Stability indicating HPTLC determination of clopidogrel bisulphate as bulk drug and in pharmaceutical dosage form

A sensitive, selective, precise and stability indicating high-performance thin layer chromatographic method of analysis of clopidogrel bisulphate both as a bulk drug and in formulations was developed and validated in pharmaceutical dosage form. The method employed TLC aluminium plates precoated with silica gel 60F-254 as the stationary phase. The solvent system consisted of carbon tetrachloride-chloroform-acetone (6:4:0.15, v/v/v). This system was found to give compact spots for clopidogrel bisulphate (R_f value of 0.30±0.01). Clopidogrel bisulphate was subjected to acid and alkali hydrolysis, oxidation, photodegradation and dry heat treatment. Also the degraded products were well separated from the pure drug. Densitometric analysis of clopidogrel bisulphate was carried out in the absorbance mode at 230 nm. The linear regression data for the calibration plots showed good linear relationship with r²=0.999±0.001 in the concentration range of 200-1000 ng. The mean value of correlation coefficient, slope and intercept were 0.999±0.001, 0.093±0.011 and 8.83±0.99, respectively. The method was validated for precision, accuracy, ruggedness and recovery. The limits of detection and quantitation were 40 and 120 ng per spot, respectively. The drug undergoes degradation under acidic and basic conditions, oxidation and dry heat treatment. All the peaks of degraded product were resolved from the standard drug with significantly different R_f values. This indicates that the drug is susceptible to acid-base hydrolysis, oxidation and dry heat degradation. Statistical analysis proves that the method is reproducible and selective for the estimation of the said drug. As the method could effectively separate the drug from its degradation products, it can be employed as a stability indicating one.     

Stability-indicating high-performance thin-layer chromatographic determination of levonorgestrel and ethinyloestradiol in bulk drug and in low-dosage oral contraceptives

A stability-indicating high-performance thin-layer chromatography (HPTLC) method was developed and validated for simultaneous determination of steroidal hormones levonorgestrel and ethinyloestradiol both in bulk drug and in low-dosage oral contraceptives. Optimization of conditions for the spectrodensitometric procedure was reached by eluting HPTLC silica gel plates in a 10 cm × 10 cm horizontal chamber. The solvent system consisted of hexane-chloroform-methanol (1.0:3.0:0.25, v/v/v). This system was found to give compact, dense and typical peaks for both levonorgestrel (R_f = 0.65 ± 0.03) and ethinyloestradiol (R_f = 0.43 ± 0.02). Densitometric analysis of the drugs was carried out in the reflectance mode at 225 nm by using a computer controlled densitometric scanner. The calibration curves of levonorgestrel and ethinyloestradiol were linear in the range of 200-800 and 40-160 ng per spot, respectively. The method was validated for precision, robustness and recovery. As the proposed method can effectively separate the drugs from their degradation products, it can be employed as a stability-indicating method.     

Validated stability-indicating densitometric thin-layer chromatography: application to stress degradation studies of minocycline

A simple, stability-indicating high-performance thin-layer liquid chromatographic (HPTLC) method for analysis of minocycline was developed and validated. The densitometric analysis was carried out at 345 nm using methanol-acetonitrile-isopropyl alcohol-water (5:4:0.5:0.5, v/v/v/v) as mobile phase.The method employed TLC aluminium plates pre-coated with silica gel 60F-254 as the stationary phase. To achieve good result, plates were sprayed with a 10% (w/v) solution of disodium ethylene diaminetetraacetic acid (EDTA), the pH of which was adjusted to 9.0. Compact spots of minocycline were found at R_f = 0.30 ± 0.02. For proposed procedure, linearity (r = 0.9997), limit of detection (3.7 ng spot⁻¹), recovery (99.23-100.16%), and precision (% R.S.D. ≤ 0.364) was found to be satisfactory. The drug undergoes acidic and basic degradation, oxidation and photodegradation. All the peaks of degradation products were well resolved from the pure drug with significantly different R_f values. The acidic and alkaline degradation kinetics of minocycline, evaluated using this method, is found to be of first order.     

Stability indicating high-performance thin-layer chromatographic determination of gatifloxacin as bulk drug and from polymeric nanoparticles

A simple, sensitive, selective, precise and stability indicating high-performance thin-layer chromatographic method for determination of gatifloxacin both as a bulk drug and from polymeric nanoparticles was developed and validated as per the International Conference on Harmonization (ICH) guidelines. The method employed thin-layer chromatography (TLC) aluminium plates precoated with silica gel 60F-254 as the stationary phase and the mobile phase consisted of n-propanol-methanol-concentrated ammonia solution (25%) (5:1:0.9, v/v/v). This solvent system was found to give compact spots for gatifloxacin (R_f value of 0.60 ± 0.02). Densitometric analysis of gatifloxacin was carried out in the absorbance mode at 292 nm. The linear regression analysis data for the calibration plots showed good linear relationship with r = 0.9953 with respect to peak area in the concentration range of 400-1200 ng spot⁻¹. The mean value (±S.D.) of slope and intercept were 9.66 ± 0.05 and 956.33 ± 27.67, respectively. The method was validated for precision, accuracy, ruggedness and recovery. The limits of detection and quantitation were 2.73 and 8.27 ng spot⁻¹, respectively. Gatifloxacin was subjected to acid and alkali hydrolysis, oxidation, photodegradation and dry heat treatment. The drug undergoes degradation under acidic and basic conditions and upon wet and dry heat treatment. The degraded products were well separated from the pure drug. The statistical analysis proves that the developed method for quantification of gatifloxacin as bulk drug and from polymeric nanoparticles is reproducible and selective. As the method could effectively separate the drug from its degradation products, it can be employed as stability-indicating one.     

Application of a validated stability-indicating densitometric thin-layer chromatographic method to stress degradation studies on moxifloxacin

A simple, sensitive, selective, precise and stability-indicating high-performance thin-layer chromatographic (HPTLC) method for densitometric determination of moxifloxacin both as a bulk drug and from pharmaceutical formulation was developed and validated as per the International Conference on Harmonization (ICH) guidelines. The method employed TLC aluminium plates pre-coated with silica gel 60F-254 as the stationary phase and the mobile phase consisted of n-propanol-ethanol-6 M ammonia solution (4:1:2, v/v/v). Densitometric analysis of moxifloxacin was carried out in the absorbance mode at 298 nm. Compact spots for moxifloxacin were found at R_f value of 0.58 ± 0.02. The linear regression analysis data for the calibration plots showed good linear relationship with r = 0.9925 in the working concentration range of 100-800 ng spot⁻¹. The method was validated for precision, accuracy, ruggedness, robustness, specificity, recovery, limit of detection (LOD) and limit of quantitation (LOQ). The LOD and LOQ were 3.90 and 11.83 ng spot⁻¹, respectively. Drug was subjected to acid and alkali hydrolysis, oxidation, dry heat, wet heat treatment and photodegradation. All the peaks of degradation products were well resolved from the standard drug with significantly different R_f values. Statistical analysis proves that the developed HPTLC method is reproducible and selective. As the method could effectively separate the drug from its degradation products, it can be employed as stability-indicating one. Moreover, the proposed HPTLC method was utilized to investigate the kinetics of the acidic and alkaline degradation processes at different temperatures. Arrhenius plot was constructed and apparent pseudo-first-order rate constant, half-life and activation energy were calculated. In addition the pH-rate profile for degradation of moxifloxacin in constant ionic strength buffer solutions within the pH range 1.2-10.8 was studied.     

Validated high-performance thin-layer chromatography method for determination of trigonelline in herbal extract and pharmaceutical dosage form

A new, simple, sensitive, selective, precise and robust high-performance thin-layer chromatographic (HPTLC) method for analysis of trigonelline was developed and validated for the determination of trigonelline in herbal extracts and in pharmaceutical dosage forms. Analysis of trigonelline was performed on TLC aluminium plates pre-coated with silica gel 60F-254 as the stationary phase. Linear ascending development was carried out in twin trough glass chamber saturated with mobile phase consisting of n-propanol-methanol-water (4:1:4, v/v/v) at room temperature (25 ± 2 °C). Camag TLC scanner III was used for spectrodensitometric scanning and analysis in absorbance mode at 269 nm. The system was found to give compact spots for trigonelline (R_f value of 0.46 ± 0.02). The linear regression analysis data for the calibration plots showed good linear relationship with r² = 0.9991 ± 0.0002 in the concentration range 100-1200 ng spot⁻¹ with respect to peak area. According to the International Conference on Harmonization (ICH) guidelines the method was validated for precision, recovery, robustness and ruggedness. The limits of detection and quantification were determined. The trigonelline content of herbal extracts quantified and estimated from the formulation was found to be well within limits (±5% of the labeled content of the formulations). Statistical analysis of the data showed that the method is reproducible and selective for the estimation of trigonelline.     

Development and validation of an HPLC method for the determination of process-related impurities in pridinol mesylate, employing experimental designs

A simple high performance liquid chromatographic method for the determination of process-related impurities in bulk drug of the central anticholinergic compound pridinol mesylate, has been developed and validated. Spectroscopically characterized synthetic impurities were used as standards. The chromatographic separation was optimized employing an experimental design strategy, and was achieved on a C₁₈ column with a mobile phase containing 50 mM potassium phosphate buffer (pH 6.4), MeOH and 2-propanol (20:69:11, v/v/v), delivered at a flow rate of 1.0 mL min⁻¹. UV detection was performed at 245 nm. The optimized method was thoroughly validated, demonstrating to be selective, when the chromatogram was recorded with a diode-array detector and peak purities were evaluated (>0.9995). The method is robust and linear (r² > 0.99) over the range 0.05-2.5% (5-250% with regards to the 1% specification limit for both process-related impurities); it is also precise, regarding repeatability (RSD ≤ 1.5% for all of the analytes) and intermediate precision aspects and LOQ values for the impurities are below 0.01%. Method accuracy, evidenced by low bias of the results and analyte recoveries in the range of 99.1-102.7%, was assessed at five analyte concentration levels. The usefulness of the determination was also demonstrated through the analysis of different lots of pridinol mesylate bulk substance. The results indicate that the method is suitable for the quality control of the bulk manufacturing of pridinol mesylate drug substance.     

Simultaneous determination of levofloxacin hemihydrate and ambroxol hydrochloride in tablets by thin-layer chromatography combined with densitometry

This paper describes the application of thin-layer chromatography (TLC) combined with densitometry to simultaneous determination of levofloxacin hemihydrate (LEV) and ambroxol hydrochloride (AMB) in bulk and tablets. The separation was achieved on aluminum sheet of silica gel 60 F ₂₅₄ using chloroform: methanol: toluene: ammonia (10: 6: 3: 0.8 v/v/v/v) as mobile phase. Quantification was carried out densitometrically at 245 nm. This system was found to give compact spots for LEV (R _f value of 0.4) and AMB (R _f value of 0.7). The calibration curves for LEV and AMB was found to be linear between 9960–16600 ng/spot (r ² = 0.999) and 600–1000 ng/spot (r ² = 0.999), respectively. The mean percentage recoveries from tablets for LEV and AMB were 99.45% and 99.58%, respectively. The TLC-densitometry method has many advantages, such as simplicity, reasonable sensitivity, rapidity, and low cost, and it can be successfully used in routine analysis of both these drugs in tablet formulations.     

Development and validation of a normal-phase high-performance thin layer chromatographic method for the analysis of sulfamethoxazole and trimethoprim in co-trimoxazole tablets

Pneumocystis carinii pneumonia (PCP) is often the ultimate mortal cause for immunocompromised individuals, such as HIV/AIDS patients. Currently, the most effective medicine for treatment and prophylaxis is co-trimoxazole, a synergistic combination of sulfamethoxazole (SMX) and trimethoprim (TMP). In order to ensure a continued availability of high quality co-trimoxazole tablets within resource-limited countries, Medicines Regulatory Authorities must perform quality control of these products. However, most pharmacopoeial methods are based on high-performance liquid chromatographic (HPLC) methods. Because of the lack of equipment, the Tanzania Food and Drugs Authority (TFDA) laboratory decided to develop and validate an alternative method of analysis based on the TLC technique with densitometric detection, for the routine quality control of co-trimoxazole tablets. SMX and TMP were separated on glass-backed silica gel 60 F₂₅₄ plates in a high-performance thin layer chromatograph (HPTLC). The mobile phase was comprised of toluene, ethylacetate and methanol (50:28.5:21.5, v:v:v). Detection wavelength was 254 nm. The R_f values were 0.30 and 0.61 for TMP and SMX, respectively. This method was validated for linearity, precision, trueness, specificity and robustness. Cochran's criterion test indicated homoscedasticity of variances for the calibration data. The F-tests for lack-of-fit indicated that straight lines were adequate to describe the relationship between spot areas and concentrations for each compound. The percentage relative standard deviations for repeatability and time-different precisions were 0.98 and 1.32, and 0.83 and 1.64 for SMX and TMP, respectively. Percentage recovery values were 99.00% ± 1.83 and 99.66% ± 1.21 for SMX and TMP, respectively. The method was found to be robust and was then successfully applied to analyze co-trimoxazole tablet samples.     

Heat-capacity measurements and thermodynamic functions of crystalline adenine; revised thermodynamic properties of aqueous adenine

The standard molar heat capacity C^°_p,m of adenine(cr) has been measured using adiabatic calorimetry over the range 6<(T/K)<310 and the results used to derive thermodynamic functions for adenine(cr) at smoothed temperatures. At T=298.15 K, C^°_p,m=(142.67±0.29) J · K⁻¹ · mol⁻¹ and the third law entropy S^°_m=(145.62±0.29) J · K⁻¹ · mol⁻¹. The standard molar Gibbs free energy of formation Δ_fG^°_m at T=298.15 K for crystalline adenine was calculated, using the standard molar enthalpy of formation for the compound and entropies of the elements from the literature, and found to be Δ_fG^°_m=(301.4±1.0) kJ · mol⁻¹. The results were combined with solution calorimetry and solubility measurements from the literature to yield revised values for the standard molar thermodynamic properties of aqueous adenine at T=298.15 K: Δ_fG^°_m=(313.4±1.0) kJ · mol⁻¹, Δ_fH^°_m=(129.5±1.4) kJ · mol⁻¹, and S_m^°=(217.68±0.44) J · K⁻¹ · mol⁻¹.     

Stability-indicating high performance thin layer chromatography determination of Paroxetine hydrochloride in bulk drug and pharmaceutical formulations

A simple selective precise and stability-indicating high performance thin layer chromatographic method of analysis of Paroxetine hydrochloride both as a bulk drug and in formulations was developed and validated. The method employed TLC (Thin Layer Chromatography) aluminum precoated with silica gel 60F-254 as the stationary phase. The solvent system consisted of butanol:acetic acid:water (8:2:0.5, v/v/v). This system was found to give compact spots for Paroxetine HCl (Rf, retardation factor, value-0.48 ± 0.02). Paroxteine HCl was subjected to acid and alkali hydrolysis, oxidation and photodegradation, where the degraded product was well separated from the pure drug. Densitometric analysis of Paroxetine hydrochloride was carried out in the absorbance mode at 295 nm. The linear regression analysis data for the calibration spots showed good relationship with (regression) r² = 0.9903 in the amount range of 300-1500 ng (nanogram) per spot. The mean value of co-relation co-efficient, slope and intercept were 0.9903 ± 0.001, 5.38 ± 0.058 and 182.5 ± 2.16 respectively. The method was validated for precision, recovery and robustness. The limits of detection and quantitation were 50 and 150 ng, respectively. The drug doesnot undergo degradation with oxidation, but gets affected in acidic and alkaline conditions. The acid and alkali degradation showed extra peaks at 0.4 and 0.08 Rf, respectively. This indicates that the drug is susceptible to acidic and alkaline medium. As the method could effectively separate the drug from its degradation products, it can be employed as a stability-indicating one.     

Simultaneous spectrophotometric flow-through measurements of pH, carbon dioxide fugacity, and total inorganic carbon in seawater

An autonomous multi-parameter flow-through CO₂ system has been developed to simultaneously measure surface seawater pH, carbon dioxide fugacity (fCO₂), and total dissolved inorganic carbon (DIC). All three measurements are based on spectrophotometric determinations of solution pH at multiple wavelengths using sulfonephthalein indicators. The pH optical cell is machined from a PEEK polymer rod bearing a bore-hole with an optical pathlength of ∼15 cm. The fCO₂ optical cell consists of Teflon AF 2400 (DuPont) capillary tubing sealed within the bore-hole of a PEEK rod. This Teflon AF tubing is filled with a standard indicator solution with a fixed total alkalinity, and forms a liquid core waveguide (LCW). The LCW functions as both a long pathlength (∼15 cm) optical cell and a membrane that equilibrates the internal standard solution with external seawater. fCO₂ is then determined by measuring the pH of the internal solution. DIC is measured by determining the pH of standard internal solutions in equilibrium with seawater that has been acidified to convert all forms of DIC to CO₂. The system runs repetitive measurement cycles with a sampling frequency of ∼7 samples (21 measurements) per hour. The system was used for underway measurements of sea surface pH, fCO₂, and DIC during the CLIVAR/CO₂ A16S cruise in the South Atlantic Ocean in 2005. The field precisions were evaluated to be 0.0008 units for pH, 0.9 μatm for fCO₂, and 2.4 μmol kg⁻¹ for DIC. These field precisions are close to those obtained in the laboratory. Direct comparison of our measurements and measurements obtained using established standard methods revealed that the system achieved field agreements of 0.0012 ± 0.0042 units for pH, 1.0 ± 2.5 μatm for fCO₂, and 2.2 ± 6.0 μmol kg⁻¹ for DIC. This system integrates spectrophotometric measurements of multiple CO₂ parameters into a single package suitable for observations of both seawater and freshwater.     

Thermomorphic fluorous phosphines as organocatalysts for Michael addition reactions

The fluorous phosphines P[(CH₂)_mR_fn]₃ (R_fn = (CF₂)_n−1CF₃; m/n = 2/8, 3/8, 3/10) are efficient nucleophilic catalysts of Michael addition reactions. They can be easily recycled based upon their highly temperature-dependent solubilities (thermomorphism), with recovery by simple liquid/solid phase separation. The phosphonium salt formed by reaction of the nucleophilic phosphine with the α,β-unsaturated system appears to be a significant component of the catalyst rest state.     

Thermochemistry of intercalation of n-alkylmonoamines into lamellar hydrated barium phenylarsonate

Hydrated layered crystalline barium phenylarsonate, Ba(HO₃AsC₆H₅)₂·2H₂O was used as host for intercalation of n-alkylmonoamine molecules CH₃(CH₂)_n-NH₂ (n = 1-4) in aqueous solution. The amount intercalated (n_f) was followed batchwise at 298 ± 1 K and the variation of the original interlayer distance (d) for hydrated barium phenylarsonate (1245 ppm) was followed by X-ray powder diffraction. Linear correlations were obtained for both d and n_f as a function of the number of carbon atoms in the aliphatic chain (n_c): d = (2225 ± 32) + (111 ± 11)n_c and n_f = (2.28 ± 0.15) − (11.50 ± 0.03)n_c. The exothermic enthalpies of intercalation increased with n_c, which was derived from the monomolecular amine layer arrangements with the longitudinal axis inclined by 60° to the inorganic sheets. The intercalation was followed by titration with amine at the solid/liquid interface and gave the enthalpy/number of carbons correlation: ΔH = −(7.25 ± 0.40) − (1.67 ± 0.10)n_c. The negative Gibbs free energies and positive entropic values reflect the favorable host/guest intercalation processes for this system.     

Measurement of methyl mercury (I) and mercury (II) in fish tissues and sediments by HPLC-ICPMS and HPLC-HGAAS

A procedure for the extraction and determination of methyl mercury and mercury (II) in fish muscle tissues and sediment samples is presented. The procedure involves extraction with 5% (v/v) 2-mercaptoethanol, separation and determination of mercury species by HPLC-ICPMS using a Perkin-Elmer 3 μm C8 (33 mm × 3 mm) column and a mobile phase 3 containing 0.5% (v/v) 2-mercaptoethanol and 5% (v/v) CH₃OH (pH 5.5) at a flow rate 1.5 ml min⁻¹ and a temperature of 25 °C. Calibration curves for methyl mercury (I) and mercury (II) standards were linear in the range of 0-100 μg l⁻¹ (r² = 0.9990 and r² = 0.9995 respectively). The lowest measurable mercury was 0.4 μg l⁻¹ which corresponds to 0.01 μg g⁻¹ in fish tissues and sediments. Methyl mercury concentrations measured in biological certified reference materials, NRCC DORM - 2 Dogfish muscle (4.4 ± 0.8 μg g⁻¹), NRCC Dolt - 3 Dogfish liver (1.55 ± 0.09 μg g⁻¹), NIST RM 50 Albacore Tuna (0.89 ± 0.08 μg g⁻¹) and IRMM IMEP-20 Tuna fish (3.6 ± 0.6 μg g⁻¹) were in agreement with the certified value (4.47 ± 0.32 μg g⁻¹, 1.59 ± 0.12 μg g⁻¹, 0.87 ± 0.03 μg g⁻¹, 4.24 ± 0.27 μg g⁻¹ respectively). For the sediment reference material ERM CC 580, a methyl mercury concentration of 0.070 ± 0.002 μg g⁻¹ was measured which corresponds to an extraction efficiency of 92 ± 3% of certified values (0.076 ± 0.04 μg g⁻¹) but within the range of published values (0.040-0.084 μg g⁻¹; mean ± s.d.: 0.073 ± 0.05 μg g⁻¹, n = 40) for this material. The extraction procedure for the fish tissues was also compared against an enzymatic extraction using Protease type XIV that has been previously published and similar results were obtained. The use of HPLC-HGAAS with a Phenomenox 5 μm Luna C18 (250 mm × 4.6 mm) column and a mobile phase containing 0.06 mol l⁻¹ ammonium acetate (Merck Pty Limited, Australia) in 5% (v/v) methanol and 0.1% (w/v) l-cysteine at 25 °C was evaluated as a complementary alternative to HPLC-ICPMS for the measurement of mercury species in fish tissues. The lowest measurable mercury concentration was 2 μg l⁻¹ and this corresponds to 0.1 μg g⁻¹ in fish tissues. Analysis of enzymatic extracts analysed by HPLC-HGAAS and HPLC-ICPMS gave equivalent results.     

Zone fluidics for measurement of octanol–water partition coefficient of drugs

A novel zone fluidics (ZF) system for the determination of the octanol–water partition coefficient (P_ow) of drugs was developed. The ZF system consisted of a syringe pump with a selection valve, a holding column, a silica capillary flow-cell and an in-line spectrophotometer. Exact microliter volumes of solvents (octanol and phosphate buffer saline) and a solution of the drug, sandwiched between air segments, were sequentially loaded into the vertically aligned holding column. Distribution of the drug between the aqueous and octanol phases occurred by the oscillation movement of the syringe pump piston. Phase separation occurred due to the difference in densities. The liquid zones were then pushed into the detection flow cell. In this method, absorbance measurements in only one of the phase (octanol or aqueous) were employed, which together with the volumes of the solvents and pure drug sample, allowed the calculation of the P_ow. The developed system was applied to the determination of the P_ow of some common drugs. The log (P_ow) values agreed well with a batch method (R² = 0.999) and literature (R² = 0.997). Standard deviations for intra- and inter-day analyses were both less than 0.1log unit. This ZF system provides a robust and automated method for screening of P_ow values in the drug discovery process.     

Formation enthalpies of rare earth titanate pyrochlores

High-temperature oxide melt solution calorimetry and Rietveld refinements of powder X-ray diffraction data were used to investigate the structure (Fd3m; Z=8) and energetics of a series of RE₂Ti₂O₇ (RE=Sm-Lu) compounds with the pyrochlore structure as well as La₂Ti₂O₇ with a layered perovskite-type structure. All of the RE-titanates were found to be stable in enthalpy with respect to their oxides. In the pyrochlore series, Lu₂Ti₂O₇ was least stable in enthalpy (ΔHf-ox at 298 K=−56.0±4.0 kJ/mol); the most stable materials were Gd-, Eu-, and Sm₂Ti₂O₇ with ΔHf-ox at 298 K=−113.4±2.7, −106.1±4.2, −115.4±4.2 kJ/mol, respectively. In general, as the radius ratio of the A- to B-site cations, R_A/R_B, decreases, the pyrochlore structure becomes less stable. The trend of ionic radius of the RE³⁺ cation vs. ΔHf-ox at 298 K is non-linear and approximately parallels the increasing “resistance” to ion-beam-induced amorphization as R_A/R_B decreases.     

Fluorimetric determination of phytic acid in urine based on replacement reaction

A sensitive fluorimetric method for determination of phytic acid in human urine samples was described. The method was based on a fluorimetric replacement reaction, in which the added phytic acid replaced the Cu²⁺ ion from Cu²⁺-gelatin complex, liberating the fluorescent gelatin molecule. The fluorescence of the solution was accordingly recovered proportionally to the amount of the foreign phytic acid. The excitation wavelength was 273.5 nm and the characteristic emission wavelength was 305.0 nm, respectively. The calibration graph was obtained by plotting the recovered fluorescent intensity at maximum 305.0 nm against the added standard phytic acid, and was divided into two sections. One section was linear over the range of 0.40-2.40 mg L⁻¹ with a linear regression equation of I_f = −0.895 + 15.146c (R² > 0.9993), and the other over the range of 2.40-9.20 mg L⁻¹ with a linear regression equation of I_f = −29.526 + 26.113c (R² > 0.9996), respectively. The relative standard deviation (R.S.D.) at 95% confidence degree for a 2.0 mg L⁻¹ of standard phytic acid within 1 month was less than 1.26% (n = 5), indicating the procedure is reproducible. The detection and the quantification limits of phytic acid were estimated to be 0.23 and 0.40 mg L⁻¹, respectively. The proposed method was applied to the determination of phytic acid in urine samples and the found concentrations of phytic acid in urine were in the range of 0.49-0.75 mg L⁻¹ with recoveries of 96.2-108.8%. Comparison of the obtained results with the reported HPLC was performed, indicating the proposed method was reliable.     

A series of new zirconium complexes bearing bis(phenoxyketimine) ligands: Synthesis, characterization and ethylene polymerization

A series of new zirconium complexes bearing bis(phenoxyketimine) ligands, bis((3,5-di-tert-butyl-C₆H₂-2-O)R₁CN (2-R₂-C₆H₄))ZrCl₂ {R₁ = Me, R₂ = H (2a); R₁ = Et, R₂ = H (2b); R₁ = Ph, R₂ = H (2c); R₁ = 2-Me-Ph, R₂ = H (2d); R₁ = 2-F-Ph, R₂ = H (2e); R₁ = 2-Cl-Ph, R₂ = H (2f); R₁ = 2-Br-Ph, R₂ = H (2g); R₁ = Ph, R₂ = Me (2h); R₁ = Ph, R₂ = F (2i)}, have been prepared, characterized and tested as catalyst precursors for ethylene polymerization. Crystal structure analysis reveals that complex 2c has a six coordinate center in a distorted octahedral geometry with trans-O, cis-N, cis-Cl arrangement which possesses approximate C₂ symmetry. When activated with methylaluminoxane (MAO), complexes 2a-2i exhibited high ethylene polymerization activities of 10⁶-10⁸ g PE (mol M h)⁻¹. Compared with the bis(phenoxyimine) zirconium analogues bis((3,5-di-tert-butyl-C₆H₂-2-O)CHNC₆H₅)ZrCl₂ (3), the introduction of substituent on the carbon atom of the imine double bond enhanced the catalytic activity and molecular weight of prepared polyethylene. Especially, when the H atom at the carbon atom of the imine double bond was replaced by 2-fluoro-phenyl with strong electronic-withdrawing property, complex 2e displayed the highest catalytic activity, and the polyethylene obtained possessed the highest molecular weight and melt point.     

New unsaturated polyesters as injectable drug carriers

New unsaturated polyesters of poly(fumaric acid-glycol-sebacic acid) copolymers and poly(maleic anhydride-glycol-sebacic acid) copolymers were prepared by melt polycondensation of the corresponding mixed monomers: sebacic anhydride, fumaric acid or maleic anhydride and glycol. Methyl-methacrylate (MMA) was used as crosslinker and dimer acid was used as thinner.In vitro studies showed that those copolymers are degradable in phosphate buffer at 37 °C and poly(fumaric acid-glycol-sebacic acid) has proper drug release rate as drug carriers. The biocompatibility of poly(fumaric acid-glycol-sebacic acid) copolymers under mice skin was also evaluated; macroscopic observation and microscopic analysis demonstrated that the copolymer is biocompatible and well tolerated in vivo. The injected poly(fumaric acid-glycol-sebacic acid) [molar ratio M_{fumaric acid}:M_glycol:M_{sebacic acid} = 1.75:2.20:0.25] containing 5% adriamycin hydrochloride (ADM) in the mice bearing Sarcoma-180 tumor exhibited a good antitumor efficacy. The volume doubling time (VDT) (18 ± 2.5 days) of the tumor growth by this treatment was longer than that (7 ± 0.9 days) by the subcutaneous injection of ADM.