, precise and sensitive colorimetric method for the determination of captopril (CAP) in bulk sample and in dosage forms is described. The method is based on oxidation of the drug by potassium permanganate in acidic medium and determination of the unreacted oxidant by measuring the decrease in absorbance for five different dyes; methylene blue (MB); acid blue 74 (AB), acid red 73 (AR), amaranth dye (AM) and acid orange 7 (AO) at a suitable λ max (660, 610, 510, 520, and 485 nm), respectively. Regression analysis of Beer's plots showed good correlation in the concentration ranges (0.4–12.5, 0.3–10, 0.5–11, 0.4–8.3 and 0.5–9.3 μg ml −1), respectively. The apparent molar absorbtivity, Sandell sensitivity, detection and quantitation limits were calculated. For more accurate results, Ringbom optimum concentration ranges were 0.5–12, 0.5–9.6, 0.6–10.5, 0.5–8.0 and 0.7–9.0 μg ml −1, respectively. The validity of the proposed method was tested by analyzing in pure and dosage forms containing CAP whether alone or in combination with hydrochlorothiazide. Statistical analysis of the results reflects that the proposed procedures are precise, accurate and easily applicable for the determination of CAP in pure form and in pharmaceutical preparations. Also, the stability constant was determined and the free energy change was calculated potentiometrically.

Sensitive spectrophotometric determination of lansoprazole in pharmaceuticals using ceric ammonium sulphate based on redox and complex formation reactions

Two simple sensitive and cost-effective spectrophotometric methods are described for the determination of lansoprazole (LPZ) in bulk drug and in capsules using ceric ammonium sulphate (CAS), iron (II), orthophenanthroline and thiocyanate as reagents. In both methods, an acidic solution of lansoprazole is treated with a measured excess of CAS followed by the determination of unreacted oxidant by two procedures involving different reaction schemes. The first method involves the reduction of residual oxidant by a known amount of iron(II), and the unreacted iron(II) is complexed with orthophenanthroline at a raised pH, and the absorbance of the resulting complex measured at 510 nm (method A). In the second method, the unreacted CAS is reduced by excess of iron (II), and the resulting iron (III) is complexed with thiocyanate in the acid medium and the absorbance of the complex measured at 470 nm (method B). In both methods, the amount CAS reacted corresponds to the amount of LPZ. In method A, the absorbance is found to increase linearly with the concentration of LPZ where as in method B a linear decrease in absorbance occurs. The systems obey Beer's law for 2.5-30 and 2.5-25 µg mL-1 for method A and method B, respectively, and the corresponding molar absorptivity values are 8.1×103 and 1.5×104 L mol-1cm-1 . The methods were successfully applied to the determination of LPZ in capsules and the results tallied well with the label claim. No interference was observed from the concomitant substances normally added to capsules.

Effects of Gd3+ doping on structural and dielectric properties of PZT (Zr:Ti = 52:48) piezoceramics

The purpose of this research is to study the effect of doping Gd into Pb(Zr0.52Ti0.48)O3 ceramics prepared by solid state reaction. X-ray diffraction patterns show that all PGZT samples are of tetragonal structure and the highest doping should be no more than 2 mole % Gd at which the unreacted oxides start to appear. The electron spin resonance (ESR) spectra of PGZT's indicate that Gd3+ can enter both A site of the perovskite structure instead of only A site as widely believed. The ESR peaks resonance shift towards low fields as the concentration is higher, which is due to the change in crystal field experienced by Gd3+ ions. At x =0.001, 0.005 and 0.01 dopings, two sets of powder ESR signals arising from Gd3+ (4f7, spin 7/2) ions at A site. The first set shows some fine structure having strong absorption peaks centered at 76.26 mT (g = 8.550). The second is a seven-peak spectrum centered at 206.01 mT (g = 3.165), which belongs to the Gd3+ ions at B sites. Furthermore, the overlapped ESR strong absorption peaks from 309.17 mT to 314.49 mT (g = 2.2818-2.1087) belong to Gd3+ of unreacted Gd2O3. The local environments of Gd3+ ions were verified from the calculated ESR spectra using appropriate spin Hamiltonian parameter, i.e. gyromagnetic tensor g, zero-field splitting D and hyperfine tensor A.