Solid-phase reactors as high stability reagent sources in flow analysis: selective flow injection spectrophotometric determination of cysteine in pharmaceutical formulations

The flow injection spectrophotometric determination of cysteine was carried out by reaction with cobalt(II) ions entrapped in a polymeric material and filling a packed-bed reactor; the released cobalt(II) complexed with the amino acid was monitored at 360 nm. The method worked with a high repeatability, even with independent reactors, days and solutions. Selectivity of the procedure was tested with twenty different foreign compounds found in pharmaceutical formulations containing cysteine, parent amino acids included; no serious interferences were observed. The calibration graph for cysteine was linear over the range 1-90 micrograms ml-1 with a relative standard deviation of 0.8% at 60 micrograms ml-1 (n = 158). The calculated sample throughput was 90 h-1. The method was applied to determine the content of cysteine in pharmaceutical formulations.     

利血平与玫瑰精B的高灵敏显色反应及分析应用

研究了利血平与玫瑰精B的显色反应,建立了测定利血平的高灵敏分光光度法。在酸性条件下,利血平的水解产物和玫瑰精B形成具有正、负吸收峰的红色离子缔合物,最大正吸收波长位于490 nm,最大负吸收波长位于520 nm,表观摩尔吸光系数(ε)分别为1.20×105L.mol-1.cm-1(正吸收)和1.83×105L.mol-1.cm-1(负吸收),利血平在0～5.0μg/mL范围内遵从比尔定律。若采用正、负峰叠加测定,灵敏度可达3.00×105L.mol-1.cm-1。探讨了适宜的反应条件、主要分析特性及方法的精密度和可靠性。该法可用于市售利血平注射液中利血平含量的测定。     

Determination of selenium in blood plasma and serum by flow injection hydride generation atomic absorption spectrometry

A flow injection hydride generation atomic absorption spectrometric (AAS) method has been used to determine the selenium concentrations of human serum and plasma samples following digestion with nitric, sulphuric and perchloric acids. In the hydride generation process, reduction was carried out by sodium tetrahydroborate to produce a hydride that was atomized in a flame-heated atomisation cell. The method had a detection limit of 1.2 ng ml-1 and a sensitivity of 2.1 ng ml-1. Within-run precisions of 5.8% at 20 ng ml-1 and 4.5% at 80 ng ml-1, and between-run precisions of 4.8% at 69 ng ml-1 and 3.4% at 80 ng ml-1 were obtained. An inter-laboratory comparison study with a graphite furnace AAS method was carried out and the results showed excellent agreement. The flow injection method of sample introduction allowed the use of a sample volume of 330 microliters with an injection rate of 90 injections per hour.     

Spectrophotometric determination of fluoxetine by batch and flow injection methods

A rapid, simple, and accurate spectrophotometric method is presented for the determination of fluoxetine by batch and flow injection analysis methods. The method is based on fluoxetine competitive complexation reaction with phenolphthalein-beta-cyclodextrin (PHP-beta-CD) inclusion complex. The increase in the absorbance of the solution at 554 nm by the addition of fluoxetine was measured. The formation constant for fluoxetin-beta-CD was calculated by non-linear least squares fitting. Fluoxetine can be determined in the range 7.0 x 10(-6)-2.4 x 10(-4) mol l(-1) and 5.0 x 10(-5)-1.0 x 10(-2) mol l(-1) by batch and flow methods, respectively. The limit of detection and limit of quantification were respectively 4.13 x 10(-6) mol l(-1) and 1.38 x 10(-5) mol l(-1) for batch and 2.46 x 10(-5) mol l(-1) and 8.22 x 10(-5) mol l(-1) for flow method. The sampling rate in flow injection analysis method was 80+/-5 samples h(-1). The method was applied to the determination of fluoxetine in pharmaceutical formulations and after addition to human urine samples.     

Determination of sub-ppb reserpine by an optosensing device based on photochemically induced fluorescence

A flow injection–solid-phase spectroscopy (FI-SPS) system implemented with photochemically induced fluorescence (PIF) is described for the rapid and very sensitive determination of reserpine in biological fluids and pharmaceutical formulations. An intensively fluorescent photoproduct is in-line generated, retained on C₁₈ silica gel in the detection area and monitored at 394/489 nm (λ _ex/λ _em). After the establishment of the appropriate working variables, the system is calibrated at two different injection volumes, 100 and 800 μL, achieving detection limits of 0.33 and 0.05 ng mL⁻¹, respectively. The RSD for reserpine at 2 ng mL⁻¹ (800 μL) was 1.5% (n = 10). The sampling rates were 46 and 43 h⁻¹ for each injection volume, respectively. The potential interference of some common species coexisting with reserpine in the analysed samples was also studied. The procedure was successfully applied to commercial formulations, urine and serum without any previous treatment of samples. Recoveries ranged from 94.9 to 100.2%.     

Flow injection spectrofluorimetric determination of reserpine in tablets by on-line acetone sensitized photochemical reaction

On-line photochemical reaction of reserpine in the presence of acetone was investigated. Acetone was found to speed up the on-line photochemical conversion of reserpine into an intensively fluorescent compound. Not only reaction acidity but also the acetate buffer concentration affected the on-line photochemical induced fluorescence signal. Based on the observation an automated flow injection photochemical fluorimetric approach was developed. An injected sample zone was carried by a water stream to be merged with a acetate buffer (pH 3.4) solution containing 0.02% acetone in a knotted PTFE reactor (KR), which was freely coiled around a 6-W low pressure mercury lamp. While passing the KR, reserpine was transformed into an intensively fluorescent compound. It was on-line detected in a flow-through cell at the emission wavelength of 490 nm and excitation wavelength of 386 nm. At optimized conditions, a detection limit 0.45 mug l(-1) was achieved at a sampling rate of 90 h(-1). Eleven determinations of a 0.5 mg l(-1) reserpine standard solution gave a R.S.D. of 0.3%. The linear dynamic range of reserpine calibration curve was 0.01-0.75 mg l(-1). The proposed method was applied to assay the reserpine content in tablets and to monitor the dissolution profile of reserpine tablets. Satisfactory results were obtained for both the assays and dissolution studies.     

A flow injection sampling resonance light scattering system for total protein determination in human serum

A novel flow injection method with resonance light scattering detection was developed for the determination of total protein concentrations. This method is based on the enhancement of RLS signals from Methyl Blue (MB) by protein. The enhanced RLS intensities at 333 nm, in a pH 4.1 acidic aqueous solution, were proportional to the protein concentration over the range 2.0-37.3 and 1.0-36.0 microg ml-1 for human serum albumin (HSA) and bovine serum albumin (BSA), respectively. The corresponding limits of detection (3sigma) of 45 ng ml-1 for HSA and 80 ng ml-1 for BSA were attained. The method was successfully applied to the quantification of total proteins in human serum samples, the maximum relative error is less than 1% and the recovery is between 98% and 102%. The sample throughput was 60 h-1.     

Simultaneous determination of acetylsalicylic and salicylic acids in human serum and aspirin formulations by second-derivative synchronous fluorescence spectrometry

A second-derivative synchronous scanning spectrofluorimetric method for the simultaneous determination of acetylsalicylic acid (ASA) and salicylic acid (SA) is described. The method is based on the native fluorescence of both acids in a 1% acetic acid-chloroform solution. Both ASA and SA can be determined within the concentration ranges 0.2-70 and 0.03-10 micrograms ml-1, respectively. The effect of each acid on the signal of the other has been studied in detail. Empirical equations have been used to overcome this effect, thus allowing the accurate determination of both acids in binary mixtures, without a separation step. The method has been applied to the determination of ASA and SA in blood serum and to the determination of SA impurities in aspirin formulations. Recoveries from sera spiked with both ASA (2.5-50 micrograms ml-1) and SA (100-160 micrograms ml-1) varied from 99.5 to 106.7% (mean = 102.6%) and from 93.0 to 98.0% (mean = 95.8%), respectively. Recoveries of SA from spiked aspirin solutions (0.25-1.5 mg g-1 of aspirin) varied from 98.0 to 102.0% (mean = 100.3%).     

Use of photochemical reactions in flow injection: determination of oxalate in urine

The use of photochemical reactions in flow injection (FI) is reported. The irradiation of an FI reactor with a suitable source facilitates the development of the iron(III)-oxalate reaction, allowing the amperometric determination of the anion in the range 1.0-13.0 micrograms ml-1, with a relative standard deviation of 1.1% and a sampling frequency of 40 h-1. The proposed method was applied successfully to the determination of oxalate in urine samples.     

Photochemical derivatization and fluorimetric determination of reserpine in a flow-injection assembly

The fluorimetric flow-injection determination of reserpine was achieved with the drug being derivatized on-line by photoreaction. PTFE tubing was helically coiled around a germicide lamp located between the injection valve and detector. Two analytical procedures are proposed using either dilute acetic acid or pure methanol as the carrier stream. The influence of foreign compounds was studied and the method was applied to the determination of reserpine in pharmaceutical formulations.     

Simultaneous determination of ascorbic acid, caffeine and paracetamol in drug formulations by differential-pulse voltammetry using a glassy carbon electrode

A simple, rapid and accurate method for the simultaneous determination of ascorbic acid, caffeine and paracetamol in drug formulations has been developed. Peak currents were measured with a glassy carbon electrode at +0.350, +0.618 and +1.425 V versus a saturated calomel electrode for ascorbic acid, paracetamol and caffeine, respectively. Perchloric acid (0.1 M) - methanol (1 + 1) was used both as a solvent and supporting electrolyte. The optimum modulation amplitude, pulse repeat time and scan rate of the polarographic analyser were found to be 50 mV, 0.5 s and 5 mV s-1, respectively and the linear calibration ranges for ascorbic acid, caffeine and paracetamol were 0-35, 0-50, and 0-55 micrograms ml-1, respectively. The relative standard deviations for 9.30 micrograms ml-1 of ascorbic acid, 8.50 micrograms ml-1 of caffeine and 7.30 micrograms ml-1 of paracetamol were 1.3, 2.5 and 0.7%, respectively. Results are reported for several commercially available drugs.     

Development and application of spectrophotometric methods for the determination of citalopram hydrobromide in dosage forms

Study was carried out to develop two simple, fast, accurate and sensitive spectrophotometric methods (A and B) for the determination of citalopram hydrobromide in commercial tablet formulations. In method A, UV spectrophotometer determined the contents of citalopram hydrobromide in tablets at 240 nm in methanol solvent. The linear range was 5-40 microg ml-1 with molar absorptivity 1.4x10(4) l mol-1 cm-1. While the method B based on the reaction of citalopram base as n-electron donor with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone as pi-acceptors to give highly colored complex species that absorb maximally at 590 nm. Beer's law was obeyed in the concentration limit of 10-250 microg ml-1 with molar absorptivity 3.3x10(3) l mol-1 cm-1 for citalopram hydrobromide. The limits of detection and limit of quantification was calculated and found to be 5.2 microg ml-1 and 17.4 microg ml-1 respectively. The proposed methods were found to be rapid, accurate, precise and sensitive for the determination of citalopram hydrobromide in commercial tablet formulations with out interferences from common additives encountered.     

Construction and performance characterization of ion-selective electrodes for potentiometric determination of pseudoephedrine hydrochloride applying batch and flow injection analysis techniques

New pseudoephedrine selective electrodes have been constructed of the conventional polymer membrane type by incorporation of pseudoephedrine-phosphotungstate (PE-PT) or pseudoephedrine-silicotungstate (PE-SiT) ion-associates in a poly vinyl chloride (PVC) membrane plasticized with dibutyl phthalate (DBP). The electrodes were fully characterized in terms of the membrane composition, temperature, and pH. The electrodes exhibited mean slopes of calibration graphs of 57.09 and 56.10 mV concentration decade(-1) of PECl at 25 degrees C for (PE-PT) and (PE-SiT) electrodes, respectively. The electrodes showed fast, stable, and near-Nernstian response over the concentration ranges 6.31 x 10(-6)-1.00 x 10(-2) and 5.00 x 10(-5)-1.00x10(-2) M in the case of PE-PT applying batch and flow injection (FI) analysis, respectively, and 1.00 x 10(-5)-1.00 x 10(-2) and 5.00 x 10(-5)-1.00x10(-2) M in the case of PE-SiT for batch and FI analysis system, respectively. Detection limit was 5.01x 10(-6) M for PE-PT electrode and 6.31x10(-6) M for PE-SiT electrode. The electrodes were successfully applied for the potentiometric determination of pseudoephedrine hydrochloride (PECl) in pharmaceutical preparations with mean recovery 101.13 +/- 0.85% and 100.77+0.79% in case of PE-PT applying batch and flow injection systems, respectively, and 100.75+0.85% and 100.79 +/- 0.77% in case of PE-SiT for batch and flow injection systems, respectively. The electrodes exhibited good selectivity for PECl with respect to a large number of inorganic cations, sugars and amino acids.     

Spectrofluorimetric determination of paroxetine hydrochloride in its formulations and human plasma

A sensitive spectrofluorimetric procedure for the determination of paroxetine-HCl in pharmaceutical formulations and human plasma has been described. The native fluorescence of the drug has been studied under different conditions. Maximum fluorescence intensity was obtained in methanol at 340 nm using 290 nm for excitation. Different surfactants showed negative effect on the fluorescence intensity of paroxetine-HCl. Regression analysis of Beer's plot showed good correlation (r=0.9999) between fluorescence intensity and concentration over the range of 0.05-0.40 microg ml-1 with lower limit of detection (LOD) of 0.015 microg ml-1. The drug was successfully determined in its tablets with average % recovery of 98.00+/-0.99% which was in accordance with those given by a compendial method. The method was also applied to the determination of paroxetine-HCl in spiked human plasma with average recovery of 77.70+/-1.06%.     

Flow—injection Chemiluminescence Determination of Reserpine in Medicine and Biological Fluids with Controlled—Reagent—Release Technology

A sensitive and rapid chemiluminescence(CL) flow injection with controlled-reagent-release technology for the determination of reserpine was proposed.The Cl reagents,luminol and dichromate,uses in this sensor,were all immobilized on anion-exchange resin.Through injection of 100μl of water,the reagents on the anion-ex-change resin column were eluted and in the presence of reserpine ,the CL intensity was decreased,by which reserpine could be sensed.Reserpine was quantified by measuring the decrement of CL intensity,which was observed linear with the logrithm of reserpine concentration in the rage of 1.0-500.0ng/mL,and the limit of detection was 0.4ng/mL(3σ)with a relative standard deviation of less than 3.0?The proposed procedure was applied in the assay of reserpine in pharmaceutical preparation and biological fhuids without any pre-treatment process and with sampling frequencies of 72 times per hour.     

Continuous flow molecular emission cavity analysis of cephalosporins by alkaline degradation to sulphide

A continuous flow method for the determination of some cephalosporins (cephradine, cephalexin, cephalosporin C, cefadroxil, cephapirin and cephalothin) in the general range 10.0-250.0 micrograms ml-1 is described. The sample is mixed with sodium hydroxide and remains for 20 min at 90 degrees C in the delay coil of an air-segmented system. The solution is then mixed with an excess of orthophosphoric acid, and the hydrogen sulphide evolved is continuously transferred into the cavity for generation of the S2 molecular emission. The analysis is automated, requires no sample pre-treatment and samples can be analysed at a rate of 30 per hour with a relative error of 1-2%. The method was evaluated by carrying out recovery experiments and by the analysis of commercial formulations. Results agreed well with those obtained by the standard methods.     

Determination of mercury(II) by invertase enzyme inhibition coupled with batch injection analysis

The determination of mercury(II) ions at the trace level by inhibition of the invertase enzyme-catalysed hydrolysis of sucrose into glucose and fructose coupled to electrochemical batch injection analysis was investigated using two approaches. In the first, the glucose produced was detected by injection of 100 microliters samples into the batch injection cell containing a platinum electrode modified by immobilised glucose oxidase. In the second, the glucose and fructose present in injected samples were oxidised directly at a copper-modified glassy carbon electrode. The experimental parameters were optimised and the degree of enzyme inhibition by mercury(II) ions under both conditions was measured. Mercury concentrations in the ng ml-1 range were determined by these two techniques with low sample and reagent consumption. Comparison is made between the two methods and perspectives as a screening test for field application are indicated.     

Validated Flow Injection Spectrophotometric Assay for the Quality and Stability Control of Gemfibrozil Tablets

Abstract

A validated flow injection spectrophotometric assay has been developed and optimized for the determination of gemfibrozil in pharmaceutical formulations. The method is based on the direct measurement of the absorbance of the analyte—under flow conditions—in basic medium, at 276 nm. The assay was optimized in terms of sample injection volume and flow rate and validated in terms of linearity, repeatability, detection limit, accuracy, and selectivity. Linear calibration curve was obtained in the range of 20–100 mg l^?1, while the detection limit (1.4 mg l^?1), the repeatability (s _r <1.0%, n=12) and the sampling rate (30 h^?1) were satisfactory. The method was applied successfully to the quality control of one batch (batch no. 052) and the stability control of three batches (batches no. 049–051) of a gemfibrozil‐containing formulation (Prelisin^®, Cosmopharm Ltd, Greece).     

High Performance Liquid Chromatographic Determination of Diuretic-Antihypertensive Combination Products. II. Polythiazide and Reserpine

Abstract

A high performance liquid chromatographic method for the simultaneous determination of polythiazide and reserpine in tablets is described. Polythiazide, reserpine, and vanillin (an excipient) are separated isocratically on an octadecylsilane column using a methanol-water-acetic acid (55:44:1) mobile phase. The column effluent was monitored by ultraviolet ab-sorbance at 254 nm. Recoveries from synthetic formulations were 100.2 ± 1.7% for polythiazide and 98.7 ± 1.1% for reserpine.     

Use of palladium(II) chloride as a colour-forming reagent for the determination of N-acetyl-L-cysteine in water and fluimukan injections

The formation of the complex between N-acetyl-L-cysteine and palladium(II) chloride in Britton-Robinson buffer solution in the pH range 2.08-8.00 was studied. The optimum conditions for this reaction were ascertained and a spectrophotometric method was developed for the determination of N-acetyl-L-cysteine in the concentration range 4.0-65.3 micrograms ml-1, using PdCl2 as the reagent. The detection limit was 1.63 micrograms ml-1 and the relative standard deviation varied from 0.63 to 1.92%. The method was applied to the determination of N-acetyl-L-cysteine in water and in injection solutions.