Sequential determination of nickel and cadmium in tobacco, molasses and refill solutions for e-cigarettes samples by molecular fluorescence.

In this work, a new procedure was developed for separation and preconcentration of nickel(II) and cadmium(II) in several and varied tobacco samples. Tobacco samples were selected considering the main products consumed by segments of the population, in particular the age (youth) and lifestyle of the consumer. To guarantee representative samples, a randomized strategy of sampling was used. In the first step, a chemofiltration on nylon membrane is carried out employing eosin (Eo) and carbon nanotubes dispersed in sodium dodecylsulfate (SDS) solution (phosphate buffer pH 7). In this condition, Ni(II) was selectively retained on the solid support. After that, the filtrate liquid with Cd(II) was re-conditioned with acetic acid /acetate buffer solution (pH 5) and followed by detection. A spectrofluorimetric determination of both metals was carried out, on the solid support and the filtered aqueous solution, for Ni(II) and Cd(II), respectively. The solid surface fluorescence (SSF) determination was performed at λem = 545nm (λex = 515nm) for Ni(II)-Eo complex and the fluorescence of Cd(II)-Eo was quantified in aqueous solution using λem = 565nm (λex = 540nm). The calibration graphs resulted linear in a range of 0.058-29.35µgL-1 for Ni(II) and 0.124-56.20µgL-1 for Cd(II), with detection limits of 0.019 and 0.041µgL-1 (S/N = 3). The developed methodology shows good sensitivity and adequate selectivity, and it was successfully applied to the determination of trace amounts of nickel and cadmium present in tobacco samples (refill solutions for e-cigarettes, snuff used in narguille (molasses) and traditional tobacco) with satisfactory results. The new methodology was validated by ICP-MS with adequate agreement. The proposed methodology represents a novel fluorescence application to Ni(II) and Cd(II) quantification with sensitivity and accuracy similar to atomic spectroscopies, introducing for the first time the quenching effect on SSF.

Monitoring of chlorsulfuron in biological fluids and water samples by molecular fluorescence using rhodamine B as fluorophore.

A new simple methodology is proposed for chlorsufuron (CS) traces quantification based upon enhancement of rhodamine B (RhB) fluorescent signal. Experimental variables that influence fluorimetric sensitivity have been studied and optimized. The zeroth order regression calibration was linear from 0.866 to 35.800µgL(-1) CS, with a correlation coefficient of 0.99. At optimal experimental conditions, a limit of detection of 0.259µgL(-1) and a limit of quantification of 0.866µgL(-1) were obtained. The method showed good sensitivity and adequate selectivity and was applied to the determination of trace amounts of CS in plasma, serum and water samples with satisfactory results analyzed by ANOVA test. The proposed methodology represents an alternative to traditional chromatographic techniques for CS monitoring in complex samples, using an accessible instrument in control laboratories.

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.

Quantification of caffeine in dietary supplements and energy drinks by solid-surface fluorescence using a pre-concentration step on multi-walled carbon nanotubes and Rhodamine B.

A new method for the determination of caffeine, a non-fluorescent analyte, based on the enhancement of the fluorescence of Rhodamine B dye on a membrane filter modified with multi-walled carbon nanotubes is proposed. The method comprises pre-concentration of caffeine on a solid support by chemofiltration in buffered solution onto multi-walled carbon nanotubes previously oxidised and dispersed in cationic surfactant admicelles. The effect of experimental parameters, including the nature of the buffer and pH, the nature of the solid support, filtration flow rate, dye and carbon nanotube concentration, and the nature of the surfactant and concentration were investigated by means univariation assays. Under optimum experimental conditions, the pre-concentration system gave detection and quantification limits of 0.3 and 1.1 µg l(-1), respectively. A wide linear range was achieved varying from concentrations of 1.1 to 9.7 × 103 µg l(-1) (r(2) = 0.999). Satisfactory recovery values were obtained using the method of standard addition, confirming the feasibility of this method for caffeine determination in energising dietary supplements and energy drinks.

Caffeine monitoring in biological fluids by solid surface fluorescence using membranes modified with nanotubes.

BACKGROUND: In this work, a new methodology based upon enhancement of rhodamine B fluorescent signal is proposed for the quantification of caffeine traces. METHODS: Membrane filters treated with multiple wall carbon nanotubes were employed as solid support for determination step by solid surface fluorescence. RESULTS: Experimental variables that influence the preconcentration step and fluorimetric sensitivity have been optimized using uni-variation assays, presenting linearity from 1.1 to 9.7×10(3) µg/l, with a correlation coefficient of 0.99. At optimal conditions, a limit of detection of 0.3 µg/l and a limit of quantification of 1.1 µg/l were obtained. The method showed good sensitivity and adequate selectivity and was satisfactorily applied to the determination of trace amounts of caffeine in urine, plasma and serum belonging to subjects with different sex, ages and habit of caffeine intake. CONCLUSIONS: Chemofiltration step eliminated the highly fluorescent matrix, thus enabling and allowing CF quantification, in the presence of other methylxanthines. The proposed methodology represents an innovative application of the solid surface fluorescence using membrane filters modified with MWCNTs.

Determination of cadmium in tobacco by solid surface fluorescence using nylon membranes coated with carbon nanotubes.

A new methodology based on fluorescent signal enhancement of o-cresolphthalein (o-CPT) for traces of cadmium determination is proposed. The dye was retained on membrane filters in the presence of a micellar surfactant solution of carbon nanotubes (CNTs). All the experimental variables that influence both the preconcentration procedure and the fluorimetric sensitivity were carefully optimized. The calibration graph using zeroth order regression was linear from 6.5 ng L(-1) to 5.65×10(5) ng L(-1), with a correlation coefficient higher than 0.999. Under optimal conditions, the limits of detection and quantification were of 2 ng L(-1) and 6.5 ng L(-1). respectively. The proposed method showed good sensitivity and selectivity, with good tolerance to foreign ions, and it was applied to the determination of trace amounts of cadmium in leachate from cigarettes' tobacco samples with satisfactory results. The trueness of the recommended procedure was assessed through parallel analysis of the samples with electrothermal atomization atomic absorption spectrometry. This methodology represents an innovative and attractive application of membrane filters that enables metal traces determination by solid surface fluorescence.