Detection of gases and organic vapors by cellulose-based sensors.

The growing interest in the development of cost-effective, straightforward, and rapid analytical systems has found cellulose-based materials, including cellulose derivatives, cellulose-based gels, nanocellulosic materials, and the corresponding (nano)cellulose-based composites, to be valuable platforms for sensor development. The present work presents recent advances in the development of cellulose-based sensors for the determination of volatile analytes and derivatives of analytical relevance. In particular, strategies described in the literature for the fabrication and modification of cellulose-based substrates with responsive materials are summarized. In addition, selected contributions reported in the field of paper-based volatile sensors are discussed, with a particular emphasis on quick response (QR) code paper-based platforms, intelligent films for food freshness monitoring, and sensor arrays for volatile discrimination purposes. Furthermore, analytical strategies devised for the determination of ionic species by in situ generation of volatile derivatives in both paper-based analytical devices (PADs) and microfluidic PADs will also be described.

Nanomaterial-Integrated Cellulose Platforms for Optical Sensing of Trace Metals and Anionic Species in the Environment.

The development of disposable sensors that can be easily adapted to every analytical problem is currently a hot topic that is revolutionizing many areas of science and technology. The need for decentralized analytical measurements at real time is increasing for solving problems in areas such as environment pollution, medical diagnostic, food quality assurance, etc., requiring fast action. Despite some current limitations of these devices, such as insufficient detection capability at (ultra)trace level and risk of interferent effects due to matrix, they allow low-cost analysis, portability, low sample consumption, and fast response. In the last years, development of paper-based analytical devices has undergone a dramatic increase for on-site detection of toxic metal ions and other pollutants. Along with the great availability of cellulose substrates, the immobilization of receptors providing enhanced recognition ability, such as a variety of nanomaterials, has driven the design of novel sensing approaches. This review is aimed at describing and discussing the different possibilities arisen with the use of different nanoreceptors (e.g., plasmonic nanoparticles, quantum dots, carbon-based fluorescent nanoparticles, etc.) immobilized onto cellulose-based substrates for trace element detection, their advantages and shortcomings.

One-pot synthesis of a magnetic nanocomposite based on ultrasound-assisted co-precipitation for enrichment of Hg(II) prior to detection by a direct mercury analyzer.

Ultrasound-assisted co-precipitation was applied to construct a magnetic nanocomposite following a 'one-pot' synthetic strategy for Hg(II) enrichment. The presence of a noble metal such as Ag(I), Au(III), Pd(II) in the synthesis medium proved to be essential in order to attain an efficient co-precipitation of Hg with the magnetic nanoparticles. Following this preconcentration procedure, thermal desorption and a further preconcentration was carried out by amalgamation onto a gold coil placed inside a direct mercury analyzer working under the principle of atomic absorption. The magnetic nanocomposite was characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy coupled to energy dispersive X-ray spectrometry (HR-TEM-EDS) and total reflection X-ray fluorescence (TXRF). Magnetic nanoparticles with a size in the range of ca. 7-11 nm were obtained. After full optimization of variables influencing the preconcentration and detection of Hg, analytical characteristics were obtained. A detection limit as low as 3.2 ng/L Hg was obtained when 50 µL of the magnetic phase were introduced in the mercury analyzer. The repeatability and reproducibility expressed as relative standard deviation (RSD) were 7% and 10%, respectively. Several certified reference materials, synthetic and unknown water samples were analyzed showing Hg recoveries in the range of 88-115%.

Study of the presence of micro- and nanoparticles in drinks and foods by multiple analytical techniques.

A variety of food and drink samples (n = 21) were analyzed to evaluate the presence of (nano-) particles in their composition. After assessment of the sample pre-treatment step, a fast screening analysis was performed for drinks by Dynamic Light Scattering showing particles from 10 to 300 nm that could correspond to organic or metallic NPs. Metallic NPs were identified in foods by Single-Particle mode Inductively Coupled Plasma Mass Spectrometry and Asymmetrical Flow Field-Flow Fractionation coupled to Multiangle Laser Light Scattering and Inductively-Coupled Plasma Mass Spectrometry. The determination of Ti, Si and Ag concentration in the initial food suspensions, after filtration and centrifugal ultrafiltration enabled to estimate the ionic and nanoparticles content. Si-containing particles can be present in cappuccino powder as large aggregates and Si- and Al-containing particles in hot chocolate. Ti-containing NPs (80-200 nm) were found in chewing gum and Ag NPs in silver pearls (50-150 nm) used for decoration pastry.

Screening of TiO2 and Au nanoparticles in cosmetics and determination of elemental impurities by multiple techniques (DLS, SP-ICP-MS, ICP-MS and ICP-OES).

Cosmetics are part of the daily life of most of the people. Thus, a complete characterization of the products we applied in our skin is necessary. In this work, an analytical investigation of a wide variety of cosmetics from the point of view of total element content and metallic nanoparticles (NPs) has been performed. Firstly, we analyzed the total element content by ICP-MS and ICP-OES after acid digestion as an assessment of the presence of metal impurities. Prohibited elements in cosmetics, according to the European Commission regulation No 1223/2009, were not detected, and only elements mentioned in the label were found (e.g. Al, Fe, Ti and Si). Secondly, a screening of the presence of NPs has been performed by Dynamic Light Scattering (DLS) and Single Particle Inductively-Coupled Plasma Mass Spectrometry (SP-ICP-MS). Two sample preparation procedures were applied. The first protocol consisted in the preparation of suspensions in 0.1% w/v SDS and the second based on defatting with hexane followed by resuspension in water. DLS was employed as a routine method for a fast analysis of NPs, but this technique showed limitations due to the lack of specificity. SP-ICP-MS analyses were then performed, first as a screening technique to evaluate the presence of TiO2 and Au NPs in cosmetics suspensions prepared in SDS; and second, when a positive answer was obtained about the presence of NPs from the screening, SP-ICP-MS was used for particle size determination. Results showed that only TiO2 NPs were present in two sunscreens, one anti-wrinkle day cream, one lip balm protector labeled as 'nano' and in one brand of toothpaste not labeled as 'nano'. Sizes obtained for both sample preparations were compared and ranged from 30 to 120nm in most of the samples.

Liquid-phase microextraction combined with graphite furnace atomic absorption spectrometry: A review.

An overview of the combination of liquid-phase microextraction (LPME) techniques with graphite furnace atomic absorption spectrometry (GFAAS) is reported herein. The high sensitivity of GFAAS is significantly enhanced by its association with a variety of miniaturized solvent extraction approaches. LPME-GFAAS thus represents a powerful combination for determination of metals, metalloids and organometallic compounds at (ultra)trace level. Different LPME modes used with GFAAS are briefly described, and the experimental parameters that show an impact in those microextraction processes are discussed. Special attention is paid to those parameters affecting GFAAS analysis. Main issues found when coupling LPME and GFAAS, as well as those strategies reported in the literature to solve them, are summarized. Relevant applications published on the topic so far are included.

Cr(VI) speciation in foods by HPLC-ICP-MS: investigation of Cr(VI)/food interactions by size exclusion and Cr(VI) determination and stability by ion-exchange on-line separations.

A method has been developed for the specific and sensitive determination of Cr(VI) in foods. First, the interactions between Cr(VI) and the matrices were investigated by size-exclusion HPLC-ICP-MS (SEC-ICP-MS). Evidence was found for the complexation of Cr(VI) potentially present with the ligands. For quantification of Cr(VI), the method was based on an alkaline extraction (NH4OH solution at pH 11.5) followed by Cr(VI) determination by anion-exchange HPLC-ICP-MS. Analytical performances of the method were satisfactory in terms of linearity, specificity, accuracy, repeatability, and intermediate precision. Detection limits ranged from 1 to 10 µg/kg, depending on the matrices investigated. The method was then applied for the determination of Cr(VI) in several products (dairy products, flour, chocolate, vegetables, fruits, meat, fish, eggs, and beverages) from different brands and origins. Cr(VI) was found in none of the samples investigated. To further investigate the reason for this absence, a stability study of spiked Cr(VI) was therefore conducted. A semi-skimmed cow milk was selected for this study. Cr(VI) was shown to be unstable in this matrix with a degradation rate increasing with the temperature.

Fast method for multielemental analysis of plants and discrimination according to the anatomical part by total reflection X-ray fluorescence spectrometry.

Fast and reliable analytical methodologies are required for quality control of plants in order to assure human health. Ultrasound-assisted extraction in combination with total reflection X-ray fluorescence is proposed as a fast and simple method for multielemental analysis of plants on a routine basis. For this purpose, five certified reference materials have been analysed for the determination of P, K, Ca, Cr, Mn, Fe, Ni, Cu, Zn and Pb. Different extractant media (acids and oxidants) were tried. A mixture of diluted HNO(3)+HCl+HF, was selected as the best option for the achievement of complete extractions. Accurate and precise results can be reached in most cases along with a high sample throughput. Different plants (i.e., herbs, spices and medicinal plants) were analysed. Linear discriminant analysis together with the elemental concentrations allowed the differentiation of commercial preparations corresponding to flower, fruit and leaf.

Enzymatic single-drop microextraction for the assay of ethanol in alcohol-free cosmetics using microvolume fluorospectrometry detection.

A green assay based on the development of an enzymatic reaction in drop format under headspace single-drop microextraction conditions is described for the first time. An aqueous drop containing the enzyme alcohol dehydrogenase and the cofactor ß-Nicotinamide adenine dinucleotide has been used as fluorescence probe for determining ethanol in alcohol-free cosmetics by microvolume fluorospectrometry. Experimental parameters affecting the microextraction performance were carefully optimized. Under the conditions employed, the contribution of other alcohols was found to be negligible. After 10 min of microextraction, a detection limit of 0.04 µg g(-1) ethanol, a repeatability, expressed as relative standard deviation, of 5.3% for a 0.05 mM ethanol standard and a preconcentration factor of 391, were reached. Accuracy of the proposed methodology was evaluated by comparison of calibration slopes corresponding to external calibration with aqueous standards and standard addition calibration. The method was successfully applied to different alcohol-free cosmetics (external calibration was carried out in all cases). Additional advantages such as simplicity and high sample throughput can be highlighted. The greenness profile of proposed methodology was established using NEMI criteria (US National Environmental Methods Index).

Fast screening of terpenes in fragrance-free cosmetics by fluorescence quenching on a fluorescein-bovine serum albumin probe confined in a drop.

A headspace single drop microextraction procedure is proposed for terpene screening in fragrance-free cosmetics. The drop is composed by an aqueous solution of a fluorescence probe formed by bovine serum albumin and fluorescein. Extracted volatile terpenes produce a fluorescence quenching that can be monitored by microvolume-fluorospectrometry. This quenching is observed on the fluorescein fluorescence only when it is linked to bovine serum albumin. A mechanism of contact quenching is proposed. Variables related to the terpene microextraction procedure were carefully studied, namely drop composition and volume, microextraction time, sample volume and temperature, stirring rate and salt addition. The only sample treatment is the dilution of cosmetic with 40% (v/v) ethanol. Citronellol was selected as a representative terpene for calibration purposes. According to the European legislation, the probability-concentration graph of the screening system was established using 0.001% (w/w) as the cut-off level. Low limits of detection with simple instrumentation, absence of matrix effects and high sample throughput can be emphasized.

Directly suspended droplet microextraction in combination with microvolume UV-vis spectrophotometry for determination of phosphate.

A miniaturized methodology for the determination of phosphate in waters has been developed by combining directly suspended droplet microextraction (DSDME) with microvolume spectrophotometry. The method is based on the extraction of the ion pair formed between 12-molybdophosphate and malachite green onto a microdrop of methyl isobutyl ketone and subsequent spectrophotometric determination with no dilution. An enrichment factor of 325 was obtained after 7.5 min of microextraction. The detection limit was 6.1 nM phosphate and the repeatability, expressed as relative standard deviation, was 2.7% (n=6). The method was successfully applied to the determination of dissolved reactive phosphorus in different freshwater samples.

Ultrasound-assisted emulsification microextraction with simultaneous derivatization coupled to fibre optics-based cuvetteless UV-vis micro-spectrophotometry for formaldehyde determination in cosmetic samples.

In this work, ultrasound-assisted emulsification microextraction in combination with fibre optics-based cuvetteless UV-vis micro-spectrophotometry has been proposed as a novel method for the determination of formaldehyde in water-based cosmetics such as shampoo, conditioner and shower gel. The use of a powerful cup-horn sonoreactor allows simultaneous extraction and derivatization of the samples without any pre-treatment. The type and volume of organic extractant solvent, need for a disperser solvent, sonication conditions (sonication time and amplitude), ionic strength and centrifuging time have been carefully studied. Matrix effects were also evaluated. The European official method for quantification of formaldehyde in cosmetic products was used for comparison purposes. An important improvement in sensitivity and sample throughput as well as miniaturization was achieved. A limit of detection of 0.02 microg g(-1) of formaldehyde and a repeatability expressed as relative standard deviation of 5.9% were obtained.