Liliana P. Fernández

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.

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.

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).

Sequential determination of lead and cobalt in tap water and foods samples by fluorescence

In this work, a new procedure was developed for the separation and preconcentration of lead(II) and cobalt(II) in several water and foods samples. Complexes of metal ions with 8-hydroxyquinolein (8-HQ) were formed in aqueous solution. The proposed methodology is based on the preconcentration/separation of Pb(II) by solid-phase extraction using paper filter, followed by spectrofluorimetric determination of both metals, on the solid support and the filtered aqueous solution, respectively. The solid surface fluorescence determination was carried out at λem=455 nm (λex=385 nm) for Pb(II)-8-HQ complex and the fluorescence of Co(II)-8-HQ was determined in aqueous solution using λem=355 nm (λex=225 nm). The calibration graphs are linear in the range 0.14-8.03×10(4) μg L(-1) and 7.3×10(-2)-4.12×10(3) μg L(-1), for Pb(II) and Co(II), respectively, with a detection limit of 4.3×10(-2) and 2.19×10(-2) μg L(-1) (S/N=3). The developed methodology showed good sensitivity and adequate selectivity and it was successfully applied to the determination of trace amounts of lead and cobalt in tap waters belonging of different regions of Argentina and foods samples (milk powder, express coffee, cocoa powder) with satisfactory results. The new methodology was validated by electrothermal atomic absorption spectroscopy with adequate agreement. The proposed methodology represents a novel application of fluorescence to Pb(II) and Co(II) quantification with sensitivity and accuracy similar to atomic spectroscopies.

Sensitive ergotamine determination in pharmaceuticals and biological samples using cloud point preconcentration and spectrofluorimetric detection

A new cloud point extraction (CPE) method for ergotamine analysis using fluorimetric detection is described. Ergotamine from an aqueous solution was preconcentrated into a smaller surfactant-rich phase using nonionic surfactant polyoxyethylene(7.5)nonylphenylether (PONPE 7.5). Differently from the conventional CPE procedure in which the resulting surfactant-rich phase is diluted by a fluidificant before its analysis, in this method the fluorescence measurements were carried out directly onto the undiluted surfactant-rich phase. The high viscosity provided by the undiluted surfactant rich phase greatly improved the fluorescence emission of ergotamine, leading to a total enhancement factor of 1325. This spectral advantage plus the preconcentration factor achieved, contributed to the method sensitivity allowing the ergotamine determination at trace level concentration. Under optimal experimental conditions, a linear calibration curve was obtained from 3.81×10(-7) to 1.10μgmL(-1), with detection and quantification limits of 0.11 and 0.38pgmL(-1), respectively. The accuracy and versatility of the present methodology were proved by analyzing ergotamine in real samples of different natures such as pharmaceuticals, urine and saliva.

Simultaneous separation of ergot alkaloids by capillary electrophoresis after cloud point extraction from cereal samples

A new and sensitive analytical methodology for ergot alkaloids (EA) determination from cereal samples based on cloud point extraction (CPE) prior to CE‐UV absorbance was developed. The methodology involves extraction under acid conditions and subsequent preconcentration by applying a simple, rapid and environmentally friendly low volume surfactant extraction procedure. After extraction, CE analysis was carried out by performing dilutions on preconcentrated surfactant rich phase, achieving a single peak or simultaneous alkaloids determination. A real preconcentration factor of 22 of total EA was obtained, demonstrating the efficiency of this methodology. The limits of detection were 2.6 and 2.2 μg/kg for ergotamine and ergonovine, respectively. Validation procedure revealed suitable linearity, accuracy and precision. The average extraction and clean‐up recoveries were compared with the theoretical values and were better than 92%. This method was successfully applied to the determination of EA in different varieties of commercial flour samples, two grain samples and one of the leading brands cereal‐based product for infant feeding. The high sensitivity achieved for EA determinations in real samples suggests CPE procedure as an interesting approach to improve CE‐UV visible detection limits. Moreover, the whole process could be considered as a contribution to green chemistry because nonorganic solvents were involved, demonstrating its great potential over conventional techniques.

Determination of thimerosal in pharmaceutical industry effluents and river waters by HPLC coupled to atomic fluorescence spectrometry through post-column UV-assisted vapor generation.

A high performance liquid chromatography coupled with atomic fluorescence spectrometry method for the determination of thimerosal (sodium ethylmercury thiosalicylate, C9H9HgNaO2S), ethylmercury, and inorganic mercury is proposed. Mercury vapor is generated by the post-column reduction of mercury species in formic acid media using UV-radiation. Thimerosal is quantitatively converted to Hg(II) followed by the reduction of Hg(II) to Hg(0). This method is applied to the determination of thimerosal (THM), ethylmercury (EtHg) and inorganic Hg in samples of a pharmaceutical industry effluent, and in waters of the San Luis River situated in the west side of San Luis city (Middle West, Argentine) where the effluents are dumped. The limit of detections, calculated on the basis of the 3σ criterion, where 0.09, 0.09 and 0.07 μg L(-1) for THM, EtHg(II) and for Hg(II), respectively. Linearity was attained from levels close to the detection limit up to at least 100 μg L(-1).