Stability-indicating liquid chromatography for determination of clopidogrel bisulfate in tablets: Application to content uniformity testing

The present study describes a simple stability-indicating reversed-phase HPLC assay for antiplatelet drug, clopidogrel bisulfate. Separation of the drug and the degradation products, under stress conditions was successfully achieved on a C-18 column utilizing 0.01 M Na₂HPO₄ (pH 4): acetonitrile in the ratio 80:20 v/v, pumped at a flow rate of 0.5 ml min^?1 with UV detection at 235 nm. The retention time of clopidogrel was 6.84 min. The method was satisfactorily validated with respect to linearity, precision, accuracy, selectivity, sensitivity and ruggedness. The response was linear in the range of 0.2–3.5 μg ml^?1 with detection limit 0.079 μg ml^?1. The suggested method was successfully applied for the analysis of clopidogrel in bulk and in commercial tablets. The results were favorably compared to those obtained by a reference method. The proposed method was successfully applied to the content uniformity testing of tablets and for determination of clopidogrel in presence of its co-administered drug, acetyl salicylic acid.     

UV-absorption and fluorimetric methods for the determination of alprazolam in pharmaceutical formulation

The development of UV and fluorescence spectrophotometric methods for the quantitative determination of alprazolam in dosage forms using As(III)?SDS system. The two simple and sensitive, spectrophotometric and spectrofluorimetric methods were developed for the determination of alprazolam (ALP) in tablets. These methods are based on formation of ALP?As(III) complex in the presence of SDS. The UV-spectrum of 30% methanolic solution of ALP (5 × 10^?5 M) at pH 6.5 (Mclivaine buffer) was run between 200 and 380 nm. The absorption spectrum of ALP exhibits two peaks with a λ_max. at 255 nm and a weak band at 325 nm. When the spectra of the drug were run at varying pH in the region 200–380 nm, one isosbestic point at 290 nm was observed, which indicated the presence of two ionic conditions in solution. The complex exhibited an absorption maximum at 265 nm and emission peak at 520 nm with respect to the excitation wavelength of 325 nm. The spectrophotometric method was found to be linear in 8.0–17.0 μg ml^?1 range with detection limit of 13.520 μg ml^?1, while 0.05–9.5 μg ml^?1 range was with detection limit of 1.048 × 10^?2 μg ml^?1 by spectrofluorimetric method. The mean percentage recovery of the added quantity was found to be 99.54 (spectrophotometric method) and 100.22 (spectrofluorimetric method) and the %RSD are lower than 0.478 and 0.296 determined spectrophotomerically and spectrofluorimtrically, respectively. This indicates that the proposed method is accurate. The apparent ionization constant of ALP was found to be 9.29. The spectra, experimental conditions were set followed by determination stoichiometry, stability constant and thermodynamic parameters of the As(III), Co(II), Ni(II), and Zn(II) complexes with ALP at pH 6.5. The proposed methods have been successfully applied to the assay of ALP in tablets and the results were statistically evaluated.     

Determination of Exemestane in bulk and pharmaceutical dosage form by HPTLC

An HPTLC method for analysis of Exemestane in bulk and pharmaceutical formulation has been established and validated. The analyte was separated on aluminium plates precoated with silica gel 60 F₂₅₄. The mobile phase was chloroform:methanol 9.2:0.8 (v/v). Quantification was done by densitometric scanning at 247 nm. Response was a linear function of Exemestane concentration in the range of 100–500 μg mL⁻¹. The limit of detection and quantification for Exemestane were 5.8 and 17.58 μg mL⁻¹, respectively. Average recovery of Exemestane was 100.1, which shows that the method was free from interference from excipients present in the formulation. The established method enabled accurate, precise, and rapid analysis of Exemestane in bulk as well as pharmaceutical formulation.     

Sensitive liquid chromatography–tandem mass spectrometry method for the determination of pantoprazole sodium in human urine

A sensitive and selective liquid chromatographic–tandem mass spectrometric (LC–MS–MS) method was developed to determine pantoprazole sodium (PNT) in human urine. After solid-phase extraction with SPE cartridge, the urine sample was analysed on a C₁₈ column (symmetry 3.5 μm; 75 mm × 4.6 mm i.d) interfaced with a triple quadrupole tandem mass spectrometer. Positive electrospray ionization was employed as the ionization source. The mobile phase consisted of acetonitrile–water (90:10, v/v). The method was linear over a concentration range of 1–100 ng mL^?1. The lower limit of quantitation was 1 ng mL^?1. The intra-day and inter-day relative standard deviation across three validation runs over the entire concentration range was <10.5%. The accuracy determined at three concentrations (8.0, 50.0 and 85.0 ng mL^?1 PNT) was within ±1.25% in terms of relative errors.     

Hollow fiber supported liquid membrane microextraction of Cu2+ followed by flame atomic absorption spectroscopy determination

Hollow fiber supported liquid membrane microextraction, a relatively new sample preparation technique, has attracted much interest in the field of environmental analysis. In the current study, a novel method based on hollow-fiber liquid-phase microextraction and flame atomic absorption spectrometry (FAAS) for the measurement of copper ion in aqueous samples is described. Hollow-fiber liquid-phase microextraction conditions such as the type of extraction solvent, pH, the stirring rate, and the amounts of chelating agents, sample volume, and the extraction time were investigated. Under the optimized conditions, the linear range was found to be 0.01–15 μg ml^?1 for copper ion, and the limit of detection to be 0.004 μg ml^?1. Tap water and surface water samples collected from Mashhad, Iran and Dorongar river; Khorasan, Iran, respectively, were successfully analyzed using the proposed method. The recoveries from the spiked water samples were 72.4% and 105%, respectively; and the relative standard deviation (RSD) at the 2 μg ml^?1 level was 6%.     

Utility of oxidation–reduction reaction for the spectrophotometric determination of amlodipine besylate

A simple, rapid, accurate, precise and sensitive spectrophotometric method for the determination of amlodipine besylate (ADB) in bulk sample and in dosage forms is described. The method is based on oxidation of the drug by potassium permanganate in acidic medium and determine the unreacted oxidant by measuring the decrease in absorbance for five different dyes; methylene blue (MB), acid blue 74 (AB), acid red 73 (AR), amaranth dye (AM) and acid orange 7 (AO) at a suitable λ_max 663, 609, 511, 520, and 484 nm, respectively. Regression analysis of Beer's law plots showed good correlation in the concentration ranges 1.0–24, 0.9–22, 1.2–26, 0.9–12.8 and 1.0–14 μg ml^?1, respectively. The apparent molar absorptivity, Sandell sensitivity, detection and quantitation limits were calculated. For more accurate results, Ringbom optimum concentration ranges were 1.2–22.4, 1.1–20, 1.4–24.5, 1.0–12.3 and 1.3–13.2 μg ml^?1, respectively. Statistical treatment of the results reflects that the proposed procedures are precise, accurate and easily applicable for the determination of amlodipine besylate in pure form and in pharmaceutical preparations.     

A simple and sensitive spectrophotometric method for the determination of trace amounts of nitrite in environmental and biological samples using 4-amino-5-hydroxynaphthalene-2,7-disulphonic acid monosodium salt

A very simple, sensitive, fairly selective and rapid spectrophotometric method for the determination of trace amounts of nitrite has been described. This method is based on the diazotized intramolecular coupling of electrophilic diazonium cation with the phenolic group of 4-amino-5-hydroxynaphthalene-2,7-disulphonic acid monosodium salt (AHNDMS) in a phosphate buffer solution of pH 7.5. The cyclic product has a purple color with maximum absorbance at 560 nm and is stable for 6 h. Optimum reaction conditions and other important analytical parameters for the maximum color development were established. Beer's law was found to obey for nitrite in the concentration range of 0.1–1.6 μg ml^?1 with molar absorptivity of 2.6 × 10⁴ l mol^?1 cm^?1 and Sandell's sensitivity of 0.0075 μg ml^?1. The effect of interfering ions on the determination is described. The recommended method was applied for the determination of nitrite in different water, soil and human saliva samples. The performance of the recommended method was evaluated in terms of Student's t-test and variance ratio F-test, which indicated the significance of proposed method over the reference method.     

Assay of caffeoylquinic acids in Baccharis trimera by reversed-phase liquid chromatography

Baccharis trimera commonly named ‘carqueja’, is wide-spread in South America and are used as raw material for herbal medicines. A reversed-phase liquid chromatography (RP-LC) method coupled to diode array detector was developed for the analysis of caffeoylquinic acids (CQAs), the main compounds responsible for its digestive activity. The identity of the quinic acids was established by mass spectrometry and were them: 5-O-[E]-caffeoylquinic acid, 3,4-O-[E]-dicaffeoylquinic acid, 3,5-O-[E]-dicaffeoylquinic acid, 4,5-O-[E]-dicaffeoylquinic acid and a tricaffeoylquinic acid. The RP-LC method for the quantitation of the caffeoylquinic acids was validated according to ICH guidelines, based on the following parameters: linearity, selectivity, robustness, limits of detection and quantification, precision and recovery. Hydroalcoholic extracts were prepared by the maceration of the plant material with ethanol:water 1:1 (v/v) in a 0.1:25 g mL^?1 plant:solvent ratio in a water bath at 40 °C. Validation data indicated that the HPLC method proposed is suitable for the analysis of caffeoylquinic acids in B. trimera raw material. The results of the LOD and LOQ analyses for the 5-CQA were 4.1 μg mL^?1 and 12.5 μg mL^?1, respectively, 1.3 μg mL^?1, 3.9 μg mL^?1 for 4,5-diCQA and 1.7 μg mL^?1, 5.1 μg mL^?1 for triCQA. The levels of total CQAs ranged from 2.1 to 4.0 g% (w/w). The influence of season harvest and site collection was also evaluated and variations were observed in the results and can be related to phonologic phase, different locations, seasons and soil. Long term and photostability of plant material were carried out and was observed a stable behavior during the time of the experiments.     

Enantiomeric separation of a melatonin agonist Ramelteon using amylose-based chiral stationary phase

A new simple isocratic chiral liquid chromatographic method was developed for the enantiomeric purity of Ramelteon[(S)-N-[2-(1,6,7,8-tetrahydro-2H-indeno[5,4-b]furan-8-yl) ethyl]-propionamide], a melatonin agonist in bulk drugs. The chromatographic separation was achieved on Chiralpak AD-H, 250 mm × 4.6 mm, 5 μm column using a mobile phase system consisting of n-hexane, ethanol and methanesulfonic acid in the ratio of 900:100:0.1 (v/v/v). The mobile phase was pumped on the column at the flow rate of 1 mL min^?1. Addition of methane sulfonic acid in the mobile phase enhanced chromatographic efficiency and resolution between the enantiomers. The resolution between the enantiomers was found to be more than four. The developed method was subsequently validated and proved to be accurate and precise. The experimentally established limit of detection and quantification of (R)-enantiomer were found to be 25.5 and 77.2 ng ml^?1, respectively, for 20 μl injection volumes. The percentage recovery of (R)-enantiomer was ranged from 98.5 to 101.9 in bulk drug samples of Ramelteon. The stability of Ramelteon sample in analytical solution was checked for about 48 h at room temperature and was found to be stable for about 48 h. The proposed method was found to be suitable and accurate for the quantitative determination of (R)-enantiomer in drug substance.     

Novel luminescent nanoparticles for DNA detection

Highly luminescent LaF₃:Ce³⁺/Tb³⁺ nanocrystals were successfully prepared and surface functionalized via Layer-by-Layer technology. These as-prepared nanocrystals are highly resistant to photobleaching and pretty dispersible in aqueous solution. Due to the efficient luminescence quenching of the nanocrystals by nucleic acids, a facile fluorescence quenching method was developed for the detection of trace amount of nucleic acids. Under optimal conditions, the fluorescence intensity was proportional to the DNA concentration over the range of 0.60–25.0 μg mL^?1 for calf thymus DNA (ct-DNA) and 0.60–30.0 μg mL^?1 for herring sperm DNA (hs-DNA), respectively. The corresponding detection limit is 0.21 μg mL^?1 for ct-DNA and 0.31 μg mL^?1 for hs-DNA, respectively. The results indicated that the reported method is simple and rapid with wide linear range. Also, the recovery and relative standard deviation of this method are reasonable and satisfactory.     

Analysis of hydrocarbon contamination with membrane-assisted solvent extraction: Comparison of agitation and sonication methods

Membrane-assisted solvent extraction (MASE) coupled to large volume injection was applied to the determination of (gasoline-type) hydrocarbon contamination in water samples. Hexane was used as acceptor phase. 50 μL extract was injected in the programmed temperature vaporizer injector using combined split–splitless evaporation. The extraction conditions were optimized both for MASE with agitation and for MASE with sonication. In the course of optimization the effect of extraction time, extraction temperature, agitation speed, solvent volume, pH, ionic strength and the addition of methanol were tested. Over 75% recovery was accomplished in the range of diesel oil hydrocarbons (n-C₉–n-C₂₄). The developed method was validated. Linearity, accuracy and precision were tested. The method showed excellent linearity between 1 and 1000 μg L^?1 for n-alkanes and between 0.05 and 50 mg L^?1 for gasoline. The method was tested with comprehensive GC × GC as well and found to be non-discriminative to all major compounds of diesel oil.     

Kinetic spectrophotometric determination of pravastatin in drug formulations via derivatization with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl)

A simple and sensitive kinetic spectrophotometric method for the quantitative analysis of pravastatin sodium (PVS) in pure and pharmaceutical formulations has been described. The method is based on the formation of colored product between PVS and 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) in acetone medium at 55 ± 2 °C. The reaction is followed spectrophotometrically by measuring the increase in absorbance at 462 nm as a function of time. The initial rate and fixed time methods were adopted for constructing the calibration curves. The linearity ranges were found to be 15.0–50.0 and 10.0–70.0 μg mL^?1 for initial rate and fixed time methods, respectively. The limits of detection for initial rate and fixed time methods are 0.029 and 0.086 μg mL^?1, respectively. Both methods have been applied successfully for the estimation of PVS in commercial dosage forms with no interference from the excipients. The results are compared with the HPLC pharmacopoeial method.     

Determination of NiII(3-OMe-salophene) in MCF7 and HT29 cancer cell lines using HR-CS-AAS and in serum albumin using LC with monolithic silica

A high-resolution continuum source atomic absorption spectrometric method was developed and validated for the determination of Ni^II(3-OMe-salophene) (a complex with anticancer activity in vitro) in MCF7 and HT29 cancer cell lines. The primarily most sensitive line 232.003 nm was selected for analysis. Compared to the standard nickel, the absorbance values obtained for Ni^II(3-OMe-salophene) complex was at least 93% at the upper end of linear range of the calibration curve. The use of common matrix modifiers including magnesium nitrate, palladium nitrate, ammonium hydrogen phosphate, lanthanum chloride and calcium nitrate brought no significant improvement in the GF AAS measurement. The dynamic linear working range of the calibration curve was found to be between 2.16 and 12.0 μg L^? 1 (ppb). This covers a concentration range of the complex from 0.036 μM to 0.204 μM. Typical coefficients of variation (n = 6) ranged from 0.2% to 6.7% for Ni in Ni^II(3-OMe-salophene). Detection and quantitation limits were 0.65 and 2.16 μg L^? 1 (ppb), respectively. The proposed method has been successfully applied to the analysis of Ni^II(3-OMe-salophene) complex in cell lines of breast cancer (MCF7) and colon cancer (HT29). However, being based on the determination of nickel in the salophene complex, the method was unsuitable for the quantitation of Ni^II(3-OMe-salophene) in serum albumin, which originally contains significant amount of nickel. For this purpose, a high performance liquid chromatographic method with a monolithic silica RP-18e column has been developed to quantitate the complex in serum albumin. The developed chromatographic method depends on detecting the whole complex in serum rather than the bounded nickel. A mobile phase consisting of 25 mM phosphate buffer pH 3/methanol (30:70, v/v) was pumped at a flow rate of 1 mL min^? 1. The eluted complex was monitored at a wavelength of 250 nm. The dynamic linear working range of the calibration curve for the developed LC method was found to be between 100 and 20,000 μg L^? 1 (0.23–46.18 μM). Detection and quantitation limits were 30 and 100 μg L^? 1 (ppb), respectively.     

Spectrophotometric determination of diphenhydramine hydrochloride in pharmaceutical preparations and biological fluids via ion-pair formation

A simple, sensitive and accurate spectrophotometric method has been described for the assay of diphenhydramine hydrochloride (DPH) in raw material and in biological samples. The method is based on extraction of DPH into dichloromethane as ion-pair complexes with patent blue (PB), eriochrome black T (EBT), methyl orange (MO) and bromocresol purple (BCP) in acidic medium. The coloured species exhibited absorption maxima at 632, 514, 428 and 414 nm for PB, EBT, MO and BCP, with molar absorptivity values of 1.32 × 10⁵, 2.36 × 10⁴, 3.68 × 10⁴ and 3.07 × 10⁴ l mol^?1 cm^?1, respectively. The reaction conditions were optimized to obtain the maximum colour intensity. Beer’s law was obeyed with a good correlation coefficient (0.9982–0.9993) in the concentration ranges 0.5–3, 2.0–16, 2.0–10 and 1.0–10 μg ml^?1 for PB, EBT, MO and BCP methods, respectively. The composition ratio of the ion-association complexes was found to be 1:1 in all cases as established by Job’s method. The conditional stability constant (K_f) and the free energy changes (ΔG°) were determined for all complexes formed. The proposed method was successfully applied for the determination of DPH in tablets and human urine with good accuracy and precision. Statistical comparison of the results with those obtained by the official method showed good agreement and indicated no significant difference in accuracy and precision.     

Column solid phase extraction and determination of ultra-trace Au,Pd and Pt in environmental and geological samples

A new sorbent based on cysteine modified silica gel (SiG-cys) was prepared and studied for preconcentration and separation of noble metals Au(III), Pd(II), Pt(II), Pt(IV). Its extraction efficiency was examined by batch and column solid phase extraction procedures. Laboratory experiments performed showed that sorbent is characterized with high selectivity, permiting quantitative sorption (93–97%) of noble metals Au, Pd and Pt from acidic media 0.1–2 mol L^? 1 HCl and unsignificant sorption (less than 2%) for common base metals like Cu, Fe, Mn and Zn. The analytes retained on the sorbent are effectively eluted with 0.1 mol L^? 1 thiourea in 0.1 mol L^? 1 HCl and measured by ETAAS or ICP OES under optimal instrumental parameters. The sorbent showed high mechanical and chemical stability and extraction efficiency was not changed after 500 cycles of sorption/desorption. The sorbent was successfully applied in analyticals procedures for preconcentration and determination of Au, Pd and Pt in geological and soil samples. Detection limits (3σ criteria) achieved, depending on the instrumental methods used are: ETAAS (0.005 μg L^? 1 for Au in river and sea water, 0.002 μg g^? 1 for Au in copper ore and copper concentrate); ICP OES (0.03 μg L^? 1 for Pd and 0.06 μg L^? 1 for Pt in river and sea water, 0.006 μg g^? 1 for Pd in copper ore and copper concentrate and 0.002 μg g^? 1 for soluble Pt in soil). The accuracy of the procedures developed was confirmed by added/found method for sea and river water; by the analysis of national certified materials (copper ore and copper concentrate for Au and Pd) and by determination of the sum of soluble Pt(II) + Pt(IV) in spiked soil samples.     

New,simple and validated kinetics spectrophotometric method for determination of moxifloxacine in its pharmaceutical formulations

The objective of this research was to develop a kinetic spectrophotometric method for determination of moxifloxacine (MOXF) in pure form and pharmaceutical formulations. The method was based on the formation of a colored N-vinyl chlorobenzoquinone derivative of MOXF by its reaction with 2,3,5,6-tetrachloro-1,4-benzoquinone in presence of acetaldehyde.The formation of the colored product was monitored spectrophotometrically by measuring the absorbance at 652 nm. Factors affecting the reaction were studied and optimized. The stoichiometry of the reaction was determined, and the reaction pathway was postulated. The activation energy of the reaction was calculated and found to be 6.65 kJ mol^?1. Under the optimized conditions, the initial rate and fixed time (at 5 min) methods were utilized for constructing the calibration graphs. The graphs were linear in concentration ranges 5–100 and 15–150 μg ml^?1 with limit of detection of 2.0 and 5.0 μg ml^?1 for the initial rate and fixed time methods, respectively. The analytical performance for both methods was fully validated, and the results were satisfactory. No interference was observed from the excipients that are commonly present in the pharmaceutical formulations. The proposed method was successfully applied to the determination of MOXF in its pharmaceutical formulations. The label claim percentages were 101.25 ± 0.73% and 100.92 ± 0.65% for the initial rate and fixed time method, respectively. Statistical comparison of the results with those obtained by a reference spectrophotometric method showed excellent agreement between the accuracy and precision of the two methods. The proposed method has great value in its application to the analysis of MOXF in quality control laboratories.     

Nano TiO2-based preconcentration for the speciation analysis of inorganic selenium by using ion chromatography with conductivity detection

A simple, sensitive, and cost-effective analytical method was developed for the speciation analysis of inorganic selenium by combining a nano-TiO₂ preconcentration with an ion chromatography-conductivity detection (IC-CD) system. The experimental conditions for the simultaneous adsorption and desorption of Se(IV) and Se(VI) were carefully investigated. Under the established optimum condition, the Se(IV) and Se(VI) ions could been simultaneously adsorbed onto the nano-TiO₂ surface at pH 4.0, and then effectively desorbed by 0.1 M sodium hydroxide eluent. The adsorption process was fast and reached adsorption equilibrium within 10 min. The nano-TiO₂ also exhibited high adsorption capacity with 11.3 mg g^? 1 for Se(IV) and 8.34 mg g^? 1 for Se(VI). The enrichment factors for Se(IV) and Se(VI) were calculated to be 39 and 30, respectively, with sample volume of 50 mL. The detection limits (3σ) were 0.8 μg L^? 1 for Se(IV) and 0.4 μg L^? 1 for Se(VI), which were sensitive enough for the routine analysis of water and drink samples. The relative standard deviation was calculated to be < 4% (n = 6) for detection of 30 μg L^? 1 Se(IV) and 30 μg L^? 1 Se(VI). The results of the present work confirmed that our developed nano-TiO₂-IC-CD method could be applied for the detection of inorganic selenium species in tap water and drink samples with good recoveries in the range of 82%–108%.     

Copper(II)–neocuproine reagent for spectrophotometric determination of captopril in pure form and pharmaceutical formulations

A simple, rapid, sensitive and accurate spectrophotometric method for the determination of captopril in pure form and pharmaceutical formulations is developed. The procedure is based on the reaction of copper(II) with captopril in the presence of neocuproine (NC) (2,9-dimethyl-1,10-phenanthroline) reagent in acetate buffer at pH 5.0. Copper(II) is reduced easily by captopril to Cu(I)–neocuproine complex, which shows an absorption maximum at 448 nm. Beer’s law was obeyed in the concentration range 0.3–3.0 μg mL^?1 with a minimum detection limit (LOD) of 0.039 μg mL^?1 and a quantification limit (LOQ) of 0.129 μg mL^?1. For more accurate results, Ringbom optimum concentration ranges was 0.5–2.7 μg mL^?1. The apparent molar absorbtivity and Sandell sensitivity were calculated. The validity of the proposed method was tested by analyzing the pure and pharmaceutical formulations and compared well with those obtained by the official method and demonstrated good accuracy and precision.     

Optimization of parameters of sampling and determination of reduced sulfur compounds using cryogenic capture and gas chromatography in tropical urban atmosphere

Reduced sulfur compounds, RSCs (H₂S, COS, CH₃SH, CH₃SCH₃, CS₂ and CH₃S₂CH₃) play a role in global cycle and acid rain formation. At trace levels RSCs in air are difficult to collect, store and analyze because of their highly adsorptive and reactive properties. This work optimizes parameters of sampling and instrumental determination of RSCs for urban measurements. The method used is based on cryogenic sampling and gas chromatography provided with a cryofocusing trap and flame photometric detection.Greater sampling efficiency was obtained with liquid argon as freezing fluid and air flow rate of 150 mL min^? 1 for two hours. Best results have been obtained with preconcentration for 3 min and injection volume of 3 ml. For H₂S, CH₃SH and CH₃S₂CH₃ the method showed a precision of 89%, limit of detection of 0.10 µg m^? 3 and limit of quantification 0.3 µg m^? 3. For CH₃SCH₃ and CS₂ the corresponding values were 89%, 0.15 µg m^? 3 and 0.5 µg m^? 3 and for COS were 75%, 0.18 µg m^? 3 and 0.8 µg m^? 3 respectively. Sampling efficiency varied between 70–80% for all the RSCs. Accuracy of H₂S from field measurements obtained with parallel measurements using a continuous monitor varied between 88 and 98%. The optimized methodology proved to be suitable for field measurements in urban tropical atmospheres with different characteristics.     

Simultaneous quantification of nimesulide,phenylpropanolamine, caffeine and chlorpheniramine in rat plasma by RP–HPLC/PDA method and application to pharmacokinetic studies in healthy rat subjects

Simultaneous determination of nimesulide, phenylpropanolamine, chlorpheniramine and caffeine in rat plasma by reversed-phase high performance liquid-chromatography (RP–HPLC) with photodiode array (PDA) detection method was developed and validated. Sample preparation based on a simple extraction procedure consisting of deproteination and extraction with methanol solution followed by volume make up with the aqueous component of the mobile phase obtained best recoveries of the analytes. The chromatographic conditions were optimized and the analytes were separated on XBridge™ C₁₈ (3.5 μm, 4.6 × 150 mm) column in isocratic elution with the mobile phase composition of acetonitrile and 10 mM ammonium acetate buffer (pH 4.0, 0.1% formic acid) (18:82 v/v%) at the flow rate of 1 mL min⁻¹ and the effluents were monitored in the wavelength range of 220–275 nm. The method was linear for all analytes over the following concentration (ng mL⁻¹) ranges: nimesulide 250–4000; phenylpropanolamine 100–1500; chlorpheniramine 20–500; and caffeine 10–100. Acceptable precision, accuracy and recoveries were obtained for quality control (QC) samples at three concentrations (low QC, middle QC and high QC). The percentage of relative standard deviation (% RSD) of Inter and intra-run precision of all molecules was <15% and the percentage of accuracy was 100 ± 10. The analytes were more stable in rat plasma at different storage conditions. Finally the method was efficiently applied to pharmacokinetics study in rat plasma.