Obtaining Recovery Percentages Research Articles

Carbon black as a cost-effective nanomodifier for (electro)chemical-free pre-treatment thermoplastic polyurethane-based 3D printed electrodes

Here, we report the investigation of carbon black as a cost-effective nanomodifier of thermoplastic polyurethane-based 3D printed electrodes for enhancing their electrochemical performances. The sensor was produced by scratching the working electrode with sandpaper, followed by the deposition of carbon black dispersion by drop casting. The morphological characterisation was carried out, showing the presence of a homogeneous coating of carbon black with a typical rough and spongy structure. Additionally, the electrochemical characterisation using electrochemical impedance spectroscopy highlighted the advantage of using carbon black as a nanomodifier of the working electrode surface after printing by obtaining the resistance of charge transfer equal to 327 ± 43 kΩ and 1.45 ± 0.06 kΩ for bare electrode and carbon black-modified electrode, respectively. When tested in cyclic voltammetry using ferro/ferricyanide, uric acid, dopamine, ascorbic acid, and free chlorine as target electroactive compounds, we demonstrated that the presence of carbon black cast onto the working electrode surface transformed the electrode from non-responsive to responsive electroanalytical tool. The analytical features of the developed responsive sensor were assessed for the detection of free chlorine in tap water with a linearity of 0.2–20 ppm and a limit of detection equal to 0.01 ppm. The accuracy was evaluated by spiking tap water samples with free chlorine concentrations equal to 0.5, 1, and 5 ppm, obtaining recovery percentages of (103 ± 2)%, (104 ± 3)%, and (95 ± 3)%, respectively. Additionally, the sustainability (electro)chemical-free pre-treatment thermoplastic polyurethane-based 3D printed electrodes modified with carbon black were evaluated by the White Analytical Chemistry principles. The advantages of 3D printed sensors modified with carbon black by drop casting were demonstrated, in terms of both the electrochemical performances and sustainable aspect, enlarging the use of carbon black as a nanomodifier to the 3D printed electrodes, beyond the 2D printed electrodes.

Electrochemical detection of nicotine at a carbon Nanofiber-Poly(amidoamine) dendrimer modified glassy carbon electrode.

Development of electrochemical sensors for important drugs such nicotine (an addictive drug) is important for the society. This study reports the electrochemical detection of nicotine at a carbon nanofiber/poly (amidoamine) dendrimer modified glassy carbon electrode. The carbon nanofiber (CNF) modified GCE was prepared by drop-coating followed by the electrodeposition of generation 4 poly (amidoamine) succinamic acid dendrimer (PAMAM) to form the sensor - CNF-PAMAM GCE. Characterization of prepared materials and modified electrodes was carried out using Fourier transmission infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). The CNF-PAMAM composite was confirmed by microscopy. A marked reduction in charge transfer resistance and increase in current of the CNF-PAMAM GCE in comparison to the bare electrode showed a synergic improvement electrochemical response because of the CNF-PAMAM nanocomposite. The CNF-PAMAM demonstrated an enhanced performance in the oxidation of nicotine in comparison to the bare GCE by shifting the anodic potential Epa of nicotine from 0.9V to 0.8V. The electrochemical sensor achieved a detection limit (LOD) of 0.02637μM in the concentration range of 0.4815-15.41μM of nicotine in 0.1M PBS at pH 7.5. The sensor ability to determine nicotine in real samples was assessed in cigarettes obtaining recovery percentages of 88.00 and 97.42%. The sensor demonstrated selectivity toward nicotine in the presence of interferences. Finally, the method was validated by ultraviolet-visible spectroscopy analysis.

Direct solid sampling for speciation of Zn2+ and ZnO nanoparticles in cosmetics by graphite furnace atomic absorption spectrometry

The application of nanoparticles (NPs) in science and technology is a fast growing field. Therefore, reliable and straightforward analytical methods are required for their fast determination in different types of samples. This work investigates a method that enables the determination of ZnO NPs, discriminating them from ionic zinc in cosmetic samples. The method is based on direct solid sampling high-resolution continuum source electrothermal atomic absorption spectrometry (SS-HR-CS-GFAAS), and has been applied to determination of ZnO NPs, Zn2+ and total Zn in eye shadow samples. In this work the deconvolution of the atomization peak and the calibration by standard additions have been done in order to discriminate and quantify ionic zinc and ZnO NPs. A Zn wavelength with low sensitivity was selected. The proper optimization of the graphite furnace temperature program, minimizing the mineralization of the sample matrix, enables different atomization profiles between the different chemical species of the analyte. Two multiple response surface designs have been used in order to optimize the adequate furnace program to achieve our aims. All the optimization experiments were performed using a sample of eye shadow. Further, a method for the determination of total Zn by direct solid sampling with calibration by aqueous standards, was also optimized. The optimized method was successfully applied to the determination of ionic Zn and ZnO NPs in different eye shadow samples, and has been validated by recovery assays, obtaining recovery percentages between 80 and 125%. Total Zn concentration in the solid samples was validated by the determination of total Zn by direct solid sampling and by the analysis of the same eye shadow samples digested in microwave oven.

Validation of a methodology to determine Benzene, Toluene, Ethylbenzene, and Xylenes concentration present in the air and adsorbed in activated charcoal passive samplers by GC/FID chromatography

This article shows the validation of the analytical procedure which allows determining concentrations of Benzene (B), Toluene (T), Ethylbenzene (E), and Xylenes (X) -compounds known as BTEX- present in the air and adsorbed by over activated charcoal by GC-FID using the (Fluorobenzene) internal standard addition as quantification method. In the process, reference activated charcoal was employed for validation and coconut -base granular charcoal (CGC) for the construction of passive captors used in sample taken in external places or in environmental air. CGC material was selected from its recovering capacity of BTEX, with an average of 89.1% for all analytes. In this research, BTEX presence in air samples, taken in a road of six lines and characterized for having heavy traffic, in Medellin city (Antioquia, Colombia), was analyzed. Samplers employed were located in pairs per point (in 7 transversal strips of the east, central, and west sidewalk), at heights ranging from 2.50 and 3.00 meters, at the floor level, inside a special housing for their protection. The number of total stations was twenty-one (21) in 3 kilometers, with exposition times of 28 days. Analytes desorption procedure was carried out with carbon disulfide as an extraction solvent, and in the chromatograhic analysis of gases this was performed (by triplicate) using a flame ionization detector (FID). An HP-INNOWAX chromatographic column was also used. Ultra-pure Helium, 99.99% purity, was used as carrier gas and quantification was performed (by triplicate) in the liquid extract in terms of concentration (µg/mL). The research allowed validating the methodology, obtaining recovery percentages ranging between 75.0 % and 98.2 % for all analytes, and quantification limits in µg/mL were 0.279; 0.337; 0.349; 0.391; 0.355; and 0.356 for benzene, toluene, ethylbenzene, p-xylene, m-xylene, and o-xylene, respectively, and it was proven that the validated method was a selective, specific, linear, accurate, and exact method. RESUMEN: En este trabajo se presenta la validacion del procedimiento analitico que permite determinar las concentraciones de Benceno (B), Tolueno (T), Etilbenceno (E) y Xilenos (X), compuestos conocidos como BTEX, presentes en el aire y adsorbidos sobre carbon activado, usando el metodo de adicion de estandar interno (Fluorobenceno) para la cuantificacion. En el proceso se empleo carbon activado de referencia para la validacion y carbon granular (CGC) a base de coco para la construccion de los captadores pasivos, empleados en la toma de muestras en exteriores o aire ambiente. El material CGC fue seleccionado a partir de su capacidad de recuperacion de BTEX, con un promedio 89,1% para todos los analitos. En la

Novel optical sensing film based on a functional nonwoven nanofibre mat for an easy, fast and highly selective and sensitive detection of tryptamine in beer

In this paper, the combination of Solid Surface-Room Temperature Phosphorescence (SS-RTP) and nanotechnology has led to a new approach in the detection of biogenic amines in complex matrices. This novel approach allows, for the first time, the direct determination of the concentration of tryptamine in beers. The novelty of the proposed optical sensor resides in its simplicity, rapidity, absence of complex chromatographic separation, sample clean-up, preconcentration, and derivatization protocols. Therefore, this novel methodology simplifies and reduces considerably the time and cost of the analysis, resolving the two major problems of the determination of tryptamine in beer up to now: low sensitivity and matrix effects.The proposed sensor is based on a novel white, uncharged, and non-luminescent functional nonwoven nanofibre mat (Tiss®-Link) formed by hydrophilic nanofibres of 300nm of diameter functionalized with a high concentration of active vinyl groups (330µmolg−1). It is used to carry out a kinetically controlled covalent immobilisation of tryptamine via Michael type-reaction. The transduction of the sensor is phosphorescence; the covalently immobilized tryptamine is quantified by SS-RTP, obtaining a detection limit of 6ngmL−1 with short response times (15min). The applicability of the sensor was demonstrated by analysing tryptamine in 10 different varieties of beers, obtaining recovery percentages close to 100%.

Extraction induced by emulsion breaking as a tool for Ca and Mg determination in biodiesel by fast sequential flame atomic absorption spectrometry (FS-FAAS) using Co as internal standard

This paper reports, for the first time, the determination of Ca and Mg in biodiesel after their extraction from samples using the novel extraction induced by emulsion breaking. The quantification of the analytes in the extracts was performed by flame atomic absorption spectrometry operating at fast sequential mode (FS-FAAS) and using cobalt as internal standard. Several parameters that could affect the extraction efficiency of the method were studied such as the influence of surfactant (Triton X-114) and acid (HNO3) in the extractant solution. Also, operating parameters of the spectrometer (flame stoichiometry and observation height) were evaluated in order to allow sensitive measurements of Ca, Mg and Co in the same conditions. Quantitative extraction of the analytes can be obtained by using 20mL of biodiesel and 4mL of a solution containing 2.1molL−1HNO3 and 7.5% m/v Triton X-114. In these conditions, the emulsions can be broken in 10min of heating at 90°C. The limits of quantification for Ca and Mg were 0.047 and 0.013μgmL−1, respectively. Five samples of soybean-based biodiesel were analyzed and recovery tests were performed, obtaining recovery percentages in the range of 88%–106%.

Application of time-resolved fluorescence to the determination of metabolites

A simple fluorescent methodology for the simultaneous determination of two major metabolites of acetylsalicylic acid – salicylic and gentisic acids – in pharmaceutical preparations and human urine is proposed. Due to the overlapping between the fluorescence spectra of both analytes, the use of the more selective fluorescence decay curves is proposed. Values of dependent instrumental variables affecting the signal-to-noise ratio were fixed with a simplex optimization procedure. A calibration matrix of thirteen standards plus two blank samples was processed using a partial least-squares (PLS) analysis. To assess the goodness of the proposed method, a prediction set of nine synthetic samples was analyzed, obtaining recovery percentages between 95% and 106%. Limits of detection, calculated by means of a new criterion, were 3.49μgL−1 and 1.66μgL−1 for salicylic and gentisic acids, respectively. The method was also tested in three pharmaceutical preparations containing salicylic acid, obtaining recovery percentages close to 100%. Finally, the simultaneous determination of both analytes in human urine samples was successfully carried out by the PLS-analysis of a matrix of thirteen standards plus five analyte blanks. Although spectra of analytes and urine overlap strongly, no extraction method neither prior separation of the analytes were needed.

Direct Determination of Danofloxacin and Flumequine in Milk by Use of Fluorescence Spectrometry in Combination with Partial Least-Squares Calibration

A new method for the simultaneous determination of danofloxacin and flumequine in milk samples was developed by using the nonlinear variable-angle synchronous fluorescence technique to acquire data and a partial least-squares chemometric algorithm to process them. A calibration set of standard samples was designed by combination of a factorial design with two levels per factor and a central star design. Whey was used as the third component of the calibration matrix. In order to assess the goodness of the proposed method, a prediction set of 11 synthetic samples was analyzed, obtaining recovery percentages between 96.1% and 104.0%. Limits of detection, calculated by means of a new criterion, were 0.90 and 12.4 ng mL(-1) for danofloxacin and flumequine, respectively. Finally, the simultaneous determination of both fluoroquinoles in milk samples containing the analytes was successfully carried out, obtaining an average recovery percentage of 99.3 ± 4.4 for danofloxacin and 100.7 ± 4.4.

A novel tridentate bis(phosphinic acid)phosphine oxide based europium(iii)-selective Nafion membrane luminescent sensor

A new europium(III) membrane luminescent sensor based on a new tridentate bis(phosphinic acid)phosphine oxide (3) system has been developed. The synthesis of this new ligand is described and its full characterization by NMR, IR and elemental analyses is provided. The luminescent complex formed between europium(III) chloride and ligand 3 was evaluated in solution, observing that its spectroscopic and chemical characteristics are excellent for measuring in polymer inclusion membranes. Included in a Nafion membrane, all the parameters (ligand and ionic additives) that can affect the sensitivity and selectivity of the sensing membrane as well as the instrumental conditions were carefully optimized. The best luminescence signal (λexc = 229.06 nm and λem = 616.02 nm) was exhibited by the sensing film having a Nafion : ligand composition of 262.3 : 0.6 mg mL(-1). The membrane sensor showed a short response time (t95 = 5.0 ± 0.2 min) and an optimum working pH of 5.0 (25 mM acetate buffer solution). The membrane sensor manifested a good selectivity toward europium(III) ions with respect to other trivalent metals (iron, chromium and aluminium) and lanthanide(III) ions (lanthanum, samarium, terbium and ytterbium), although a small positive interference of terbium(III) ions was observed. It provided a linear range from 1.9 × 10(-8) to 5.0 × 10(-6) M with a very low detection limit (5.8 × 10(-9) M) and sensitivity (8.57 × 10(-7) a.u. per M). The applicability of this sensing film has been demonstrated by analyzing different kinds of spiked water samples obtaining recovery percentages of 95-97%.

Hg2+-selective sensing film based on the incorporation of a rhodamine 6G derivative into a novel hydrophilic water-insoluble copolymer

We describe a Hg2+-selective sensing film based on the incorporation of a spirocyclic phenylthiosemicarbazide rhodamine 6G derivative (called FC1) into a novel hydrophilic water-insoluble copolymer synthesized by Reverse Atom Transfer Radical Polymerization. It is demonstrated that the chemodosimeter preserves its sensing ability and displays intense fluorescence in the presence of mercury(II) after being immobilized in the novel MMA-co-HEMA water insoluble linear copolymer containing 29.6% HEMA. This paper describes the synthesis and characterization of the MMA-co-HEMA copolymer, and the careful optimization of all the instrumental and experimental variables which can affect the sensitivity of the sensing film. It responds to Hg2+ concentrations in water between 0.9 and 12 μM, with a detection limit of 0.3 μM Hg2+ and the response is highly selective to Hg2+ and methylmercury. The applicability of the sensing film has been demonstrated by analysing two real samples (tap and mineral waters) obtaining recovery percentages close to 100% with RSD lower than 5%.

Simultaneous Determination of Mefenamic and Flufenamic Acids in Real Samples by Terbium-Sensitized Luminescence

A simple luminescent methodology for the simultaneous determination of mefenamic and flufenamic acids is proposed. The method takes advantage of the lanthanide-sensitized luminescence, which provides increased sensitivity. Due to the strong overlapping between the luminescence spectra, the use of decay curves to resolve mixtures of the analytes is proposed, particularly as these curves are more selective. A factorial design with three levels per factor coupled to a central composite design was selected to obtain a calibration matrix of thirteen standards plus three blank samples which was processed using a partial least-squares (PLS) analysis. In order to assess the effectiveness of the proposed method, a prediction set of synthetic samples was analyzed, and recovery percentages between 96 and 106% were obtained. Limits of detection, calculated by means of a new criterion, were 3.73 µg L−1 and 14.61 µg L−1 for flufenamic and mefenamic acids, respectively. The method was tested in two different pharmaceutical preparations containing the analytes, obtaining recovery percentages close to 100%. Finally, the simultaneous determination of both fenamates in human urine samples was successfully carried out by means of a correction of the aforementioned model. No extraction method or prior separation of the analytes were needed.

Simultaneous Determination of Mefenamic and Tolfenamic Acids in Real Samples by Terbium-Sensitized Luminescence

A simple luminescent methodology for the simultaneous determination of mefenamic and tolfenamic acids in pharmaceutical preparations and human urine is proposed. Since the native fluorescence of both analytes is not intense, the method takes advantage of the lanthanide-sensitized luminescence, which provides a higher sensitivity. Due to the strong overlapping between the luminescence spectra of both terbium complexes, the use of luminescence decay curves to resolve mixtures of the analytes is proposed, since these curves are more selective. A factorial design with three levels per factor coupled to a central composite design was selected to obtain a calibration matrix of thirteen standards plus eight blank samples that was processed using a partial least-squares (PLS) analysis. In order to assess the goodness of the proposed method, a prediction set of synthetic samples was analyzed, obtaining recovery percentages between 90 and 104 %. Limits of detection, calculated by means of a new criterion, were 14.85 μg L(-1) and 15.89 μg L(-1) for tolfenamic and mefenamic acids, respectively. The method was tested in a pharmaceutical preparation containing mefenamic acid, obtaining recovery percentages close to 100 %. Finally, the simultaneous determination of both fenamates in human urine samples was successfully carried out by means of a correction of the above-explained model. No extraction method neither prior separation of the analytes were needed.

Simultaneous determination of nabumetone and its principal metabolite in medicines and human urine by time-resolved fluorescence

A simple fluorescent methodology for the simultaneous determination of nabumetone and its main metabolite, 6-methoxy-2-naphthylacetic acid (6-MNA), in pharmaceutical preparations and human urine is proposed. Due to the strong overlapping between the fluorescence spectra of both analytes, the use of fluorescence decay curves to resolve their mixture is proposed, since these curves are more selective. Values of dependent instrumental variables affecting the signal-to-noise ratio were fixed using a simplex optimization procedure. A factorial design with three levels per factor coupled to a central composite design was selected to obtain a calibration matrix of thirteen standards plus one blank sample that was processed using a partial least-squares (PLS) analysis. In order to assess the goodness of the proposed method, a prediction set of ten synthetic samples was analyzed, obtaining recovery percentages between 97 and 105%. Limits of detection, calculated by means of a new criterion, were 0.96 μg L(-1) and 0.88 μg L(-1) for nabumetone and 6-MNA, respectively. The method was also tested in the pharmaceutical preparation Relif, which contains nabumetone, obtaining recovery percentages close to 100%. Finally, the simultaneous determination of both analytes in human urine samples was successfully carried out by the PLS-analysis of a matrix of fifteen standards plus four analyte blanks and the use of the standard addition technique. Although urine shows native fluorescence, no extraction method or prior separation of the analytes was needed.

SIMULTANEOUS SPECTROPHOTOMETRIC DETERMINATION OF ATRAZINE AND DICAMBA IN WATER BY PARTIAL LEAST SQUARES REGRESSION

It is presented the development of a new and easy analytical method for the simultaneous determination of atrazine and dicamba in water. Under the experimental conditions proposed, atrazine showed a linear dynamic range of 0.3 to 4.9 µg mL-1, a limit of detection of 0.1 µg mL-1 and a limit of quantification of 0.3 µg mL-1; similarly, dicamba showed a linear dynamic range of 0.8 to 8.8 µg mL-1, a limit of detection of 0.2 µg mL-1 and a limit of quantification of 0.8 µ mL-1. Partial Least Squares Regression (Type 1) was applied for the resolution of spectral interferences between analytes, obtaining recovery percentages higher than 95 % for both compounds in synthetic mixtures. Finally, quantitative determination of both herbicides in tap, well and sea water samples, was carried out successfully by the proposed method, previous preconcentration of the analytes by solid phase extraction

The development and comparison of a fluorescence and a phosphorescence optosensors for determining the plant growth regulator 2-naphthoxyacetic acid

We describe two luminescence methods based on a flow-through optical sensor. A fluorescence and a phosphorescence optosensors have been developed and compared. Both techniques are fast (response time of 150 and 90 s, respectively) and simple. The fluorescence optosensor is based on the on-line immobilization of 2-naphthoxyacetic acid (β-NOA) on a non-ionic resin (Amberlite XAD-7) solid support in a continuous-flow system (10 mM glycine/HCl buffer solution at pH 2.5) and the phosphorescence one on the on-line immobilization of β-NOA on silica gel solid support in a 175 mM TlNO 3 and 10 mM Na 2SO 3 continuous-flow system. Fluorescence and phosphorescence intensities were measured at λ exc/em = 328/348 and 276/516 nm, respectively. The fluorescence optosensor was sensitive to a linear concentration range of between 2.0 and 225.0 ng mL −1 with a detection limit of 2.0 ng mL −1 and a standard deviation of 2.8% at 125 ng mL −1, and for the phosphorescence a linear concentration range between 4.9 and 250.0 ng mL −1, a detection limit of 4.9 ng mL −1 and a standard deviation of 2.23% at 150 ng mL −1. Also, a study of applicability was carried out obtaining recovery percentages around 100% with standard deviations slower than 2.2%.

Application of micellar electrokinetic capillary chromatography to the analysis of uncharged pesticides of environmental impact.

A test mixture of five pesticides and metabolites (naphthalene acetamide, carbaryl, 1-naphthol, thiabendazole, and carbendazime) has been investigated by capillary electrophoresis with an ultraviolet diode array detector. These compounds were separated in <10 min by micellar electrokinetic capillary chromatography (MEKC). MEKC was performed in 30 mM ammonium chloride/ammonia buffer (pH 9.0) containing 15 mM sodium dodecyl sulfate. The lowest detection limit was obtained for the insecticide carbaryl (0.22 microg mL(-)(1)) and the highest for its metabolite 1-naphthol (1.13 microg mL(-)(1)). This method was applied to the analysis of the pesticides in cultivated vegetables such as cucumbers, which were extracted with a liquid-liquid extraction procedure, obtaining recovery percentages ranging from 90.1 to 110.2%.

Determination of phytohormones of environmental impact by capillary zone electrophoresis.

A test mixture of five phytohormones [naphthaleneacetic acid (NAA), naphthoxyacetic acid (NOA), indoleacetic acid (IAA), indolebutyric acid (IBA), and indolepropionic acid (IPA)] was investigated. These compounds were cleanly separated with good resolution by capillary zone electrophoresis with a UV diode array detector using 20 mM sodium phosphate buffer (pH 7.25). The lowest detection limit was obtained for IPA (0.45 mg L(-)(1) or 0.005 mg kg(-)(1)) and the highest for NAA (1.04 mg L(-)(1) or 0.014 mg kg(-)(1)). The method has been applied for tomato samples fortified with the five phytohormones using a liquid-liquid extraction procedure, obtaining recovery percentages ranging from 91 to 109.0%.