Simultaneous voltammetric determination of paracetamol and caffeine in pharmaceutical formulations using a boron-doped diamond electrode

A simple and highly selective electrochemical method was developed for the single or simultaneous determination of paracetamol (N-acetyl-p-aminophenol, acetaminophen) and caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) in aqueous media (acetate buffer, pH 4.5) on a boron-doped diamond (BDD) electrode using square wave voltammetry (SWV) or differential pulse voltammetry (DPV). Using DPV with the cathodically pre-treated BDD electrode, a separation of about 550 mV between the peak oxidation potentials of paracetamol and caffeine present in binary mixtures was obtained. The calibration curves for the simultaneous determination of paracetamol and caffeine showed an excellent linear response, ranging from 5.0 × 10⁻⁷ mol L⁻¹ to 8.3 × 10⁻⁵ mol L⁻¹ for both compounds. The detection limits for the simultaneous determination of paracetamol and caffeine were 4.9 × 10⁻⁷ mol L⁻¹ and 3.5 × 10⁻⁸ mol L⁻¹, respectively. The proposed method was successfully applied in the simultaneous determination of paracetamol and caffeine in several pharmaceutical formulations (tablets), with results similar to those obtained using a high-performance liquid chromatography method (at 95% confidence level).     

Selective determination of trace iron in different oxidation states in natural water by flow injection-solid phase spectrometry

A novel method for the selective determination of Fe(II) and Fe(III) in water using 2-nitroso-5-[N-n-propyl-N-(3-sulfopropyl)amino]phenol (PSAP) was developed. QAE-Sephadex anion exchanger packed in a flow-through cell was used as a medium not only for both the concentration and the spectrophotometric measurements of the Fe-PSAP complex, but also for reduction of the Fe(III)-PSAP complex. The PSAP complex of Fe(II) or Fe(III) was strongly adsorbed on the anion exchanger in a weakly acidic to weakly basic region, but the Fe(III) complex was readily and completely reduced to the Fe(II) complex only in a neutral to weakly alkaline region in the solid phase. These properties were utilized to determine the Fe(II) and total Fe concentration without the addition of any reducing agent. The detection limits (3σ) were 0.18 ng for Fe(II) and 0.18 ng for total Fe using a 3.2-cm(3) sample solution. The present method is applicable to the determination of dissolved iron species present at μg dm(-3) levels in natural water samples.     

Simultaneous spectrophotometric determination of paracetamol, ibuprofen and caffeine in pharmaceuticals by chemometric methods

In this study, the simultaneous determination of paracetamol, ibuprofen and caffeine in pharmaceuticals by chemometric approaches using UV spectrophotometry has been reported as a simple alternative to using separate models for each component. Spectra of paracetamol, ibuprofen and caffeine were recorded at several concentrations within their linear ranges and were used to compute the calibration mixture between wavelengths 200 and 400 nm at an interval of 1 nm in methanol:0.1 HCl (3:1). Partial least squares regression (PLS), genetic algorithm coupled with PLS (GA-PLS), and principal component-artificial neural network (PC-ANN) were used for chemometric analysis of data and the parameters of the chemometric procedures were optimized. The analytical performances of these chemometric methods were characterized by relative prediction errors and recoveries (%) and were compared with each other. The GA-PLS shows superiority over other applied multivariate methods due to the wavelength selection in PLS calibration using a genetic algorithm without loss of prediction capacity. Although the components show an important degree of spectral overlap, they have been determined simultaneously and rapidly requiring no separation step. These three methods were successfully applied to pharmaceutical formulation, capsule, with no interference from excipients as indicated by the recovery study results. The proposed methods are simple and rapid and can be easily used in the quality control of drugs as alternative analysis tools.     

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.     

Simultaneous determination of paracetamol and caffeine in pharmaceutical formulations and synthetic urine using cork-modified graphite electrodes

Journal of Solid State Electrochemistry - Cork-modified graphite electrodes were used to develop a simple and selective sensor for the simultaneous determination of paracetamol (PAR) and caffeine...     

An optosensor for tryptophan with C18 silica gel as a substrate

 A flow-through optosensor for tryptophan with C18 silica gel as a substrate is proposed. It has been developed in conjunction with a flow-injection analysis system and is based on the retention of tryptophan on the C18 column and the enhancement of its fluorescence. The detection limit is 25 ng mL^-1 with a relative standard deviation of 2.9% for 7 determinations of 10 μg mL^-1 of tryptophan. Most of the common species do not interfere. The method has been successfully applied to a pharmaceutical preparation. Received: 8 July 1996/Revised: 26 September 1996/Accepted: 30 September 1996     

Simultaneous voltammetric determination of acetylsalicylic acid,caffeine and paracetamol in pharmaceutical formulations using screen-printed carbon electrode

Electrochemical oxidation of Paracetamol (PAR), Acetylsalicylic acid (ASA) and Caffeine (CAF) was investigated employing square wave stripping voltammetry (SWSV) using screen–printed carbon electrodes (SPCE). Determinations were performed in 0.1 mol L⁻¹ BR buffer (pH 2.0) without accumulation step. SWV were obtained by scanning the potential from 0.00 to 1.40 V employing a scan increment of 4 mV, pulse amplitude 25 mV and frequency of 25 Hz. PAR, ASA and CAF presents oxidation signals at 0.45, 1.03 and 1.32 V. The detection limits were 1.2, 1.7 and 1.7 mg L⁻¹, respectively. The method was applied in the PAR-ASA-CAF determination on pharmaceutical formulations.     

Simultaneous determination of paracetamol and chlorpheniramine in human plasma by liquid chromatography-tandem mass spectrometry

An analytical method for the determination of paracetamol and chlorpheniramine in human plasma has been developed, validated and applied to the analysis of samples from a phase I clinical trial. The analytical method consists in the extraction of paracetamol and chlorpheniramine with diethyl ether, followed by the determination of both drugs by an LC–MS–MS method, using 2-acetamidophenol as internal standard. The intra-assay and inter-assay precision and accuracy of this technique were good and the limit of quantitation was 0.5 μg/ml of plasma for paracetamol and 0.2 ng/ml for chlorpheniramine. The concentration working range was established between 0.5 μg/ml and 25 μg/ml for paracetamol and between 0.2 ng/ml and 50 ng/ml for chlorpheniramine. This method has been used for analyzing more than 1200 human plasma samples from a clinical study with 24 volunteers.     

Quercetin immobilized on silica gel as a solid phase reagent for tin(IV) determination by using the sorption-spectroscopic method

New chelating sorbents are prepared by 3,3',4',5,7-pentahydroxyflavone adsorption from butanol and acetone-hexane (1:4) solutions, characterized by isotherm of sorption, IR-spectroscopy and studied for pre-concentrating and sorption-spectroscopic determination of Sn(IV). The solid-phase Quercetin with satisfactory analytical characteristics was formed by adsorption from acetone-hexane (1:4) mixture. The quantitative recovery of Sn(IV) from aqueous solution with modified sorbent was observed at pH 1.8-2.2. The tolerance limits of heavy metal ions in the sorption of Sn(IV) are reported. The limit of Sn detection is 0.06 mg l(-1). The linearity of calibration graph has been observed up to 1.2 mg l(-1). The method has been applied to determine Sn in high purity zinc materials.     

On-line electrochemical oxidation of Cr(III) for the determination of total Cr by flow injection-solid phase spectrophotometry.

A novel on-line oxidation method of ultra-trace Cr(III) dissolved in natural water has been developed using a flow electrolysis cell. This method was successfully applied to the determination of the total Cr concentration by flow injection-solid phase spectrophotometry using diphenylcarbazide as a coloring agent. With the applied potential of 1.35 V (vs. Ag/AgCl) and the flow rate of 0.80 cm(3) min(-1), Cr(III) was quantitatively oxidized to Cr(VI) at room temperature. The total Cr concentration of sub-microg dm(-3) in 3 - 4 samples could be determined within 1 h using an aqueous sample volume of 7.1 cm(3). The analytical values of the total Cr concentration in natural water were in good agreement with those obtained by ICP-MS. The detection limit of the proposed method was 0.014 microg dm(-3) (3sigma, n = 7). This method could be applied to the specific determination of Cr(III) and Cr(VI) in river water samples.     

GC法同时测定酚氨咖敏片中4种组分

建立了同时测定酚氨咖敏片中对乙酰氨基酚、氨基比林、咖啡因和马来酸氯苯那敏4组分含量的毛细管气相色谱法。采用SE-30大口径毛细管色谱柱(30 m×0.53 mm,1.0μm),柱温190℃,汽化室温度220℃,检测器为FID,检测温度250℃,载气为高纯N2,分流比为1∶6,内标为盐酸麻黄碱,以无水乙醇为溶剂,样品无需衍生化处理,直接进样测定。样品中各组分完全分离,辅料无干扰,对乙酰氨基酚、氨基比林、咖啡因和马来酸氯苯那敏分别在20~2000μg/mL、15~1500μg/mL、10~500μg/mL和20~100μg/mL范围内线性关系良好(r0.999),各组分的平均回收率在99.6%~101.2%范围内,RSD2%。     

Separation and determination of molybdenum by inductively coupled plasma optical emission spectrometry using quercetin immobilization on silica gel

A new method is described for the separation of molybdenum based on its chelation in a column packed with quercetin, immobilized on silica gel in a slightly acidic medium (pH 5.0). Recovery ranged from 95% (NIST 1515 apple leaves) to 99% (deionized, distilled water; DDW) with an absolute blank of 27.5±1.6 pg obtained for the analysis of DDW. Detection limits, absolute and relative, based on a 5.0-ml sample volume were 4.8 pg and 1 ng l⁻¹, respectively. Results are presented for molybdenum determination in two standard reference materials, NIST 1515 and NIST 1547 peach leaves, using simple calibration curves for quantification. α-Benzoinoxime was used as the eluent.     

Simultaneous determination of propacetamol and paracetamol by derivative spectrophotometry

The present paper describes a procedure that phenols in air were preconcentrated in a membrane cell and their content was determined by adsorptive polarography. First, the phenols in air samples were preconcentrated in a membrane cell using 2.0 M NaOH solution, then in a pH 1.3 buffer solution p-bromophenylamine forms a diazoate with NaNO(2), and into the mixture the collected phenols were added to form azo-compound in a pH 13 buffer solution. The azo-compound can be adsorbed at the mercury electrode and yields a sensitive oscillopolarographic wave. Over the range 2.0x10(-8)-2.0x10(-5) M, the peak currents are linearly proportional to the concentration of phenols. The detection limit is 5.0x10(-9) M.     

Determination of trace amounts of cobalt(II) by flow injection-solid phase spectrometry (FI-SPS) with 5-Br-PADAB.

Flow injection-solid phase spectrometry (FI-SPS) has been applied to the determination of cobalt(II) in water samples. The complex formed between cobalt and 5-Br-PADAB was on-line protonated and concentrated on an AG 50W-X2 cation-exchanger in a flow-through cell. The increase in absorbance caused by the accumulation of the complex in the resin was continuously measured. The interference by copper could be effectively eliminated by using EDDP as a masking agent. The detection limit was 40 ng dm(-3) with a 4.0 cm3 sample solution.     

Simultaneous on-line pre-concentration and determination of trace metals in environmental samples by flow injection combined with inductively coupled plasma mass spectrometry using silica gel modified with niobium(V) oxide

This work presents the development of an on-line pre-concentration system for simultaneous determination of Cd, Cu, Ni, V, Zn, Co and Pb in aqueous environmental samples and detection by inductively coupled plasma mass spectrometry. The system is based on cationic retention of the analytes onto a mini-column filled with silica gel modified with niobium(V) oxide. The effects of chemicals and flow variables have been investigated. The optimized operating conditions, selected as a compromise between sensitivity and analytical frequency were: sample pH 7.0, sample flow rate of 6.0mL min(-1), eluent flow rate of 2.0mL min(-1), and eluent (HNO(3)) concentration of 2.5mol L(-1). The relative standard deviation (n=7), enrichment factor and linear working range were 0.8-4.5%, 23.3-37.2 and 0.05-25.0microg L(-1), respectively. Limits of detection were between 0.01 and 0.03microg L(-1). The accuracy of the proposed method was checked with certified materials (NASS-4, NASS-5, CASS-4 and SRM 1643e). Values obtained were in accordance with those reported for the certified materials. Recovery was found to be in the range of 90-110% for a suit of water samples with variable matrices (seawater, tap water and ground water) collected in Florianopolis, Brazil.     

Solid phase extraction of penicillins from milk by using sacrificial silica beads as a support for a molecular imprint

We have prepared molecularly imprinted beads with molecular recognition capability for target molecules containing the penicillanic acid substructure. They were prepared by (a) grafting mesoporous silica beads with 6-aminopenicillanic acid as the mimic template, (b) filling the pores with a polymerized mixture of methacrylic acid and trimethylolpropane trimethacrylate, and (c) removing the silica support with ammonium fluoride. The resulting imprinted beads showed good molecular recognition capability for various penicillanic species, while antibiotics such as cephalosporins or chloramphenicol were poorly recognized. The imprinted beads were used to extract penicillin V, nafcillin, oxacillin, cloxacillin and dicloxacillin from skimmed and deproteinized milk in the concentration range of 5–100 μg·L^?1. The extracts were then analyzed by micellar electrokinetic chromatography by applying reverse polarity staking as an in-capillary preconcentration step, and this resulted in a fast and affordable method within the MRL levels, characterized by minimal pretreatment steps and recoveries of 64–90 %.

Solid phase extraction of penicillins from milk by using sacrificial silica beads as a support for a molecular imprint

We have prepared molecularly imprinted beads with molecular recognition capability for target molecules containing the penicillanic acid substructure. They were prepared by (a) grafting mesoporous silica beads with 6-aminopenicillanic acid as the mimic template, (b) filling the pores with a polymerized mixture of methacrylic acid and trimethylolpropane trimethacrylate, and (c) removing the silica support with ammonium fluoride. The resulting imprinted beads showed good molecular recognition capability for various penicillanic species, while antibiotics such as cephalosporins or chloramphenicol were poorly recognized. The imprinted beads were used to extract penicillin V, nafcillin, oxacillin, cloxacillin and dicloxacillin from skimmed and deproteinized milk in the concentration range of 5–100 μg·L⁻¹. The extracts were then analyzed by micellar electrokinetic chromatography by applying reverse polarity staking as an in-capillary preconcentration step, and this resulted in a fast and affordable method within the MRL levels, characterized by minimal pretreatment steps and recoveries of 64–90 %.

Penicillanic acid-imprinted beads prepared in preformed porous silica by an imprinting &; etching approach show selectivity towards β-lactams antibiotics. Molecularly imprinted solid phase extraction/micellar electrokinetic chromatography coupled with in-capillary preconcentration resulted in a fast and affordable method for penicillins in milk at MRL levels.

     

Simultaneous determination of organotin compounds by hydride generation-gas phase molecular absorption spectrometry

This study describes the determination of ternary mixtures of dimethyltin chloride (DMT), trimethyltin chloride (TMT) and monobutyltin chloride (BT) by hydride generation-gas phase molecular absorption spectrometry and the application of different chemometric methods: principal components regression (PCR) and partial least squares (PLS). The two methods are applied to the absorption spectra of mixtures of DMT, TMT and BT. Two different experimental designs are tested for the mixtures, a triangular design and a central composite design. The models obtained from the triangular design offer the best prediction results. The effects of the number of working wavelengths and the number of factors included in the calibration model is studied and a different behaviour is seen for each compound and calibration model. The methods are applied to the analysis of artificial aqueous samples containing different concentrations of DMT, TMT and BT species. No significant differences are observed between the calibration models investigated.     

Matrix-assisted laser desorption/ionization mass spectrometry using porous silicon and silica gel as matrix

Porous silicon powder and silica gel particles have been applied as inorganic matrices for the analysis of small molecules in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOFMS). In contrast to conventional MALDI-TOFMS, the signal interference of low-molecular analytes by the matrix has been eliminated. Almost no fragmentations of the analytes were observed. Effects of various factors, such as the particle and pore size, the suspending solution, and sample preparation procedures, on the intensity of mass spectra have been investigated. The pore structure of the inorganic matrix and penetration of the analytes into the pores must be optimized for effective desorption and ionization of the analytes. Matrices (DHB and HCCA) were covalently bound to silica gel for improvement of spectrum intensity. Copyright © 2001 John Wiley & Sons, Ltd.