S. Vera

Chemical sensors based on polymer composites with carbon nanotubes and graphene: the role of the polymer

This review provides an overview of recent research on chemical sensors based on polymer composites with carbon nanotubes (CNTs) and graphene (G) for quantitative and qualitative analysis in diverse application fields such as biosensing (DNA, enzymes, proteins, antigens and metabolites), and chemical and gas sensing using electrochemical and optical detection methods. Both CNTs and G show outstanding electrical, chemical, electrochemical and optical properties that make them ideal candidates for use in chemical sensors. The incorporation of polymers into the development of this type of sensor not only improves the CNT and G dispersion, but also enhances some of their properties like redox behaviour and biocompatibility, and provides additional properties such as photoelectric or swelling capacity. Moreover, unique synergistic effects arising from the combination of the matrix and nanofiller contributions are described by means of several examples highlighting the most important achievements in this field. Special emphasis has been placed throughout the review on analysing the role of the polymer in different sensing platforms. The combination of polymers with carbon nanomaterials for the preparation of chemical sensors opens up exciting areas of research due to their biocompatibility, and excellent sensitivity and selectivity.

Spectrophotometric determination of copper(II), nickel(II) and cobalt(II) as complexes with sodium diethyldithiocarbamate in cationic micellar medium of hexadecyltrimethylammonium salts

The determination of copper(II), nickel(II) and cobalt(II) was carried out as diethyldithiocarbamate (DDTC) complexes in presence of aqueous solutions of cationic surfactants of hexadecyltrimethylammonium bromide, chloride and hydroxide (CTAB, CTAC, CTAOH). The presence of micellar systems avoids the previous step of solvent extraction necessary to the formation of the DDTC complexes in absence of micelles. The influence of the different micellar counterions on the analytical characteristics (sensitivity and detection limits) of the proposed method for spectrophotometric determination of Cu(II), Ni(II) and Co(II) was studied.

Separation and Determination of Phenolic Antioxidants by HPLC with Surfactant/n‐Propanol Mobile Phases

The influence of cationic and anionic surfactants and short-chain alcohols in the mobile phase on the retention of five antioxidants has been studied. The solutes chosen were butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and propyl, octyl, and dodecyl gallates (PG, OG, DG).The surfactants were hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS), and n-propanol (PrOH) was the selected alcohol. A simple isocratic reversed-phase method for the antioxidant determination is proposed. Separation of five primary antioxidants takes 18 min with the mobile phase SDS 0.10 M/H 3 PO 4 0.01 M/PrOH 30%. Variation of the percentage of alcohol in the mobile phase permits optimization of the retention times of the antioxidants. Detection limits in the pg range were obtained for the all solutes. The method was used to determine the antioxidants in olive oil at three different levels, giving mean recoveries close to 100% for all the solutes (BHA 102%, PG 99%, OG 99%, DG 99%) except BHT (84%).

Determination of the micelle-solute association constants of some benzene and naphthalene derivatives by micellar high performance liquid chromatograph

SummaryThe interaction of some benzene and naphthalene derivatives with sodium dodecyl sulphate, hexadecyltrimethylmmonium bromide and polyoxyethylene [23] dodecanol micelles has been evaluated by high operformance liquid chromatography using micellar mobile phases. The micelle-solute association constants have been obtained for the compounds investigated. Good correlation between free energy of transfer for water-micelles and for octanol-water has been observed.

Antioxidant, antibacterial and ACE-inhibitory activity of four monofloral honeys in relation to their chemical composition

Different monofloral honeys from Castilla-La Mancha (Spain) have been studied in order to determine their main functional and biological properties. Thyme honey and chestnut honey possess the highest antioxidant capacity, which is due to their high vitamin C (in thyme honey) and total polyphenolic content (in chestnut honey). On the other hand, chestnut honey showed high antimicrobial activity against Staphylococcus aureus and Escherichia coli, whilst others had no activity against S. aureus and showed very small activity against E. coli. Moreover it was found that the antimicrobial activity measured in chestnut honey was partly due to its lysozyme content. In addition the angiotensin I-converting enzyme (ACE) inhibitory activity was measured, and the ACE inhibition is one mechanism by which antihypertensive activity is exerted in vivo. All the types of honey showed some activity but chestnut honey had the highest ACE inhibitory activity.

Vitamin C and Sugar Levels as Simple Markers for Discriminating Spanish Honey Sources

UNLABELLED In this work, 7 Spanish honeys with different botanical origins were studied. The honey origins were rosemary, chestnut, lavender, echium, thyme, multifloral, and honeydew. The chemical compounds determined were ascorbic acid (vitamin C), hydroxymethylfurfural, and major sugar contents (glucose and fructose). The physicochemical parameters, pH, conductivity, moisture, free acidity, and color, were also measured. Vitamin C is an important antioxidant in food, and the possibility to use it as discriminate parameter among different honeys was studied. The determination of vitamin C in honey samples was carried out by 2 different methods, volumetric and chromatographic comparing the results by both statistically. Vitamin C content was higher in thyme honeys than in the other types; however a wide dispersion in the values was found. Through a linear discriminant analysis (LDA), conductivity, glucose, fructose, and vitamin C content were the most important discriminant parameters. PRACTICAL APPLICATION Vitamin C content in different honey sources has been determined by a simple and rapid chromatographic method (less than 3 min) in honeys from 6 botanical origins. The results together with glucose and fructose content and some physicochemical parameters have been studied in order to discriminate the botanical origin of honeys and in the future certified their quality. A statistical LDA was applied to the data, and differentiation of honey sources was possible with very good agreement. The vitamin C content found in thymus honeys was significantly higher than in other types. This fact makes vitamin C a special marker for thymus honeys that have a higher antioxidant effect than the others giving it special properties. The identification of honey sources is essential for beekeepers in order to certify honeys for consumers.

Determination of Ni(II), Co(II) and Cu(II) as diethyldithiocarbamate complexes by high-performance liquid chromatography using hexadecyltrimethylammonium bromide in the mobile phase

Abstract The enhancement of the selectivity and sensitivity in high-performance liquid chromatography due to the presence of the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) in the mobile phase in the determination of three metal ions as complexes with sodium diethyldithiocarbamate was studied. The presence of an organic modifier such as 1-propanol in the mobile phase contributes to the decrease in the retention times of the complexes. The results show that under these conditions, the separation of the three metal ions is possible whereas in the absence of surfactant it is not possible. Also, the detection limits and selectivity are better in the presence of CTAB than in its absence. The method was applied to the determination of nickel and copper in real samples.

Optimization of the separation selectivity of a group of benzene and naphthalene derivatives in micellar high-performance liquid chromatography using a C18 column and alcohols as modifiers in the mobile phase

The separation selectivity of fifteen benzene and naphthalene derivatives in micellar high-performance liquid chromatography, using a C18 column, was studied as a function of the parameters on which it depends. A multiple linear regression programme was used to find the dependence of the selectivity coefficient on the following parameters: nature of the surfactant in the mobile phase (sodium dodecyl sulphate or hexadecyltrimethylammonium bromide), surfactant concentration (0.02–0.1 M), nature of the additive in the mobile phase (methanol, n-propanol, n-butanol and sodium chloride) and percentage of the alcohol (0, 5 or 10%). Selectivity optimization corresponds to the use of sodium dodecyl sulphate at low concentrations and the addition of an alcohol of medium chain length.

Determination of water-soluble vitamins in pharmaceutical preparations by reversed-phase high-performance liquid chromatography with a mobile phase containing sodium dodecylsulphate andn-propanol

SummaryA reversed-phase liquid chromatographic method with sodium dodecylsulphate-n-propanolwater as mobile phase has been used to separate and determine six water-soluble vitamins in twelve minutes. The analytical characteristics linear range, sensitivity, detection limits, and precision were evaluated. The lowest detection limits were those of nicotinic acid (not usually present in pharmaceutical products), 0.7 mgL−1, nicotinamide, 1.3 mg L−1, and pyridoxine, 1.4 mg L−1. When the method was applied to the determination of the vitamins in pharmaceutical samples the values found agreed with those on the labels.

Determination of micelle-solute association constants of some benzene and naphthalene derivatives by micellar high-performance liquid chromatography with butanol and sodium chloride additives to mobile phase

SummaryThe interaction between some benzene and naphthalene derivatives and sodium dodecyl sulphate and hexadecyltri-methylammonium bromide in the presence of n-butanol and sodium chloride has been evaluated by high-performance liquid chromatography using micellar mobile phases. Micelle-solute association constants are given for the compounds investigated. The results show that addition of n-butanol to the mobile phase decreases the association constant values relative to those in the absence of any additive. Conversely, when sodium chloride is added to the mobile phase, an increase of the association constant is obtained in most cases. Good correlation between free energy of transfer for water-micelles and for octanol-water has been observed.