Marta O. Luconi

Cloud point extraction of lead in saliva via use of nonionic PONPE 7.5 without added chelating agents

A new micelle-mediated phase separation of metal ions to preconcentrate trace levels of lead as a prior step to its determination by flame atomic spectroscopy has been developed. The methodology is based on the cloud point extraction of lead with PONPE 7.5 in the absence of chelating agent. The chemical variables affecting the sensitivity of the extractive-spectrometric procedure were evaluated in detail, optimised and successfully applied to the determination of lead in saliva samples. Under the optimal conditions, a %E higher than 99.9 was achieved. The proposed method showed linear calibration within the range: 0.6-4 mug ml(-1) Pb(II). The sensitivity was 0.053 mug ml(-1). The method has been applied to the determination of lead in human saliva. The nature of the extracting species as well as the location of lead in the micelle were studied. The analytical performance of the proposed method clearly satisfies the typical requirements for control processes.

Spectrophotometric determination of trace aluminium content in parenteral solutions by combined cloud point preconcentration–flow injection analysis

A cloud point preconcentration and flow injection (FI) analysis methodology for aluminium(III) determination has been developed. The analyte in the initial aqueous solution was complexed with Chrome Azurol S (CAS) in the presence of the cationic surfactant benzyldimethyltetradecylammonium chloride (BDTAC). The absorption spectroscopic characteristics of the ternary complex [Al(III)-CAS-BDTAC] were examined in detail. The preconcentration step was carried out by means of the non-ionic surfactant polyethylene glycol p-nonylphenyl ether (PONPE 7.5). The enriched analyte solution was injected into an FI system using an HPLC pump. The chemical variables affecting the analytical performance of the combined methodology were studied and optimised. The developed approach was successfully applied to the determination of trace amounts of aluminium in parenteral solutions without previous treatment. Under the optimum experimental conditions, 99.9% extraction was achieved for a preconcentration factor of 50. The limit of detection was 1.12 x 10(-7) mol(-1). The calibration plot was linear over at least two orders of magnitude of aluminium concentration. The developed coupled methodology, which thoroughly satisfies the typical requirements for pharmaceutical control processes, is appropriate for monitoring the aluminium concentration in parenteral nutrition.

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.

Determination of terazosin by cloud point extraction-fluorimetric combined methodology

A new sensitive and selective preconcentration-fluorimetric method for determination of terazosin based on its native fluorescence was developed. The analyte, initially present in aqueous matrix, was treated with an extractive non-ionic surfactant solution and separated by the clouding phenomenon. The optimum analytical conditions for terazosin assay were established. Under these conditions, linear calibration curves were obtained over the range of 1x10(-5) to 7.0 microg mL(-1) with detection and quantification limits of 1.11x10(-5) and 3.7x10(-5)microg mL(-1), respectively. Additionally, the binding constant (K(B)) for the terazosin-PONPE 7.5 system was determined given a value of 1028 L mol(-1). The developed coupled methodology, which thoroughly satisfies the typical requirements for pharmaceutical control processes, was proved to be appropriate for monitoring terazosin in actual pharmaceutical formulations and biological fluid sample. The results were validated by recovery test and by comparison with other reported methods, being highly satisfactory.

Cadmium monitoring in saliva and urine as indicator of smoking addiction.

Cadmium is one of the many substances that may be acquired through active and passive smoking of tobacco. Saliva and urine are proposed for cadmium monitoring of non-smokers, second hand smokers, smokers and tobacco chewing appertaining to San Luis citizens without occupational exposition. Biological samples were collected by the same subjects, under strict proceeding instructions of sampling. Physical characteristics of samples were observed and checked with commercial test. Samples were analyzed using an adapted molecular fluorescence methodology with a previous extraction step. Stability of biological samples was daily studied for a period of one month. The method was successfully validated for accuracy, precision, linearity, specificity, and sensitivity. The simplicity and low coefficient of variance confirm the suitability of the method for urinary and salivary cadmium analyses. On the other side, the obtained results are in concordance with previous national epidemiological dates.

Derivatized silver nanoparticles as sensor for ultra-trace nitrate determination based on light scattering phenomenon

New silver nanoparticles coated with EDTA (EDTA-AgNPs) have been synthesized by citrate reduction method and characterized by UV-vis spectroscopy, molecular fluorescence and scanning electron microscopy (SEM). The derivatized nanoparticles show fluorescent emission and second order scattering (SOS) signals which in presence of nitrate are both attenuated. The SOS decreasing is greater than its fluorescent quenching; considering this fact, a new ultra sensitive methodology using the derivatized silver nanoparticles as sensor for nitrate determination has been developed. Under optimal established conditions, a linear response has been obtained within the range of 6.4 x 10(-4) to 3.0 microg mL(-1) nitrate concentrations, with a detection limit of 1.8 x 10(-4) microg mL(-1). This novel technique provides a sensitive and selective methodology for nitrate determination and has been satisfactorily applied to its quantification in parenteral solutions.

Determination of cadmium at ultra-trace levels by CPE–molecular fluorescence combined methodology

A highly sensitive micelle-mediated extraction methodology for the preconcentration and determination of trace levels of cadmium by molecular fluorescence has been developed. Metal was complexed with o-phenanthroline (o-phen) and eosin (eo) at pH 7.6 in buffer Tris medium and quantitatively extracted into a small volume of surfactant-rich phase of PONPE 7.5 after centrifugating. The chemical variables affecting cloud point extraction (CPE) were evaluated and optimized. The RSD for six replicates of cadmium determinations at 0.84 microg L(-1) level was 1.17%. The linearity range using the preconcentration system was between 2.79 x 10(-3) microg L(-1) and 2.81 microg L(-1) with a correlation coefficient of 0.99. Under the optimal conditions, it obtained a LOD of 8.38 x 10(-4) microg L(-1) and LOQ of 2.79 x 10(-3) microg L(-1). The method presented good sensitivity and selectivity and was applied to the determination of trace amounts of cadmium in commercially bottled mineral water, tap water and water well samples with satisfactory results. The proposed method is an innovative application of CPE-luminescence to metal analysis comparable in sensitivity and accuracy with atomic spectroscopies.

Flow injection spectrophotometric analysis of lead in human saliva for monitoring environmental pollution

A new highly sensitive, simple and low-cost methodology for the direct determination of Pb (II) with 2-(5-bromo-2-pyridylazo)-5-dimethylaminophenol in ethanolic medium has been developed. The absorption spectroscopy of the complex has been examined in detail, and the chemical variables affecting the sensitivity of procedure studied, optimized and applied to the determination of trace amounts of lead in human saliva. Under the optimal experimental conditions, a precision of 1.61x10(-4) mug cm(-2) was achieved, the molar absorptivity being (epsilon) 5.6x10(4) l mol(-1) cm(-1). An FI technique is proposed, and it is possible to determine trace levels of lead by injection into a steam buffered at pH 7.15, containing 70% ethanol: 30% Tris buffer 3.5x10(-3) mol l(-1) (pH=7.2), 1x10(-4) mol l(-1) 5-BrDMPAP. The FIA configuration allows the analysis of 45 samples per hour. The lower limit of detection (LOD) was 1x10(-7) mol l(-1). The calibration plot was linear at least within two orders of magnitude of lead concentration. The use of an HPLC pump for the FI analysis led to a substantial improvement in the analytical performance of the method, which clearly satisfies the typical requirements for control processes.

Evaluation of carbon nanotubes as chiral selectors for continuous-flow enantiomeric separation of carvedilol with fluorescent detection

Single-walled carbon nanotubes (SWNT) are proposed as chiral selectors for separation of carvedilol stereoisomers beginning since its racemic mixture. The novel developed FIA-methodology employs a microcolumn (mC) packed with a few milligrams of SWNT which showed to be effective in S(-) and R(+) carvedilol separation. Attending to spectral properties of analytes, molecular fluorescence was employed in the detection step. Separation of carvedilol enantiomers was achieved in less than 70s with an acceptable resolution factor of 3.16. Variables that influence the chiral separation such as pH and composition of eluent solution, sample injection volume and flow rate, activation mode of NTs and mass of the same in column have been examined in detail. At optimal operational conditions, well repeatability was achieved using the same column for more than 100 injections, putting in evidence the stability of nanomaterial and the efficacy and versatility of the proposed FIA-configuration. The new methodology was successfully applied to S(-) and R(+) carvedilol quantification in pharmaceutical preparations, resulting an attractive alternative to traditional separative methods being fast, simple, using low cost instrumentation and producing scarce waste.

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