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A microfluidic paper-based analytical device integrating carbon dot (CDs) is fabricated and used for a fluorometric off-on assay of biothiols. Vinyl sulfone (VS) click immobilization of carbon dots (CDs) on paper was accomplished by a one-pot simplified protocol that uses divinyl sulfone (DVS) as a homobifunctional reagent. This reagent mediated both the click oxa-Michael addition to the hydroxyl groups of cellulose and ulterior covalent grafting of the resulting VS paper to NH2-functionalized CDs by means of click aza-Michael addition. The resulting cellulose nanocomposite was used to engineer an inexpensive and robust microfluidic paper-based analytical device (μPAD) that is used for a reaction-based off-on fluorometric assay of biothiols (GSH, Cys, and Hcy). The intrinsic blue fluorescence of CDs (with excitation/emission maxima at 365/450 nm) is turned off via the heavy atom effect of an introduced iodo group. Fluorescence is turned on again due to the displacement of iodine by reaction with a biothiol. The increase in fluorescence is related to the concentration over a wide range (1 to 200 μM for GSH and 5–200 μM for Cys and Hcy, respectively), and the assay exhibits a low detection limit (0.3 μM for GSH and Cys and 0.4 μM for Hcy). The method allows for rapid screening and can also be used in combination with a digital camera readout.

This work presents a microfluidic paper-based analytical device (μPAD) for glucose determination using a supported metal-organic framework (MOF) acting as a peroxidase mimic. The catalytic action of glucose oxidase (GOx) on glucose causes the formation of H2O2, and the MOF causes the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2 to form a blue-green product with an absorption peak at 650 nm in the detection zone. A digital camera and the iOS feature of a smartphone are used for the quantitation of glucose with the S coordinate of the HSV color space as the analytical parameter. Different factors such as the concentration of TMB, GOx and MOF, pH and buffer, sample volume, reaction time and reagent position in the μPAD were optimized. Under optimal conditions, the value for the S coordinate increases linearly up to 150 μmol·L−1 glucose concentrations, with a 2.5 μmol·L−1 detection limit. The μPAD remains stable for 21 days under conventional storage conditions. Such an enzyme mimetic-based assay to glucose determination using Fe-MIL-101 MOF implemented in a microfluidic paper-based device possesses advantages over enzyme-based assays in terms of costs, durability and stability compared to other existing glucose determination methods. The procedure was applied to the determination of glucose in (spiked) serum and urine.

A multi-analyte platform based on a portable instrument is presented that enables oxygen and carbon dioxide to be determined in sample gases. The use of four sensing channels (two channels for each analyte to provide redundancy) warrants high system reliability. The sensing scheme in case of oxygen is based on the quenching of the phosphorescence of the platinum octaethylporphyrin complex. In case of carbon dioxide, a secondary inner-filter effect is exploited that is caused by a pH indicator whose color is reversibly changed. The sensing membranes were placed directly on the detectors and on the light sources so to make additional optical element dispensable, reduce system costs, avoid problems related to optical alignment, optimize the efficiency of data acquisition, and enable facile replacement of sensors. The resulting microcontroller-based system is immune against optical and electrical interferences, contains simple digital signal processing circuitry, and has low power consumption. The response of the system to the two gases was modeled, and calibration curves are corrected for effects of temperature. The instrument was characterized in terms of cross-sensitivity and dynamic response. It can determine oxygen and carbon dioxide in terms of volume percentage.

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 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 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.

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 spectrophotometric method for the simultaneous determination of Tartrazine (TT) and Sunset Yellow (SY) in cosmetic products has been developed. An extraction process was carried out using methylene chloride and the colouring matters were measured in the aqueous phase formed, the other components of the sample remaining in the organic phase. The applicable concentration ranges were 0.5–10 ug/ml TT and 0.5–12 μg/ml SY. The detection limits were 26 and 11 ng/ml and the relative standard deviations were 1.0 and 0.9% for TT and SY, respectively. The method was applied to the determination of both compounds in cosmetics.

A spectrophotometric method for determination of quinoline yellow spirit soluble (QYSS) in the presence of sulphonated quinoline yellow water soluble (QYWS) in soft drinks at trace levels is reported. The method is based on the fixation of QYSS on C-18 silica gel, followed by measurement of its absorbance at λ = 418 nm in the solid phase after being packed in a 1-mm cell. The applicable concentration range was 1.5–15.0 ng/ml, the detection limit 0.4ng/ml and the relative standard deviation 5.2%. The method was applied satisfactorily to the determination of this compound in samples of commercial soft drinks.

Benzo(a)pyrene (BaP) and pyrene (Pyr) are two polycyclic aromatic hydrocarbons (PAHs) showing native fluorescence in solution. Both compounds have been determined in water at trace levels by solid-phase spectrofluorimetry, in which BaP and Pyr are fixed on Sephadex G-25 gel and the relative fluorescence intensity is measured after the system is packed in a 1-mm silica cell. First-derivative synchronous spectra obtained at Δλ=38 nm were used to determine BaP and Pyr in the presence of other potentially interferent PAHs. The spectral characteristics of the PAHs-gel system are described, the applicable concentration ranges being 0.4–2.5 ng/ml for BaP and 0.7–4.5 ng/ml for Pyr. The relative standard deviations were 1.1% and 1.4% for BaP and Pyr respectively. The detection limits were 0.04 ng/ml for BaP and 0.1 ng/ml for Pyr. The method was applied to the analysis of both compounds in water at trace levels and a recovery study on tap, natural and sea waters was carried out.