Rapid spectrophotometric determination of fosfestrol following on-line hydrolysis by alkaline phosphatase using flow injection and chasing zones

A new flow injection (FI) method is reported for the spectrophotometric determination of fosfestrol (diethyl-stilbestrol (DES) diphosphate) in pharmaceutical formulations. The proposed method is based on the on-line hydrolysis of the analyte by alkaline phosphatase (Al-Pase) using a “chasing zones” FI manifold. The orthophosphate ions, thus, generated are determined spectrophotometrically (λ_max=690 nm) using the molybdenum blue approach. The chemical and FI variables affecting the enzymatic reaction were investigated. The proposed method is very precise (s_r=1.1% at 1×10⁻⁴ mol l⁻¹ fosfestrol, n=12), fast (allowing up to 40 samples h⁻¹ to be analyzed) and has a determination range of 2×10⁻⁵ to 2×10⁻⁴ mol l⁻¹, with a satisfactory 3σ detection limit of 5×10⁻⁶ mol l⁻¹. The method was shown to provide accurate determinations of the fosfestrol concentration in a pharmaceutical formulation, giving relative errors, e_r, of +0.6 and −0.5% compared to the value stated by the supplier (Asta Medica Inc.) and the concentration derived using a method recommended by the United States Pharmacopoeia XXI, respectively. In addition, the average recoveries of known amounts of the analyte ranged between 99.2 and 101.2%.     

Novel flow injection spectrophotometric determination of fosinopril using UV-assisted digestion and an orthophosphates calibration graph

This work describes the first flow injection (FI) method for the spectrophotometric determination of the anti-hypertension drug fosinopril (FSP), a phosphorus-containing compound. The method is based on the UV-assisted digestion of the analyte using ammonium peroxodisulfate as the oxidizing reagent. The yielded orthophosphate ions are determined by a rapid and robust FI method employing the molybdenum blue approach. The time needed for complete conversion of a maximum FSP amount concentration of 2.0×10⁻⁴ mol l⁻¹ was 30 min. Based on the capability of the home-made UV digester used in this work to process eight samples simultaneously, an acceptable samples analysis frequency of 16 h⁻¹ was achieved. Additionally, a very important advantage of the proposed method is that an orthophosphate ions calibration graph can be used instead of FSP, as 100% conversion of FSP was achieved. Quantitative measurements of FSP were made in the range 1.0×10⁻⁶ to 2.0×10⁻⁴ mol l⁻¹. The application of the developed FI method to the analysis of two commercially available pharmaceutical formulations produced accurate results, as the relative errors were <1.5% in both cases, compared to the labeled values.     

Sub-picogram determination of Vitamin B12 in pharmaceuticals and human serum using flow injection with chemiluminescence detection

A sensitive chemiluminescence (CL) method, based on the enhancive effect of cobalt(II) on the CL reaction between luminol and dissolved oxygen in a flow injection (FI) system, was proposed for determination of Vitamin B₁₂. The increment of the CL intensity was proportional to the concentration of Vitamin B₁₂, giving a calibration graph linear over the concentration from 2.0×10⁻¹⁰ to 1.2×10⁻⁶ g l⁻¹ (r²=0.9992) with the detection limit of 5.0×10⁻¹¹ g l⁻¹ (3σ). At a flow rate of 2.0 ml min⁻¹, a complete determination of Vitamin B₁₂, including sampling and washing, could be accomplished in 0.5 min with the relative standard deviations (R.S.D.) of less than 5.0%. The proposed method was applied successfully to the determination of Vitamin B₁₂ in pharmaceuticals, human serum, egg yolk and fish tissue.     

Voltammetric determination of isoprenaline in pharmaceutical preparations using a copper(II) hexacyanoferrate(III) modified carbon paste electrode

The electroanalytical determination of isoprenaline in pharmaceutical preparations of a homemade carbon paste electrode modified with copper(II) hexacyanoferrate(III) (CuHCF) was studied by cyclic voltammetry. Several parameters were studied for the optimization of the sensor such as electrode composition, electrolytic solution, pH effect, potential scan rate and interferences in potential. The optimum conditions were found in an electrode composition (in mass) of 15% CuHCF, 60% graphite and 25% mineral oil in 0.5 mol l⁻¹ acetate buffer solution at pH 6.0. The analytical curve for isoprenaline was linear in the concentration range from 1.96×10⁻⁴ to 1.07×10⁻³ mol l⁻¹ with a detection limit of 8.0×10⁻⁵ mol l⁻¹. The relative standard deviation was 1.2% for 1.96×10⁻⁴ mol l⁻¹ isoprenaline solution (n=5). The procedure was successfully applied to the determination of isoprenaline in pharmaceutical preparations; the CuHCF modified carbon paste electrode gave comparable results to those results obtained using a UV spectrophotometric method.     

Determination of Cr(VI) in the presence of Cr(III) and humic acid by cathodic stripping voltammetry

A voltammetric procedure in the flow system for determination of traces of Cr(VI) in the presence of Cr(III) and humic acid is presented. The calibration graph is linear from 5×10⁻¹⁰ to 1×10⁻⁷ mol l⁻¹ for an accumulation time of 120 s. The R.S.D. for 1×10⁻⁸ mol l⁻¹ Cr(VI) is 5.3% (n=5). The detection limit estimated from 3σ for a low concentration of Cr(VI) and accumulation time of 120 s is 2×10⁻¹⁰ mol l⁻¹. The method can be used for Cr(VI) determination in the presence of up to 50 mg l⁻¹ of humic acid. The validation of the method was carried out by studying the recovery of Cr(VI) from spiked river water and by the comparison of the results of determination of Cr(VI) in a soil sample. The method cannot be used for analysis of samples containing high concentrations of chloride ions such as seawater and estuarine water.     

Determination of adrenaline by using inhibited Ru(bpy)3 electrochemiluminescence

Adrenaline was found to inhibit strongly the electrochemiluminescence (ECL) from the Ru(bpy)₃²⁺/tripropylamine system when a working Pt electrode was maintained at 1.05 V (versus Ag/AgCl) in pH 8.0 phosphate buffer. On this basis, a flow injection (FI) procedure with inhibited electrochemiluminescence detection has been developed for determination of adrenaline. The method exhibited a good reproducibility, sensitivity, and stability with a detection limit (signal-to-noise ratio = 3) of 7.0×10⁻⁹ mol l⁻¹ and dynamic concentration range of 2×10⁻⁸ to 1×10⁻⁴ mol l⁻¹. The relative standard deviation was 2.2% for 1.0×10⁻⁶ mol l⁻¹ adrenaline (n=11). The method was successfully applied to the determination of adrenaline in pharmaceutical samples. Moreover, ECL emission spectra, UV-Vis absorption spectra and cyclic voltammograms of Ru(bpy)₃²⁺/tripropylamine/adrenaline were studied. The inhibition mechanism has been proposed as the interaction of electrogenerated Ru(bpy)₃^2+* and the o-benzoquinone derivatives, adrenochrome and adrenalinequinone, at the electrode surface.     

Determination of diethylstilbestrol by enhancement of luminol-hydrogen peroxide-tetrasulfonated cobalt phthalocyanine chemiluminescence

The ability of diethylstilbestrol to enhance the chemiluminescence reaction of luminol-H₂O₂, catalyzed by tetrasulfonated cobalt phthalocyanine in an alkaline medium, has been exploited to develop a new flow injection chemiluminescence method for the determination of diethylstilbestrol. Under the optimum conditions, the linearity of the calibration graph for the determination of diethylstilbestrol was in the range from 1.00×10⁻⁷ to 4.00×10⁻⁶ mol/l. The assay was sensitive (the detection limit was 6.42×10⁻⁸ mol/l, S/N=3), reproducible (the relative standard deviation was 2.6%, n=11), and accurate (recovery up to 92%). The method has been successfully applied to the determination of diethylstilbestrol in the pharmaceutical formulations. Dienestrol and hexestrol were specifically alkylphenols, which are similar to diethylstilbestrol, could be detected by this method. Furthermore, the enhanced mechanism of estrogen-like compounds was also discussed in this paper.     

The spectrophotometric determination of molybdenum and phosphorus by carminic acid method

A spectrophotometric method for the determination of molybdenum based on the use of carminic acid is proposed. Conformity to Beer's law was observed with an optimum concentration range of 1.5 to 8 ppm of molybdenum when absorbance measurements are made at 565 nm. The molar absorptivities for the determination of molybdenum are 1.4 × 10⁴ mol l⁻¹ cm⁻¹ at 565 nm and 5.1 × 10³ mol l⁻¹ cm⁻¹ at 336 nm. An indirect spectrophotometric procedure for the determination of orthophosphate based on the determination of the equivalent molybdenum in 12-molybdophosphoric acid was developed suitable for the determination of 0.03 to 0.18 ppm of phosphorus.     

Spectrophotometric flow-injection analysis of mercury(II) in pharmaceuticals with p-nitrobenzoxosulfamate

A new, simple and rapid spectrophotometric FI method for the accurate and precise determination of Hg(II) in pharmaceutical preparations has been developed. The method is based on the measuring the decrease of absorbance intensity of p-nitrobenzoxosulfamate (NBS) due to the complexation with Hg(II). The absorption peak of the NBS, which is decreased linearly by addition of Hg(II), occurs at 430 nm in 2×10⁻⁴ mol l⁻¹ HNO₃ as a carrier solution. Optimization of chemical and FI variables has been made. A micro column consisting of several packing materials applied instead of reaction coil was also investigated. A background level of Fe(III) maintained in reagent carrier solution with NBS was found useful for sensitivity and selectivity. Under the optimized conditions, the sampling rate was over 100 h⁻¹, the calibration curve obtained were linear over the range 1-10 μg ml⁻¹, the detection limit was lower than 0.2 μg ml⁻¹ for a 20 μl injection volume, and the precision [S_r=1% at 2 μg ml⁻¹ Hg(II) (n=10)] was found quite satisfactory. Application of the method to the analysis of Hg(II) in pharmaceutical preparations resulted a good agreement between the expected and found values.     

Determination of ethamsylate in pharmaceutical preparations by irreversible biamperometry

A novel flow-injection irreversible biamperometric method is described for the determination of ethamsylate. The proposed method is based on the oxidation of ethamsylate at one platinum electrode and the reduction of permanganate at another to form an irreversible biamperometric detection system. Ethamsylate can be determined over the range 1.0×10⁻⁶-1.0×10⁻⁴ mol l⁻¹ with a sample measurement frequency of 180 samples h⁻¹. The detection limit for ethamsylate is 4.0×10⁻⁷ mol l⁻¹. The stability of the proposed method is shown by a RSD of 0.52% for 11 replicate determinations of 2.0×10⁻⁵ mol l⁻¹ ethamsylate. The proposed method was applied to the determination of ethamsylate in pharmaceutical preparations.     

Spectrofluorimetric determination of aliphatic amines using a new fluorigenic reagent: 2,6-dimethylquinoline-4-(N-succinimidyl)-formate

A new amino fluorescence probe, 2,6-dimethylquinoline-4-(N-succinimidyl) formate (DMQF-OSu) has been synthesized. Based on the selective reaction of DMQF-OSu with primary and secondary aliphatic amines to yield strong fluorescence, a new spectrofluorimetric method for the determination of total aliphatic amines has been developed. At λ_ex/λ_em=324.4/416 nm, the linear calibration range was 6×10⁻⁸-6×10⁻⁶ mol l⁻¹ with the detection limit (3σ) of 1.94×10⁻¹⁰ mol l⁻¹ for the determination of aliphatic amines in weak basic media. The proposed method has been applied to the determination of aliphatic amines in tap water and lake water with the recoveries of 99-104%. Compared with the reported methods, the method presented here is rapid, simple, sensitive and feasible.     

Determination of methimazole and carbimazole by flow-injection with chemiluminescence detection based on the inhibition of the Cu(II)-catalysed luminol-hydrogen peroxide reaction

This paper reports an indirect flow-injection (FI) method for the determination of the anti-hyperthyroid drugs methimazole and carbimazole in pharmaceuticals. The method was based on the inhibition that these thioimidazole drugs caused on the Cu(II)-catalysed chemiluminescence (CL) reaction between luminol and H₂O₂. The CL reaction was induced on-line and injection of the sample produced negative peaks as a result of the Cu(II) complexation by the analytes. The height of the FI peaks was proportional to the drug concentration in the sample. The linear range was 2-100 and 3-120 mg l⁻¹ for methimazole and carbimazole, respectively. The relative standard deviation was 1.9% for methimazole and 2.1% for carbimazole at the 50 mg l⁻¹ level (n=10). Common excipients present in pharmaceutical tablets were found not to interfere with the analysis. The method was applied to the determination of methimazole and carbimazole in pharmaceutical formulations with recoveries in the range 100±4%.     

Flow injection spectrophotometric method for chloride determination in natural waters using Hg(SCN)(2) immobilized in epoxy resin

A flow injection (FI) spectrophotometric method was proposed for the determination of chloride ion in natural waters. The determination of chloride was carried out by reaction with Hg(SCN)₂ immobilized in an epoxy resin bead in a solid-phase reactor (SPR) and the thiocyanate ions released were determined spectrophotometrically at 480 nm after complexing reaction with Fe(III). The analytical curve for chloride was linear in the concentration range from 5.6 × 10⁻⁵ to 2.2 × 10⁻⁴ mol l⁻¹ with a detection limit of 1.4 × 10⁻⁵ mol l⁻¹. The relative standard deviation (R.S.D.) was 2.2% for a solution containing 2.2 × 10⁻⁴ mol l⁻¹ (n = 10). The simple manifold allows a routine analytical frequency of 100 determinations per hour. The main advantage of the developed method is the 400% reduction of the Hg waste solution generated when compared to conventional methods for chloride determination based on the same spectrophotometric reaction.     

A flow injection method for biamperometric determination of dipyrone in pharmaceuticals

A flow-injection method for determination of dipyrone (novalgin, metamizol) in pharmaceutical tablets with biamperometric detection is described. Flow-parameters such as flow rate, coil length and sample injection volume were optimized. The calibration graph was linear (r=0.9997) within the range of 10-50 mg l⁻¹ in a 1-mmol l⁻¹ HCl carrier solution for an applied potential of 100 mV between the two platinum wire electrodes. Two indicating redox systems were studied, namely Fe(III)/Fe(II) and I₂/I⁻. The former proved to be well suited as a selective and sensitive biamperometric indicating system for dipyrone in the presence of ingredients commonly accompanying the drug. The developed method was successfully applied to the determination of dipyrone in several commercial pharmaceutical preparations. The sampling rate was 71 samples per hour with a rsd of 1.6% (eight injections of a 14-mg l⁻¹ dipyrone solution). Recoveries close to 100% demonstrated the reliability of the proposed method.     

Using silica nanoparticles as a catalyst carrier to the highly sensitive determination of thiamine

The preparation and utilization of silica nanoparticles as a carrier of tetra-substituted carboxyl iron phthalocyanine (TCFePc, a novel mimetic peroxidase) is reported in this article. Compared with free TCFePc, the experimental results indicated that the TCFePc entrapped in silica nanoparticles exhibited an improved catalytic activity and good reusability. By using tetra-substituted carboxyl iron phthalocyanine-silica nanoparticles (TCFePc-SiO₂ Nps) to catalyze the oxidation reaction of thiamine by hydrogen peroxide, a new fluorimetric method was developed for the quantitative analysis of thiamine in pharmaceutical tablets. The influences of different conditions, such as the medium acidity, the reaction time and temperature, the concentrations of reagents and foreign substances, were all investigated. Under the optimum conditions, the calibration graph for thiamine was linear over the range of 5.0 × 10^− 9-1.0 × 10^− 6 mol L^− 1, with a detection limit of 2.0 × 10^− 9 mol L^− 1. The proposed method was successfully applied to the direct analysis of thiamine in two kinds of pharmaceutical tablets, and offered the advantages of simple pretreatment, rapid determination, high sensitivity and good reusability. Hence, as a carrier of the mimetic enzyme, the silica nanoparticles are effective for enzymatic reaction processes. This method is supposed to be hopeful for the determination of thiamine in other complex raw materials.     

On-line galvanic cell generated electrochemiluminescence determination of acyclovir based on the flow injection sampling

A new simple, rapid and cost effective flow injection (FI) electrochemiluminescence (ECL) method was described for the determination of acyclovir (9,2-hydroxyethoxy) methyl guanine. In the presence of acyclovir, the luminol electrochemiluminescence generated by a mini on-line galvanic cell could be greatly sensitized in alkaline medium. The relative electrochemiluminescence intensity was found to increase linearly with increasing concentration of acyclovir, which was corroborated by the calculated correlation coefficient value of 0.9994 (n=7). The limit of detection was 1.6×10⁻⁷ mol l⁻¹ and the limit of quantification was 7.9×10⁻⁷ mol l⁻¹. The proposed method was applied to the determination of acyclovir in pharmaceutical formulations. The reliability of the assay method was established by parallel determination and by standard-addition method. Experiment results demonstrated the described mini analysis system, while being simple and less time consuming, was accurate, precise and reproducible (R.S.D. = 1.6%, recoveries = 99 - 103%). Further experiments indicated that there was no significant difference between the results obtained by the proposed and official methods.     

Flow injection determination of thyroxine in pharmaceutical preparations using tris(2,2′-bipyridyl)ruthenium(III)-NADH chemiluminescence detection

A flow injection (FI) method is reported for the determination of thyroxine based on its enhancement of chemiluminescence (CL) from the Ru(bpy)₃³⁺-NADH system. The calibration graph was linear over the range 2.0-10 × 10⁻⁸ mol L⁻¹ (r² = 0.9989) with relative standard deviations (R.S.D.) in the range 2.0-4.5% (n = 4). The limit of detection (3σ blank) was 1.0 × 10⁻⁹ mol L⁻¹ with sample throughput of 120 h⁻¹. The effect of some organic compounds, anions and cations were studied for l-thyroxine determination. The method was applied to pharmaceutical preparations and the results obtained were in reasonable agreement with the amount labeled. The method was statistically compared with the results obtained by RIA; no significant disagreement at 95% confidence limit was observed. A calibration graph of NADH over the range 1.3 × 10⁻⁸-1.3 × 10⁻⁶ mol L⁻¹ was also established (r² = 0.9992) with R.S.D. in the range1.0-3.5% (n = 4). The limit of detection (3σ) was 1.0 × 10⁻¹⁰ mol L⁻¹ NADH.     

Determination of bismuth and zinc in pharmaceuticals by first derivative UV-Visible spectrophotometry

A first order derivative spectrophotometric method has been developed for the simultaneous determination of bismuth and zinc by dithizone without time-consuming extraction step. The reactions of bismuth and zinc with dithizone in a three component solution prepared in water, acetone and n-propanol mixture have been investigated. These cations react with dithizone in this mixture at pH 5.0, forming coloured complex that is stable for at least 2 h. The linear range in D evaluation was between 3.0 × 10⁻⁶ and 1.8 × 10⁻⁵ mol l⁻¹ for Zn and 2.4 × 10⁻⁶ and 1.2 × 10⁻⁵ mol l⁻¹ for Bi. The limits of detection for the analytical procedure were found 0.05 mg l⁻¹ for both cations. The relative standard deviations for the determination of 0.5 mg l⁻¹ bismuth and 0.5 mg l⁻¹ zinc were 1.2 and 1.1%, respectively, for five determinations. The procedure is simple, rapid and reliable. This method was applied to the determination of bismuth and zinc in the pharmaceutical materials successfully. Good agreement was achieved between the results obtained by the proposed and comparative methods.     

Flow-injection chemiluminescence determination of fluoroquinolones by enhancement of weak chemiluminescence from peroxynitrous acid

A flow-injection chemiluminescence (CL) method is described for the determination of fluoroquinolones including ciprofloxacin, norfloxacin and ofloxacin. The method is based on the enhancement by these compounds of the weak CL from peroxynitrous acid. The linear ranges are 1.0×10⁻⁷ to 1.0×10⁻⁵ mol l⁻¹ for ciprofloxacin and norfloxacin, and 3.0×10⁻⁷ to 3.0×10⁻⁵ mol l⁻¹ for ofloxacin, respectively. The detection limits (S/N=3) are 4.5×10⁻⁸ mol l⁻¹ ciprofloxacin, 5.9×10⁻⁸ mol l⁻¹ norfloxacin and 1.1×10⁻⁷ mol l⁻¹ ofloxacin, respectively. The proposed method was applied to the determination of fluoroquinolones in pharmaceutical preparations.