Flow-injection turbidimetric determination of homatropine methylbromide in pharmaceutical formulations using silicotungstic acid as precipitant reagent

A flow-injection turbidimetric procedure exploiting merging zones is proposed for determining homatropine methylbromide (HMB) in pharmaceutical preparations. The determination is based on the precipitation reaction of homatropine methylbromide with silicotungstic acid in acidic medium to form a precipitate, which was measured at 410 nm. The analytical curve was linear in the HMB concentration range from 8.1 × 10⁻⁵ to 2.2 × 10⁻⁴ mol l⁻¹, with a detection limit of 5.0 × 10⁻⁶ mol l⁻¹. The recoveries ranged from 96 to 103%, the sampling frequency was 70 determinations per hour and relative standard deviations were less than 1.5% (n = 10). The results obtained for commercial formulations using the FIA procedure were in good agreement with those obtained by using a comparative method.     

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.     

Sensitized extraction spectrophotometric determination of Hg(II) with dithizone after its flotation as ion-associate using iodide and ferroin

This paper describes a simple and highly selective method for the separation, preconcentration and spectrophotometric determination of extremely low concentration of mercury. The method is based on the flotation of an ion-associate of HgI₄²⁻ and ferroin between aqueous and n-heptane interface at pH 5. The ion-associate was then separated and treated with ammonia and dithizone solutions to extract only the mercury chelate with CH₂Cl₂. The measurement is feasible when the volume of the water sample containing Hg(II) was varied over 50-800 ml. Beer's law was obeyed over the concentration range of 8 × 10⁻⁹ to 1.6 × 10⁻⁷ mol l⁻¹ with an apparent molar absorptivity of 6.53 × 10⁶ l mol⁻¹ cm⁻¹ for a 500 ml aliquot of the water sample. The detection limit (n = 7) was 5.0 × 10⁻¹⁰ mol l⁻¹ and the R.S.D. (n = 5) for 8.0 × 10⁻⁷ mol l⁻¹ of Hg(II) was 3.7%. A notable advantage of the method is that the determination of Hg(II) is free from the interference of almost all cations and anions found in the environmental and waste water samples. The determination of Hg(II) in tap, synthetic sea water and human hair samples was carried out by the present method and cold vapor atomic absorption spectrometry (CV-AAS). The results were satisfactorily comparable so that the applicability of the proposed method was confirmed to the real samples.     

Flow-injection investigation of the chemiluminescent reaction of bis(2,4,6-(trichlorophenyl)oxalate) with free chlorine

This work investigated the chemiluminescent reaction of free chlorine with bis(2,4,6-(trichlorophenyl)oxalate) (TCPO) in the presence of 9,10-diphenylanthracene in acetonitrile/water medium, with analytical application for free chlorine in tap water. In the absence of free chlorine, the background signal increased with the pH and the chemiluminescence emission showed strong dependence with the sample acidity. A flow injection analysis system, for free chlorine determination, was developed. The linear range for free chlorine was (0.2-3.0)×10⁻⁵ mol l⁻¹. Chloramine 1.0×10⁻⁵ mol l⁻¹ and chlorite 1.0×10⁻⁶ mol l⁻¹ also enhanced the chemiluminescence intensity.     

Post-column terbium complexation and sensitized fluorescence detection for the determination of norepinephrine, epinephrine and dopamine using high-performance liquid chromatography

Terbium sensitized fluorescence was used as a post-column detection system to develop a simple, sensitive and rapid high-performance liquid chromatographic method for the simultaneous determination of catecholamines norepinephrine (NE), epinephrine (E) and dopamine (DA).Catecholamines were separated by an ion-pair reversed-phase chromatography on a BDS-Hypersil analytical column with a mobile phase of methanol and 50 mmol l⁻¹ acetate buffer (pH 4.7) containing 1.1 mmol l⁻¹ SOS and 0.11 mmol l⁻¹ EDTA (15+85 v/v).Catecholamines and the internal standard (3,4-dihydroxybenzylamine, DHBA) were post-column derivatized by the addition to the eluent of an alkaline solution containing a stoichiometric mixture of terbium(III) chloride and EDTA. Fluorescence detection (λ_ex=300 nm, λ_em=545 nm) is based on the sensitization of terbium ion fluorescence after complexation with catecholamines.The chemical compatibility between the eluent and the post-column reagent was studied and the analytical characteristics of the method were established. Detection limits found were 1.0×10⁻⁸, 4.0×10⁻⁸ and 7.0×10⁻⁸ mol l⁻¹ for NE, E and DA, respectively. The method has been successfully applied to the determination of catecholamines in urine samples after solid-phase extraction (SPE) pre-treatment. Recoveries from urine spiked with NE (4.0×10⁻⁷, 2.0×10⁻⁶ and 4.0×10⁻⁶ mol l⁻¹), E (8.2×10⁻⁸, 4.1×10⁻⁷ and 8.2×10⁻⁷ mol l⁻¹) and DA (1.0×10⁻⁶, 5.0×10⁻⁶ and 1.0×10⁻⁵ mol l⁻¹) varied from 98 to 100% (mean=99.3%), from 106 to 107% (mean=106.3%) and from 98 to 101% (mean=99.3%), respectively. The between-run precision (relative standard deviation, R.S.D.) for the method for three urine samples at different concentration levels of each catecholamine varied from 3.6 to 7.0%.     

Voltammetry determination of trace manganese with pretreatment glassy carbon electrode by linear sweep voltammetry

This paper described the determination of trace manganese using linear sweep voltammetry at a pretreatment glassy carbon electrode. The glassy carbon electrode pretreated by electrochemical method in the 0.1 mol l⁻¹ NaOH solution greatly improved the electrode responsibility in the determination of manganese(II). The barrier to the detection of low manganese concentration was overcome by means of autocatalytic effect of manganese oxide deposited on the electrode in advance. Under the optimum experiments condition (0.04 mol l⁻¹ NH₃-NH₄Cl buffer solution, pH 9.0), the linear range was 4×10⁻⁸ to 1×l0⁻⁶ mol l⁻¹ Mn(II) for linear sweep voltammetry and 1×10⁻⁹ to 4×10⁻⁸ mol l⁻¹ Mn(II) for convolution voltammetry. The relative standard deviation for 2×10⁻⁸ mol l⁻¹ Mn(II) is 3.4%. The proposed method is simple, rapid, sensitive and selective. It had been applied to the determination of trace manganese in samples with satisfactory results.     

Sequential injection system for simultaneous determination of chloride and iodide by a Gran’s plot method

This paper describes an automated set-up based on the sequential injection analysis (SIA) concept with potentiometric detection for the determination of chloride and iodide at low concentrations. The assessment of both ion concentrations is accomplished by titration with silver ions using the Gran’s plot approach. The proposed procedure enables chloride and iodide to be determined simultaneously in the range 6.0×10⁻⁶ to 1.0×10⁻⁴ mol l⁻¹ if a minimum silver concentration in the volumetric solution is chosen (5×10⁻⁵ mol l⁻¹). Conventional titrations based on the first derivative evaluation of the equivalence points applied to the same solutions fail, especially for chloride determinations. Although, a comparison of results obtained for higher analyte concentrations shows that they have similar accuracy and precision.     

An environmentally friendly multicommutated alternative to the reference method for anionic surfactant determination in water

It has been developed a fully mechanized procedure for the spectrophotometric determination of anionic surfactants in water expressed in terms of SDS concentration. The reference method, based on the reaction of SDS with methylene blue (MB) followed by extraction in chloroform, was mechanized in order to reduce the consumption of organic solvents. The system was based on the multicommutation approach and provided a 35 times reduction of the waste production without sacrificing the figures of merit of the method in terms of sensitivity and repeatability, for a dynamic linear range from 0.2 to 1.7 mg l⁻¹. Results obtained for washing water samples were comparable with those obtained using the reference method and no significant differences, at 95% confidence level, were observed. Other useful characteristics are a solvent consumption of 0.7 ml per determination, a sampling throughput of 40 determinations per hour, a relative standard deviation of 5.9% (n = 10) for a sample containing 2 × 10⁻⁶ mol l⁻¹ (576 μg l⁻¹) surfactant and a limit of detection of 6.1 × 10⁻⁹ mol l⁻¹ (1.7 μg l⁻¹).     

Spectrophotometric determination of tungsten based on molybdotungsten isopolyanions in presence of non-ionic surfactant

Simple and sensitive method was developed for the spectrophotometric determination of tungsten. The method was based on the formation of the colour associate of molybdotungsten isopolyanion (IPA) with organic dye malachite green and solubilization in the solution of non-ionic surface-active substance (SAS). Recommended procedure permits tungsten determination in the linear range 10⁻⁶ to 10⁻⁵ mol l⁻¹ with ε=7.1×10⁴ mol⁻¹ l cm⁻¹. More than 100-fold excess of molybdenum do not interfere. The proposed method was applied to the determination of tungsten in cobalt-molybdenum catalyst and in stainless steel with satisfactory results.     

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.     

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.     

An optical redox chemical sensor for determination of iodide

A novel optical sensor based on a redox reaction for the determination of iodide has been developed. The optode membrane is constructed by immobilization of methyltrioctylammonium chloride on triacetylcellulose polymer. The exchange of chloride as counter ion with iodate in the membrane changes the color to yellow, when it is placed in acidic solution of iodide. The sensor can readily be regenerated by 0.1 mol L⁻¹ NaOH in less than 15 s. The optode has a linear range of 3.94 × 10⁻⁶ to 5.51 × 10⁻⁵ mol L⁻¹ of iodide ions with a limit of detection 7.44 × 10⁻⁷ mol L⁻¹. The relative standard deviation for eight replicate measurements of 3.94 × 10⁻⁶ and 1.57 × 10⁻⁵ mol L⁻¹ of iodide was 2.83 and 1.38%, respectively. The sensor was successfully applied to the determination of iodide in tablet, powdered milk and urine samples.     

New potentiometric sensors for creatinine

Three main types of creatinine potentiometric membrane sensors are described. They are based on the use of dibenzo-30-crown-10 (DB30C10) with potassium tetrakis(p-chlorophenyl)borate type (I), dibenzo-30-crown-10 alone type (II), and potassium tetrakis(p-chlorophenyl)borate alone type (III), incorporating in poly(vinyl chloride) matrix membrane plasticized with either o-nitrophenyl octyl ether or dioctylphthalate. The sensors are used for quantification of creatinine after soaking the membranes in 0.1 M creatinine solution for 2 days. The sensors show almost the same potentiometric response characteristics. Sensor type (I) exhibits Nernstian responses over a concentration range of 5.0 × 10⁻⁵ mol l⁻¹-1.0 × 10⁻² mol l⁻¹ creatinine with cationic slopes of 59.5 ± 0.1 and 60 ± 0.2 mV decade⁻¹ and detection limits of 1.1 × 10⁻⁵ mol l⁻¹ and 8 × 10⁻⁶ mol l⁻¹ creatinine, over the pH range of 3.5-6.5 and 3.5-7.0, for o-NPOE and DOP solvent mediators, respectively. Sensor type (II) displays Nernstian responses over a concentration range of 6.0 × 10⁻⁵ mol l⁻¹-1.0 × 10⁻² mol l⁻¹ creatinine with cationic slopes of 60.0 ± 0.1 and 65.0 ± 0.2 mV decade⁻¹ and detection limits of 1.5 × 10⁻⁵ mol l⁻¹ and 1.4 × 10⁻⁵ mol l⁻¹ creatinine over the pH range of 2.6-6.2 and 2.5-6.0, for o-NPOE and DOP solvent mediators, respectively. Sensor type (III) shows Nernstian responses over a concentration range of 7.0 × 10⁻⁵ mol l⁻¹-1.0 × 10⁻² mol l⁻¹ creatinine with cationic slopes of 60 ± 0.1 and 62.0 ± 0.2 mV decade⁻¹ and detection limits of 2.7 × 10⁻⁵ mol l⁻¹ and 2.0 × 10⁻⁵ mol l⁻¹ creatinine over the pH range of 2.5-6.0, for o-NPOE and DOP solvent mediators, respectively. The response times of the sensors for 10⁻³ mol l⁻¹ creatinine solution are instantaneous (4-10 s). The sensors show long-term stability with life span of ∼6 months. The sensors are used for determination of serum creatinine of rats (Rattus Norvigicus) with mean R.S.D. of 2.62%, and the results agreed well with the Jaffe kinetic method.     

Voltammetric determination of food colorants using a polyallylamine modified tubular electrode in a multicommutated flow system

This work describes the construction of a polyallylamine modified tubular glassy carbon electrode and its application in the electroreduction of food azo colorants (tartrazine, sunset yellow and allura red) by square wave voltammetry. The electrode modification prevented the surface fouling and, simultaneously, enhanced the analytical signal intensity. The developed unit was coupled to a multicommutated flow system which, given the complexity of samples, was designed to allow the implementation of the standard additions method in an automatic way, using only one standard solution.The described method presented a linear range up to about 2.0 × 10⁻⁴ mol l⁻¹ for the referred colorants, with a detection limit of 1.8 × 10⁻⁶ mol l⁻¹ for tartrazine, 3.5 × 10⁻⁶ mol l⁻¹ for sunset yellow and 1.4 × 10⁻⁶ mol l⁻¹ for allura red. The method was applied in the analysis of these colorants in several food samples, and no statistically significant difference between the results obtained by the proposed and the comparative method (HPLC) was found, at a 95% confidence level. Repeatability in the analysis of samples (expressed in R.S.D.) was about 3% (n = 10).     

Flow-injection chemiluminescence determination of ascorbic acid by use of the cerium(IV)-Rhodamine B system

A highly sensitive flow-injection (FI) method with chemiluminescence (CL) detection is used for the determination of l-ascorbic acid. The method is based on the CL reaction of Rhodamine B with cerium(IV) in sulfuric acid media. l-Ascorbic acid is suggested to be a catalyst utilized in the energy-transferred excitation process. The proposed procedure allows quantitation of l-ascorbic acid in the range 3.8×10⁻¹³ to 1.0×10⁻¹⁰ mol l⁻¹ with a correlation coefficient of 0.9998 (n=5) and relative standard deviation (R.S.D.) of 0.92% (n=11) at 1.0×10⁻¹¹ mol l⁻¹. The detection limit (3×blank) was 1.0×10⁻¹³ mol l⁻¹. The method is successfully used to determine l-ascorbic acid in fresh vegetables. The possible mechanism of the chemiluminescence in the system is discussed.     

Flow injection system with in-line Winkler's procedure using 16-way valve and spectrofluorimetric determination of dissolved oxygen in environmental waters

Flow injection spectrofluorimetry with in-line Winklers procedure was developed for the dissolved oxygen (DO) determination. 2-Thionaphthol reacted with iodine produced by Winkler’s method to form fluorescence inactive disulfide compound. To automate the process completely, a 5-channel flow system with a newly designed 16-way valve was assembled. The system consisted of a dispersion coil (DC), a precipitate formation coil (PFC), a precipitate dissolving coil (PDC), and extraction coil (EC). A calibration can be constructed by using a standard iodine solution for dissolved oxygen. The calibration graph was linear over the range 1.2×10⁻⁴∼6.0×10⁻⁴ mol l⁻¹ iodine (1.96∼9.80 mg O l⁻¹)). The relative standard deviation (n=6) was below 0.3% for the 4×10⁻⁴ mol l⁻¹ iodine (6.27 mg O l⁻¹) determination. The sample throughput was 12/h.     

Chemiluminometric determination of carvedilol in a multi-pumping flow system

In this work a simple, fast, sensitive and selective flow-based procedure for the chemiluminometric determination of carvedilol, a recent non-cardioselective β-blocker with noteworthy antioxidant activity, is proposed. The developed methodology takes advantage of the antioxidant capacity of carvedilol to inhibit the chemiluminescence response resulting from the oxidation of luminol by hypochlorite, by acting as a hypochlorite scavenger. The analytical process was implemented in a multi-pumping flow system that employs multiple solenoid actuated micro-pumps as the only active components. These acted as solution insertion, propelling and commuting units assuring an easily controlled, low cost, compact and reliable analytical system.A linear working range for carvedilol concentrations ranging from 1.2 × 10⁻⁷ to 3.0 × 10⁻⁶ mol l⁻¹ (r > 0.999, n = 6), was obtained, with a detection limit of 8.7 × 10⁻⁹ mol l⁻¹. The system handles about 65 samples per hour yielding precise results (R.S.D. < 1.3%, n = 10). Recoveries within 95 and 104% were obtained.     

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%.     

Determination of trace amount of bismuth(III) by adsorptive anodic stripping voltammetry at carbon paste electrode

A sensitive method is described for the determination of trace bismuth based on the bismuth-bromopyrogallol red (BPR) adsorption at a carbon paste electrode (CPE). The overall analysis involved a three-step procedure: accumulation, reduction, and anodic stripping. Optimal conditions were found to be an electrode containing 25% paraffin oil and 75% high purity graphite powder, a 0.30 mol l⁻¹ HCl solution containing 2.0×10⁻⁵ mol l⁻¹ BPR as supporting medium; accumulation potential and time, −0.10 V, 3 min; reduction potential and time, −0.35 V, 60 s; scan rate 100 mV s⁻¹; scan range from −0.35 to 0.15 V. It was found that the Bi(III)-BPR complex could be accumulated on the electrode surface during the accumulation period. Then the Bi(III) in the Bi(III)-BPR complex on the CPE surface was reduced to Bi(0) during reduction interval and finally reoxidized during the anodic stripping step for voltammetric quantification. Factors affecting the accumulation, reduction, and stripping steps were investigated. Interferences by other ions were studied as well. The detection limit was found to be 5×10⁻¹⁰ mol l⁻¹ with a 3 min accumulation time. The linear range was from 1.0×10⁻⁹ to 5.0×10⁻⁷ mol l⁻¹. Application of the procedure to the determination of bismuth in water and human hair samples gave good results.     

Chemiluminometric photo-induced determination of Strychnine in a Multicommutation flow assembly

This paper deals on the determination of Strychnine, a potent and dangerous pesticide and the analytical procedure is based on the photo-induced chemiluminescence of the pesticide by means of the Multicommutation continuous-flow methodology. Small segments of the pesticide solution were sequentially alternated with segments of the solution for adjusting the suitable medium for the photodegradation. The required time of UV irradiation was obtained by stopped-flow during 150 s; then, the resulting solution formed alternated segments with the oxidizing solution containing 5 × 10⁻³ mol l⁻¹ Ce(IV) in 0.6 mol l⁻¹ nitric acid. The calibration range, from 2 μg l⁻¹ to 50 mg l⁻¹, resulted in a linear behaviour over the range 25 μg l⁻¹ to 20 mg l⁻¹ and fitting the equation: I = 4706x + 624 with a correlation coefficient of 0.9955. The limit of detection was 2 μg l⁻¹ and the sample throughput 15 h⁻¹. After testing the influence of a large series of potential interferents, the method was applied to different kinds of samples.