Liliana Fernandez

Cloud point extraction, preconcentration and spectrophotometric determination of erbium(III)-2-(3,5-dichloro-2-pyridylazo)-5-dimethylaminophenol

The extraction and preconcentration of metal chelates via surfactant-mediated phase separation was studied. The effects on extraction parameters of several experimental variables were evaluated. A successive approximation method, using a least-squares computer program, was employed for the calculation of partition and acid dissociation constants of the chelating reagent. A new, high-sensitive and low-cost methodology for the determination of Er(III)-2-(3,5-dichloro-2-pyridylazo)-5-dimethylaminophenol — with the nonionic surfactant, polyethyleneglycolmono-p-nonylphenylether (PONPE 7.5), with a cloud point extraction step prior to absorptiometric determination — was developed and optimized. Under the optimal experimental conditions, the molar absorptivity was 1.27 × 105 1 mol−1cm−1. Calibration plot of absorbance (584 nm) vs. concentration was linear within the range 0.02–2 mg l−1 Er(III). The lower limit of detection (LOD) was 1.48 × 10−7 mol l−1. The proposed procedure was successfully applied to the determination of Er(III) in synthetic samples, reproducing superconducting materials and permanent magnets.

Assessment of trace aluminium content in parenteral solutions by combined cloud point preconcentration—flow injection inductively coupled plasma optical emission spectrometry

A micelle-mediated phase separation without added chelating agents to preconcentrate trace levels of aluminium in parenteral solutions as a prior step to its determination by flow injection inductively coupled plasma optical emission spectrometry has been developed. The enrichment step is based on the cloud point extraction of aluminium with the non-ionic surfactant polyethyleneglycolmono-p-nonylphenylether (PONPE 7.5). The chemical variables affecting the sensitivity of the extractive-spectrometric procedure were studied in detail. After optimization, a preconcentration factor of 200 and a %E higher than 99.9 were achieved. The detection limit (DL) value of aluminium for the preconcentration of 50 ml of parenteral solution was 0.25 microgl(-1). The calibration graph using the preconcentration system for aluminium was linear with a correlation coefficient of 0.9997 at levels near the DLs up to at least 200 microgl(-1). The developed hyphenated assay, which thoroughly satisfies the typical requirements for pharmaceutical control processes, is appropriate to monitor the aluminium concentration in parenteral nutrition.

Silver Nanoparticles as Optical Sensors

The use of silver nanoparticles (AgNPs) as analytical and bioanalytical sensors is receiving significant attention. This relevance arises from its unusual optical, electronic, and chemical properties (Schultz et al., 2000; Taton et al., 2000; Yguerabide & Yguerabide, 1998). The optical excitation of the surface plasmon resonance (SPR) caused by a collective excitation of the conduction band electrons of the nanoparticle, produces an absorption with large molar extinction coefficients and relevant scattering, usually when the particle size is larger than a few tens of nanometers (Haes et al., 2004). Colloid suspensions display brilliant colors as a result of intense light absorption and scattering, a fact first recognized by Faraday (Faraday & Philos, 1857), more than a century ago. SPR is associated with the coupled oscillation of free electrons on the conduction band accompanying enhanced local electromagnetic field, which is intensely sensitive to surrounding medium conditions. When a nanoparticle is exposed to an electromagnetic wave, the electrons in the particle oscillate at the same frequency as the incident wave. Spectral characteristics of silver nanoparticles are strongly dependent on their size, shape, interparticle spacing and environment (b-Rao et al., 2002). Therefore, the geometry of noble metal nanoparticles would provide important control over linear and nonlinear optical properties (Bruzzone et al., 2005; b-Jiang et al., 2005; Roll et al., 2003). Optical scattering has shown to be usefull in imaging methods to detect biosystems and has been applied to the diagnostics of cancer cells (Hirsch et al., 2003; El-Sayed et al., 2005). Other potentialities are related to single-nanoparticle use as chemical and biological sensors (Cognet et al., 2003; McFarland & Van Duyne, 2003); changes in the plasmonic resonance wavelength of maximum absorption or scattering are monitored as a function of changing the chemical and physical environment of the surface of the nanoparticles. The spectral response, SPR or scattering band, must be very sensitives to the changes in the refractive index of the surroundings. Many theoretical and experimental studies (Kelly et al., 2003; Gole & Murphy, 2004) have been made on metal nanoparticles with different geometries with the purpose to find the best nanoparticle configuration and enhance the sensitivity of the plasmon resonance response. 12

On-line enantioseparation of chlorpheniramine using β-cyclodextrin and carbon nanotubes after multivariate optimization

Multiwalled carbon nanotubes are evaluated here as solid phase extraction (SPE) sorbent aiming to (±)-chlorpheniramine (CPA) enantioresolution with fluorimetric detection. β-cyclodextrin (CD) was added to the racemate and solutions with HCl and sodium dodecyl sulfate (SDS) in different proportions were assayed as eluents to achieve the separation between both enantiomers. The overall methodology involved a flow injection (FI) strategy enabling high sample throughput and low reagents consumption making it suitable for drug routine quality control. An adequate enantioresolution (2.08) with satisfactory responses for both (R)-CPA (peak area=285) and (S)-CPA (peak area=380) was achieved applying the proposed FI-SPE strategy under the optimized conditions [β-CD] = 1.0 mmol L(-1), [HCl] = 1.0 × 10(-2) mol L(-1), [SDS] = 4.0 × 10(-4) mol L(-1) and eluent flow rate = 8.0 rpm.

Extraction and sensitive spectrophotometric determination of ytterbium with 2-(3,5-dichloro-2-pyridylazo)-5-dimethylaminophenol

The operating conditions for the absorptiometric determination of Yb(III) with the reagent 2-(3,5-dichloro-2-pyridylazo)-5-dimethylaminophenol (3,5-diClDMPAP) by a liquid-liquid extraction technique are presented. The complex yields a molar absorptivity of 1.54 x 10(5)l.mole(-1).cm(-1) (lambda(max) = 588 nm) and an optimum concentration range of 0.025-1.360n mg/l., at pH = 10. The method developed has been applied to the determination of Yb(III) in synthetic and concrete mixtures.

Synthesis and characterization of 2-(3,5-Dichloro-2-pyridylazo)-5-dimethylaminophenol as a reagent for determination of lanthanum.

2-(3,5-Dichloro-2-pyridylazo)-5-dimethylaminophenol (3,5-diCIDMPAP) has been synthesized and its spectral properties, acid-base equilibria, physical constants, and solubility and stability are presented. This reagent is highly promising for the determination of lanthanides. The influence of Triton X-100 on the dissociation constant has been investigated and the association constant between the reagent and the surfactant determined. Analytical data for the 3,5-diCIDMPAP complexes with La(III), Eu(III), Gd(III), Er(III) and Yb(III) are given, La(III) in synthetic samples has been determined with 3,5-diCIDMPAP.

Green Photoluminescent Methodology for Aluminium Traces Quantification in 24-Hour Urine of Subjects with Different Exposition to Tobacco Smoke

The aim of this work has been to evaluate the aluminium (Al(III)) traces contents in 24-hour urine samples from subjects with different tobacco smoke expositions using a new methodology with 1,4-dihydroxy-9, 10-anthraquinone (Quinizarine, QZ) as a fluorosphore. Biological samples were tested using commercial reagent strips and clinical parameters. Al(III) was determined complexing with QZ followed by a solid phase extraction step using Nylon membranes as a solid support. The analyte was subsequently quantified by solid surface fluorescence (SSF, λem= 573, λexc= 490) with a detection limit of 0.88 μg L-1 and quantification limit of 2.69 μg L-1. The calibration curve was linear from 2.69 to 499.13 μg L-1 Al(III) (R2 = 0.9973). Urine samples were successfully analysed with an average recovery close to 100%. Solid phase extraction step showed efficacy to eliminate foreign ions and the highly fluorescent matrix own of urine. Results were validated by electrothermal atomic absorption spectrometry (ETAAS) with an adequate concordance. The new methodology has low operation cost with simple instrumentation and without organic solvent.

Novel spectrofluorimetric method for boldine alkaloid determination in herbal drugs and phytopharmaceuticals

A new green on-line method for Boldine determination (BOL) in herbal drugs and phytopharmaceuticals, using its native fluorescence in acid media (λex=282nm; λem=373nm) has been developed. The presented methodology involves for the first time, a flow injection (FI) strategy using a mini-column of multiwalled carbon nanotubes as retention agent coupled with molecular fluorescence. Different parameters influence as sample pH and flow rate, eluent flow rate and composition; on BOL sensitivity and elution time was investigated by multifactorial techniques. Adequate dynamic calibration range (r2=0.9993) was obtained over a concentration interval of 0.029-27.0μgmL-1 BOL. The limits of detection (LOD) and quantification (LOQ) were 0.008 and 0.029μgmL-1, respectively. The average recoveries in explored samples ranged from 95% to 103%. Under optimized conditions, the throughput sample as high as 30h-1 was achieved with high repeatability performance (99%). The proposed development represents a useful and valuable tool emulating the analytical efficiency of the official methodologies for quality control of herbal and phytopharmaceutical drugs containing BOL. Moreover, this approach shows advantages respect to low cost, simplicity and environmental and analyst friendly.