Determination of Lead in Bee Products by Solid Surface Fluorescence Using Complexation and Coacervation at Room Temperature Processes. An Environmental Friendly Methodology.

An accurate, economic and green methodology for Pb(II) monitoring in bee products is proposed. Complexed metal traces were preconcentrated on Nylon membranes using the coacervation phenomenon based on room temperature reaction between the cationic surfactant hexadecyltrimethylammonium bromide and the bile salt sodium cholate. The increase in solid surface fluorescence signal of dyes 8-hydroxyquinoleine and o-phenanthroline due to Pb(II) presence was used for the metal quantification. Experimental variables that influence on preconcentration step and fluorimetric sensitivity were optimized using uni-varied assays. Pb(II) concentration was determined on membranes by solid surface fluorescence at λem = 470 nm (λexc = 445 nm), using a solid sample holder. The calibration at optimal experimental conditions showed a LOD of 4.2 × 10-4 mg Kg-1 with a linear range of 1.28 × 10-3 mg Kg-1 to 8.73 mg Kg-1 and was successfully applied to Pb(II) quantification in different bee products produced in central west region of Argentina. The proposed methodology was applied to all samples after appropriate dilution. Accuracy methodology was evaluated by comparison of the obtained results with those found by ICP-MS, with percentage relative error under 8%. The precision was better than 0.0344 CV for Pb(II) determination.

Sonochemical Synthesized Manganese Oxide Nanoparticles as Fluorescent Sensor for Selenium (IV) Quantification. Application to Food and Drink Samples.

Manganese oxide nanoparticles (MnO Nps), sonochemical synthesized and characterized in our laboratory, are proposed as fluorescent sensor for selenium (Se) determination. The new methodology has been developed based on the enhancing effect of the Se(IV) on fluorescent emission of MnO Nps. Experimental variables that influence on fluorimetric sensitivity were optimized. The calibration graph using zeroth order regression was linear from 0.189 ng L-1 to 8.00 × 103 µg L-1, with correlation coefficient better than 0.99. Under the optimal conditions, the limits of detection and quantification were of 0.062 ng L-1 and 0.189 ng L-1, respectively. The trueness of the methodology was assessed through standard addition method obtaining recovery near to 100%. This method showed good tolerance to foreign ions, particularly to Se(VI), and was applied to determination of Se(IV) trace in food and drink samples with satisfactory results. With the intention of preserving the environment from harmful effects, a degradation study of the used nanomaterials has been included for their subsequent disposal.

Copper Traces Quantification in Bee's Products by Solid Surface Fluorescence. A Green Analytical Proposal.

A new methodology based on the fluorescence of Cu(II) ternary system with o-phenanthroline (o-Phen) and eosin (Eo) dyes is proposed. The metal was selectively retained on Nylon membranes and the solid surface fluorescence (SSF) was used for anayte quantification. Experimental variables that influence the formation of Cu(II)-o-Phen-eo system and retention step were studied and optimized. At optimal experimental conditions, an adequate tolerance to foreign species was shown with a LOD of 1.18 ng L-1 and a LOQ of 3.57 ng L-1. The methodology was evaluated for their greenness profile and successfully applied to analyte determination in bee's products of West-Center Argentina. Recovery studies showed values near to 100% being satisfactorily validated by ICP-MS.

Tolfenamic acid on-line preconcentration strategy on carbon nanotubes minicolumn with fluorimetric detection.

Nonsteroidal anti-inflammatory agents (NSAIDs) are a group of pharmaceuticals considered one of the most popular drugs used in clinical practice applied to the treatment of acute and chronic conditions. Some pharmaceuticals products are excreted reaching the environment and altering the balance of ecosystems. This work proposes a new fluorimetric flow injection (FI) methodology for the NSAID tolfenamic acid quantification based on the quenching effect of the analyte on fluorescent signal of bovine serum albumin fluorophore. Results put in evidence a mechanism of static quenching, with a Stern Volmer constant value of 1.8 × 107 L mol-1. To achieve the selective on-line preconcentration of analyte, a carbon nanotubes mini column was introduced in the FI configuration producing a beneficial effect on high sampling frequency, minimum sample and reagents consumption. The experimental factors that influence batch fluorescent signal and FI analysis have been studied and optimized. At optimal experimental conditions, an adequate tolerance to foreign species was shown. With the flow configuration, a LOD of 0.019 µg L-1, a LOQ of 0.058 µg L-1 were obtained with a sampling rate of 30 samples h-1. The new methodology was successfully applied to analyte determination in tap water and pharmaceutical and factory waste samples with recuperation near to 100%.

Determination of lead traces in honey using a fluorimetric method.

Heavy traces metals may be present in honey being their detection very important for the quality control and it also serves as an indicator of environmental pollution. A new methodology for lead traces determination has been developed based on the quenching effect of the metal on fluorescent emission of 8-hydroxyquinoline and o-phenanthroline at λem = 360 nm (λexc = 250 nm). Experimental variables that influence on fluorimetric sensitivity were optimized by uni-variation assays. The calibration graph using zeroth order regression was linear from 0.105 µg L-1 to 51.8 µg L-1, with correlation coefficient better than 0.998. Under the optimal conditions, the limits of detection and quantification were of 0.035 µg L-1 and 0.105 µg L-1, respectively. The trueness of the methodology was assessed trough parallel samples analysis by ICP-MS. The proposed method showed good sensitivity, adequate selectivity with good tolerance to foreign ions, and was applied to the determination of lead trace amounts in honey from San Luis city (Argentina) with satisfactory results.

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.

Novel method for determination of zinc traces in beverages and water samples by solid surface fluorescence using a conventional quartz cuvette.

A new method for zinc pre-concentration/separation and determination by molecular fluorescence is proposed. The metal was complexed with o-phenanthroline and eosin at pH 7.5 in Tris; a piece of filter paper was used as a solid support and solid fluorescent emission measured using a conventional quartz cuvette. Under optimal conditions, the limits of detection and quantification were 0.36 × 10(-3) and 1.29 × 10(-3) µg L(-1), respectively, and the linear range from 1.29 × 10(-3) to 4.50 µg L(-1). This method showed good sensitivity and selectivity, and it was applied to the determination of zinc in foods and tap water. The absence of filtration reduced the consumption of water and electricity. Additionally, the use of common filter papers makes it a simpler and more rapid alternative to conventional methods, with sensitivity and accuracy similar to atomic spectroscopies using a typical laboratory instrument.

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.

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.

Solid surface spectroscopic methodology for ultra-trace urinary nickel monitoring in smokers and non-smokers' subjects.

Nickel chemical enrichment on nylon membranes previously treated with eosin (eo) is proposed for subsequent quantification by spectrofluorimetry (lambda(em)=547 nm, lambda(exc)=515 nm). Operational variables which have influence on quantitative metal retention have been studied. At optimal experimental conditions, quantitative recovery was reached (superior to 99%), with a detection limit of 0.13 ng L(-1) and quantification limit of 0.44 ng L(-1). The calibration sensitivity was of 6x10(13) ng L(-1) for the new methodology with a linear range of 0.44-410 ng L(-1) Ni(II). The tolerance levels, respect to cations and anions as potential interferents, were studied, with good results. The methodology was validated by standard addition method and satisfactorily applied to urinary nickel determination of 50 subjects including smokers, second hand smokers and non-smokers' samples without previous treatment. Stability of biological samples was daily studied for a period of 1 month. Within-day precision was better than 0.02 CV. The reproducibility (between-day precision) was also evaluated over 3 days by performing six determinations each day with a CV of 0.052. The different groups were evaluated using one-way analysis of variance (ANOVA) followed by Tukey-Kramer multiple comparison test with satisfactory results.

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.