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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.

Polarographic behaviour of Schiff bases derived from 2-pyrrolecarboxaldehyde and 2-thiophenecarboxaldehyde has been investigated in 50%, dioxane-water medium in pH range 4 to 10. The experimental conditions for the study were so chosen that no appreciable hydrolysis of the Schiff bases occurred during the recording of polarograms. Schiff bases gave two well separated monoelectronic waves in the pH range studied, which shifted to more negative potentials as the pH was increased. Dependence of diffusion current on concentration of depolarizer and height of mercury reservoir suggest that both the waves are diffusion controlled. On the basis of the polarographic and cyclic voltammetry data an overall electrode reaction is given.

The combination of an ultra-short C18 monolithic column (5 mm long) with a flow injection analysis (FIA) scheme results in a versatile and efficient system that has been used for the chromatographic determination of four preservatives — methylparaben (MP), ethylparaben (EP), propylparaben (PP) and butylparaben (BP). The separation is carried out by using two carriers, A and B, consisting of a mixture of ACN: water in different proportions. The described procedure is able to separate the analytes in only 150 s. The applicable concentration range, detection limit and the relative standard deviation were the following: for MP from 1.6 × 10-5 to 1.1 × 10-3 M; 4.8 × 10-4 M; 0.65%; for EP between 3.7 × 10-5 and 2.0 × 10-3 M; 1.2 × 10-5 M; 1.2%; for PP between 3.9 × 10-5 and 2.0 × 10-3 M; 1.2 × 10-5 M; 1.2%; and for BT between 6.0 × 10-5 and 2.0 × 10-3 M; 1.8 × 10-5 M; 1.8%. The method was applied and validated satisfactorily for the determination of these parabens in commercial cosmetics samples, comparing the results with those obtained by HPLC reference method.

The people, places, economic and political influences of importance in the history of chemistry in Spain have been reviewed from the early XVIII century until today with particular reference to Analytical Chemistry.

A hand-held luminometer for measuring electrochemiluminescence (ECL) for lactate determination and based on one-shot biosensors fabricated using screen-printed electrodes is described. The lactate recognition system is based on lactate oxidase and the transduction system consists of electro-oxidation of luminol, with all the reagents immobilized in a Methocel membrane. The membrane composition and reaction conditions have been optimized to obtain adequate sensitivity. The luminometer is based on a large silicon photodiode as detector and includes a programmable potentiostat to initialize the chemical reaction and signal processing circuitry, designed to acquire a low level photocurrent with offset cancelation, low pass filtering for noise attenuation and adjustable gain up to 1012 V/A. The one-shot biosensor responds to lactate rapidly, with an acquisition time of 2.5 min, obtaining a linear dependence from 8 × 10−6 to 2 × 10−4 M, a detection limit of 2.4 × 10−6 M and a sensor-to-sensor reproducibility (relative standard deviation, RSD) of around 7–10 % at the medium level of the range., We acknowledge financial support from Ministerio de Educación y Ciencia, Dirección General de Enseñanza Superior (Spain) (Projects CTQ2005-09060-CO2-01, CTQ2005-09060-CO2-02) and from Junta de Andalucía (Projects P06-FQM-01467 and P08-FQM-3535).

The combination of an ultra-short C18 monolithic column (5 mm long) with flow injection analysis results in a versatile and efficient system that has been used for the determination of three antioxidants [propylgallate (PG), butylhydroxyanisole (BA), and butylhydroxytoluene (BT)]. Due to the wide variety of polarities of the analytes, two different carriers (carrier A: methanol-water 42% and carrier B: methanol-water 70%) were able to separate the analytes in only 85 s. The applicable concentration range, the detection, and the relative standard deviation (n=10) were: for PG, from 2.77 to 300 microg/mL, 0.84 microg/mL, 2.84%; for BA, between 1.51 and 300 microg/mL, 0.46 microg/mL, and 2.70%; and for BT, between 1.65 and 100 microg/mL, 0.55 microg/mL, and 2.22%, respectively. The method was applied and validated satisfactorily for the determination of PG, BA, and BT in food and cosmetic samples.

A multi-analyte flow through method is proposed for the simultaneous determination of aspartame (AS), acesulfame-K (AK), and saccharin (SA) in several food and soft drink samples. The procedure is based on the transient retention of the three sweeteners in a commercial quaternary amine ion exchanger monolithic column, placed in its specific holder, and allocated in a monochannel FIA setup using pH 9.0 Tris buffer 0.03 M, NaCl 0,4 M, and NaClO4 0,005 M as carrier. In these conditions AS is very weakly retained, while AK and SA are more strongly retained, making it possible to measure the intrinsic UV absorbance of, first, AS and then AK and SA after desorption by the carrier itself. The applicable concentration range, the detection limit, and the relative standard deviation were the following: for AS, from 9.5 to 130.0 µg·mL−1; 2.87 µg·mL−1; 1.46% (at 65 µg·mL−1); for AK, between 2.2 and 600.0 µg·mL−1; 1.0 µg·mL−1, and 0.08% (at 300 µg·mL−1); and for SA, between 3.0 and 600.0 µg·mL−1; 0.9 µg·mL−1,...

A one-shot multisensor based on ionophore-chromoionophore chemistry for optical monitoring of potassium, magnesium and hardness in water is presented. The analytical procedure uses a black and white non-cooled CCD camera for image acquisition of the one-shot multisensor after reaction, followed by data treatment for quantitation using the grey value pixel average from a defined region of interest from each sensing area to build the analytical parameter 1-alpha. In optimised experimental conditions, the procedure shows a large linear range, up to 6 orders using the linearised model and good detection limits: 9.92 x 10(-5)mM, 1.86 x 10(-3)mM and 1.30 x 10(-2)mgL(-1) of CaCO(3) for potassium, magnesium and hardness, respectively. This analysis system exhibits good precision in terms of relative standard deviation (RSD%) from 2.3 to 3.8 for potassium, from 5.0 to 6.8 for magnesium and from 5.4 to 5.9 for hardness. The trueness of this multisensor procedure was demonstrated comparing it with results obtained by a DAD spectrophotometer used as a reference. Finally, it was satisfactorily applied to the analysis of these analytes in miscellaneous samples, such as water and beverage samples from different origins, validating the results against atomic absorption spectrometry (AAS) as the reference procedure.

A high-performance liquid chromatography-diode array detection method was developed and validated to simultaneously determine tramadol (TMD), metamizole (MTZ), ropivacaine (RPV), and bupivacaine (BPV) in the presence of 4-methylaminoantypirine (4-MAA), the metabolite of MTZ, in analgesic mixtures samples used in Patient Controlled Analgesia (PCA). Chromatographic separation is achieved with a C-18 column using a mixture of ACN-methanol-water adjusted to pH 3.0 with NaH(2)PO(4) 0.05M (10:25:65 v/v) in an isocratic mobile phase at a flow rate of 0.8 mL/min. 0.5 mg/mL of Na(2)SO(3) in the water of the mobile phase was necessary to prevent the fast MTZ hydrolysis process to 4-MAA. Ultraviolet-diode array detection was used and chromatograms were registered at the wavelength of 230 nm. The method was linear in the range of 2.2-80.0 mg/L for TMD, 4.1-140.0 mg/L for MTZ, 2.3-40.0 mg/L for RPV, and 2.9-40.0 mg/L for BPV. Validation of the method was made in terms of accuracy, intra- and interday precision, as well as quantification and detection limits. The hydrolysis of MTZ to 4-MAA was studied and verified by mass spectrometry. The developed method was used successfully to evaluate the chemical stability of binary analgesic TMD mixtures with MTZ, RPV, or BPV. The mixtures were tested at standard concentrations used in PCA and in different storage conditions. When mixtures contained MTZ, a chromatographic peak from the metabolite 4-MAA was always detected in the chromatograms.

We report two methods that have allowed the attachment of glu- cose, mannose and lactose to one or both of the cyclopentadienyl rings of ferrocene. The resulting ferrocene-car- bohydrate conjugates were synthesised by the reaction of thioglycosides with ferrocenemethanol and 1,1'-ferrocene- dimethanol in acidic media. A second method based on the regiospecific cop- per(I)-catalysed cycloaddition of prop- argyl glycoside, azidomethyl and bis- Arocene as well as azi- doethyl glycoside and ethynylferrocene was also used and led to the synthesis of 1,2,3-triazole-containing glycoconju- gates. The electrochemical behaviour of the synthesised glycoconjugates was investigated. In addition, their binding interactions with b-cyclodextrin were studied by means of NMR spectrosco- py, isothermal titration calorimetry, and cyclic and differential pulse vol- tammetric experiments. These tech- niques allowed the determination of the thermodynamic parameters of the complexes, the stability constants for the complexes formed with both the neutral and the oxidised states of the ferrocenyl glycoconjugates, the mode of inclusion and the diffusion coeffi- cients for both the glycoconjugates and the complexes.

Spectroradiometric measurements of reflectance and CIELAB hue-angle, were tested for K(I) determination using disposable optical sensors based on ion exchange mechanism. The linearisation of the sigmoidal response function, using a logistic regression, increases the linear range noticeably to 7.65 x 10(-8)-1.5 M and 1.22 x 10(-7)-1.5 M for CIELAB hue-angle and reflectance, respectively. The trueness of both procedures was demonstrated comparing it with results obtained by a DAD spectrophotometer used as a reference measurement procedure. The usefulness of the procedure was checked by analysing K(I) in different types of waters and beverages. Additionally, we studied the possible visual discrimination for the whole potassium range tested, obtaining the possibility of discriminating twelve groups of concentrations.

A conventional flatbed scanner is used to acquire the analytical parameters for quantitative determination in one-shot optical sensors based on ionophore–chromoionophore chemistry. Variables affecting the acquisition of the images and treatment were studied. The analytical parameter, an estimated reflection density, is obtained from an area of the sensing zone of the disposable sensor using the average luminosity of the best channel that fits the sensor theoretical model. The fit of the experimental results to the theoretical sigmoidal model and the precision of the results, in terms of relative standard deviation (R.S.D.%), are used to optimize the scanner variables. In order to improve the reliability and validity of the results we worked with scanner color management. Applying this methodology, we tried to make color measurements as independent as possible from the particular scanner used. Furthermore, the perceptual stimulus, that is, the color sensor response, is preserved and enhanced across this imaging treatment without any loss of information. Using this scanner protocol for measurement and the relation between digital output of the color scanner and the concentration of potassium into the sensing zone it is possible to analyze potassium between 6.58 × 10−6 and 10−2 M with a precision, expressed as R.S.D. of log ⁡ a K + , ranging from 0.45 to 1.80%. These results are good when compared to the same procedure using a DAD spectrophotometer in which the concentration range is 1.31 × 10−5 and 0.1 M and the precision range between 3.31 and 7.66%.

This paper presents the study of a disposable optical sensor to determine potassium by an ion-exchange mechanism based on the conventional ionophore dibenzo-18-crown-6. The normalised signal used as analytical parameter is obtained from measurements in transflectance mode and the results are compared with those obtained by transmission mode. The sensor responds linearly in activities up to 100 mM with a detection limit of 19 mM and a precision around 7%. It is possible to linearise the sigmoidal calibration curve by means of a decimal logistic transformation applied to transflectance data, in this way increasing the linear dynamic range with a detection limit of 8.4 mM. The potential utility of the disposable sensor was checked in the determination of potassium in different types of waters, validating the results against a reference procedure. The viability of the semi-quantitative determination of potassium using this disposable sensor was studied using a colour-difference CIELAB-base formula, designed to give quantitative values of the perceived colour difference between a pair of coloured samples under specific experimental conditions, obtaining seven intervals of discriminable concentrations in the colour chart between 10 −7 and 10 −1 M.

Today it is common to find samples with various additives from several families. This is the case of sweeteners, preservatives and antioxidants. We have selected a set of additives broadly used in foods and cosmetics with an ample variety of polarities, namely: aspartame (AS), acesulfame (AK)/saccharin (SA), metylparaben (MP), ethylparaben (EP), propylparaben (PP), butylparaben (BP), propylgallate (PG) and butylhydroxyanysole (BA). The monolithic column used as separative system is a 5 mm commercial precolumn of silica C 18 coupled to a flow injection manifold working with a peristaltic pump. The mixture was separated in only 400 s with resolution factors greater than 1.1 in all cases. To achieve the separation in the FIA system we used two carriers: first, a mixture of ACN/water buffered with 10 mM pH 6.0 phosphate buffer and second, a methanol:water mixture to improve the carrier strength and speed up the more apolar analytes at 3.5 mL min −1 . Detection is accomplished by means of a diode array spectrometer at the respective wavelength of each compound. The comparison of the analytical parameters obtained for this procedure with a standard HPLC method validates our new method, obtaining a method that is quick, with high repeatability and reproducibility and with good resolution between analytes. We have successfully applied the method to real food and cosmetics samples.

This report addresses the task of calibrating an optical sensor for oxygen determination. Detailed analyses of the functional dependences from our measurement system results have been carried out with the additional aim of temperature compensation. As a result, an empirical calibration function has been successfully derived for the luminescent quenching-based oxygen sensor included in a self-designed portable instrument. This function also compensates for the temperature influence on the quenching luminescence process in the range from 0 to 45 degrees C. Moreover, the calibration procedure is extremely simple because only a single standard is needed. In fact, the oxygen measurement system can be calibrated with exposure to an open air atmosphere, and therefore, neither laboratory standards nor trained personnel are required. The method has been applied to a set of 11 units of the mentioned sensor (up to 24% oxygen concentration) giving an overall deviation between our calibrated system results and the laboratory standards of 0.3% oxygen concentration (calculated with 95% confidence level). The proposed calibration function has shown itself to be applicable for different sensing film thicknesses and luminophore concentrations using the same fittings parameter. Additionally, this function has been successfully applied to other oxygen dyes. Good agreement has also been found when the performance of the instrument was compared to a commercially available portable instrument based on an electrochemical sensor. We believe that this work could be an interesting finding for spreading the use of optical sensors for atmospheric oxygen determination in commercial measurement equipment for different purposes in confined working atmospheres, such as mines, undergrounds, warehouses, vehicles, and ships.

A novel measurement system comprised of a portable electronic instrument with an opto-chemical sensor for atmospheric oxygen sensing is presented. Optical sensors based on luminescence quenching have been thoroughly investigated in the search for sufficient sensitivity and high stability. The dye platinum octaethylporphyrin complex immobilised in a polystyrene membrane was selected as an oxygen probe that was stabilised with the heterocyclic amine DABCO, achieving in this way a mean drift of 0.01% oxygen concentration per day. The portable instrument is based on a microcontroller. Its main features are: a single optical sensor channel, lack of optical filters, fully digital signal processing, autonomous operation with computer communication capability for reprogramming and data saving and low power consumption. The use of a digital output photodetector makes it possible to avoid analogue processing with the consequent circuitry saving and better noise immunity. The measured parameter in the transduction process is quite similar to the luminescence lifetime. The typical measurement range is from 0 to 30% oxygen and the response time is below 30 s for full range swing. Typical instrument characteristics are temperature effect correction, low drift and an accuracy of 0.5% in oxygen concentration for the collective calibration curve. Better accuracy can be obtained with individual sensor calibration. Dimensions and weight are 110 mm × 66 mm × 28 mm and 95 g (without battery), respectively. Powering it with a standard 9 V PP3 battery for more than 10 days of operation is possible.

A liquid chromatography-mass spectrometry method for the determination of the coccidiostats metronidazole, ronidazole, dimetridazole, secnidazole, tinidazole and ipronidazole in feedstuff was developed. The 5-nitroimidazoles were extracted from animal feed with a pH 2 phosphate buffer solution followed by a solid phase extraction procedure based on HLB cartridges. The liquid chromatographic separation of the extracts was performed on a C18 bonded silica column applying a gradient of elution with pH 4.3 ammonium acetate buffer solution and acetonitrile. Quantification for each 5-nitroimidazole was carried out monitoring its molecular ion [M + H]+ obtained by positive electrospray ionisation mode. A pool of feedstuffs was used to optimise and validate the method. Linearity, quantification limit, intra-day and inter-day reproducibility and accuracy were estimated using this pool of feedstuffs spiked with the drugs. For the confirmatory assay, several fragment ions from each 5-nitroimidazole were obtained and monitored. The method was applied successfully to determine 5-nitroimidazoles in feedstuff at level of 0.05 mg kg−1.

Chemical analysis based on colour changes recorded with imaging devices is gaining increasing interest. This is due to its several significant advantages, such as simplicity of use, and the fact that it is easily combinable with portable and widely distributed imaging devices, resulting in friendly analytical procedures in many areas that demand out-of-lab applications for in situ and real-time monitoring. This tutorial review covers computer vision-based analytical (CVAC) procedures and systems from 2005 to 2015, a period of time when 87.5% of the papers on this topic were published. The background regarding colour spaces and recent analytical system architectures of interest in analytical chemistry is presented in the form of a tutorial. Moreover, issues regarding images, such as the influence of illuminants, and the most relevant techniques for processing and analysing digital images are addressed. Some of the most relevant applications are then detailed, highlighting their main characteristics. Finally, our opinion about future perspectives is discussed.

Levels of metalloids (As – urine) and heavy metals (Hg – urine, Cd – whole blood and Zn – serum) were determined by atomic absorption spectrometry in 601 subjects living in the area affected by the Aznalcollar mine spill (SW, Spain) and compared with those of a representative sample (960 subjects) selected from the Andalusian community (non-affected area), southern Spain. The characteristic parameters of the analytical method including uncertainty were determined for each metal. Potential associations of metal concentration with age, sex and body mass index as well as life-style habits (smoking, alcohol consumption and food habits) were explored. Concentrations of all the metals studied were statistically higher in the population of the affected area with respect to that of the non-affected area in Andalusia, although levels were always lower or similar to the values reported for the general population and below occupational reference limits. In conclusion, there is a lack of evidence that the spill had any incidence on human health in the population living in the affected area. There are few references in scientific literature reporting values from large series of samples, and hence our data could be useful for further studies.

A linear curve is obtained when a decimal logistic transformation is applied to the sigmoidal calibration curve of ion-selective bulk optodes for the determination of cations based on ionophore–chromoionophore chemistry. In this way, problems derived from the use of a sigmoidal shape calibration functions are solved and the linear dynamic range is increased. The method is easier to use and eliminates the need for prior treatment of the sample. The influence of different parameters on the linearization of the theoretical model was studied: charge of the analyte, ionophore:chromoionophore ratio and complex stoichiometry, and the goodness of the linearization of the theoretical fit to experimental data for two experimental systems was checked. The procedure was applied to the determination of potassium and hardness using disposable sensors in different types of waters (tap, well, stream, rain, snow and sea), validating the results against a reference procedure. This new linear calibration proposed for cation determination increases the linear dynamic range up to 7–8 orders of magnitude. The main advantage is that it is possible to directly quantify samples with very different analyte contents in a fast and simple way.

A new optical disposable sensor to determine mercury is presented. The procedure uses a polyester sheet with a sensing area composed of plasticized PVC that incorporates a tetraarylborate salt as Hg(II) selective recognition reagent and a porphyrin proton-selective fluoroionophore as the optical transducer. The sensing scheme is based on the decomposition of tetraarylborate anion induced by Hg(II) taken by the membrane which compels the deprotonation of the porphyrin, recovering its fluorescence. The fluorescence increases after 15 min contact with Hg(II) at pH 2.4 which makes it possible to determine Hg(II) up to 25 μg L−1 with an intermembrane reproducibility of 6.5% as R.S.D. The disposable sensor presents good selectivity to Hg(II) over other metal ions. The response mechanism is discussed and the effect of different experimental variables is reported.

A new chemiluminescence-based disposable sensor for EDTA is described. The EDTA-sensitive element is a transparent bilayer membrane containing Ru(Bipy)32+ complex and Ce(IV), respectively, on a polyester support. The sample is injected by means of a syringe, acting pneumatically, into a 10 mm cell containing the CL membrane and placed in the external holder of a luminometer. The composition of the membrane and reaction conditions have been adjusted to obtain adequate sensitivity and selectivity. The disposable sensor responds to EDTA rapidly over a dynamic range from 6.6 × 10−6 M to 7.0 × 10−4 M, with sensor-to-sensor reproducibility around 6% as RSD (relative standard deviation) at the medium level of the range. The performance of the optical disposable sensor was tested for the analysis of EDTA in ophthalmic collyrium and different types of sauce samples, validating the results against a reference procedure. The sensing approach presented here demonstrates the feasibility of chemiluminescent disposable sensors for quantitative analysis with good features.

A multianalyte flow‐through sensor is proposed for the simultaneous determination of aspartame (AS) and acesulfame‐K (AK) in tabletop sweeteners. The procedure is based on the transient retention of AK in the ion exchanger Sephadex DEAE A‐25 placed in the flow‐through cell of a monochannel flow injection analysis (FIA) set‐up using pH 2.70 ortophosphoric acid/sodium dihydrogen phosphate buffer 0.06 M as carrier. In these conditions AS is very weakly retained, which makes it possible to measure the intrinsic ultraviolet (UV) absorbance of first AS and then AK after desorption by the carrier itself. The applicable concentration range, the detection limit, and the relative standard deviation were the following: for AS, from 10 to 100 µg mL−1; 5.65 µg mL−1; 3.4% (at 50 µg mL−1); and for AK, between 40 and 100 µg mL−1; 11.9 µg mL−1 and 1.61% (at 50 µg mL−1). The method was applied and validated satisfactorily for the determination of AS and AK blends in tabletop sweeteners. The results were compared a...

An integrated solid-phase spectrophotometry-FIA method is proposed for simultaneous determination of the mixture of saccharin (1,2-benzisothiazol-3(2H)-one-1,1-dioxide; E-954) (SA) and aspartame (N-L-alpha-aspartyl-L-phenylalanine-1-methyl ester; E-951) (AS). The procedure is based on on-line preconcentration of AS on a C18 silica gel minicolumn and separation from SA, followed by measurement, at lambda = 210 nm, of the absorbance of SA which is transiently retained on the adsorbent Sephadex G-25 placed in the flow-through cell of a monochannel FIA setup using pH 3.0 orthophosphoric acid-dihydrogen phosphate buffer, 3.75x10(-3) mol L(-1), as carrier. Subsequent desorption of AS with methanol enables its determination at lambda = 205 nm. With a sampling frequency of 10 h(-1), the applicable concentration range, the detection limit, and the relative standard deviation were from 1.0 to 200.0 microg mL(-1), 0.30 microg mL(-1), and 1.0% (80 microg mL(-1), n = 10), respectively, for SA and from 10.0 to 200.0 microg mL(-1), 1.4 microg mL(-1), and 1.6% (100 microg mL(-1), n = 10) for AS. The method was used to determine the amounts of aspartame and saccharin in sweets and drinks. Recovery was always between 99 and 101%. The method enabled satisfactory determination of blends of SA and AS in low-calorie and dietary products and the results were compared with those from an HPLC reference method.

The application of a decimal logistic transformation to the sigmoidal calibration curve of ion-selective bulk optodes for the determination of anions based on hydrophobic membranes containing neutral ionophore and chromoionophore is formally established and, consequently, a wide linear calibration function is obtained. The problems derived from the use of a sigmoidal curve in the calibration are therefore solved and the linear dynamic range is increased. The general equation resulting from the logistic transformation is discussed considering the stoichiometric factors for monovalent anions, and the linearization of the theoretical fit to experimental data was checked for two real cases. The strategy was applied to the determination of chloride and nitrate using disposable sensors for different types of waters (tap, well, stream, rain, snow and sea), validating the results against a reference procedure. This new linear calibration proposed for anion determination increases the linear dynamic range up to six orders of magnitude. The main advantage is that it is possible to directly quantify samples with very different analyte contents in a fast and simple way. The methods are easy to use and eliminate the need for prior treatment of the sample.

A disposable sensor has been developed for the measurement of copper(II) concentration in aqueous solution based on a change in the fluorescence of porphyrazine 2,7,12,17-tetra- tert -butyl-5,10,15,20-tetraaza-21H,23H-porphine (TP). The sensor was constructed by spin-coating a polyester support with a PVC solution containing TP, a plasticizer, the chelating agent Zincon and the ion-pairing benzetonium chloride. The measurement principle is based on the radiationless resonance energy transfer (RET) from TP immobilized in membrane, and acting as fluorescence donor, to Zincon acting as an acceptor induced by copper(II). The absorption spectrum of the Zincon–Cu(II) complex presents adequate overlapping with the emission spectrum of TP, producing a useful analytical signal by the RET process. The disposable sensor responds to copper(II) irreversibly over a dynamic range from 0.039 to 14 μmol L −1 (2.5–890 μg L −1 ) with a sensor-to-sensor reproducibility (relative standard deviation RSD) of 1.9%, as log a C u 2 + , at the medium level of the range and a response time of 10 min. The performance of the optical disposable sensor was tested for the analysis of copper in different types of natural waters (river, well, spring and swimming pool), validating results against a reference procedure.

The europium–tetracycline complex [Eu(Tc)] is known to show only weak fluorescence with an emission maximum at 615 nm. On addition of hydrogen peroxide (HP), the strongly fluorescent [Eu(Tc)(HP)] complex is formed, which displays a 15-fold stronger luminescence intensity. This study describes the decrease in luminescence intensity of the [Eu(Tc)(HP)] complex in aqueous solution in the presence of Cu2+, Fe3+, Ag+, Al3+, Zn2+, Co2+, Ni2+, Mn2+, Ca2+, and Mg2+. Static and dynamic quenching can be induced by Cu2+, and these processes were quantified by means of their quenching constants. Stern–Volmer plots were also derived from lifetime imaging measurements accomplished by the rapid lifetime determination (RLD) technique based on microwell plate assays, and also by the time-correlated single photon counting (TCSPC) technique. According to those data, a time-resolved fluorescent method for copper determination can be proposed that is based on dynamic quenching of the [Eu(Tc)(HP)] complex by Cu2+ ions. The response to copper concentrations is linear up to 1.6 μmol L−1, providing a detection limit of 0.2 μmol L−1.

A new optical absorption-based one-shot sensor for the determination of citrate is described. The citrate-sensitive element is a plasticized polymeric membrane containing a synthetic guanidinium receptor and a pH-sensitive lipophilic dye. The rigid amide-based receptor with C3 symmetry controls the anion selectivity pattern of the optical element. The optical selectivity coefficients obtained for citrate over a variety of common carboxylate anions meet the requirements for the determination of citrate in different types of samples. The one-shot sensor responds rapidly – in 40 s – and reversibly to citrate over a dynamic range of 0.779 to 25.0 mM with a sensor-to-sensor reproducibility of 5.7%, as log acit, in the medium level of the range. The performance of the optical one-shot sensor has been tested in the analysis of citrate in soft drinks and pharmaceuticals, validating the results against a reference procedure. The proposed method is quick, inexpensive, selective and sensitive, and uses conventional instrumentation only.

A new optical absorption-based disposable sensor for nitrate is described. The nitrate-sensitive element is a bicyclic cyclophane receptor next to a suitable pH-sensitive lipophilic dye immobilized in a plasticized polymeric membrane. The rigid amide-based receptor with C3 symmetry controls the anion selectivity pattern of the optical element. The optical selectivity coefficients obtained for nitrate over a variety of naturally occurring anions in natural waters meet the requirements for the determination of nitrate in waters. The disposable sensor responds to nitrate rapidly-the typical response time is 5 min-and reversibly over a wide dynamic range (26 microM-63 mM) with sensor-to-sensor reproducibility (relative standard deviation, RSD, 3.68%, as log aNO3-, at the medium level of the range and RSD 1.39% for repeated measurements with the same sensor). The performance of the optical disposable sensor was tested for the analysis of nitrate in different types of natural waters (river, well, spring), validating results against a reference procedure. The proposed method is quick, inexpensive, selective, and sensitive and uses only conventional instrumentation.

A preconcentration membrane for the retention and phosphorimetric determination of pharmaceuticals nalidixic and piromidic acids is proposed. The membrane has a circular zone of plasticized PVC adhered to the surface of a polyester strip, which constitutes the preconcentration area where the analytes are retained by absorption from a solution that contains it. Measurement of intrinsic phosphorescence in the synchronous phosphorescence spectra performed at 281/371 nm for nalidixic acid and 331/471 nm for piromidic acid make the resolution of the mixture possible. The applicable concentration range, detection limit, and precision (as relative standard deviation) are from 0.3 to 3.0 mg · l−1, 0.08 mg · l−1, and 5.1% for nalidixic acid and from 0.03 to 0.15 mg · l−1, 0.002 mg · l−1, and 5.2% for piromidic acid. The method was applied to the determination of residues of both pharmaceuticals in cow milk and human urine.

A test strip for the determination of mercury in aqueous solution has been developed. It has a circular sensing zone containing all the reagents necessary to produce a selective response to mercury and formed by plasticised PVC incorporating the cation-selective neutral ionophore 1,4,7,10-tetraazacyclododecane, the chromoionophore 9-dimethylamino-5-[4-(15-butyl-1,13-dioxo-2,14-dioxanonadecyl)phenylimino]benzo[a]phenoxazine and tetrabutylammonium tetraphenylborate as lipophilic salt. The measurement principle is based on an ion-exchange mechanism. When the sensor is introduced for a period of time depending on the mercury content into a water sample at a pH of 4.7, there is a colour change from blue to red, making it possible to use absorbance at 670 nm as the analytical signal. All experimental variables that influence the test strip response, especially in terms of selectivity and response time, were studied. The sensor responded linearly to mercury concentration in the range 0.3 and 5.1 μM with a reproducibility in mid-calibration of 1.6% relative standard deviation (R.S.D.) for 60 min agitation. Similarly, it responded linearly to concentrations in the range 7.9–108 μM with a mid-range R.S.D. of 1.8% (for 5 min without agitation). The procedure was applied to the determination of mercury in different types of waters (tap, mineral and spring), validating the results against a reference procedure.

[structure: see text] We report two methods for the attachment of mono- and disaccharides to one or both of the cyclopentadienyl rings in ferrocene. The first strategy involves the reaction in acidic media of thioglycosides with ferrocenemethanol or 1,1'-ferrocenedimethanol. The second method consists of the regiospecific catalytic cycloaddition of propargyl glycoside and azidomethyl and bis(azidomethyl)ferrocene leading to the 1,2,3-triazole derivatives. The inverse strategy was also explored. The electrochemical behavior of the synthesized ferrocene-containing glycoconjugates was investigated.

We have developed a selective and reusable chemiluminescent test strip to determine hypochlorite. The hypochlorite-sensitive test strip contains a 10 mm × 9 mm piece of anionic cellulose paper in fluoresceinate cycle, glued to a 10 mm × 4 cm × 0.5 mm polyester strip. The measurement of the chemiluminescence in a luminometer when 1 ml of sample is injected into a conventional cell containing the strip makes it possible to determine hypochlorite. The composition of the membrane and reaction conditions have been adjusted to obtain adequate sensitivity and selectivity. The test strip responded linearly to hypochlorite over two linear ranges, the first 2.0–10.3 mg L −1 and the second 10.3–51.4 mg L −1 , with a detection limit of 0.4 mg L −1 . The reproducibility using the same disposable test strip at a medium level of the range was 6.6%, as relative standard deviation (R.S.D.), and 12.3% using different test strips. The procedure was applied to the determination of hypochlorite in different types of waters.

Continuous flow injection and UV spectrophotometric detection have been proposed for simultaneous determination of the two binary mixtures, butylated hydroxytoluene (BHT)/ n -propyl gallate ( n -PG) and butylated hydroxytoluene (BHT)/butylated hydroxyanisole (BHA), in food and cosmetics samples. The method is based on the different residence times of each antioxidant when the flow cell is packed to a height of 25 mm with silica C 18 using methanol–water 50:50% (v/v) as a carrier with a flow rate of 1.25 and 1.10 ml min −1 , respectively. The determination of each antioxidant is based on the measurement of its absorbance at its maximum wavelengths using a DAD detector at 30 and 180 s for the mixture n -PG–BHT and 90 and 220 s for BHA–BHT. Calibration graphs were linear over the range 10.0–300.0 μg ml −1 for each antioxidant in both mixtures. The relative standard deviations were 2.5% for BHT and 2.0% for the co-existing antioxidant. Resolution of the n -PG–BHT mixture in ratios between 1:8 and 8:1 and the BHA–BHT mixture in ratios between 1:10 and 10:1 is possible. The method was applied to the determination of both antioxidants in fat foods and cosmetics samples with recoveries ranging between 101 and 105%.

We have developed a selective and reversible test strip based on an ion-exchange mechanism to determine calcium. The optical test strip contains a polymeric film of plasticised PVC that contains all of the reagents necessary to produce a response to calcium, among them the new ionophore, 4,13-bis[(N-adamantylcarbamoyl)propionyl]-1,7,10,16-tetraoxa-4,13-diazacyclooctadecane. The measurement of the absorbance at 655 nm in a standard photometer makes it possible to determine calcium activities. The composition of the membrane and reaction conditions have been adjusted to obtain adequate selectivity. The test strip responded linearly to calcium between 0.050 and 135 mM in activities. The reproducibility intermembrane at a medium level of the range was 6.2%, as RSD, of log a(Mg(2+)), and 3.4% as RSD intramembrane. The procedure was applied to the determination of calcium ion in different types of waters (tap, well, spring and mineral) and milks (whole, skimmed, skimmed with calcium added, special types) validating the results against a reference procedure.

A simple, rapid and inexpensive monoparameter flow-through sensor has been developed for the determination of saccharin in low calorie and dietary products. The method is based on the transient adsorption of the sweetener on Sephadex G-25 solid phase packed to a height of 20 mm in the flow cell. The optimal transient retention of the synthetic sweetener, in terms of sensitivity and sampling frequency, was obtained when pH 2.75 citric acid-sodium citrate buffer 5 x 10(-3) M was used as a carrier at a flow-rate of 1.5 ml min(-1). Saccharin was determined measuring its intrinsic absorbance at 217 nm at its residence time. Calibration graphs for peak height and peak area were linear over the range 5.0-200.0 microg ml(-1), RSD 1.18%, and 1.0-200.0 microg ml(-1), RSD 0.78%, respectively. Saccharin was determined in several food samples measuring height or area peak, obtaining recoveries ranging between 98-104 and 99-102% for height and area peak, respectively. The procedure was validated for use in the determination of saccharin in low calorie and dietary products giving reproducible and accurate results.

An optical and reversible test strip that uses an ion-exchange mechanism which responds equally to calcium and magnesium and makes it possible to determine water hardness is described. The transparent test strip, made of a polyester sheet, has a circular polymeric film of plasticised poly(vinyl chloride) (PVC) that contains all of the reagents necessary to produce an equal response to calcium and magnesium, namely, a cation-selective neutral ionophore, such as 4,13-[bis(N-adamantylcarbamoyl)acetyl]-1,7,10,16-tetraoxa-4,13-diazacyclooctadecane, a chromoionophore, such as lipophilised Nile Blue, and potassium tetrakis (4-chlorophenyl)borate as a lipophilic salt, which it is evaluated by absorbance measurement at 655 nm in a standard photometer. All experimental variables that influence test strip response, especially in terms of selectivity and response time, have been studied. The sensor responded linearly to hardness up to 14,800 mg l −1 , in activities, expressed as CaCO3. The detection limit is 1.9 mg l −1 as CaCO3, the reproducibility intermembrane at a medium level of the range was 7.0%, as R.S.D., of log aCa2+/Mg2+ and 2.6% as intramembrane. The procedure was applied to the determination of hardness in different types of waters (tap, well, mineral and spring) validating results against a reference procedure. This proposed method is quick, inexpensive, selective and sensitive and uses only conventional instrumentation. © 2003 Elsevier Science B.V. All rights reserved.

A phosphorimetric method for the determination of o-phenylphenol (OPP) using filter paper as solid support and Tl(I) as heavy metal enhancer of the phosphorescent signal is proposed. The phosphorescence measurements were carried out by placing the paper with the sample between two plates of quartz, thus avoiding the quenching effect produced by atmospheric oxygen and moisture. The linear dynamic range of the method was 0.5-4.0 mg L(-1) and the detection and quantification limits were 0.03 and 0.11 mg L(-1), respectively. The precision of the method (expressed as relative standard deviation) was 1.7% for a sample containing 2.0 mg L(-1) of analyte. The method has been applied to the determination of OPP in different types of water, lettuce, string beans and peppers, with recoveries ranging between 97.1 and 100.7%

A disposable single-use optical sensor to determine potassium based on an ion-exchange mechanism is described. The test strip is formed by a circular sensing film zone 6 mm in diameter and 4.7 μm in thickness that contains all the reagents necessary to produce a selective response to potassium on a polyester sheet. The sensing zone is formed by a plasticised PVC that incorporates the cation-selective neutral ionophore dibenzo-18-crown-6, lipophilised Nile Blue, and a lipophilic salt. At pH 9.0, the absorbance response of the test strip at 660 nm shows a good correlation with the theoretical behavior. All experimental variables that influence response, especially in terms of selectivity and response time, have been studied. The sensor responded linearly in activities in the range of 0.0125 and 76.8 mM. The detection limit is 0.0125 mM, the reproducibility intermembrane, at a medium level of the range, is 3.4%, as R.S.D. of log a K + and the intramembrane, 3.0%. The procedure was applied to the determination of potassium in different human plasma samples, pharmaceutical compounds and seawater samples, validating results against a reference procedure.

A rapid liquid chromatography–mass spectrometric method for the determination of five nitroimidazoles in water from different sources is described. The extraction procedure was based on HLB solid-phase extraction with acetonitrile followed by an evaporation step. Ternidazol, another nitroimidazole, was used as the internal standard. The liquid chromatographic separation was made on a C18 bonded silica column applying a gradient with an ammonium acetate buffer solution and acetonitrile. Following electrospray ionisation, the protonated molecular ions [M+H]+ were obtained. Quantification for each nitroimidazole was carried out by monitoring its molecular ion. Calibration functions, quantification and detection limits, intra- and inter-day reproducibility and accuracy were estimated. For the confirmatory assay, several fragment ions from each nitroimidazole were obtained and monitored. The method was applied successfully to determine and identify nitroimidazoles in water from different sources at a level of 0.2 μg l−1.

A flow-through optosensor with solid phase UV spectroscopic detection is proposed for the direct determination of the antioxidant Butilated Hydroxytoluene (BHT) without previous derivatization. The method is based on the transient retention of this compound in a flow-through cell packed with C18 silica using ethanol : water mixture as a carrier, and its intrinsic absorbance monitored at 274 nm. Afterwards, the recording of the analytical signal BHT was easily and quickly desorbed from the solid support by the same carrier. The calibration graphs were linear over the range 2.0–300.0 mg L−1 using area as the analytical parameter. The relative standard deviation (RSD) was between 0.5 and 1.6%. The method was applied to the determination of this antioxidant in several cosmetics samples and was validated using the standard addition methodology and an HPLC reference method.

A method for the simultaneous determination of codeine and pyridoxine was developed, based on the measurement of their native fluorescence signals, by using first-derivative spectrofluorimetry to resolve the mixture. Codeine was measured at λem = 309 nm, and pyridoxine was measured at λem = 450 nm. Instrumental parameters were optimized, and the emission spectra were recorded between 275 and 475 nm, at λex = 255 nm and excitation and emission slit widths of 2.5 and 10 nm, respectively. Systematic studies on the influence of species usually present along with the analytes (such as caffeine, ascorbic acid, paracetamol, and thiamine) were also performed. The calibration graphs were linear over the ranges of 0.5–7.0 and 0.1–1.0 μg/mL for codeine and pyridoxine, respectively, and the relative standard deviations (n = 10) were about 3%. The method was successfully applied to the determination of codeine and pyridoxine in solutions of synthetic mixtures and in synthetic and semisynthetic pharmaceutical formulations.

An integrated solid-phase spectrophotometry/flow injection analysis (FIA) method is proposed for the determination of the synthetic colorant matter Ponceau 4R (P4R) in the presence of its unsulfonated derivative 2-hydroxy-1-[(naphthalenyl)azo] naphthalene (N2N). The procedure is based on the measurement of P4R at λ = 508, followed by retention and preconcentration of the low level concentration of N2N on a C18 silica gel minicolumn and subsequent measurement of the absorbance of N2N at λ = 508 nm after its elution. The applicable concentration range, the detection and the relative standard were the following: for P4R, from 0.30 to 20.0 mg/L; 0.052 mg/L 1.1%; and for N2N, between 0.020 to 3.0 mg/L 0.003 mg/L and 1.1%. The method was applied to the determination of small amounts of N2N present in P4R in food and cosmetic products. Percentages of recovery between 95 and 105% were obtained in all instances. The method was applied satisfactorily to the determination of the compounds P4R and N2N in samples of sweets and cosmetic products when compared to results offered by a HPLC reference method.

A new procedure to determine copper has been proposed using an irreversible and disposable multilayer optical test strip. Two layers form the sensing zone: a copper sensitive and a dialysis layer. The test strip is characterised to be a disposable polyester sheet contained in a circular film 6 mm in diameter and 25 µm in thickness, with all reagents necessary to produce a selective response. The sensing zone was formed by Nafion as polymer, bathocuproine as a chromogenic reagent and p-anisidine as reducer. When it is applied to determination of copper in plasma samples, another layer of hydrogel D-6 is put on this membrane to eliminate the interference of proteins. When the test strip was introduced for 60 min into a plasma sample an orange colour developed. The absorbance at 475 nm was used as the analytical signal. The test strip responded linearly in the range 0.05–1.00 mg L−1. The reproducibility in the measurement of copper at 3.0 mg L−1, was 7.8%. The procedure was applied to the determinat...

An optical strip test to determine calcium is proposed. The membrane consists of a polyester sheet and an active layer composed of a cation-selective neutral ionophore, such as 18-crown-6-ether, a proton selective neutral chromoionophore, such as lipophilised Nile Blue, and potassium tetrakis(4-chlorophenyl)borate as a lipophilic salt. The membrane responds reversibly to calcium ions by an ion-exchange mechanism, changing its colour from blue to red. All experimental variables that influence test strip response, especially in terms of selectivity and response time, have been studied. The system responded linearly in activities in the range 0.046–134 mM. The detection limit is 0.046 mM, the reproducibility intermembrane at a medium level of the range was 8.5%, as relative standard deviation (R.S.D.) of loga Ca 2+ and 2.7% as intramembrane. Calcium was determined by using the test strip proposed in different types of waters (tap, mineral and spring) validating results against a reference procedure. This proposed method for calcium determination in waters is quick (less than 5 min), inexpensive, selective and sensitive and uses only conventional instrumentation. © 2002 Elsevier Science B.V. All rights reserved.

A sulphide selective colorimetric metal complexing indicator-displacement assay has been developed using an immobilized copper(II) complex of the azo dye 1-(2-pyridylazo)-2-naphthol printed by inkjetting on a nylon support. The change in colour measured from the image of the disposable membrane acquired by a digital camera using the H coordinate of the HSV colour space as the analytical parameter is able to sense sulphide in aqueous solution at pH 7.4 with a dynamic range up to 145 μM, a detection limit of 0.10 μM and a precision between 2 and 11%.

One of the main limiting factors in optical sensing arrays is the reproducibility in the preparation, typically by spin coating and drop casting techniques, which produce membranes that are not fully homogeneous. In this paper, we increase the discriminatory power of colorimetric arrays by increasing the reproducibility in the preparation by inkjet printing and measuring the color from the image of the array acquired by a digital camera, using the H coordinate of the HSV color space as the analytical parameter, which produces robust and precise measurements. A disposable 31 mm × 19 mm nylon membrane with 35 sensing areas with 7 commercial chromogenic reagents makes it possible to identify 13 metal ions and to determine mixtures with up to 5 ions using a two-stage neural network approach with higher accuracy than with previous approaches.

This article gives an overview of the different techniques used to identify, characterize, and quantify engineered nanoparticles (ENPs). The state-of-the-art of the field is summarized, and the different characterization techniques have been grouped according to the information they can provide. In addition, some selected applications are highlighted for each technique. The classification of the techniques has been carried out according to the main physical and chemical properties of the nanoparticles such as morphology, size, polydispersity characteristics, structural information, and elemental composition. Microscopy techniques including optical, electron and X-ray microscopy, and separation techniques with and without hyphenated detection systems are discussed. For each of these groups, a brief description of the techniques, specific features, and concepts, as well as several examples, are described. © 2014 Taylor and Francis Group, LLC.

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.

A new test procedure to determine the pesticide morestan based on solid phase room temperature phosphorescence using a disposable optical sensor is proposed. The device consists of a disposable polyester sheet ( 5 cm ×1 cm) with a circular micro zone (6 mm in diameter and 25 μm in thickness), formed by polyvinylchloride and tributylphosphate as a plasticizer, on its surface. When the sensor was introduced for 2 h into a solution containing morestan, the pesticide was fixed in the sensing zone and its phosphorescence emission could be directly measured at λem=520 and λexc=363 nm. Construction and use of the sensor, and characterization of the fixation parameters have been studied. The applicable morestan concentration range was 1.0–200.0 ng ml−1 with a detection limit of 0.28 ng ml−1 and a precision (as relative standard deviation) of 2.9%. The method was applied to the determination of the pesticide in different water samples (natural, tap, sea, river and waste water) with recovery percentages ranging between 82.2 and 105.7%. A study of the interference produced by other pesticides and various organic and inorganic species frequently present in these waters showed the selectivity of the method. The method was validated chemometrically.