Showing papers in "Analytical Methods in 2010"

Glucosinolates, structures and analysis in food

Abstract: Glucosinolates (GLS) are sulfur rich, anionic secondary metabolites found principally in the plant order Brassicales. This review focuses on identifying the range of GLS structures identified to date and summarises the current state of taxonomic reclassifications of GLS producing plants. Those Brassica species that are available to growers in the UK are highlighted and progress in the aspects of analytical chemistry relevant to conducting accurate determinations of GLS content of foods is reviewed. The degradation and derivatisation workflows that have been utilized for conducting “glucosinolate analysis” are summarized. A review is made of aspects of extraction, isolation, determination of purity, ultraviolet (UV) and mass spectrometry (MS) parameters, extinction coefficients, UV response factors, quantification procedures, and the availability of stable isotope labeled internal standards, and certified reference materials. An electronic database of structures, formulae and accurate masses of both the 200 known, and a further 180 predicted GLS, is provided for use in mass spectrometry.

A wearable electrochemical sensor for the real-time measurement of sweat sodium concentration

Abstract: We report a new method for the real-time quantitative analysis of sodium in human sweat, consolidating sweat collection and analysis in a single, integrated, wearable platform. This temporal data opens up new possibilities in the study of human physiology, broadly applicable from assessing high performance athletes to monitoring Cystic Fibrosis (CF) sufferers. Our compact Sodium Sensor Belt (SSB) consists of a sodium selective Ion Selective Electrode (ISE) integrated into a platform that can be interfaced with the human body during exercise. No skin cleaning regime or sweat storage technology is required as the sweat is continually wicked from the skin to a sensing surface and from there to a storage area via a fabric pump. Our results suggest that after an initial equilibration period, a steady-state sodium plateau concentration was reached. Atomic Absorption Spectroscopy (AAS) was used as a reference method, and this has confirmed the accuracy of the new continuous monitoring approach. The steady-state concentrations observed were found to fall within ranges previously found in the literature, which further validates the approach. Daily calibration repeatability (n = 4) was ±3.0% RSD and over a three month period reproducibility was ±12.1% RSD (n = 56). As a further application, we attempted to monitor the sweat of Cystic Fibrosis (CF) sufferers using the same device. We observed high sodium concentrations symptomatic of CF (∼60 mM Na+) for two CF patients, with no conclusive results for the remaining patients due to their limited exercising capability, and high viscosity/low volume of sweat produced.

Carbon nanofiber based electrochemical biosensors: A review

Abstract: Carbon nanofibers (CNFs), a novel carbon nanomaterial, have the similar conductivity and stability to carbon nanotubes (CNTs). The main distinguishing characteristic of CNFs from CNTs is the stacking of graphene sheets of varying shapes, producing more edge sites on the outer wall of CNFs than CNTs, which can facilitate the electron transfer of electroactive analytes. The unique chemical and physical properties make CNFs exceptional candidates for electrode materials and promising candidates as immobilization substrates. This review is an attempt to give an overview on electrochemical biosensors based on CNFs and their various applications. We discussed the application of CNFs as electrode material in electroanalysis, as well as their functionalization and surface immobilization. Vertically aligned carbon nanofibers (VACNFs) as substrates for the immobilization of biological molecules have also been discussed.

Adaptation of dinitrosalicylic acid method to microtiter plates

Abstract: A microtiter plate adaptation of the well-known dinitrosalicylic acid (DNS) colorimetric method, for measurement of reducing sugars, is described. This method allows a substantial volume reduction of the reagents and a rapid analysis of a large number of samples, having an economic cost benefit and a positive impact on the environment. Therefore, it is well suited as an high-throughput technique for reducing sugars determination.

Detection of apoptosis: A review of conventional and novel techniques

Abstract: Apoptosis, or programmed cell death, has been shown to play a role in a number of diseases, including heart disease and cancer. Apoptosis is also a vital cellular process that helps to regulate tissue growth, fetal development, immune response, and a host of other biological processes. Deviation from the careful regulation of apoptosis is responsible for a host of diseases and health concerns. As such, understanding the process of apoptosis is vital for therapy development. Over the years, a number of methods have been discovered and developed to detect apoptosis. There are several standard techniques such as electron microscopy, the TUNEL assay, and flow cytometry. In addition, new techniques are quickly emerging, such as microfluidic devices, single molecule spectroscopy, and electrochemical methods. This review will cover some examples of the most common techniques as well as some new techniques in order to show the broad spectrum of methods available to detect apoptosis in cells.

Microfluidic colourimetric chemical analysis system: application to nitrite detection.

Abstract: The design, fabrication, analysis and characterisation of a continuous flow, microfluidic absorption cell and detection system is described. A low cost optical illumination and detection method is integrated with a simple microfluidic system. Nitrite is detected at nM concentration using the Griess reaction. The device is based on a novel optical absorption scheme with microfluidic channels made from tinted PMMA. An absorbance path length of 25 mm enables nitrite to be detected from 50 nM to 10 μM with a limit of detection of 14 nM. The system was used to characterise the reaction kinetics and maximum sample resolution. In this report the system is used to detect nitrite, but it could equally be used to assay a range of different chemistries using colourimetric methods. The system provides a cost-effective, simple system that could be deployed in a range of scenarios for environmental monitoring.

Trends in process analytical technology

Abstract: Since the promotion of Process Analytical Technology (PAT) by the U.S. Food and Drug Administration (FDA), there has been a flurry of activities happening across related fields. This excitement permeates regulatory agencies, professional societies, academia and industry worldwide. This review surveys the PAT related developments that have taken place in the period 2004–2009. It serves as an introduction to PAT, with highlights on the parallel advances and convergence points across various fields and applications. From this review, five common threads are identified from the underlying trends of the recent global PAT endeavor, namely, organisational objectives, enabling sciences, economic outlook, collaborative efforts and emerging trends. There are also six potential gaps that require further efforts to bridge. The overall PAT venture is promising for delivering an integrated systems approach for quality design, process analyses, understanding and control, continuous improvement, knowledge and risk-based management within the FDA 21st century pharmaceuticalcGMP initiative.

Simultaneous determination of dihydroxybenzene isomers using disposable screen-printed electrode modified by multiwalled carbon nanotubes and gold nanoparticles

Abstract: A disposable electrode, modified with multiwalled carbon nanotubes (MWCNTs) and gold nanoparticles (AuNPs), was developed to serve as a sensor for the simultaneous determination of dihydroxybenzene isomers (hydroquinone, catechol and resorcinol). The modified electrode was fabricated by electrodepositing AuNPs on a MWCNTs decorated screen-printed electrode (SPE), then it was characterized in morphology and electrochemical properties and utilized to determine the isomers of dihydroxybenzene in water samples. Compared with bare SPE, AuNPs-modified SPE, and MWCNTs-modified SPE, the fabricated SPE has much stronger electrocatalytic activity for the oxidation of dihydroxybenzenes with the increase of the peak current and the decrease of the potential difference (△Ep) between the anodic and cathodic peaks. By using differential pulse voltammetry (DPV), the three isomers can be determined simultaneously and sensitively at the modified SPE. For hydroquinone, catechol and resorcinol, the oxidation peak currents are linear to the concentrations at the range of 2.0 × 10−6∼7.3 × 10−4 M, 2.0 × 10−6∼7.3 × 10−4 M and 3.0 × 10−6∼9.6 × 10−4 M with the detection limits of 3.9 × 10−7 M, 2.6 × 10−7 M and 7.2 × 10−7 M, respectively. Moreover, a rapid on-filed determination is convenient to be performed at this disposable modified SPE incorporated in a portable electrochemical system. These results reveal that the presented sensor can be used for the simultaneous and sensitive on-field determination of dihydroxybenzene isomers.

In situ Raman and IR spectroscopic analysis of indigo dye

Abstract: Non-destructive analysis of indigo dye in biological and textile samples is presented. Using different but complementary techniques of vibrational spectroscopy (FT-Raman and ATR-IR) detection of indigo in various samples is performed. This work shows the possibility of both vibrational analytical methods to identify indigo directly in plant tissue, commercially available pigments and cotton and silk textiles. The experimental work is supported by quantum-chemical calculations at the B3LYP/6-311++g(d,p) level of theory. Additionally, in order to follow the process of indigo formation upon leaf drying Raman mapping of Polygonum tinctorium is demonstrated.

A novel antioxidant assay of ferric reducing capacity measurement using ferrozine as the colour forming complexation reagent.

Abstract: Since antioxidants are health-beneficial compounds capable of removing reactive species, assay of total antioxidant capacity (TAC) by simple and low-cost methods is important. The magenta-coloured iron(II)-ferrozine (Fe(II)-FZ) complex showing an absorbance maximum at 562 nm has previously been utilized for iron-binding assays, but not for antioxidant determination. Ferrozine is a highly ferrous-stabilizing ligand such that ferric ion in the presence of ferrozine easily oxidizes antioxidants and is itself reduced to Fe(II)-FZ, yielding a very high molar absorptivity and thus enhanced sensitivity for most antioxidants. The hierarchic order of antioxidant power for common antioxidants was in accordance with known structure–activity relationships. The Fe(III)-FZ assay was applied to synthetic antioxidant mixtures to yield additive absorbance values, which is a prerequisite for precise determination of antioxidant capacity of complex mixtures. The calibration curves (lines) of trolox and quercetin individually and in herbal infusions—by using the method of standard additions—were parallel, confirming that the herbal antioxidants and trolox did not chemically interact among each other so as to cause apparent deviations from Beer's law. The proposed method was applied to medicinal plant infusions for total antioxidant capacity assay as trolox-equivalents, and the results were compared to those found with CUPRAC (cupric reducing antioxidant capacity), FRAP (ferric reducing antioxidant power) and Folin total phenols assays, the highest correlation being achieved with CUPRAC. In short, a novel ferric reducing assay for food antioxidants was introduced, which was superior to FRAP in regard to its realistic pH, enhanced sensitivity, faster kinetics, and absence of free Fe(II)—which can cause Fenton-type oxidations—in the reaction products.

Recent advances in on-line multidimensional liquid chromatography

Abstract: Multidimensional liquid chromatography (MD LC) has, due to enhanced peak capacity compared to one-dimensional LC, become an important analytical tool for separating components in complex samples, e.g. in proteomics. MD LC can be performed both on-line and off-line. Because of the advantages like possible automation and minimal sample loss, on-line MD LC has appeared to be very attractive also for high throughput analysis. This review includes only on-line coupled MD LC. Different aspects related to the compatibility of separation principles and column dimensions are highlighted and recent applications using on-line mainly two-dimensional (2D) LC have been included.

Detection of biomolecules from solutions with high concentration of salts using probe electrospray and nano-electrospray ionization mass spectrometry

Abstract: Probe electrospray ionization (PESI) is a recently developed ionization technique which uses a solid needle or wire as sampling probe and ESI emitter instead of capillary. PESI is free from the clogging problem and it has high tolerance to salts and urea. We present herein a comparative study of the probe electrospray ionization (PESI) and nano-electrospray ionization (nano-ESI) for the measurement of biomolecules in the sample solutions with high concentrations of salts and urea. Our results show that PESI could provide equivalent ionization performance with nano-ESI, and in certain cases it could be superior to nano-ESI for the samples with high concentration (>100 mM) of salts and urea. Therefore, PESI can be useful for the direct analysis of cell/tissue extracts and protein digestion without or reduced procedures in sample purification.

Multivariate calibration methods in near infrared spectroscopic analysis

Abstract: Near infrared (NIR) spectroscopy has been demonstrated as a powerful technique for both qualitative and quantitative analysis of complex systems in various fields. Calibration, however, is one of the important techniques needed to ensure the quality and practicability of the analyses. In this mini-review, recent developments in multivariate calibration methods for NIR spectroscopic analysis, including non-linear approaches and ensemble techniques, are briefly summarized. The advantages and disadvantages of these methods are compared and discussed critically.

Ochratoxin A nanostructured electrochemical immunosensors based on polyclonal antibodies and gold nanoparticles coupled to the antigen

Abstract: Competitive electrochemical immunosensors, based on disposable screen-printed electrodes (SPCEs), have been developed for the determination of the mycotoxin ochratoxin A (OTA). Two indirect immunoassays schemes were assessed using polyclonal antibodies and through the physical adsorption of OTA conjugated to albumin from bovine serum (OTA-BSA) and newly synthesized OTA-BSA bound to gold nanoparticles (OTA-BSA-AuNPs) onto the working electrode surface. After the competition step, detection was facilitated by a secondary aIgG antibody labelled with alkaline phosphatase and differential-pulse voltammetry using α-naphtyl-phosphate as substrate. The performance of the optimized immunosensors in terms of sensitivity, reproducibility and selectivity was studied. The linear working range of the described biosensors ranged between 0.9 and 9.0 ng mL−1 for the OTA-BSA based immunosensor and between 0.3 and 8.5 ng mL−1 for the gold nanostructured immunosensor, with a limit of detection (LOD) equal to 0.86 ng mL−1 (RSD = 10.6%) and 0.20 ng mL−1 (RSD = 8.0%) of OTA, respectively. The nanostructured immunosensor was applied to a certified wheat standard and a non-contaminated wheat material spiked with OTA, obtaining recoveries from about 104 ± 0.07% to 107 ± 0.08%. The influence of the wheat matrix on the analytical performance of the immunoassay was also studied.

Ultra-sensitive detection of heavy metal ions in tap water by laser-induced breakdown spectroscopy with the assistance of electrical-deposition

Abstract: The trace heavy metal ions in tap water were electrically deposited on the surface of a high purity aluminium rod and then analyzed with laser-induced breakdown spectroscopy (LIBS). Cr3+, Mn2+, Cu2+, Zn2+, Cd2+ and Pb2+ in tap water samples were quantitatively analyzed and the calibration curves have been built up within the concentration range of 1–1000 μgL−1. The limits of detection of these ions were determined to be 0.16–1.35 μgL−1, which are improved 5–6 orders than directly analyzing aqueous solutions by LIBS. The influence of Ca2+ and Mg2+ in water at different concentrations to the quantitative analysis of trace heavy metal ions was evaluated. It is possible to realize reliable quantitative analysis by using different calibration curves according to the hardness of the analyzed water samples. LIBS plus electrochemical enrichment is a potential approach to high sensitivity detection of trace heavy metal ions in tap water and natural water samples, and it will find applications in environmental pollution monitoring.

Analysis of five benzophenone -type UV filters in human urine by liquid chromatography-tandem mass spectrometry

Abstract: Benzophenone (BP)-type UV (ultraviolet) filters, especially 2-hydroxy-4-methoxybenzophenone (2OH–4MeO–BP), are widely used in the US, to protect the skin and hair from UV irradiation Despite human exposures to UV filters through the dermal application of products containing sunscreen agents, few studies have examined the occurrence of UV filters in humans Thus far, few sensitive methods are available for the determination of 2OH–4MeO–BP in human urine Furthermore, methods for the determination of other BP derivatives, including 2,4-dihydroxybenzophenone (2,4OH–BP), which is formed from 2OH–4MeO–BP via metabolic activities of the cytochrome P450 enzymes, have not been available In this study, we have developed a method for the analysis of five BP derivatives: 2OH–4MeO–BP, 2,4OH–BP, 2,2′-dihydroxy-4-methoxybenzophenone (2,2′OH–4MeO–BP), 2,2′,4,4′-tetrahydroxybenzophenone (2,2′,4,4′OH–BP), and 4-hydroxybenzophenone (4OH–BP) in human urine, using liquid–liquid extraction and liquid chromatograph (LC)-tandem mass spectrometer (MS/MS) analysis The instrumental calibration range for each of the BP derivatives ranged from 005 to 100 ng ml−1, and showed excellent linearity (r > 099) The respective limits of detection (LODs) and limits of quantification (LOQs) were determined to be 0082 and 028 ng ml−1 for both 2,4OH–BP and 4OH–BP; 013 and 044 ng ml−1 for 2,2′OH–4MeO–BP; and 028 and 090 ng ml−1 for both 2OH–4MeO–BP and 2,2′,4,4′OH–BP Recoveries of BP derivatives through the entire analytical procedure were between 852 and 996% The coefficients of variation (CVs) of five replicate analyses within 1 day, and across 5 days, were respectively 14 and 37% for 2,4OH–BP; 17 and 30% for 2OH–4MeO–BP; and 28 and 45% for 4OH–BP When BP derivatives were determined in urine samples from 23 US (Albany, New York) and 22 Japanese (Matsuyama, Ehime) volunteers, higher concentrations of 2,4OH–BP, 2OH–4MeO–BP, and 4OH–BP were found in samples collected from females in the Albany cohort, probably reflecting great usage by US females The urine sample from a known sunscreen user contained very high concentrations of 2,4OH–BP and 2OH–4MeO–BP 2,2′,4,4′OH–BP and 2,2′OH–4MeO–BP were not detected in any of the urine samples analyzed Our results indicate considerable exposure to highly estrogenic 2,4OH–BP and 2OH–4MeO–BP by females in the US, and suggest the need for further studies on potential health effects

Simultaneous colorimetric determination of dopamine and ascorbic acid based on the surface plasmon resonance band of colloidal silver nanoparticles using artificial neural networks

Abstract: A new method for simultaneous determination of dopamine (DA) and ascorbic acid (ASC) is proposed. The method is based on the reaction of dopamine and ascorbic acid with the oxidizing agent (silver nitrate) in the presence of PVP (as a stabilizer) and the formation of silver nanoparticles in a slightly basic medium. Spectrophotometry is used to monitor the changes of the surface plasmon resonance (SPR) band at a maximum wavelength of silver nanoparticles (440 nm) vs. time. Three-layered feed-forward artificial neural networks (ANN) trained by back propagation learning algorithm is used to model the relationship between absorbance and concentration to quantify analyte in mixtures under optimum conditions. Sigmoidal and linear transfer functions were used in the hidden and output layers, respectively. Linear calibration graphs were obtained in the concentration range of (3.2 × 10−6 – 2.0 × 10−5 mol L−1) for DA and (2.0 × 10−6 – 4.8 × 10−5mol L−1) for ASC. The detection limits were 8.0 × 10−7 and 6.2 × 10−7 mol L−1 for DA and ASC, respectively, which are comparable by different spectrophotometric and colorimetric methods. The method was applied successfully to the determination of dopamine (DA) and ascorbic acid in human serum samples.

Ionic liquids in the assay of proteins

Abstract: As a group of novel green solvents, ionic liquids have attracted extensive attention and gained popularity in various applications including protein assays. Ionic liquids are not only an excellent reaction medium to replace the conventional organic solvents, but are also an efficient participant to achieve better performances. The aim of the present mini-review is to illustrate the state-of-the-art progress of implementing ionic liquids in protein assays, focusing on the investigations of protein stability/activity, protein extraction and isolation/purification, protein crystallization, separation of protein species and their detections.

Electrochemical determination of oxalic acid using palladium nanoparticle-loaded carbon nanofiber modified electrode

Abstract: We have developed a novel electrochemical oxalic acid (OA) sensor based on the palladium nanoparticle-loaded carbon nanofiber (Pd/CNF) composites. These composites with large amounts of spherical nanoparticles well dispersed on the carbon nanofibers (CNF) were produced by combination of electrospinning technique with thermal treatment method. When applied to oxidation of OA, the Pd/CNF modified carbon paste electrode (Pd/CNF-CPE) exhibited high electrocatalytic performances with fast voltammetric responses and notably decreased overpotential compared to the bare and even the CNF modified CPE. A detection limit of 0.2 mM with linear ranges of 0.2–13 mM and 13–45 mM can be obtained at the Pd/CNF-CPE. Based on its high sensitivity and good selectivity, the proposed method was applied to determination of OA in spinach, and the satisfactory results confirmed the applicability of this sensor in practical analysis.

Microwave-assisted digestion in closed vessels: effect of pressurization with oxygen on digestion process with diluted nitric acid

Abstract: The efficiency of diluted nitric acid solutions under oxygen pressure for decomposition of bovine liver was evaluated using microwave-assisted wet digestion. Calcium, Cu, Fe, Mg, Mn and Zn were determined by inductively coupled plasma optical emission spectrometry (ICP OES). Efficiency was evaluated by determining the residual carbon content (RCC) by ICP OES and residual acidity in digests. Samples (up to 500 mg) were digested using nitric acid solutions (0.1, 0.5, 1, 2, 3, 7, and 14 mol L−1 HNO3) and the effect of oxygen pressure was evaluated using pressures of 0.5, 1, 1.5 and 2 MPa. It was demonstrated that 2 and 0.5 mol L−1 nitric acid solutions may be used for efficient digestion of 500 and 100 mg of bovine liver, respectively, with oxygen pressures ranging from 0.5 to 2 MPa. Using these conditions, less than 0.86 and 0.21 mL of concentrated nitric acid were necessary to digest 500 and 100 mg of sample, respectively. Similar digestion efficiencies for both conditions were obtained under pressures of O2 ranging from 0.5 to 2 MPa. The residual acidities in final digests were lower than 24% when compared to the initial amount of acid used for digestion. The accuracy of the proposed procedure was evaluated using certified reference materials of bovine liver and bovine muscle. Using a solution of 2 mol L−1 with oxygen pressure of 0.5 MPa for 500 mg of sample, the agreement with certified values ranged from 96 to 105% (n = 5). Using the proposed procedure with diluted nitric acid it was possible to obtain RCC values lower than 15% that is important for minimizing the generation of laboratory residues and improving limits of detection.

Energy transfer with gold nanoparticles for analytical applications in the fields of biochemical and pharmaceutical sciences

Abstract: Gold nanoparticles (AuNPs) are the most interesting nanomaterials for analytical purposes owing to their unique optical and electrochemical properties resulting from the localized surface plasmon resonance (LSPR) of the electrons, displaying strong absorption and scattering of light from visible to near-infrared region by tuning the particles sizes and shapes. In fluorescence resonance energy transfer (FRET) process, AuNPs have been identified to act as excellent acceptors to replace traditional organic quenchers. Starting from quenching advantages of AuNPs in FRET system and energy transfer mechanism of donor to AuNPs, herein we try to summarize and discuss typical AuNPs based FRET methods in terms of DNA hybridizations, immunoreactions, specific molecular bindings or adsorptions, and provide their analytical applications in biochemical and pharmaceutical analysis.

Application of dispersive liquid–liquid microextraction combined with sweeping micellar electrokinetic chromatography for trace analysis of six carbamate pesticides in apples

Abstract: A rapid and sensitive method for the multiresidue analysis of six commonly used carbamate pesticides in apples was developed by using dispersive liquid–liquid microextraction (DLLME) coupled with sweeping micellar electrokinetic chromatography (MEKC). Parameters that affect the extraction and sweeping efficiency, such as the kind and volume of the extraction and disperser solvent, extraction time, salt addition, sample matrix and concentration of organic modifiers in the separation buffer were investigated and optimized. Under optimized conditions, the enrichment factors were achieved in the range from 491 to 1834. The linearity of the method for methiocarb, diethofencarb, carbaryl and isoprocarb was in the range of 6–500 ng g−1, and for fenobcarb and tsumacide in the range of 9–500 ng g−1, with the correlation coefficients (r) ranging from 0.9952 to 0.9990. The limits of detection (LODs) at a signal-to-noise ratio of 3 ranged from 2.0 to 3.0 ng g−1. The recoveries of the six carbamates for apple samples at spiking levels of 20.0 and 100.0 ng g−1 were 85.5–108.1% and 85.4–113.3%, respectively. The proposed method has been successfully applied to the analysis of the target carbamate residues in apple samples with satisfactory results.

Chemically bonded maltose via click chemistry as stationary phase for HILIC

Abstract: A HILIC stationary phase was synthesized through bonding maltose on silica particles via click chemistry. A set of representative polar compounds including sugars, amino acids and small peptides were employed to evaluate chromatographic properties of Click Maltose. The results illustrated the surface adsorption mechanism from the direct hydrogen bonding interaction between sugars and Click Maltose played an important role on retention behavior of sugars under HILIC mode. The chromatographic behavior of anions on Click Maltose was consistent with HILIC/WAX mechanism, while the retention of cations was depended on electrostatic repulsion-hydrophilic interaction chromatography (ERLIC) mechanism. The Click Maltose stationary phase was successfully used in the separation of standard samples of polar compounds and complex samples of oligosaccharides from the natural product. The Click Maltose also exhibited good reproducibility and stability, which were helpful to further application. Our study confirmed the advantages and application potential of bonded oligosaccharides for HILIC separation.

A practical method for determination of molybdenite Re-Os age by inductively coupled plasma-mass spectrometry combined with Carius tube-HNO3 digestion

Abstract: A simplified method for the determination of molybdenite Re-Os ages using inductively coupled plasma-mass spectrometry (ICP-MS) is presented. By the means of Carius tube method, molybdenite and pyrite were digested using concentrated HNO3, and were then changed into MoO3 and Fe(NO3)3 precipitates, respectively. Rhenium was determined directly by ICP-MS after removal of Os by heating for the molybdenite supernatant or by cation-exchange purification for the pyrite supernatant. Osmium distilled as OsO4 from the supernatant was trapped using pure water and could be directly analyzed by ICP-MS. This method was validated using two molybdenite reference materials, GBW 04435 and GBW 04436, and their Re-Os ages obtained are 220.3 ± 1.1 Ma (1.0%, 2s), and 140.5 ± 0.9 Ma (1.2%, 2s), respectively, consistent with literature values. The proposed Re-Os dating method was applied to molybdenite and pyrite sampled from a porphyry Mo-deposit. The results show that this deposit is the oldest Mo-deposit so far found in China.

Extraction of environmental pollutants using magnetic nanomaterials

Abstract: Magnetic nanomaterials are particularly useful for extracting and enriching a large volume of target analytes because they provide high surface-to-volume ratio, easy surface modification, and strong magnetism. This review summarizes the recent advance in synthesis, modification, and application of magnetic nanomaterials for the preconcentration of environmental pollutants. The extraction of environmental pollutants with magnetic nanomaterials is generally based on hydrophobic interaction, electrostatic attraction, and/or covalent bonding formation. Environmental pollutants adsorbed on the surface of nanomaterials are released by exchanging ligands, adjusting pH, or adding organic solvent. The liberated environmental pollutants are commonly detected by gas chromatography, high-performance liquid chromatography, and inductively coupled plasma-optical emission spectrometry. The basic principle of each nanomaterial and its advantages for the extraction of environmental pollutants are discussed in this review.

Chromatographic analysis of major non-structural carbohydrates in several wood species – an analytical approach for higher accuracy of data

Abstract: The exact and reliable determination of non-structural carbohydrates (NSC) in wood samples of different origin allows to gain further insight into the biogeochemical carbon cycle, i.e. processes that determine how carbon – and carbon dioxide – migrate between the land, the sea and the atmosphere. Plants are an essential part of this cycle using carbon dioxide in photosynthesis and locking up carbon within proteins and carbohydrates. Analytical determination of NSC is complicated by the complexity of the carbohydrate mixtures. However, most of them are present at the trace level only, and do not substantially contribute to the global NSC. Most important are glucose, sucrose, fructose and starch. Traditionally, these carbohydrates are analyzed spectrophotometrically. The spectrophotometric method does not provide any information on concentrations of sugar alcohols and raffinose. They can make up to a quarter of total NSC in deciduous tree samples. Consequently, ignoring them will severely impair the accuracy of NSC data in these samples. We will therefore present a method that allows the reliable determination of the following sugar alcohols and carbohydrates: inositol, sorbitol, mannitol, glucose, fructose, sucrose, raffinose and starch. These were the major contributors to the pool of non-structural carbohydrates in the samples we examined. It is important to note, that the portion of sugar alcohols and raffinose in the samples ranged from <2–25% of total NSC, irrespective of the plant species, with strongest impact (≥15% of NSC) for the conifer species “Pine” and the deciduous species “Ash Tree” and “Wild Cherry”. Application of our method substantially improved the accuracy of NSC data in these samples if compared to those of the spectrophotometrical analysis.

Indirect determination of sulfide ions in water samples at trace level by anodic stripping voltammetry using mercury film electrode

Abstract: A simple and sensitive indirect determination method for sulfide in water samples by anodic stripping voltammetry (ASV) using mercury-film electrode (MFE) has been developed, which is based on the determination of residual cadmium ion after reaction of Cd2+ with S2−. The linear range is adjustable depending on Cd2+ concentration, for example, the determination of S2− can be achieved in the range of 1.5–7.0 × 10−6 mol L−1 by selecting 3.0 × 10−6 mol L−1 Cd2+. The detection limit is 1.3 × 10−8 mol L−1 under optimum conditions, and the relative standard deviation (RSD, n = 10) for 2.0 × 10−6 mol L−1 S2− is 0.7%. Compared with other methods, this method has the following prominent advantages: with low detection limit, easy to operate and less interference. The proposed method has been successfully applied to the determination of S2− in synthetic wastewater, lake water, beverage, spring water and real wastewater samples.

Sol-Gel-Au nano-particle modified carbon paste electrode for potentiometric determination of sub ppb level of Al(III)

Abstract: This work describes a new carbon paste electrode modified by Sol-Gel-Au nano-particle (SGAN) in the presence of 2,2′-dihydroxy-1-naphthylidine-1′-naphthyl methyl amine (DNMA) as ionophore for determination of Al(III) by potentiometric method. Gold nano-particles (GNPs) were self-assembled onto silica Sol-Gel network and incorporated within carbon paste. The nano-structured matrix with DNMA shows well-defined potentiometric behavior for the determination of Al3+ in aqueous solutions. The sensor exhibits significantly enhanced selectivity toward Al3+ ions over a wide concentration range of 5.0 × 10−10 to 5.0 × 10−2 M with a lower detection limit of 2.0 × 10−10 M (0.054 ppb) and a Nernstian slope of 20.0 ± (0.1) mV decade−1 of Al3+ activity. It has a fast response time of 5 s and can be used for at least 70 days without any considerable divergence in potentials. The potentiometric response of the electrode is independent of pH of test solution in the pH range 3–7. The interaction between DNMA and Al3+ was studied spectrophotometrically and it exhibits that stoichiometry of complex is 1 : 1 in methanol solution. Finally, this electrode was successfully used as an indicator electrode for potentiometric determination of Al3+ in some real samples.

Determination of cytokinins in plant samples by polymer monolith microextraction coupled with hydrophilic interaction chromatography-tandem mass spectrometry

Abstract: In this study, a sensitive assay of cytokinins was developed using polymer monolith microextraction/hydrophilic interaction chromatography/electrospray ionization-tandem mass spectrometry (PMME/HILIC/ESI-MS/MS). The extraction was realized on a poly(2-acrylamido-2-methyl-1-propanesulfonic acid-co-ethylene dimethacrylate) (poly(AMPS-co-EDMA)) capillary monolith and the subsequent separation was carried out on a Luna silica column. Several parameters of PMME and HILIC were optimized to obtain the optimum results. After optimizing the extraction conditions, 10 mM ammonium formate of pH 2.5 was chosen as the matrix solution to obtain the highest extraction efficiency. The MS sensitivity for cytokinins investigated could be enhanced 3-fold by the use of hydrophilic interaction chromatography with the mobile phase of 85% acetonitrile with 0.01% (v/v) formic acid and 15% water with 0.01% (v/v) formic acid, when compared to the use of conventional reversed phase liquid chromatography (RPLC). Good linearities were obtained for five cytokinins with correlation coefficients (R2) > 0.9962. The LODs (S/N = 3) for the targets were found to be 0.0028–0.068 ng mL−1. Reproducibility of the method was obtained with intra-day and inter-day relative standard deviations (RSDs) less than 12.7% and the recoveries in plant samples ranged from 70.3% to 113.3%. The method was applied to the determination of cytokinins in Oryza sativa, Arabidopsis thaliana and oil seed rape tissues.

Quantitative NMR spectroscopy for the rapid measurement of methylglyoxal in manuka honey

Abstract: The accurate and rapid measurement of methylglyoxal in honey at concentrations applicable to those found in manuka honey using qNMR is reported. The qNMR method gave comparable results to those obtained by derivatisation of methylglyoxal with ortho-phenylenediamine and subsequent LC-MS or LC-UV detection. Uniquely, the qNMR method is performed directly on the diluted honey without chromatographic separation, sample derivatisation or generation of a calibration series.