L.F. Capitán-Vallvey

Carbon dots for copper detection with down and upconversion fluorescent properties as excitation sources.

Carbon dots were synthesized by a simple and green strategy for selective and sensitive Cu(2+) ion detection using both down and upconversion fluorescence. These fluorescent nanosensors show low cytotoxicity and are applied for intracellular sensing and imaging of Cu(2+) in biological systems.

Smartphone-Based Simultaneous pH and Nitrite Colorimetric Determination for Paper Microfluidic Devices

In this work, an Android application for measurement of nitrite concentration and pH determination in combination with a low-cost paper-based microfluidic device is presented. The application uses seven sensing areas, containing the corresponding immobilized reagents, to produce selective color changes when a sample solution is placed in the sampling area. Under controlled conditions of light, using the flash of the smartphone as a light source, the image captured with the built-in camera is processed using a customized algorithm for multidetection of the colored sensing areas. The developed image-processing allows reducing the influence of the light source and the positioning of the microfluidic device in the picture. Then, the H (hue) and S (saturation) coordinates of the HSV color space are extracted and related to pH and nitrite concentration, respectively. A complete characterization of the sensing elements has been carried out as well as a full description of the image analysis for detection. The results show good use of a mobile phone as an analytical instrument. For the pH, the resolution obtained is 0.04 units of pH, 0.09 of accuracy, and a mean squared error of 0.167. With regard to nitrite, 0.51% at 4.0 mg L(-1) of resolution and 0.52 mg L(-1) as the limit of detection was achieved.

Use of the Hue Parameter of the Hue, Saturation, Value Color Space As a Quantitative Analytical Parameter for Bitonal Optical Sensors

The hue or H component of the hue, saturation, value (HSV) color space has been studied as a quantitative analytical parameter for bitonal optical sensors. The robust nature of this parameter provides superior precision for the measurement of sensors which change colors with the speciation of some indicator molecule. This parameter has been compared to red, green, blue (RGB) intensity and RGB absorbance along with differences and ratios of both intensity and absorbance and has been demonstrated to be 2 to 3 times superior. The H value maintains this superior precision with variations in indicator concentration, membrane thickness, detector spectral responsivity, and illumination. Because this parameter is stable, simple to calculate, easily obtained from commercial devices such as scanners and digital cameras, continuous over the entire color gamut, and bound between values of 0 and 1, it shows great promise for use in a variety of sensing applications including imaging, automated analysis, pharmaceutical sensing, lab-on-a-chip devices, and quality control applications.

Recent developments in handheld and portable optosensing—A review

Recent developments in portable and handheld opto-chemical analytical instrumentation over the last decade (2000-2010) are reviewed. First, the characteristics of typical portable/handheld instrumentation are discussed from different points of view: in situ operation, low energy consumption, ease of use, and self-contained devices. These advancements have improved or hastened improvements in the development of miniaturized optoelectronic and optical components, mainly solid-state devices such as different types of semiconductor lasers, light-emitting diodes, and photodiodes. A brief review of advances in these components is also presented. The numerous examples of portable instrumentation presented have been classified according to direct-recognition and reagent-based sensing, and within these, by absorption and emission-based systems. The conclusion discusses some key trends and future perspectives for this technology.

Solid-phase spectrophotometric determination of trace amounts of hydrazine at sub-ng ml−1 level

Abstract A very sensitive method for the determination of trace amounts of hydrazine by Solid-phase spectrophotometry has been developed. The method is based on the fixation of an aldazine derivative of hydrazine on a cation-exchange resin and the resin phase absorbance being measured directly. It allows the determination of hydrazine in the range 0.08–1.20 ng ml −1 (with a RSD of 3.4% and an apparent molar absorptivity of 2.7 × 10 8 1 mol −1 cm −1 ). The method was applied to the determination of hydrazine in boiler feed and natural water samples, urine and isoniazid tablets.

Determination of colorant matters mixtures in foods by solid-phase spectrophotometry

Abstract A new, simple, sensitive and inexpensive method for simultaneous determination of Sunset Yellow FCF (SY), Quinoline Yellow and their respective unsulphonated products (Sudan I (SUD) and Quinoline Yellow Spirit Soluble (QYSS)) in mixtures is proposed. Sunset Yellow and Quinoline Yellow were selectively fixed in Sephadex DEAE A-25 gel (pH 5.0) and SUD and QYSS were selectively fixed in C 18 silica gel (pH 5.0) and the absorbances of both systems were measured directly in solid-phase. The applicable concentration ranges were from 3.0 to 500.0 ng ml −1 for Quinoline Yellow Water Soluble (QYWS), from 3.0 to 200.0 ng ml −1 for QYSS, from 15.0 to 500.0 ng ml −1 for SY and from 20.0 to 200.0 ng ml −1 for SUD. The method was applied to the determination of these compounds in soft drinks, fruit liqueurs and ice creams.

Analysis of parabens in cosmetics by low pressure liquid chromatography with monolithic column and chemiluminescent detection

This paper presents an application of chromatographic separation based on an ultra-short monolithic column and chemiluminescent detection in an FIA type instrument manifold for the determination of four paraben mixtures: methylparaben (MP), ethylparaben (EP), propylparaben (PP) and butylparaben (BP). The separation is achieved in 150 s using two consecutive carriers: first 12% ACN:water that changes 75 s after injection to 27% ACN:water. The detection is based on the oxidation of the hydrolysis product of parabens, p-hydroxybenzoic acid, with Ce(IV) in the presence of Rhodamine 6G which evokes chemiluminescence of sufficient intensity to enable a sensitive determination of these species. After optimization of the variables involved, the analytical method is characterized, displaying the following values for concentration ranges, detection limits and precision, as relative standard deviation at low concentration (0.15 mg l(-1))-MP: from 9.9x10(-7) to 3.3x10(-4)M; 1.9x10(-8); 5.6%; EP: from 9.0x10(-7) to 3.3x10(-4)M; 2.8x10(-8); 3.5%; PP: from 8.3x10(-7) to 9.9x10(-5)M; 2.3x10(-8); 4.2%; and BP: from 7.7x10(-7) to 9.9x10(-5)M; 4.2x10(-8)M; 6.2%. The method was applied and validated satisfactorily for the determination of these parabens in cosmetic samples, comparing the results against a liquid chromatography reference method.

Flow injection analysis of the insecticide imidacloprid in water samples with photochemically induced fluorescence detection

A flow injection analysis (FIA) system, combined with photochemical induced fluorescence (PIF) detection is developed for the sensitive and rapid determination of imidacloprid. It is based on the conversion of imidacloprid into the fluorophore 1-(6-chloro-3-pyridyl-methyl)-2-(hydroxyimino)-3,4-didehydroimidalozolidene. In an aqueous medium, this compound shows native fluorescence with an excitation maximum at 334 nm and an emission maximum at 377 nm. The linear concentration range of application was 1.0–60.0 ng ml −1 of imidacloprid, with a relative standard deviation of 2.1% (for a level of 10 ng ml −1 ) and a detection limit of 0.3 ng ml −1 . The method was applied to check whether imidacloprid was present above this limit in waters from Cuenca and Granada (Spain). It was validated applying a recovery test (Student’s t-test). Recovery levels of the method reached around 100% in all cases.

Simultaneous determination of the colorants tartrazine, ponceau 4R and sunset yellow FCF in foodstuffs by solid phase spectrophotometry using partial least squares multivariate calibration.

A method is proposed for the simultaneous determination of the colorants tartrazine (TT), sunset yellow FCF (SY) and ponceau 4R (PR) in foods. The colorants were fixed in Sephadex DEAE A-25 gel at pH 2.0 and then packed in a 1-mm silica cell. The spectra of the analytes fixed in the solid support were recorded between 400 and 800 nm against a blank and the partial least squares (PLS) multivariate calibration was used to obtain the results. The linear dynamic ranges of the calibration graphs were from 50.0 to 650.0 ng ml(-1) for the three colorants and these ranges were taking in account the optimisation of the calibration matrix using the PLS-1 algorithm. The experimental results showed that the optimum number of factors for the calibration matrix was four in all instances and the residual means standard deviation was 5.5267 for SY, 6.3878 for TT and 6.9816 for PR. The square of the correlation coefficients were 0.9977, 0.9978 and 0.9954 for SY, TT and PR respectively. The method was applied to the determination of the colorants in foods and results were compared with those obtained by means of HPLC as reference method. The results obtained can be considered as acceptable in most cases (eight of nine commercial samples). The relative standard deviations ranging between 0.5 and 10.8 for the commercial samples analysed.

Full-range optical pH sensor based on imaging techniques.

A new colour-based disposable sensor array for a full pH range (0-14) is described. The pH sensing elements are a set of different pH indicators immobilized in plasticized polymeric membranes working by ion-exchange or co-extraction. The colour changes of the 11 elements of the optical array are obtained from a commercial scanner using the hue or H component of the hue, saturation, value (HSV) colour space, which provides a robust and precise parameter, as the analytical parameter. Three different approaches for pH prediction from the hue H of the array of sensing elements previously equilibrated with an unknown solution were studied: Linear model, Sigmoid competition model and Sigmoid surface model providing mean square errors (MSE) of 0.1115, 0.0751 and 0.2663, respectively, in the full-range studied (0-14). The performance of the optical disposable sensor was tested for pH measurement, validating the results against a potentiometric reference procedure. The proposed method is quick, inexpensive, selective and sensitive and produces results similar to other more complex optical approaches for broad pH sensing.