Quantitative Analysis of Terpenic Compounds in Microsamples of Resins by Capillary Liquid Chromatography.

A method has been developed for the separation and quantification of terpenic compounds typically used as markers in the chemical characterization of resins based on capillary liquid chromatography coupled to UV detection. The sample treatment, separation and detection conditions have been optimized in order to analyze compounds of different polarities and volatilities in a single chromatographic run. The monoterpene limonene and the triterpenes lupeol, lupenone, ß-amyrin, and α-amyrin have been selected as model compounds. The proposed method provides linear responses and precision (expressed as relative standard deviations) of 0.6% to 17%, within the 0.5-10.0 µg mL-1 concentration interval; the limits of detection (LODs) and quantification (LOQs) were 0.1-0.25 µg mL-1 and 0.4-0.8 µg mL-1, respectively. The method has been applied to the quantification of the target compounds in microsamples. The reliability of the proposed conditions has been tested by analyzing three resins, white copal, copal in tears, and ocote tree resin. Percentages of the triterpenes in the range 0.010% to 0.16% were measured using sample amounts of 10-15 mg, whereas the most abundant compound limonene (≥0.93%) could be determined using 1 mg portions of the resins. The proposed method can be considered complementary to existing protocols aimed at establishing the chemical fingerprint of these kinds of samples.

Sensitive and selective plasmonic assay for spermine as biomarker in human urine.

A simple, fast, and highly selective and sensitive colorimetric assay to detect nanomolar levels of spermine in human urine (healthy donors, cancer patients) is reported. This assay is based on the absence of a competitive organic capping on the gold nanoparticles together with the high affinity of the amine groups of the analyte for the nanoparticle surface.

Silica supported Fe(3)O(4) magnetic nanoparticles for magnetic solid-phase extraction and magnetic in-tube solid-phase microextraction: application to organophosphorous compounds.

This work demonstrates the application of silica supported Fe3O4 nanoparticles as sorbent phase for magnetic solid-phase extraction (MSPE) and magnetic on-line in-tube solid-phase microextraction (Magnetic-IT-SPME) combined with capillary liquid chromatography-diode array detection (CapLC-DAD) to determine organophosphorous compounds (OPs) at trace level. In MSPE, magnetism is used as separation tool while in Magnetic-IT-SPME, the application of an external magnetic field gave rise to a significant improvement of the adsorption of OPs on the sorbent phase. Extraction efficiency, analysis time, reproducibility and sensitivity have been compared. This work showed that Magnetic-IT-SPME can be extended to OPs with successful results in terms of simplicity, speed, extraction efficiency and limit of detection. Finally, wastewater samples were analysed to determine OPs at nanograms per litre.

Miniaturized liquid chromatography in environmental analysis. A review.

The greater and more widespread use of chemicals, either from industry or daily use, is leading to an increase in the discharge of these substances into the environment. Some of these are known to be hazardous to humans and the environment and are regulated, but there is a large and increasing number of substances which pose a potential risk even at low concentration and are not controlled. In this context, new techniques and methodologies are being developed to deal with this concern. Miniaturized liquid chromatography (LC) emerges as a greener and more sensitive alternative to conventional LC. Furthermore, advances in instrument miniaturization have made possible the development of portable LC instrumentation which may become a promising tool for in-situ monitoring. This work reviews the environmental applications of miniaturized LC over the last 15 years and discusses the different instrumentation, including off- and on-line pretreatment techniques, chromatographic conditions, and contributions to the environmental knowledge.

Colorimetric analysis platform based on thin layer chromatography for monitoring gluten cross-contamination in food industry.

Monitoring of the accidental presence of gluten (Glu), resulting from cross-contamination, is imperative in different industries, in particular food industry. The objective of this study was the development of an analytical platform utilizing thin-layer chromatography (TLC) with colorimetric read-out for making binary (yes/no) decisions on surfaces and/or point of these industries. The composition of the extractive phase was optimized with commercial products used in cleaning processing lines. Subsequently, an exploration of TLC separation and detection was undertaken. CN-modified nanosilica plates and 30:70 acetonitrile:water were used to achieve a selective signal for Glu residues. The study of the detection performance showed that both spectroscopic measurement and image analysis were resulted in satisfactory results for quantitate analysis (RSD = 5 %, LOD = 0.12 mg). The practical application of the proposed methodology on surfaces of the food processing lines. This work demonstrated the operational feasibility in detecting gluten cross-contaminations within the food processing industry.

Towards a zero liquid discharge process from brine treatment: Water recovery, nitrate electrochemical elimination and potential valorization of hydrogen and salts.

This research addresses the issues related with treatment and valorization of brines and nitrate decontamination of surface and ground waters. The objective was to approximate to zero liquid discharge (ZLD) minimizing the environmental impact of brines of an electrodialysis reversal water treatment plant (EDRWTP) as an example. The innovative in flow process was developed from lab to pre-industrial scale and joined several main concepts: ion-exchange equilibrium for softening or demineralization of brines; reversed osmosis to recover suitable water and to enrich the waste in nitrate for efficient electrochemical reduction of NO3- to N2; valorization of subproducts by direct use or by precipitation; and assessment of the whole process by measuring in-line several parameters. The achieved softening was around 98 % and the recovered water from this current by reversed osmosis was 75 %. The brine of this step (25 %) contained around 1500 mg/L of nitrate and it was treated by electrochemical reduction with a Bi/Sn cathode providing a gas current of 60 % of initial nitrate reduced to N2, O2, H2O, NH3 and at least 97 % of H2. The aqueous current contained around 40 % of initial nitrate as ammonium and nitrite lower than 50 and 5 mg/L, respectively. Hypochlorite was added to this last current for oxidizing ammonium and nitrite to N2 and nitrate, respectively, being nitrate and ammonium lower than 50 and 5 mg/L, respectively. After the obtained water was demineralized and conducted to the EDRWTP inlet. The recovery of insoluble salts as calcium carbonate, reuse of saline solutions for the regeneration of process resins and the potential use of hydrogen generated as a by-product during the electrochemical reduction are other possible utilities.

In situ colorimetric quantification of silver cations in the presence of silver nanoparticles.

Silver ions (Ag(+)) can be quantified in situ in the presence of AgNPs by using a colorimetric sensing probe (3,3',5,5'-tetramethylbenzidine). Interestingly, it also enables detection of the Ag(+) adsorbed on the AgNP surface. This is relevant to design new methods to make AgNPs while ensuring the total reduction of Ag(+).

Study of the degradation of diphenyl-ether herbicides aclonifen and bifenox in different environmental waters.

The degradation of the diphenyl-ether herbicides aclonifen (ACL) and bifenox (BF) in water samples has been studied under different laboratory conditions, using in-tube solid-phase microextraction (IT-SPME) coupled to capillary liquid chromatography (capLC). The working conditions were selected in order to detect also bifenox acid (BFA), a compound formed as a result of the hydroxylation of BF. Samples (4 mL) were processed without any previous treatment, which allowed the detection of the herbicides at low ppt levels. The effects of temperature, light and pH on the degradation of ACL and BF have been tested using standard solutions prepared in nanopure water. The effect of the sample matrix has been evaluated by analysing different environmental waters spiked with the herbicides, namely ditch water, river water and seawater. The kinetics of the degradation have been studied and the half-life times (t1/2) have been calculated. The results obtained have demonstrated that the sample matrix is the most important parameter affecting the degradation of the tested herbicides. The degradation of both ACL and BF was much faster in ditch and river water samples, where t1/2 values of only a few days were observed. However, both compounds showed a better stability in seawater samples, where they can persist for several months. In all matrices ACL was found to be more stable than BF. In samples where BF had been substantially degraded, BFA was also detected, although the stability of this compound was also limited. Other degradation products have been detected along the study.

A modified micro-solid phase extraction device for in-port elution and injection into portable liquid chromatography: A proof-of-concept study.

A micro-solid phase extraction (micro-SPE) device packed with a C18 sorbent (10 mg) has been developed for the enrichment and purification of organic water pollutants prior to their analysis using a portable liquid chromatograph with a dual UV detector. To this end, the sorbent was immobilized at the inlet of a 4 mm syringe filter (0.20 µm), which was modified to reduce its internal volume. The filter was coupled to the needle of the chromatograph. After loading the sample and cleaning the sorbent for analyte purification, the device was installed into the injection port of the chromatograph, and the target compounds were desorbed and transferred directly to the chromatographic column with a small volume of organic solvent. Under optimized conditions, sample volumes as large as 50 mL could be processed with the micro-SPE device, while the analytes were desorbed with only 60 µL of methanol. As a result, efficient preconcentration could be reached, as demonstrated for different water contaminants, namely aclonifen, bifenox, tritosulfuron, triflusulfuron-methyl and caffeine. The proposed micro-SPE device was applied to the analysis of different types of water (river, well, sea, ditch and wastewater). The recoveries of the target compounds in samples ranged from 76 % to 109 %, which allowed their detection at low to sub µg/L levels. All operations were carried out manually, and thus, no additional laboratory instruments such as centrifuges, stirrers or evaporators were required. This proof-of-concept study shows that the proposed micro-SPE approach can be considered a reliable and effective option for the on-site analysis of pollutants in environmental water samples by portable liquid chromatography.

Portable determinations for legislated dissolved nitrogen forms in several environmental water samples as a study case.

In this work, we have studied the main species involved in determining total dissolved nitrogen (TDN) in water samples for accommodating a variety of quantitation methodologies to portable instruments and with the goal to achieve in situ analysis. The rise of water eutrophication is becoming an ecological problem in the world and TDN contributes markedly to this. Traditionally the several forms of DN are measured in the laboratory using conventional instrumentation from grab samples, but their analysis in place and in real time is a current demand. Inorganic nitrogen: NO3-, NO2- and NH4+, and organic nitrogen, such as amino nitrogen were tested here. For nitrate that presents native UV absorption suitable for direct water analysis, a portable optical fiber probe was compared with benchtop equipment and an in place analyzer. For nitrate, nitrite and ammonium, in situ solid devices that deliver reagents needed were tested and water color was measured by a smartphone coupled with a miniaturized optical fiber spectrometer and a miniaturized spectrometer or from images obtained and their RGB components. Amino nitrogen of some aromatic aminoacids with native fluorescence was followed by a portable optical fiber probe. Organic amino nitrogen and ammonium were determined by a portable luminometer and luminol supported in a measurement tube. Moreover, a portable miniaturized liquid chromatograph was shown suitable for monitoring priority nitrogen environmental pollutants. All options provided suitable results in comparison with lab estimations and were useful for evaluating if the legislation is fulfilled for the variety of tested waters. A discussion about the several portable options proposed for in place analysis, in function of the legislated determinations needed for each type of water was carried out.

Magnetic in-tube solid phase microextraction.

We report a new in-tube solid phase microextraction approach named magnetic in-tube solid phase microextraction, magnetic-IT-SPME. Magnetic-IT-SPME has been developed, taking advantage of magnetic microfluidic principles with the aim to improve extraction efficiency of IT-SPME systems. First, a magnetic hybrid material formed by Fe(3)O(4) nanoparticles supported on SiO(2) was synthesized and immobilized in the surface of a bared fused silica capillary column to obtain a magnetic adsorbent extraction phase. The capillary column was placed inside a magnetic coil that allowed the application of a variable magnetic field. Acetylsalicylic acid, acetaminophen, atenolol, diclofenac, and ibuprofen were tested as target analytes. The application of a controlled magnetic field resulted in quantitative extraction efficiencies of the target analytes between 70 and 100%. These results demonstrated that magnetic forces solve the low extraction efficiency (10-30%) of IT-SPME systems, which is one of their main drawbacks.

Plasmonic sensor for hydrogen sulphide in saliva: Multisensor platform and bag format.

In recent years, there is a growing demand for optical sensors given their analytical properties, and the possibility of in situ implementation. Among all the types of optical sensors, plasmonic sensors have aroused great interest in the scientific community. In this work, the ability of a plasmonic sensor based on AgNPs retained on a Nylon surface is studied to determine hydrogen sulfide, which can be an indicator of oral diseases. This compound produces a color change of the sensor from yellow to brown directly related to its concentration. The sensor response is evaluated in two different assay formats such as bag and well microplates. The figures of merits of both methodologies have been obtained and compared. The advantages and disadvantages of the different formats have been shown. Finally, the sensor is applied to quantify sulfides in real saliva. Concentrations ranged from 30 µ L-1 to 600 µ L-1 have been obtained for the voluntaries. Besides that, in this approach the RGB coordinates from images have been used as analytical signal too. The results achieved have demonstrated that the sensor and the methodology applied provide good selectivity, sensibility, rapidity, it is non-invasive and it can be used as indirect method to measure problems in the oral cavity.

Determination of caffeine in dietary supplements by miniaturized portable liquid chromatography.

In this study three miniaturized liquid chromatography (LC) instruments have been evaluated and compared for the analysis of caffeine in dietary supplements, namely a benchtop capillary LC (capLC) system, a benchtop nano LC (nanoLC)system and a portable LC system. Commercial products derived from different sources of caffeine have been analyzed. Under optimized conditions, the methods based on benchtop systems were superior in terms of sensitivity. The limits of detection (LODs) found with the capLC and nanoLC systems were 0.01 and 0.003 µg mL-1, respectively, whereas the LOD obtained with the portable LC instrument was of 1 µg mL-1. The portable LC-based method was superior in terms of simplicity and throughput (total analysis time < 15 min). On the basis of the results obtained, a new method for the rapid measurement of caffeine in dietary supplements by portable miniaturized LC is presented. This method provided good linearity within the 1-20 µg mL-1 interval, and it allowed the quantification of caffeine even in products derived from decaffeinated green coffee extracts. The contents of caffeine found with the proposed portable LC method in the real samples analyzed ranged from 1.38 to 7 mg per gram of product, which were values statistically equivalent to those found with the benchtop capLC and nanoLC methods, being the precision, expressed as relative standard deviation (RDS), of 2 -14% (n = 3). The proposed portable LC based method can be used as a simple and rapid alternative to estimate the quality, effectiveness and safety of dietary supplements, regarding their caffeine content.

Towards in field miniaturized liquid chromatography: Biocides in wastewater as a proof of concept.

Solving and/or evaluating given problems or decision making in place and in real time is a goal of the analytical chemistry science. In this context, the performance of a commercial portable miniaturized liquid chromatograph (minLC) with LED UV (255 nm) detector was compared with those provided by two lab minLCs (capillary and nano) coupled on-line to in-valve in-tube solid phase microextraction (IT-SPME) with diode array detector (DAD). In addition, responses of the portable LC for in-field analysis in several conditions were tested. Besides, two evaluation tools, BETTER criteria for portability and HEXAGON pictogram for sustainability and greenness were applied for comparison purposes. The benchtop LCs provided lower limits of detection (LODs) as expected, in the order of low µg L-1, than those achieved by the portable LC, with LODs around mg L-1 for compounds covering several polarities (logKow between -1.72 and 3.82). The used portable LC gave excellent resolution, reducing the analysis time and being the consumption of solvents negligible. As a practical application, fruit washing residual waters, which contained a suitable level of concentrations of several biocides for employing the portable minLC, were analyzed and quantified from the three minLCs as a proof of concept with comparable results.

Sustainable and green persulfate-based chemiluminescent method for on-site estimation of chemical oxygen demand in waters.

The standard method for estimating the chemical oxygen demand (COD) of water bodies uses dichromate as the main oxidant, a chemical agent whose use has been restricted in the European Union since 2017. This method is hazardous, time-consuming, and burdensome to adapt to on-site measurements. As an alternative and following the current trends of sustainable and green chemistry, a method using the less toxic reagent sodium persulfate as the oxidizing agent has been developed. In this method an excess of persulfate, activated through heating in an alkaline solution, oxidizes the chemically degradable organic fraction through a 2-step radical mechanism. The remaining persulfate is evaluated by chemiluminescence (CL) using luminol and a portable charge-coupled device (CCD) camera. The method provided quantitative recoveries and a sample throughput of >60 samples h-1. It was validated in river water samples by comparison of COD estimations with the standard dichromate method (R = 0.973, p < 0.05) and with a UV-Vis permanganate-based method (R = 0.9998, p < 0.05), the latter being also used for drinking waters. The proposed method is a sustainable and green alternative to the previous used methods. Overall, the method using activated persulfate is suitable for use as COD quantitation/screening tool in surface waters. Considering that its main components are portable, it can be ultimately adapted for in situ analysis at the point of need.

New silica based adsorbent material from rice straw and its in-flow application to nitrate reduction in waters: Process sustainability and scale-up possibilities.

This paper shows a particular example to move to a sustainable circular economical process from valorization of rice straw ashes by developing a green synthesis for obtaining a useful sub-product. This strategy can palliate negative effects of the agriculture waste practices on the environment and also the obtained silica reduced nitrate content in waters. It is demonstrated that the silica synthesis developed at lab was scalable more than a hundred times with good results. Adsorption studies of nitrate in standards and real well waters at lab scale and scaling-up provided similar results. Adsorption values near to 15 mg/g for nitrate standards and 8.5 mg/g for well water were obtained until achieving the initial nitrate concentration. Experimental breakthrough curves fitted to Thomas model, which gave similar results for adsorption capacities. The adsorption capacity was checked with that obtained by a commercial resin, providing improved results. The method at large scale was compared with industrial traditional methods and green adsorbents.

Scopolamine analysis in beverages: Bicolorimetric device vs portable nano liquid chromatography.

Scopolamine (SCP) is often involved in sexual assaults and robberies, particularly in recreational environments. Therefore, analytical tools are required for the analysis of this compound amenable for the field. In this work, a sensor for SCP is described based on the entrapment of KMnO4 into polydimethylsiloxane (PDMS). The possibility of using KMnO4 in combination with the reagent 1,2-naphtoquinone-4-sulfonate (NQS) giving a double sensor acting as a bicolorimetric device is also demonstrated. In contact with the sample, the PDMS composite delivers MnO4-, which reacts rapidly with SCP under basic conditions causing a change of the color of the solution that can be related to the concentration of drug using both, absorbances and color coordinates, while the NQS part of the sensor remains unchanged. After an exposure time to the sensors of 10 min, satisfactory linearity was obtained for concentrations of SCP up to 865 µg/mL, being the limit of detection (LOD) 108 µg/mL. A method using a portable nano liquid chromatograph with detection at 255 nm has been also developed; in this case the LOD was 100 µg/mL and the working linear interval was 250-2000 µg/mL. The precision, expressed as relative standard deviation (RDS), was ≤8% for both methods. Different beverages (cola, cola-whisky, tonic water-vodka, red wine and green tea) were assayed. The potential of the two proposed approaches for on-site tests is discussed.

In-tube solid phase microextraction coupled to miniaturized liquid chromatography for both, noble metal nanoparticle assessment and sensitive plasmonic assay development.

Colorimetric localized surface plasmon resonance (LSPR) as analytical response is applied for a wide number of chemical sensors and biosensors. However, the dependence of different factors, such as size distribution of nanoparticles (NPs), shape, dielectric environment, inter-particle distance and matrix, among others, can provide non-reliable results by UV-vis spectrometry in complex matrices if NP assessment is not carried out, particularly at low levels of analyte concentrations. Miniaturized liquid chromatography, capillary (CapLC) and nano (NanoLC), coupled on line with in-tube solid phase microextraction (IT-SPME) is proposed for the first time for both, controlling suitability of used noble metal NP dispersions and developing plasmonic assays. Several capped noble NPs and target analytes were tested from variations in the chromatographic profiles obtained by using diode array detection. The IT-SPME step, which influenced the chromatographic fingerprint provided by noble NP dispersions, was studied by asymmetrical flow field flow fractionation (AF4) too. We monitored NP aggregation induced by interaction with several analytes like acids and spermine (SPN). Assessment of NPs was achieved in less than 10 min and it permitted to develop suitable plasmonic tests. Here, it was also demonstrated that these assays can be followed by IT-SPME-miniaturized LC-DAD and more sensitivity and selectivity than those provided by UV-Vis spectrometry were achieved. Analysing urine samples to determine SPN as a cancer biomarker as a proof of concept is presented.

Ionic-liquid doped polymeric composite as passive colorimetric sensor for meat freshness as a use case.

A composite membrane containing 1,2-naphthoquinone-4-sulfonic acid sodium salt (NQS) embedded in an ionic liquid (IL)- polydimethylsiloxane (PDMS)- tetraethyl orthosilicate (TEOS)- SiO2 nanoparticles (NPs) polymeric matrix is proposed. The selected IL was 1-methyl-3-octylimidazolium hexafluorophosphate (OMIM PF6). It is demonstrated that ILs chemical additives of PDMS influenced the sol-gel porosity. The sensor analytical performance for ammonia atmospheres has been tested as a function of sampling time (between 0.5 and 312 h), temperature (25 °C and 4 °C) and sampling volume (between 2L and 22 mL) by means of diffuse reflectance measurements and sensor photos, which can be registered and saved as images by a smartphone, which permit RGB measurements too. Flexible calibration was possible, adapting it to the sampling time, temperature and sampling volume needed for its application. Calibration linear slopes (mA vs ppmv) between 1.7 and 467 ppmv-1 were obtained for ammonia in function of the several studied conditions. Those slopes were between 48 and 91% higher than those achieved with sensors without ILs. The practical application of this sensing device was demonstrated for the analysis of meat packaging environments, being a potential cost-effective candidate for in situ meat freshness analysis. NQS provided selectivity in reference to other family compounds emitted from meat products, such as sulphides. After 10 days at 4 °C ammonia liberated by the assayed meat was 20 ± 4 µg/kg and 18 ± 3 µg/kg, quantified by using diffuse reflectance and %R measurements, respectively. Homogeneity of the ammonia atmosphere was tested by using two sensors placed in two different positions inside the packages.

Bimodal copper oxide nanoparticles doped phase for the extraction of highly polar compounds by in-tube solid-phase microextraction coupled on-line to nano-liquid chromatography.

Polymers obtained from tetraethyl orthosilicate (TEOS) and triethoxymethylsilane (MTEOS) have been functionalized with different metal and metal oxide nanoparticles (NPs), and used as coatings of extractive capillaries for the extraction of polar compounds by in-tube solid-phase microextraction (IT-SPME) coupled on-line to nano-liquid chromatography (nano-LC). The extraction capabilities of the new phases have been studied using several triazinic herbicides with log of octanol/water partition coefficients (Kow) ranging from -0.7 to 3.21 under reversed phase chromatographic conditions. Best extraction efficiencies for the most polar compounds (log Kow ≤ 2.3) were typically obtained with the CuO NPs doped phase. The TEOS-MTEOS polymer can be modified with two types of NPs in order to obtain extractive phases capable of interacting with compounds of a wide range of polarities; alternatively, two capillaries each with a different type of NPs can be combined in series with the same goal. Under the later approach the limits of detection (LODs) found for the tested herbicides were 0.02-1.5 µg/L, and the precision expressed as relative standard deviation (RSD) varied from 2 to 10% (n = 3). The recoveries found in sea water samples ranged from 80 to 107%. In addition, the developed CuO NPs doped phase can be used in hydrophilic interaction chromatography (HILIC), which is the separation mode recommended for highly polar compounds. This has been illustrated using the amino acids tyrosine (log Kow = -2.26) and tryptophan (log Kow = -1.06) as model compounds, being their respective LOD 0.1 and 0.3 µg/mL. Examples of application of the developed bimodal extractive phase to different environmental and waste waters are given in order to show its utility and versatility.