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In this work, a freshness colorimetric sensor has been integrated with pork meat packages. The sensor tracks rising CO2 levels in the package associated with meat spoilage, as CO2 levels increase with bacterial population. The color of the sensor changes depending on the quantity of bacteria present, therefore it can be correlated with the freshness of meat, in this case pork loin. Detection is achieved by a simple photograph using a smartphone, and analyzing the grey scale from the RGB space color with a custom made app. Only 2 μL of the cocktail (all components are nontoxic) is needed to prepare the sensor, which have been integrated inside meat packages using a variety of support materials prior to sealing. The Smartphone measurements have been validated using a reference method (Checkpoint Analyzer) and the results suggest it can provide the basis for a quick test of the quality of the packaged pork.

We present a new chemistry to determine nitrites implemented in a microfluidic paper-based analytical device (µPAD). The device is fabricated in cellulose paper with a sample reception area and three replicate detection areas with recognition chemistry immobilized by adsorption. The method involves the use of nitrite in an acid medium reaction to generate nitrous acid, which produces the oxidation of s-dihydrotetrazine: 1,2-dihydro-3,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)-1,2,4,5-tetrazine (DHBPTz), which change the detection zone from colorless to pink. We used a digital camera and smartphone for the quantitative analysis of nitrite with the color coordinate S of the HSV color space as the analytical parameter. Parameters such as concentration and volume of s-dihydrotetrazine, pH, sample volume and reaction time were studied. The detection limit for this method is 1.30µM nitrite. To estimate the selectivity of the method an interference study of common ions in water samples was performed. The procedure was applied to natural water and compared with reference procedures.

A poly(luminol–3,3′,5,5′-tetramethylbenzidine) copolymer manufactured by electropolymerization on screen-printed gold electrodes greatly improves the electrochemiluminescence of hydrogen peroxide. Cholesterol oxidase was immobilized on the surface of a poly(luminol–3,3′,5,5′-tetramethylbenzidine) screen-printed cell modified with chitosan to prepare an ECL biosensor for cholesterol. Working under the optimized conditions, the linear dynamic range of cholesterol was 2.4 × 10−5–1.0 × 10−3 M with a limit of detection of 7.3 × 10−6 M and a precision of 10.3% (5.0 × 10−4 M, n = 5) expressed as relative standard deviation. This biosensor was applied to the determination of total cholesterol in serum samples obtaining satisfactory results with respect to the reference procedure. This cholesterol biosensor offers an alternative analytical method with low cost and high speed.

The correct identification of drying oils plays an essential role in providing an understanding of the conservation and deterioration of artistic materials in works of art. To this end, this work proposes the use of peak area ratios from fatty acids after ensuring that the linear responses of the detector are tested. A GC-MS method, previously reported in the literature, was revisited to its developed and validated in order to identify and quantify of eight fatty acids that are widely used as markers for drying oils in paintings, namely myristic acid (C(14:0)), palmitic acid (C(16:0)), stearic acid (C(18:0)), oleic acid (C(18:1)), linoleic acid (C(18:2)), suberic acid (2C(8)), azelaic acid, (2C(9)) and sebacic acid (2C(10)). The quaternary ammonium reagent m-(trifluoromethyl)phenyltrimethylammonium hydroxide (TMTFAH) was used for derivatization prior to GC-MS analysis of the oils. MS spectra were obtained for each methyl ester derivative of the fatty acids and the characteristic fragments were identified. The method was validated in terms of calibration functions, detection and quantification limits and reproducibility using the signal recorded in SIR mode, since two of the methyl derivatives were not totally separated in the chromatographic run. The proposed method was successfully applied to identify and characterise the most widely used drying oils (linseed oil, poppy seed oil and walnut oil) in the painting La Encarnación. This 17th century easel painting is located in the main chapel of the cathedral in Granada (Spain) and was painted by the well-known artist of the Spanish Golden Age, Alonso Cano (1601-1667).

A spectrofluorometric method for the quantitative determination of flufenamic, mefenamic and meclofenamic acids in mixtures has been developed by recording emission fluorescence spectra between 370 and 550 nm with an excitation wavelength of 352 nm. The excitation-emission spectra of these compounds are deeply overlapped which does not allow their direct determination without previous separation. The proposed method applies partial least squares (PLS) multivariate calibration to the resolution of this mixture using a set of wavelengths previously selected by Kohonen artificial neural networks (K-ANN). The linear calibration graphs used to construct the calibration matrix were selected in the ranges from 0.25 to 1.00 μg ml-1 for flufenamic and meclofenamic acids, and from 1.00 to 4.00 μg ml-1 for mefenamic acid. A cross-validation procedure was used to select the number of factors. The selected calibration model has been applied to the determination of these compounds in synthetic mixtures and pharmaceutical formulations. (C) 2000 Elsevier Science B.V.

A flow injection method with chemiluminescence (CL) detection is proposed for the determination of sodium 2-mercaptoethane sulfonate (MESNA), a drug often used to reduce the urotoxic effects of antineoplastic alkylating agents. The procedure is based on the reaction of the thiol with Ce(IV) in a sulfuric acid medium and measurement of the CL intensity produced by quinine used as a sensitizer. The optimum conditions for CL emission were investigated. Using the CL peak height as the analytical parameter, MESNA was determined over the concentration range 0.29‐2.21 ng (1.97‐9.85 mg·l 1 ) with a detection limit of 0.21 ng (1.38 mg·l 1 ) and a relative standard deviation (R.S.D.) of 4.1%. The method was applied satisfactorily to the determination of MESNA in pharmaceutical preparations with percentages of recovery between 94 and 105. © 2000 Elsevier Science B.V. All rights reserved.

A study of different alternatives to improve the stability and lifetime of sensors for the determination of gaseous CO 2 has been performed. It includes the characterization of different sensing membranes, a discussion of the results obtained and possibilities for the future. The solid sensor membrane for gaseous CO 2 based on changes in the luminiscence of a luminophore immobilized on O 2 -insensitive film, concurrent with the displacement of a pH indicator, has some drawbacks, such as the loss of efficiency over time and the need to maintain the sensor in special atmospheric conditions. As a solution to these drawbacks, two alternatives were tested, the first alternative was replacing the newly proposed tetraoctyl ammonium hydroxide (TOAOH ) phase transfer agent with other basic agents that did not undergo a Hoffman degradation reaction, and the second alternative was the use of hydrophilic polymers that could retain water needed for CO 2 sensing more efficiently. The different membranes tested indicated that the use of tetramethyl ammonium (TMAOH) instead of TOAOH as the phase transfer agent produced better results regarding stability and sensitivity. In addition, replacing the membrane polymer with hydrophilic polymers improved the sensing characteristics in terms of response time and stability over hydrophobic polymers. With a detection limit of 0.006%, the response time is 19 s and the recovery time is 100 s. The lifetime of the sensing membranes, which do not need to be held in any special atmosphere other than darkness, is longer than at least 300 days for membranes with TMAOH in hydrophilic polymer and 515 days for membranes with TMAOH in ethyl cellulose.

A method for the simultaneous determination of quinoline yellow (QY) and brilliant blue FCF (BB) in mixtures by solid-phase spectrophotometry has been developed. Both colorants were isolated in Sephadex DEAE A-25 gel showing maximum absorbances at 632 nm and 415 nm for BB and QY respectively. The applicable concentration ranges were between 25.0 and 500.0 mug 1(-1) for BB and between 50.0 and 750.0 mug 1(-1) for QY. The detection limits were 6.1 and 13.4 mug (-1) for BB and QY respectively. Application of the method to real samples (colognes, after shave lotions and shampoo gels) involves a previous extraction process of the colorants before their isolation on the gel.

Derivative spectrophotometry was applied to solid-phase spectrophotometry in order to enhance its sensitivity and remove the large background noise caused by the absorption of the resin layer itself, and avoid the necessity of preparing a blank. The determination of micro-amounts of molybdenum (at the ng ml(-1) level) with pyrocatechol violet to form a 11 blue complex in acid medium, which is fixed on a dextran-type anion-exchange resin (Sephadex QAE-A-25), is described as an example of the application of this technique. The absorbance of the resin, packed in a 1 mm spectrophotometric cell, was measured directly. The characteristic peak amplitude of the signal at 716 nm in the first-derivative spectra is useful for quantitative determination of molybdenum (2-8 ng ml(-1); RSD = 4, 30%) in natural and industrial water samples, plant tissues and soil extracts.

Solid-phase spectrophotometry has been applied to analysis for trace amounts of vanadium. Vanadium was sorbed in a styrene-divinylbenzene-type anion-exchanger Dowex 1-X8 as a vanadium-4-(2-pyridylazo)resorcinol complex. Resin phase absorbances at 562 and 800 nm were measured directly which allowed the determination of vanadium in the range of 0.1–2.4 ng/ml with a RSD of 1.5%. The method has been applied to the determination of vanadium in different samples, namely toadstool tissue, mussel tissue, petroleum crudes and swamp water.

A spectrofluorimetric method for the simultaneous determination of carbaryl (CBL) and o-phenylphenol (OPP) residue mixtures in waters has been developed. Carbaryl was hydrolysed in alkaline medium to give 1-naphthol. This compound and o-phenylphenol were fixed on QAE Sephadex A-25 gel at pH 10.75. The fluorescence of the gel, packed in a 1-mm silica cell, was measured directly with a solid-surface attachment. Overlapping of conventional fluorescence spectra is resolved by using first-derivative synchronous spectrofluorimetry and allows for the complete resolution of the mixture. The range of application is between 0.4 and 25.0 ng/ml for OPP and 0.8 and 25.0 ng/ml for CBL. The detection limits for o-phenylphenol and carbaryl were 0.1 and 0.2 ng/ml, respectively. The accuracy and precision of the method are reported. The method is suitable for determination of carbaryl and o-phenylphenol residues in natural waters. Recoveries from 95 to 105% have been obtained for natural waters spiked with CBL and OPP.

A microdetermination method at sub-mug/1. level for aluminium by solid-phase spectrophotometry has been developed. Chrome azurol S was used as chromogenic reagent to form a blue complex which was easily and strongly sorbed and concentrated on a dextran-type anion-exchange resin. The resin-phase absorbances at 615 and 800 nm were measured directly. Aluminium can be determined in the 0.6-4.0 mug/1. range with a RSD of 2.1%. The method is applied to the determination of aluminium in micaschist, natural and tap water samples.

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 9.9 × 10−7 to 3.3 × 10−4 M; 1.9 × 10−8; 5.6%; EP: from 9.0 × 10−7 to 3.3 × 10−4 M; 2.8 × 10−8; 3.5%; PP: from 8.3 × 10−7 to 9.9 × 10−5 M; 2.3 × 10−8; 4.2%; and BP: from 7.7 × 10−7 to 9.9 × 10−5 M; 4.2 × 10−8 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.

This work presents a preliminary study on the ageing process of proteinaceous binder materials used in painting under UV light. With this aim, two sets of model samples were prepared: samples prepared using a single protein material and complex samples prepared in a similar way to the sequence of layers in a real painting from lowest to highest complexity (protein, drying oils, pigment and varnish). The study focuses on acquiring information about the possible degradation process of proteinaceous binders due to ageing and how this process be affected by the presence of characteristic non-proteinaceous painting materials, such as lipids from linseed oil, terpenic compounds from varnish and inorganic pigments. Samples simulated the accelerated ageing process, as did the UV light exposition. The FT-IR spectra were recorded after 100, 500, 1000 and 1500 h of exposition. The study of the accelerated ageing process was performed by means of principal component analysis (PCA) using the FT-IR spectra obtained. Loadings from the significant principal components were analysed to find the FT-IR frequency (cm(-1)) involved in the degradation process. The study showed the lack of any relevant modification on the proteins in the single model samples. On the contrary, the complex model samples showed the ageing process. The accelerated ageing process can be explained by a principal component from PCA. The most affected IR region was 2900-3600 cm(-1), where the amide band was included.

In this paper, we performed a comparison between commonly used strategies amino acid ratios (Aa ratios), two-dimensional ratio plots (2D-Plot) and statistical correlation factor (SCF) and a classification technique, soft independent modelling of class analogy (SIMCA), to identify protein binders present in old artwork samples. To do this, we used a natural standard collection of proteinaceous binders prepared in our laboratory using old recipes and eleven samples coming from Cultural Heritage, such as mural and easel paintings, manuscripts and polychrome sculptures from the 15-18th centuries. Protein binder samples were hydrolyzed and their constitutive amino acids were determined as PITC-derivatives using HPLC-DAD. Amino acid profile data were used to perform the comparison between the four different strategies mentioned above. Traditional strategies can lead to ambiguous or non-conclusive results. With SIMCA, it is possible to provide a more robust and less subjective identification knowing the confidence level of identification. As a standard, we used proteinaceous albumin (whole egg, yolk and glair); casein (goat, cow and sheep) and collagen (mammalian and fish). The process results in a more robust understanding of proteinaceous binding media in old artworks that makes it possible to distinguish them according to their origin.

Liquid chromatography-mass spectrometry has become a powerful analytical tool, with high selectivity and sensitivity. Usually in this technique, the calibration function is estimated from the molecular peak signal. This report describes the improvement in sensitivity when the signals from several fragments in addition to the molecular peak are used to establish the calibration function. The influence of the dwell time has also been analysed as an important instrumental parameter that influences the signal range, and consequently, the sensitivity. The calibration function obtained by adding fragment signals was used to estimate the instrumental detection limit using three different procedures, comparing and discussing the results obtained.

The characterization of a new irreversible optical absorption-based one-shot sensor for magnesium is described. The magnesium photoactive probe is 7-diethylamino-3-(3,4-ethylendioxybenzoyl)coumarin immobilized in a plasticized polymeric membrane. The magnesium selectivity can be explained in terms of size and charge density of magnesium and charge-separated resonance forms contribution in the excited state of coumarin. The selectivity obtained for magnesium over a variety of naturally occurring species in natural waters meets the requirements for the determination of this ion in water. The one-shot sensor responds between 0.14 and 14 mg L −1 with a sensor-to-sensor reproducibility of 1.3% as log aMg2+ , at the medium level of the range. The performance of the optical one-shot sensor was tested in the analysis of magnesium in different types of natural waters and soft drinks validating results against a reference procedure. © 2005 Elsevier B.V. All rights reserved.

A selective test strip based on an ion-exchange mechanism to determine magnesium is described. This optical and reversible test strip, made on a transparent polyester sheet, has a circular polymeric film of plasticised PVC that contains all of the reagents necessary to produce a response to magnesium, namely, a cation-selective neutral ionophore, 2-amino-N,N � -diheptyl-N,N � -dimethyl-butanediamide, a chromoionophore, N,Ndiethyl-5-(octadecanoylimino)-5H-benzo[a]phenoxazine-9-amine, and potassium tetrakis (4-chlorophenyl)borate (TCPB) as a lipophilic salt, which is evaluated by absorbance measurement at 655 nm in a standard photometer. The experimental variables that influence test strip response, especially in terms of selectivity and response time, have been studied. The test strip responded linearly to magnesium between 0.009 and 160 mM in activities. The reproducibility intermembrane at a medium level of the range was 8.0%, as R.S.D., of log aMg2+ , and 5.9% as R.S.D. intramembrane. The procedure was applied to the determination of magnesium in different types of waters (tap, well and mineral) validating the results against a reference procedure. This proposed method is quick, inexpensive, selective and sensitive and uses only conventional instrumentation. © 2004 Elsevier B.V. All rights reserved.

A single-use phosphorimetric drop plane sensor for the determination of oxolinic acid (OXA) is proposed. The sensor was formed by a 30x16 mm(2) rectangular strip of Mylar type polyester as solid support that contained a circular sensing zone, 6 mm in diameter and 20 mum in thickness, formed by PVC plasticized with tributylphosphate adhered to its surface. When the strip was introduced for 1 hour into a sample solution, the analyte was retained in the sensing zone, making it possible to directly measure the phosphorescence intensity emitted by the OXA in the solid phase, at lambda(exc)=330 nm and lambda(em)=449 nm. The variables that affect the construction of the sensor have been studied, along with the experimental variables that influence the fixation of the analyte in the sensor. The method's detection limit was 0.01 mg l(-1) with an applicable concentration range from 0.04 to 1.50 mg l(-1) and a repeatability of 2.6% at the concentration range of 0.8 mg l(-1). The method was applied to samples of human urine and cows' milk, with recovery percentages ranging between 97.6 and 108.7%.

A method for the speciation of selenium (IV) based on solid-phase spectrophotometry (SPS), has been developed. In acidic conditions selenium (IV) oxidizes potassium iodide and the I3 forms an ionic association with Rhodamine B (RB) which is fixed on a dextran type lipophilic gel. The gel phase absorbances at 590 and 800 nm are measured directly, and allows for the determination of selenium (IV) in the range of 0.7‐18.0 m gl 1 , with a relative standard deviation (RSD) of 2.8%. The method has been applied to the determination of Se(IV) in natural waters. © 1999 Elsevier Science B.V. All rights reserved.

A cationic exchanger paper is used to retain analytes in solution and, after drying, to analyze directly by measuring the UV-Vis absorbance of the paper. The method was applied to determination of iron using its known 1,10-phenanthroline complex. Using 100 ml of sample the applicable concentration range was between 1.0 and 10.0 ng/ml with a detection limit of 0.2 ng/ml and a RSD around 2%. The method was applied to determination of iron total in snow, human serum and wine.

A spectrophotometric method for the determination of sulphathiazole (ST) has been developed, based on solid-phase spectrophotometry. The influence of experimental variables on fixation on Sephadex SP C-25 is discussed. The applicable concentration range is 0.10–10.00 mg/l., with a relative standard deviation of 0.62% and a detection limit of 0.02 mg/l. The accuracy and precision of the method are reported. The proposed method has been satisfactorily applied to the determination of sulphathiazole in pharmaceuticals.

A method for the simultaneous determination of aluminium and beryllium in mixtures by first-deravative synchronous solid-phase spectrofluorimetry has been developed. Aluminium and beryllium reacted with morin to give fluorescent complexes, which were fixed on a dextran-type resin. The fluoresnce of the resin, packed in a 1-mm silica cell, was measured directly with a solid-surface attachment. The constant wavelength difference chosen to optimize the determination was Deltalambda = lambda(em) = 75 nm. Aluminium was measured at lambda(em)lambda = 445/520 nm and beryllium at lambda(em)lambda(em) = 430/505 nm. The range of application is between 0.5 and 5.0 ng/ml for both aluminium and beryllium. The accuracy and precision of the method are reported. The method has been successfully applied to the determination of aluminium and beryllium in synthetic mixtures and natural waters.

The stability constants of some metal complexes of these two reagents have been determined.