Automated stopped-flow system in pharmaceutical and clinical analysis : Kinetic determination of acetaminophen in formulations and serum by using the iron(II)—2,4,6-tris(2-pyridyl)-s-triazine

The development of automated stopped-flow spectrophotometric systems, their potential in automated routine determinations using kinetic and fast equilibrium techniques and several examples of applications are briefly reviewed. The use of a compact, inexpensive laboratory-made stopped-flow system for the measurement of reaction rates and a fast equilibrium method for the determination of acetaminophen in formulations and serum are described. The reaction-rate method is based on monitoring the oxidation of acetaminophen by iron(III) in the presence of the chelating agent 2,4,6-tris(2-pyridyl)-s-triazine to form a highly absorbing complex of iron(II). The calibration graph is linear in the range 20–200 μg ml^?1, with a precision of 0.8–2.6%, a detection limit of 5.5 μg ml^?1 and a measurement throughput of 120 per hour. Common excipients do not interfere and the analysis of commercial formulations gave results similar to those of a reference method. The optimization of the experimental conditions was done by a kinetic study of the reaction and some kinetic parameters are given.The method for the determination of acetaminophen in serum is based on a rapid measurement of the absorbance of the reaction mixture after a delay time of 15 s in the presence of chlorpromazine, which catalyses the reaction. Acetaminophen is isolated by extraction with ethyl acetate and the calibration graph is linear in the range 0.5–6 μg ml^?1 with a detection limit of 0.04 μg ml^?1 and a precision of 1.5%. The proposed method showed a decreased interference from drugs that also react with iron(III).     

Flow-injection determination of europium after on-line reduction

A zinc reductor minicolumn is used in a flow-injection system for reduction of europium(III) to europium(II). Europium(II) is indirectly determined either spectrophotometrically by oxidation with iron(III) and reaction of the iron(II) formed with 1,10- phenanthroline, or spectrofluorimetrically by reaction with cerium(IV) and measurement of the cerium(III) produced. The reductor functions efficiently at flow rates up to 1 ml min^?1, which allows sample injection rates up to 100 h^?1. Linear calibration is achieved for 10–200 and 0.5–4 μg ml^?1 with detection limits of 2.5 and 0.25 μg ml^?1, by spectrophotometry and spectrofluorimetry, respectively.     

Modular stopped-flow/diode-array detection system for simultaneous kinetic analysis

The coupling of a stopped-flow module to a diode-array spectrophotometric detector has been exploited for the simultaneous kinetic resolution of mixtures. The analytical possibilities are shown with the resolution of a mixture of two analytes (hydrazine and phenylhydrazine), yielding products with different spectral features (after reaction with p-dimethylaminobenzaldehyde), so that only the simultaneous measurement of their respective initial rates at their corresponding maximum absorption wavelengths is possible. The method allows 0.02–30 μg ml^?1 hydrazine and 8–2200 μg ml^?1 phenylhydrazine to be determined simultaneously.     

Colorimetric Determination of Propofol in Bulk form,Dosage Form and Biological Fluids

ABSTRACT

Propofol is coupled with 2, 6-dichloroquinone-4-chlorimide (DCQ) in a reaction buffered at pH 9.6 to give a colored product having an analytically useful maximum at 635 nm. The factors affecting the color generation were optimized and incorporated in the procedure. The reacted propofol has a molar absorptivity of 3.9 × 10^?4 L mol^?1 cm^?1, and Beer's law is obeyed for concentrations 1-5 μg ml^?1 with detection limit 0.25 μg ml^?1. The method was found applicable to biological fluids (plasma and urine) spiked with propofol at concentration levels 1-5 μg ml^?1 for plasma and 1-5 μg 0.5 ml^?1 urine (less sensitivity is obtained with urine volumes above 0.5 ml) with detection limits 0.28 μg ml^?1 for plasma and 0.4 μg 0.5 ml^?1 urine. The average recovery for the commercial preparation (1% w/v propofol emulsion intravenous injection for infusion) was 99.54% with an RSD of 1.05%. The method was validated by an adopted HPLC method. The results obtained by the HPLC method for the commercial preparation were statistically compared with the proposed method and evaluated at the 95% confidence limits.     

Spectrophotometric determination of iron(III) with EDTA tetrahydrazide

The tetrahydrazide of ethylenediamine tetraacetic acid (NH₂NH)₄-EDTA was synthesized from the EDTA ester and hydrazine hydrate in ethanolic solution, the resulting (NH₂NH)₄-EDTA being recrystallized in 60% ethanol. When the spectrophotometric study of the iron(III) (NH₂NH)₄-EDTA complex in aqueous solution was made two absorption maxima at 530 and 450 nm at pH 4.5 and 11.0, respectively, were found. Beer's law is obeyed in the range 1.0–20.0 μg Fe(III) ml^?1 at 530 nm and pH 4.5 and 0.5–12.0 μg Fe(III) ml^?1 at 450 nm and pH 11.0, the molar absorptivities being 1.95 × 10³ 1 mol^?1 cm^?1 at 530 nm and 3.35 × 10³ 1 mol^?1 cm^?1 at 450 nm, respectively. The Ringbom optimal interval falls between about 3 and 18 μg Fe(III) ml^?1 at 530 nm and about 2–14 μg Fe(III) ml^?1 at 450 nm. The reaction between the metal and the ligand was also investigated. The method has been successfully applied to the determination of iron in talcs.     

Utility of p-chloranilic Acid and 2,3 Dichloro-5,6-dicyano p-Benzoquinone (DDQ) for the Spectrophotometric Determination of Triamterene

Abstract

Two simple and sensitive spectrophotometric procedures are suggested for analysis of triamterene. The first procedure is based on the reaction of triamterene with p-chloranilic acid (p-CA) in methylene chloride to form a highly stable coloured product, exhibiting maximum absorbance at λ 530 nm. Beer's law is obeyed in the range of 40–220 μg.ml^?1 with a mean percentage accuracy of 99.98 ± 0.446. Limit of determination is 20 μg.ml^?1. In the second procedure, the drug is determined via charge transfer complex formation with 2,3 dichloro-5,6-dicyano p-benzoquinone (DDQ) using methylene chloride as a solvent. Here the reaction product has two well defined maxima at 460 nm and 530 nm where each has been utilized for quantitative determination. Beer's law is obeyed in concentration ranges of 25–125 μg.ml^?1 and 25–150 μg.ml^?1 with mean percentage accuracies of 99.92 ± 0.449 and 100.00 ± 0.511 for both maxima. 460 and 530 nm. respectively. Limit of determination is 12.5 μg.ml^?1 at both maxima. Optimum conditions for each procedure have been studied and the stoichiometry of both reactions was ascertained using Job's method of continuous variation. The validity of the suggested procedures was assessed by applying the standard addition technique using the drug capsules. Both procedures are statistically analyzed as compared with BP method for analysis of triamterene (non aqueous titration) revealing good accuracy and precision as indicated by t and F tests.     

Inductively-coupled plasma atomic emission spectrometric determination of boron based on generation of methyl borate

Boron is converted to methyl borate, distilled and condensed, and selectively volatilized at 50°C into the plasma without interference from methanol, which quenches the plasma. The 3σ detection limit is 40 ng ml^?1 boron, the calibration graph is linear up to 10 μg ml^?1 and the r.s.d. 3.0% for 2.0 μg ml^?1 (n = 10). Boron is determined in plant-tissue and steel standards.     

Spectrophotometric determination of osmium with phthalimide dithiosemicarbazone by means of complex formation and catalytic reactions

Phthalimide dithiosemicarbazone forms a 1:1 complex with osmium at pH 3.3–4.5 (?₄₅₀ = 1.3 · 10⁴ l mol^?1 cm^?1 ) which is applied to the photometric determination of osmium; Beer's law is obeyed for the range 1–12 μg Os ml^?1. The oxidation of the reagent with cerium(IV) is catalyzed by osmium(VIII), and this reaction allows a more sensitive procedure for the determination of osmium; the calibration curve is linear over the range 0.05–0.4 μg Os ml^?1. The interferences in both procedures are described.     

Controlled anodic generation of the catalyst in kinetic continuous flow analysis

Controlled anodic dissolution of copper in a separate generator cell yields well-defined concentrations of catalyst, depending on the voltage applied. This adjustable generation of copper catalyst makes it possible to determine iron over a wide range of concentration (10–1500 μg Fe³⁺ ml^-1) via the iron(III)—thiosulphate reaction. By the copper(II)-catalyzed hydrogen peroxide—hydroquinone reaction, EDTA can be determined as an inhibitor (0.5–5 μg ml^-1) and cadmium(II) as a reactivator (1–10 μg ml^-1). As zinc(II) forms complexes with 2,2'-bipyridine, which activates copper in this reaction, it can be determined (5–50 μg Zn²⁺ ml^-1) by measuring the decrease in activation. The electrogeneration of silver ion as a catalyst is also described. The sulphanilic acid—peroxodisulphate reaction is catalyzed by silver(I), which is again activated by 2,2'-bipyridine. Zinc(II) can be determined (0.29–2.9 mg Zn²⁺ ml^-1) by the same principle as in the copper(II)-catalyzed reaction.     

Integrated Retention/Spectrophotometric Detection Method for the Determination of Formaldehyde

Abstract

An integrated-sensor method for the determination of formaldehyde based on retention of the reaction product of the analyte with p-rosaniline and sulfite in a flow-cell packed with Dowex 1-X-8 anion exchange resin was developed. The method has a good selectivity with a detection limit of 0.3 μg ml^?1 (1 ml sample) or 75 ng ml^?1 (2 ml sample), and a linear range between 1–30 μg ml^?1. The relative standard deviations (n = 11) were 2.8 and 1.3% for 2 and 20 μg ml^?1 formaldehyde, respectively. Depending on the working conditions, the sampling frenquency ranged between 10 and 18 h^?1. The method was applied to the determination of formaldehyde in well water.     

Flow-injection spectrophotometric determination of ascorbic acid by reduction of vanadotungstophosphoric acid

Ascorbic acid may be determined spectrophotometrically at 360 nm based on reduction of vanadotungstophosphoric acid using flow-injection analysis. The carrier stream was distilled water and the reagent streams were buffer solution (pH 3.0), 1.735 × 10^?3 M dodecatungstophosphoric acid and 1.735 × 10^?3 M sodium vanadate. The injection rate was 80 h^?1. The calibration graph was linear up to 80 μg ml^?1 ascorbic acid and the relative standard deviation for the determination of 20 μg ml^?1 ascorbic acid was 1.5% (n=10). The detection limit was 1.0 μg ml^?1 ascorbic acid, based on an injection volume of 250 μl. The system was applied to the determination of ascorbic acid in vitamin C tablets.     

Flow injection spectrophotometry followed by atomic Absorption spectrometry for the determination of iron(II) and total iron

In the flow system described, iron(II) is measured spectrophotometrically with 1,10-phenanthroline, and total iron is determined in the same flow line by atomic absorption spectrometry. Linear calibration ranges are 0.1–35 and 0.1–10 μg ml^?1 for iron(II) and total iron, respectively.     

Double indication in catalytic-kinetic analysis: simultaneous photometric and thermometric indication of the iodine-azide reaction in closed and flow systems

The iodine—azide reaction catalyzed by sulphur-containing compounds is followed simultaneously by optical and thermometric measurements in closed and flowing systems. In the closed system, thiosulphate can be determined in the range 32.4–324 μg ml^-1, by observing the turbidity caused by the nitrogen formed during the reaction and the temperature changes. With the flow apparatus, thiosulphate can be determined in the range 112–1120 μg ml^-1 by continuously mixing the sample and reagent solutions. H₂S in nitrogen 5–100 ppm) is measured by sweeping the gas into the reaction Cuvette. In a third flow procedure, H₂S is liberated continuously from sodium sulphide solutions (0.1–10 μg S^2- ml^-1) by ascorbic acid, and swept to the measuring cuvette with nitrogen.     

Determination of mixtures of ampicillin and cloxacillin in pharmaceuticals by second-derivative spectrophotometry

Mixtures of ampicillin-Na and cloxacillin-Na are assayed by peak-to-baseline and zero-crossing second-derivative spectrophotometry. The procedure does not require any separation step. Calibration plots are linear (r = 0.9999) up to 30 μg ml^?1 of ampicillin-Na at 216 nm and up to 40 μg ml^?1 ampicillin-Na or cloxacillin-Na at 228 nm or 248.8 nm, respectively, in the presence of one another. Detection limits at the p = 0.05 level of significance, range from 0.15 pg ml^?1 to 0.33 μg ml^?1. The method was successfully applied to commercial injections and capsules containing these penicillins.     

The spectrophotometric determination of gold with bromopyrogallol red

Optimum conditions were found for the reaction of Au(III) with bromopyrogallol red and a new spectrophotometric determination of Au(III) ions was developed. At a wavelength of 400 nm the Lambert-Beer law is followed in a range of 0.1 to 3.0 μg Au ml^?1 and the absorption coefficient ? = 3 × 10⁴M^?1 cm^?1. The effect of cationic tensides on the studied reaction was also studied; it was found that in their presence the properties of the system are strongly affected by the ionic strength of the solution. The changes observed are a result of the effect of the ionic strength on the dissociation constant of the DG-tenside system.     

Fluorimetric kinetic method for the determination of total ascorbic acid with o-phenylenediamine

A fluorimetric reaction-rate method for the determination of L-ascorbic acid (AA) in aqueous solution is presented. The technique is based on the rapid oxidation of AA by mercury(II) chloride to dehydro-L-ascorbic acid, which then reacts with o-phenylenediamine to form a fluorescent quinoxaline. The formation of the product is monitored fluorimetrically with a data acquisition system based on a microcomputer, a voltage-to-frequency converter and a timer-counter board. The initial rate is estimated with a fixed-time computational method. With a 20-s measurement time (after a 5-s delay from initiation of the reaction), the detection limit for AA is 0.02 μg ml^?1 with a linear dynamic range extending to 10 μg ml^?. The procedure is applied to the determination of the AA in vitamin pills and juice. The relative standard deviation is 1.9% or better.     

Spectrophotometric determination of total cyanide in waste waters in a flow-injection system with gas-diffusion separation and preconcentration

An automated flow-injection system with gas diffusion separation and preconcentration and spectrophotometric detection is described for the determination of total cyanide in waste waters. An unstable red intermediate product of the reaction of cyanide with isonicotinic acid and 3-methyl-1-phenyl-2-pyrazolin-5-one is used instead of the conventional blue final product to improve the efficiency. A novel combination of a gas-diffusion separator with the sampling valve enables efficient on-line separation, preconcentration and sampling of cyanide. The sampling frequency is 40 h^?1 and the detection limit is 0.006 μg ml^?1 (3σ) when a 2-ml sample is taken and a preconcentration factor of 3.5 is achieved. The relative standard deviation is 1.4% (n = 22) at the 0.5 μg ml^?1 level. Results obtained with the proposed method are in good agreement with the standard manual spectrophotometric method. Interference studies show that in the presence of 1,10-phenanthroline, most potential interferents present in appreciable amounts do not interfere, but the interference from cobalt is not overcome in this system.     

Determination of Pindone in Baits by using Time-Resolved Lanthanide-Sensitized Luminescence and Kinetic Methodology

ABSTRACT

A simple and fast kinetic method for the determination of pindone in baits was developed. It is based on the inhibitory effect of this indanedione rodenticide on the luminescence of the europium(III)-thenoyltrifluoracetone system in the presence of cetyltrimethylammonium bromide. The relatively long lifetime of this system allows the time-resolved mode to be used, which eliminates any fluorescence signal. To avoid the potential static background signal of the sample, the difference between the initial rate obtained in the absence and presence of pindone is used as the analytical parameter, which is obtained within only 0.2 s with the aid of a stopped-flow mixing technique. The calibration graph is linear in the range 0.1-10.0 μg ml^?1 pindone and the detection limit is 0.04 μg ml^?1. The relative standard deviation is close to 3%. The recoveries obtained by applying the method directly to the analysis of bait samples ranged from 92.0 to 114%.     

Gas-chromatographic determination of 1-(2-chloroethyl)-3-(trans-4-methylcyclohexyl)-1-nitrosourea in plasma after reaction with trifluoroacetic anhydride

The reaction of 1-(2-chloroethyl)-3-(trans-4-methylcyclohexyl)-1-nitrosourea (methyl-CCNU) with trifluoroacetic anhydride is reported. Gas-liquid chromatography of the resulting trifluoroacetyl derivative is applied to determine methyl-CCNU in plasma with a limit of detection of 1.5 μg ml^?1.     

A Fluorosensor with Immobilized Cyclodextrin As A Substrate

Abstract

A flow-through optosensor for phenylalanine and tyrosine is described in this paper. The sensor is developed in conjunction with a flow-injection analysis system and uses immobilized β-cyclodextrin as the sensing agent. The analytical performance characteristics of the proposed sensor for analysis of very low levels of phenylalanine and tyrosine were as follows: the detection limits for phenylalanine and tyrosine were 0.20 μg ml^?1 and 8.9 ng ml^?1, respectively. The observed relative standard deviations were 1.03% for 50 μg ml^?1 of phenylalanine (n = 7) and 3.6% for 0.1 μg ml^?1 of tyrosine (n = 7), respectively.