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Two simple boron-dipyrromethene-type fluorophore (azaBODIPYs) dyes are synthesized and tested for the determination of CO2 gas by an inner filter process. The indicators are noncovalently entrapped in suitable polymers according to their polarity, featuring absorption maxima at 620 nm and fluorescent emission maxima in the range 675–720 nm. Molar absorptivity and fluorescence quantum yield data were determined for these two synthesized azaBODIPYs. These indicators have high molar absorption coefficients of 7.1 × 104 and 2.1 × 104 M−1 cm−1 and quantum yields of 21 and 9%. The pKa values of the indicators are determined from absorbance and fluorescence measurements with values of 7.9 and 8.5, depending on the positioning of the substitution pattern of the electron-donating functionalities. The two azaBODIPYs present excellent photostability, making them suitable for long duration measurements. These azaBODIPY dyes act as fluorescent pH indicators in a polymeric sensing membrane along with microcrystalline powder of chromium-doped gadolinium aluminium borate as the luminophore, a transfer phase agent (tetraoctyl or tetramethyl ammonium hydroxide) and a plasticizer or surfactant to improve membrane permeability to gaseous CO2. The response time ranges from 42 to 60 s and recovery time from 103 to 120 s, with a detection limit of 0.04 and 0.57% CO2. The store time of the sensing membranes is longer than 570 days in the best case, and it does not need to be kept in any special atmosphere other than darkness.

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 single-use phosphorimetric sensor to determine the germicide nalidixic acid is proposed. The sensing action is based on the absorption of the analyte into the sensing zone and the subsequent measurement of the phosphorescence intensity emitted by the analyte fixed in the sensor. This plane drop sensor is made up of a 3 × 1.6 cm sheet of the polyester Mylar as solid support, and a circular film 5 mm in diameter and 20 μm in thickness, formed by poly(vinyl chloride) and tributyl phosphate as the plasticizer, adhered to its surface. The sensor is introduced for 2 h into the sample solution, after which it is dried and the phosphorescence intensity is measured directly at λex = 332 nm, λem = 412 nm, with a delay time of 0.15 ms and a gate time of 10 ms, under a dry nitrogen stream. The characteristic parameters of the construction of the sensing zone and of the processes of fixing the analyte along with the emission of phosphorescence were studied. The applicable concentration range was from 60 to 1500 ng ml−1, with a detection limit of 20 ng ml−1 and a precision of 2% expressed as relative standard deviation. The method was applied to the determination of nalidixic acid in milk and human urine with recoveries ranging between 96.0 and 103.7%. The calibration process was carried out by applying a mathematical method of finite elements that expresses the analytical signal as a function of the analyte concentration and equilibration time between the sensor and the sample solution.

Mixtures of the pesticides carbaryl and thiabendazole were studied using solid phase spectrophosphorimetry at room temperature with Whatman No. 4 filter-paper as solid support and Pb(II) as enhancer of the phosphorescence. The transmitted phosphorescence was used as an analytical signal and its measurement was performed by placing the paper containing the sample between two quartz plates. In this way, the use of a dry inert gas flow to avoid the quenching of atmospheric agents (oxygen and moisture) is not needed. The influence of several experimental parameters (e.g., pH, nature of the enhancers and solid supports, gate and delay times) on the phosphorescent emission of both chemicals was also studied. As a result, a new method for the simultaneous determination of these pesticides is proposed, using partial least squares (PLS-1) multivariate calibration. The statistical parameters of the optimised matrix, are included as a table. The applicable concentration ranges were from 0.16 to 1.20 mg l–1 for thiabendazole and from 0.50 to 4.00 mg l–1 for carbaryl. The method was applied to the determination of both pesticides in water, with recoveries between 93.4 and 105.6% for carbaryl and between 90.0 and 105.0% for thiabendazole. HPLC was used as a reference method.

A new, sensitive and simple spectrophotometric method for the simultaneous determination of Sunset Yellow FCF and Sudan I in mixtures is proposed. The method is based on the isolation of Sunset Yellow FCF on Sephadex diethylaminoethyl (DEAE) A-25 gel (pH 5.0) and the isolation of the Sudan I on C18silica gel (pH 5.0) measuring, directly, their absorbances in the solid phase at λ= 487 nm in both cases. The concentration ranges applicable were between 15 and 500 ng ml–1 for Sunset Yellow FCF and between 20 and 200 ng ml–1 for Sudan I with detection limits of 3.5 and 4.4 ng ml–1, respectively. The method was applied to the determination of mixtures of both compounds in synthetic colourings used as additives in food, drugs and cosmetic products.

The polycyclic aromatic hydrocarbons (PAHs) benzo[a]pyrene (BaP), benzo[a]anthracene (BaA) and pyrene (Pyr), which exhibit native fluorescence in solution, were determined in water at trace levels by solid-phase spectrofluorimetry. The relative fluorescence intensity of BaP, BaA and Pyr fixed on Sephadex G-25 gel was measured after packing the gel beads in a 1 mm silica cell. By using the synchronous spectra at different values of Δλ, BaA, BaP and Pyr can be simultaneously determined in the presence of other PAHs. Spectral characteristics of the PAH–gel system are described. The concentration ranges over which the method was applicable were 0.3–2.5 ng ml–1 of BaP, 0.4–3.5 ng ml–1 of BaA and 0.5–4.5 ng ml–1 of Pyr with relative standard deviations of 1.4, 1.3 and 1.5% for BaP, BaA and Pyr, respectively. The detection limits were 0.03 ng ml–1 of BaP, 0.05 ng ml–1 of BaA and 0.08 ng ml–1 of Pyr. The method was applied to the analysis of waters from different sources.

A spectrofluorimetric method for the determination of trace amounts of aluminium was developed, based on solid-phase spectrofluorimetry. Aluminium reacted with salicylidene-o-aminophenol to form a fluorescent complex that was adsorbed on a dextran-type cation-exchange gel. The fluorescence of the gel, packed in a 1 mm silica cell, was measured directly with use of a solid-surface attachment. The applicable concentration range was from 0.20 to 14.00 µg l–1, with a relative standard deviation of 1.0% and a detection limit of 0.02 µg l–1. The method was applied to the determination of aluminium in natural waters. The method is more sensitive and selective than that based on salicylidene-o-aminophenol alone.

An electrochemiluminescence-based disposable biosensor for lactate is characterized. The lactate recognition system is based on lactate oxidase (LOx) and the transduction system consists of luminol. All the needed reagents, luminol, LOx, BSA, electrolyte and buffer have been immobilized by a Methocel membrane placed on the working electrode of the screen-printed electrochemical cell. The measurement of the electrochemiluminescence (ECL) is made possible via a photocounting head when 50 microl of sample is placed into the screen-printed cell with a circular container containing the disposable sensing membrane. The compositions of the membrane and reaction conditions have been optimized to obtain adequate sensitivity. The disposable biosensor responds to lactate after 20 s when two 1 s pulses at 0.5 V are applied to obtain the analytical parameter, the ECL initial rate. The linearized double logarithmic dependence for lactate shows a dynamic range from 10(-5) to 5 x 10(-4) M with a detection limit of 5 x 10(-6) M and a sensor-to-sensor repeatability, as relative standard deviation, RSD, of 3.30% at the medium level of the range. The ECL disposable biosensor was applied to the analysis of lactate in human saliva as an alternative procedure for obtaining the lactate level in a non-invasive way. Interferences coming from components of saliva were studied and eliminated in a simple way that was easy to handle. The procedure was validated for use in human saliva, comparing the results against an enzymatic reference procedure. The proposed method is quick, inexpensive, selective and sensitive and uses conventional ECL instrumentation.

A spectrofluorimetric method for the determination of trace amounts of tungsten was developed, based on ion-exchange spectrofluorimetry. Tungsten reacts with carminic acid to give a red fluorescent complex, which was fixed on a dextran-type anion-exchange resin. The fluorescence of the resin, packed in a 1-mm quartz cell, was measured directly using a solid-surface attachment. The applicable concentration range was 1.0–20.0 µg l–1, with a relative standard deviation of 1.5% and a detection limit of 0.3 µg l–1. The method was applied to the determination of tungsten in natural waters. The method is more sensitive and selective than that using carminic acid alone.

A sensitive spectrofluorimetric method for the determination of trace amounts of benomyl was developed, based on solid-phase spectrofluorimetry. The relative fluorescence intensity of the benomyl fixed on C18 silica gel was measured directly after packing the gel beads in a 1 mm silica cell, using a solid-phase attachment. The wavelengths of excitation and emission were 293 and 375 nm, respectively. The applicable concentration range was from 0.2 to 20.0 ng ml–1, with a relative standard deviation of 1.1% and a detection limit of 0.04 ng ml–1. The method was applied to the determination of benomyl residues in natural waters. Recoveries were 96–103%. The method is more sensitive and selective than other methods described in the literature.

A flow-through optosensor with solid phase UV spectroscopic detection is proposed for the direct determination of single antioxidants, namely butylated hydroxyanisole (BHA) and n-propyl gallate (n-PG), without previous derivatization. The methods are based on the transient retention behaviour of these compounds in a flow-through cell packed with C-18 silica using ethanol–water mixtures as a carrier, and on the intrinsic absorbance monitored at 290 and 283 nm, respectively. After recording the analytical signal, the antioxidants were easily and quickly desorbed from the solid support by the same carrier. For BHA, calibration graphs were linear over the range 1.0–300.0 mg L−1 using area as the analytical parameter. The relative standard deviation (RSD) was between 0.5 and 1.6%. For n-PG, calibration graphs were linear over the range 1.0–300.0 mg L−1 in area and the RSD was between 1.4 and 1.5% .The methods were applied to the determination of these antioxidants in several food and cosmetics samples, and were validated using the standard additions method and an HPLC reference method.

A method for the simultaneous determination of the colorants Sunset Yellow FCF and Quinoline Yellow using solid-phase spectrophotometry is proposed. The colorants were isolated in Sephadex DEAE A-25 gel at pH 5.0, the gel–colorants system was packed in a 1 mm silica cell and spectra were recorded between 400 and 600 nm against a blank. Statistical results were obtained by partial least squares (PLS) multivariate calibration. The optimized matrix by using the PLS-2 method enables the determination of the colorants in artificial mixtures and commercial soft drinks.

The feasibility and performance of a procedure to evaluate previously developed one-shot optical sensors as single and selective analyte sensors for potassium, magnesium and hardness are presented. The procedure uses a conventional colour digital photographic camera as the detection system for simultaneous multianalyte detection. A 6.0 megapixel camera was used, and the procedure describes how it is possible to quantify potassium, magnesium and hardness simultaneously from the images captured, using multianalyte one-shot sensors based on ionophore-chromoionophore chemistry, employing the colour information computed from a defined region of interest on the sensing membrane. One of the colour channels in the red, green, blue (RGB) colour space is used to build the analytical parameter, the effective degree of protonation (1-α(eff)), in good agreement with the theoretical model. The linearization of the sigmoidal response function increases the limit of detection (LOD) and analytical range in all cases studied. The increases were from 5.4 × 10(-6) to 2.7 × 10(-7) M for potassium, from 1.4 × 10(-4) to 2.0 × 10(-6) M for magnesium and from 1.7 to 2.0 × 10(-2) mg L(-1) of CaCO(3) for hardness. The method's precision was determined in terms of the relative standard deviation (RSD%) which was from 2.4 to 7.6 for potassium, from 6.8 to 7.8 for magnesium and from 4.3 to 7.8 for hardness. The procedure was applied to the simultaneous determination of potassium, magnesium and hardness using multianalyte one-shot sensors in different types of waters and beverages in order to cover the entire application range, statistically validating the results against atomic absorption spectrometry as the reference procedure. Accordingly, this paper is an attempt to demonstrate the possibility of using a conventional digital camera as an analytical device to measure this type of one-shot sensor based on ionophore-chromoionophore chemistry instead of using conventional lab instrumentation.

A method for the determination of microgram per litre levels of fluoride has been developed, based on ion-exchange spectrophotometry (IES). The fluoride reacts with slightly polymerised zirconium and xylenol orange and the reaction product is sorbed on Dowex 1-X8 resin. The absorbance of the resin phase at 580 and 750 nm is measured directly. The calibration graph is linear in the concentration range 2–20 µg l–1 and the RSD is 1.8%. The determination limit with 500 ml of sample is 1.1 µg l–1; the sensitivity can be enhanced by increasing the sample volume. The method has been applied to the determination of fluoride in tap and raw water using 500 ml of sample.

A method for the determination of trace amounts of beryllium has been developed, based on ion-exchange spectrofluorimetry. Beryllium reacts with morin to give a highly fluorescent complex, which was fixed on a dextran-type anion-exchange resin. The fluorescence of the resin, packed in a 1-mm quartz cell, was measured directly using a solid-surface attachment. The concentration range of the method is 0.10–0.70 µg l–1, the relative standard deviation 1.4% and the detection limit 0.02 µg l–1. The method was applied to the determination of beryllium in natural waters. The aluminium and calcium levels can be determined first in order to reduce their interfering effect. The proposed method is more sensitive and selective than that using morin alone.

A method for the simultaneous determination of molybdenum and tungsten in mixtures by first-derivative synchronous spectrofluorimetry is described. The method is based on the formation of fluorescent complexes with carminic acid at pH 5.1. The constant wavelength difference chosen to optimise the determination was Δλ=λem.-λex.= 50 nm. Molybdenum was measured at λex./λem.= 550/600 nm and tungsten at λex./λem.= 561/611 nm. The range of application is between 1 and 12 µM molybdenum and between 1 and 6 µM tungsten. The accuracy and precision of the method are reported.

The reaction between titanium(IV) and 5,5′-methylenedisalicylohydroxamic acid (MEDSHA) was studied spectrophotometrically. At various hydrochloric acid concentrations, MEDSHA forms 1 : 2, 2 : 3, 1 : 1, 3 : 2 and 2 : 1 (MEDSHA-Ti) complexes with titanium(IV). The yellow complex (λmax.= 360 nm; Iµ= 9.9 × 103 l mol–1 cm–1), formed in 5 M hydrochloric acid solution, has been used for the spectrophotometric determination of trace amounts of titanium in the range 0.5–6.0 p.p.m. The proposed procedure was applied to the determination of titanium in ore and synthetic samples with good results.