Adriana N. Masi

On-line micellar-enhanced spectrofluorimetric determination of rhodamine dye in cosmetics

A simple FI-fluorimetric analytical methodology for the continuous and sequential determination of rhodamine B (RhB) in cosmetic products has been developed and evaluated in terms of sensibility and selectivity. The influence of several surfactant solutions on RhB fluorescence signal has been studied; particular attention was paid in the aggregation behavior of RhB-SDS system. Linear response has been obtained in the range of 1.6 x 10(-9) and 1 x 10(-6) mol L(-1), with a detection limit of 5 x 10(-10) mol L(-1). The novel technique provides a simple dissolution of sample, on-line filtration with sampling rate higher than 100 samples h(-1) and has been satisfactorily applied to the RhB determination in commercial lipsticks.

Selective spectrofluorimetric method for paracetamol determination through coumarinic compound formation.

A spectrofluorimetrical selective method was designed for determination of paracetamol in tablets. This important technique can be characterized by its sensitivity, simplicity, celerity and cheaper cost than current official methods. The employed methodology involves coumarinic compound formation obtained by reaction between paracetamol and ethylacetoacetate (EAA) in the presence of sulphuric acid as catalyst. The reaction product is highly fluorescent at 478nm, being excited at 446nm. The linear concentration range of the application was 0.1-0.4microg/ml of paracetamol and the detection limit was 57ng/ml. The influence of different variables was studied and optimized through chemometric techniques. Applying the above-mentioned method good results were obtained with regard to pharmaceutical formulations containing paracetamol. Therefore, it is relevant to suggest this profitable technique for medicament control analysis.

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.

A novel application of immobilization on membranes for the separation and spectrofluorimetric quantification of amiloride and furosemide in pharmaceutical samples

A new, simple and highly sensitive method for spectrofluorimetric determination of amiloride (AMI) and furosemide (FUR) in pharmaceuticals is presented. The proposed method is based on the separation of AMI from FUR by solid-phase extraction using a nylon membrane, followed by spectrofluorimetric determination of both drugs, on the solid surface and the filtered aqueous solution, respectively. AMI shows low native fluorescence, but its separation-preconcentration by immobilization (solid-phase extraction) on nylon membrane surface provides a considerable enhancement in fluorescence intensity. The fluorescence determination is carried out at lambda(ex)=237, lambda(em)=415 nm for FUR; and lambda(ex)=365, lambda(em)=406 nm for AMI. The calibration graphs are linear in the range 3.20 x 10(-4) to 0.8 microg mL(-1) and 1.33 x 10(-3) to 4.0 microg mL(-1), for AMI and FUR, respectively, with a detection limit of 9.62 x 10(-5) and 4.01 x 10(-4) microg mL(-1) (S/N=3). The commonly found excipients in commercial pharmaceutical formulations do not interfere. The developed method is successfully applied to the determination of both drugs in pharmaceutical formulations.

Flow injection spectrofluorimetric determination of carvedilol mediated by micelles

A novel flow injection (FI)-spectrofluorimetric methodology for the determination of carvedilol in microheterogeneous medium has been developed. In the sodium dodecyl sulfate (SDS) surfactant medium, an additional fluorescence enhancement was produced by the electrolyte NaCl. A total enhancement of 3.1-fold in the native fluorescent response was achieved respect to aqueous medium. Using an excitation and emission wavelength of 286 and 341 nm, respectively, a good linear relationship was obtained in the range of 9x10(-8) to 1x10(-6) mol L(-1) with a detection limit of 3.63x10(-9) mol L(-1) (S/N=3). This method was applied to determine carvedilol in commercial pharmaceutical formulations. Good concordance was found between the nominal (6.25, 12.5 and 25.0 mg) and experimental values. The new methodology developed showed high selectivity respect to the common excipients used in pharmaceuticals. The sampling rate was 30 samples h(-1). From the fluorescent properties, binding constant for carvedilol-SDS determined was 3.2x10(2) L mol(-1).

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

Sensitive surfactant-mediated spectrofluorimetric determination of sildenafil.

Two simple and sensitive surfactant-mediated spectrofluorimetric methods for the determination of sildenafil are proposed in this paper. These methods are based on the interaction of sildenafil with normal micelles of HTAB (hexadecyltrimethylammonium bromide, method A) and the formation of ion-association complexes of sildenafil with SDS (sodium dodecyl sulfate, method B). In both methods, the formed species produce considerable fluorescence enhancement, which allows sildenafil to be quantitatively determined. Linearity was obtained for sildenafil in the concentration range 0.004 to 25 μg mL−1 with a detection limit of 0.0012 μg mL−1 by method A; and a linearity range of 0.005 to 50.0 μg mL−1 with a detection limit of 0.0016 μg mL−1 by method B. The proposed methods have been applied to the analysis of bulk drug, tablets, herbal medicine and beverages. Validation processes were performed by recovery studies and statistical analysis with satisfactory results.