Analytical Methods (v.11, #31)

Front cover (3923-3923).

Inside front cover (3924-3924).

Contents list (3925-3930).

Herein, a mitochondria-targeted ratiometric fluorescent probe for SO2 was proposed based on the FRET coumarin–phenylchromenylium dyad. The probe showed two distinct emission bands centered at 485 and 650 nm. Upon exposure to SO2, the acceptor emission was inhibited, and a significant enhancement in donor fluorescence was simultaneously induced; this resulted in a satisfactory ratiometric fluorescence signal. Importantly, the probe was biocompatible and successfully applied to monitor SO2 in live HeLa cells and zebrafish.

Fast determination of oxide content in cement raw meal using NIR spectroscopy with the SPXY algorithm by Zhenfa Yang; Hang Xiao; Lei Zhang; Dejun Feng; Faye Zhang; Mingshun Jiang; Qingmei Sui; Lei Jia (3936-3942).
NIR spectroscopy combined with the partial least squares (PLS) algorithm has been investigated to yield a new analytical method for the fast determination of CaO, SiO2, Al2O3 and Fe2O3 in cement raw meal samples in the process of cement production. An improved algorithm based on Kennard–Stone (KS), named sample set partitioning based on joint x–y distance (SPXY), which takes into account both x (spectral variables) and y (chemical values) spaces, was applied to divide cement raw meal samples into calibration and prediction subsets, and the effect of SPXY was compared with that of random sampling (RS), KS and Duplex. Optimal predictions were obtained in most cases with the SPXY method, and the average prediction errors were 0.1430%, 0.1206%, 0.0667% and 0.0306% for CaO, SiO2, Al2O3 and Fe2O3, respectively, showing that the calibration subset selected by the SPXY method is superior to that of the other three methods, and NIR spectroscopy coupled with SPXY and PLS algorithms can achieve rapid and accurate determination of oxide content in cement raw meal samples.

We have revisited the large volume sampling (LVS) technique and its analytical methodologies to develop and validate (step by step) a home-made solid-phase extraction (SPE) system (Amberlite® XAD-2 resin-based) connected to a particle collector in situ pump (McLane WTS-LV04) for high sample pre-concentration and determination of chemical contaminants (e.g. aliphatic and aromatic petroleum hydrocarbons) and their 13C/12C isotope ratio. The SPE laboratory extraction/elution procedure was newly adapted from the Bligh and Dyer method to facilitate the removal of the residual water derived from the sampling. The comprehensive sampling and analytical method was validated in the framework of a “top-down” single-laboratory approach using coastal seawater samples. In the dissolved phase of seawater, full quantitative validation was achieved for semi-volatile polycyclic aromatic hydrocarbons (PAHs; from naphthalene to methylpyrene) by gas chromatography mass spectrometry (GC-MS). The LVS approach was also validated for performing compound-specific stable 13C/12C ratio measurements by gas chromatography (combustion) isotope ratio mass spectrometry (GC-C-IRMS). Overall, both the long field sampling and analytical operational times, as well as the blank levels and interference from resins might restrict this LVS technique as a routine procedure for monitoring contaminants in seawater, but for research and non-routine measurements it will still be the state of the art to investigate and trace unknown chemical contaminants in deep sea marine environments.

A simple camphor based AIE fluorescent probe for highly specific and sensitive detection of hydrazine and its application in living cells by Yan Zhang; Zhonglong Wang; Jie Song; Mingxin Li; Yiqin Yang; Xu Xu; Haijun Xu; Shifa Wang (3958-3965).
In this work, a novel fluorescent probe CDA, which was synthesized via a facile derivatization from natural and renewable camphor, exhibited aggregation-induced emission (AIE) characteristics in mixed aqueous media. The fluorescent aggregates showed an obviously enhanced fluorescence response toward N2H4. The response time of CDA aggregates for detecting N2H4 was within 20 s, and the detection limit was 2.26 ppb, which was far lower than the U.S. Environmental Protection Agency (EPA) standard (10 ppb). Moreover, probe CDA was also applied to detect gaseous and aqueous N2H4. Additionally, the cell imaging experiments demonstrated that probe CDA could be employed to visualize N2H4 in living organisms.

Metal-conducting polymer hybrid nanoparticles (NPs), due to the synergistic effect of metal NPs and polymers, have attracted significant attention and shown versatile applications. In this work, we proposed a simple and quick method for the synthesis of (Au nanorod (NR)@Ag)–polyaniline (PANI) Janus nanoparticles (JNPs) with the use of a droplet-based microfluidic platform. Precise control of droplet volumes and reliable manipulation of individual droplets during synthesis enabled the (AuNR@Ag)–PANI JNPs to possess excellent dispersion and uniform size. Moreover, the reaction time for the fabrication of the (AuNR@Ag)–PANI JNPs was largely shortened with such a microfluidic platform. The application of the prepared (AuNR@Ag)–PANI JNPs, which can act as a surface enhanced Raman scattering (SERS) sensor, for the detection of Hg2+ ions with high sensitivity and good selectivity was demonstrated. This SERS nanosensor displayed a fairly good response to Hg2+ ions over other possible interfering metal cations, owing to the strong binding affinity between PANI and Hg2+ ions and causing an increase in the Raman intensity of PANI. A good linear relationship between the Raman intensity increment of PANI and Hg2+ ion concentration was obtained in the range of 1–150 nM, and the detection limit of Hg2+ ion concentration was 0.97 nM. Besides, the (AuNR@Ag)–PANI-based SERS nanosensor was successfully applied to the detection of Hg2+ ions in real water samples. Thus, a facile route for the fabrication of (AuNR@Ag)–PANI JNPs by using a droplet-based microfluidic platform is presented, which have been employed to determine Hg2+ ions in combination with SERS spectroscopy. We envision that such a droplet-based microfluidic synthesis strategy can provide a new insight into the design and fabrication of novel NPs, which may be applied in various fields, such as catalysis, photovoltaics, bioscience, and environmental science.

An electrostatic self-assembly route to prepare C-dots/gold nanoclusters for dual-emission ratiometric optical thermometry in living cells by Yunxiao Jia; Xiaojie Zhang; Chunxia Yin; Xun Zhang; Jiaping Zhang; Xinwai Wang; Jingwei Xin (3974-3980).
It is of great significance to construct fluorescence-based nanothermometers via a convenient method. Herein, based on the opposite surface charges of carbon dots (CDs) and gold nanoclusters (Au NCs), a simple and facile self-assemble strategy was developed to obtain the CD/Au NC fluorescent hybrid nanomaterials via electrostatic interactions. At the excitation of 380 nm, the hybrid nanomaterials displayed a typical dual-emission behavior (455 nm and 600 nm). Because of the different thermal sensitivities of CDs and Au NCs, the dual-emission nanomaterials achieved the colorimetric detection of temperature in the range from 20 °C to 80 °C and showed high reproducibility. Furthermore, by taking advantage of the high stability and biocompatibility, the CD/Au NC fluorescent hybrid nanomaterials were further applied to achieve intracellular temperature detection. We expect that this dual-emission fluorescent nanothermometer will be a promising candidate for intracellular imaging and temperature sensing at the subcellular level.

A differential extended gate-AlGaN/GaN HEMT sensor for real-time detection of ionic pollutants by Lei Zhao; Xinsheng Liu; Bin Miao; Zhiqi Gu; Jin Wang; HuoXiang Peng; Jian Zhang; Bin Zeng; Jiadong Li (3981-3986).
In this study, we propose a differential extended gate (DEG)-AlGaN/GaN high electron mobility transistor (HEMT) sensor to detect ionic pollutants in solution. The DEG-AlGaN/GaN HEMT sensor consists of two extended gate sensing units, which combine the differential method with the extended gate structure. Ionic pollutant Fe3+ is used to test the feasibility of the device. Compared to the conventional AlGaN/GaN HEMT sensor, DEG-AlGaN/GaN HEMT sensors can effectively reduce the effect of noise factors and successfully improve the detection limit to 10 fM. At the same time, the DEG sensor shows that Fe3+ can be detected in a wide range of concentrations, varying from 10 fM to 100 μM, and it shows better linearity (R2 = 0.9955) than the conventional AlGaN/GaN HEMT sensor. These results demonstrate that the unique DEG design can overcome the drawbacks of the conventional AlGaN/GaN HEMT sensor, and significantly improve the overall performance of the AlGaN/GaN HEMT sensor. As a result, this novel sensor has the potential to be a real-time and high-performance test tool for environmental monitoring.

The manufacturing of conventional electroless-based sensors often suffers from mechanical instability leading to irreversible changes in the sensor architecture and morphology resulting in insufficient signal reproducibility and overall degradation of the system. In addition, understanding the transduction mechanisms is a key aspect in the development of crucial sensing technologies. Therefore, the development of tools and analytical approaches that could allow us to gain deeper insight into the operating processes or validation of the design would significantly accelerate the progress in the field of sensors. Herein, we present a novel effective strategy for non-destructive control and validation of sensors consisting of hybrid silicon nanowires deposited with gold nanoparticles (AuNPs/SiNWs) produced via a hydrofluoric acid-assisted electroless fabrication method. To validate the fabrication method and to monitor the deposition rates of hydrofluoric acid-assisted deposition of AuNPs on SiNWs, specific analytical protocols for high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) and electron microscopy (SEM/TEM) were developed. Moreover, HR-ICP-MS was used for the non-destructive monitoring of the impact of experimental conditions on the quality of the synthesized hybrid nanostructures. Thus, the impact of certain synthesis conditions, viz. acid ratio, deposition time and surface pretreatment, on the deposition rates, morphology and stability of the prepared AuNPs/SiNWs hybrid structures was investigated in detail. The obtained knowledge based on nanoanalytical studies was applied to develop hybrids with a reproducible surface morphology, homogenous AuNPs distribution and stable attachment to the SiNWs surface to be implemented as reliable substrates for surface enhanced Raman scattering (SERS).

Herein, a simple, fast and reliable method based on vortex-assisted solid-phase extraction (VA-SPE) followed by flame atomic absorption spectrometry was developed for the simultaneous preconcentration and trace detection of cadmium and lead. Nano-sized clinoptilolite as a natural zeolite was modified with 5(p-dimethylaminobenzylidene) rhodanine and used as an adsorbent in the VA-SPE procedure. The modification process was assisted by the preliminary formation of a nano clinoptilolite-ZnO composite. The adsorbent was characterized by various techniques including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Under optimized conditions, the adsorbent exhibited good sorption potential as compared to nano clinoptilolite and nano clinoptilolite–ZnO composite. The calibration curves were linear in the range of 5–100 and 20–120 ng mL−1 for Cd(ii) and Pb(ii), respectively. The limit of detection for Cd(ii) and Pb(ii) was 1.0 and 6.5 ng mL−1, respectively. This method was successfully applied to the determination of cadmium and lead in fish, rice and water samples.

Fast and sensitive simultaneous determination of antihypertensive drugs amlodipine besylate and ramipril using an electrochemical method: application to pharmaceuticals and blood serum samples by Jaqueline Tobias Moraes; Carlos Alberto Rossi Salamanca-Neto; Ana Paula Pires Eisele; Bruna Coldibeli; Graziela Scalianti Ceravolo; Elen Romão Sartori (4006-4013).
In this work, a simple and sensitive voltammetric method for simultaneous determination of antihypertensive drugs amlodipine besylate (AML) and ramipril (RMP) is described. A cathodically pretreated boron-doped diamond electrode (CP-BDDE) was employed wherein AML and RMP were irreversibly oxidized at 0.68 and 1.70 V (vs. Ag/AgCl (3.0 mol L−1 KCl)), respectively, in Britton–Robinson buffer solution (pH 6.0). Under optimized instrumental parameters of differential pulse voltammetry, the oxidation current of AML and RMP linearly increased in the concentration range of of 0.99–14 and 0.29–1.9 μmol L−1, obtaining limits of detection of 0.26 and 0.08 μmol L−1, respectively. The feasibility of the proposed method was successfully assessed by simultaneous quantification of these drugs in commercially available pharmaceutical formulations and rat blood serum samples. The results obtained further verify the fact that the CP-BDDE coupled with the differential pulse voltammetric technique may constitute an electroanalytical platform for fast simultaneous determination of these analytes in pharmaceutical formulations and biological samples.

A dual-mode colorimetric sensor based on copper nanoparticles for the detection of mercury-(ii) ions by Qiang Li; Feng Wu; Mao Mao; Xiang Ji; Luyao Wei; Jieying Li; Lan Ma (4014-4021).
In this study, water-soluble citrate-capped copper nanoparticles (Cu NPs) were synthesized by a simple and rapid method. We found that these citrate-capped Cu NPs possessed an intrinsic peroxidase-like activity, which could catalyse the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to generate a light blue product in the presence of hydrogen peroxide (H2O2). It was also found that mercury ions (Hg2+) could enhance the peroxidase-like activity of the citrate-capped Cu NPs, causing the colour to turn bright blue. The colour change was dependent on the concentration of Hg2+. Therefore, a colorimetric method for Hg2+ detection was established with a linear range from 0.050 μM to 10.000 μM and a detection limit of 0.185 Mm. More interestingly, citrate-capped Cu NPs have a characteristic absorption peak at 260 nm, we also found that Hg2+ could cause the absorption peak at 260 nm to change. Therefore, we developed another colorimetric method for Hg2+ detection based on the absorption peak of citrate-capped Cu NPs at 260 nm. This colorimetric method was shown to enable convenient and sensitive quantification of Hg2+ in the concentration range of 0.100 μM to 6.000 μM with a limit of detection of 0.052 μM. In this study, a dual-mode sensor for detection of Hg2+ was constructed, which exhibited good sensitivity and selectivity.

Monitoring of nine pesticides in different cereal flour samples with high performance liquid chromatography-diode array detection by Maryam Abbaspour; Mir Ali Farajzadeh; Saeed Mohammad Sorouraddin; Ali Mohebbi (4022-4033).
In the present work, a sample preparation method based on liquid–liquid–liquid extraction combined with dispersive liquid–liquid microextraction has been developed and validated for the extraction and preconcentration of nine multiclass pesticide residues from selected cereals and their determination by high-performance liquid chromatography-diode array detection. The extraction mechanism is based on different affinities of the components of the samples towards each of the involved phases (aqueous solution, acetonitrile, and n-hexane). In this procedure, initially acetonitrile is added to the solid sample and vortexed to extract the analytes along with other co-extracted compounds such as fats, lipids, etc. To clean-up the sample an aqueous phase (NaOH solution), a clean-up solvent (n-hexane) and a phase separating agent (NaCl) are added into the extract. In the presence of the phase separating agent a three-phase system is formed and simultaneously hydrophobic compounds are extracted into n-hexane and polar compounds migrate into the aqueous phase, while the analytes remain in the acetonitrile phase. Next, for more enrichment of the analytes, the acetonitrile phase is mixed with dichloromethane to perform the following dispersive liquid–liquid microextraction procedure. The influence of different experimental parameters on the extraction efficiency of the method was investigated. Under the optimum extraction conditions, enrichment factors for the selected pesticides were obtained in the range of 221–359. Limits of detection and quantification were obtained in the ranges of 0.16–0.60 and 0.53–2.0 ng g−1, respectively, with extraction recoveries of 55–90%. Relative standard deviations were in the ranges of 2–6% for intra- (n = 6) and 3–7% for inter-day (n = 5) precisions (C = 10 or 50 ng g−1 of each analyte). Finally, the proposed method was applied on different types of cereals including wheat, buck wheat, barley, rice, corn, chickpea, soya, and semolina. Clodinafop-propargyl was determined at the concentrations of 21 ± 2 and 16 ± 1 ng g−1 (n = 3), respectively, in whole wheat and wheat sprout flour samples.

Asparaginase (ASPA) is an enzyme that is of crucial importance as an anti-neoplastic drug and in the food industry. In this study, core–shell surface imprinted nanospheres (MIP) have been synthesized for the selective extraction of asparaginase via a simple and effective method. A nanothin molecularly imprinted shell was prepared by co-polymerization of asparaginase and 3-aminophenylboronic acid monohydrate (APBa) serving as the functional monomer. This was followed by a polymerization initiated via ammonium persulfate (APS). Non-imprinted polymers (NIP) were prepared using the same procedure, but in the absence of the template. The effects of amine functionalities at the surface of silica and molar ratios of 3-aminopropyl-triethoxysilane (APTES) to tetraethyl orthosilicate (TEOS) (MR) were investigated for optimizing the synthesis and maximizing the imprinting efficiency. Silica spheres with sufficient amine functionalities showed a pronounced binding capacity (Q) of 14.45 ± 0.35 and 29.43 ± 0.34 mg g−1 polymer for NIP and MIP, respectively, achieving an imprinting factor of up to 2.04 ± 0.03. The obtained nanospheres were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) analysis for surface area analysis, and the Barrett–Joyner–Halenda (BJH) method for obtaining pore size and volume. The molecular recognition properties of the nanoparticles were investigated by evaluating their adsorption capacity, the binding kinetics, and their selectivity versus the corresponding NIP. Finally, imprinted core–shell nanospheres were successfully applied for the selective extraction of ASPA in its pure form, and in a real-world pharmaceutical preparation. These nanospheres are promising architectures for targeted drug delivery. Furthermore, they are of substantial interest in food treatment, as they may minimize acrylamide formation. Also, they could be applied in the quantification of ASPA in real samples.

In this paper, counter flow salting-out homogeneous liquid–liquid extraction (CFSHLLE) was used for the determination of seven kinds of phenolic acids (PAs) in honey by ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). In this method, an aqueous sample was mixed with an organic solvent and then the mixture was driven to pass through the salt layer. Owing to the salting-out effect, fine droplets of organic solvent formed at the interface of the salt layer and the aqueous sample, then rose up through the remaining mixture and aggregated as a separate layer on the top, thus the analytes were extracted into the organic phase. Phase separation occurs naturally without the assistance of centrifugation. Parameters affecting the extraction efficiency were optimized, such as the species and volume of extractant, the species and amount of salt, the flow rate and pH value. Appropriate linear ranges were obtained for the PAs with coefficients of determination between 0.9984 and 0.9998. The limits of detection were in the range of 1.6–63.9 ng g−1. Relative standard deviations for intra-day (n = 5) and inter-day (n = 5) precision were lower than 5.51% and 7.65%, respectively. The proposed method proved to be simple, rapid, cost-effective and environmentally friendly. It has been successfully applied to the analysis of PAs in ten kinds of honey samples.

Glyphosate is the highest-selling pesticide in Brazil. It is one of the most-seized pesticides by the Brazilian Federal Police. However, smuggled agrochemicals show characteristics unknown from chemical, physical, and biological viewpoints, which should be determined. Quantitative nuclear magnetic resonance (qNMR) spectroscopy is a simple, rapid, and non-destructive methodology that allows simultaneous qualification and quantification of various substances (target and non-target). We developed and validated a method for quantification of the target (glyphosate) in commercial and smuggled products, and qualified the not-target contaminants. Validation was undertaken according to regulation ABNT NBR 14029: 2016 and Association of Analytical Communities criteria. Samples were diluted in D2O and analysed NMR. The method was applied to analyses of 10 glyphosate-based samples: eight commercial and two illegal. All commercial samples demonstrated the percentage of active principle specified by the manufacturer. However, the illegal GLIFP02 sample had a concentration of 33.57% over the reported content. GLIFP01 did not show any formulation description on the label, and showed only 6.10% of active principle in relation to GLIFP02. Also, it was possible to detect polyethoxylated alkyl amine (POEA) in legal and illegal samples. POAE has proven toxicity. Principal component analysis was used to demonstrate that the qNMR method could differentiate between samples of these pesticides. This was the first work to report application of qNMR spectroscopy, an easy, rapid, and non-destructive method, for qualification and quantification of target and not-target compounds in pesticide samples based on glyphosate.

An automated high-throughput sample preparation method using double-filtration for serum metabolite LC-MS analysis by Minjoong Joo; Jong-Moon Park; Van-An Duong; Dami Kwon; Jongho Jeon; Miso Han; Byung-Kwan Cho; Hyung-Kyoon Choi; Choul-Gyun Lee; Hee-Gyoo Kang; Hookeun Lee (4060-4065).
The rapid and reproducible preparation of biological samples is an essential requirement for LC-MS-based clinical metabolomic profiling. Herein, we proposed a novel, automated sample preparation method for serum metabolite LC-MS analysis. This method included a one-step double-filtration process with two filters (30k and 10k MWCO). High sample throughput (up to 96 samples) was achieved in an automated manner by incorporating the process in a liquid handling robotic system. The effectiveness of the developed method was evaluated through comparison with a conventional manual centrifugation-based method using seven human serum samples. A higher metabolite recovery and better reproducibility were achieved in quantitative analysis using the automated double-filtration method. The results suggested that the multiplexed serum sample preparation system can be applied to large-scale untargeted metabolomics studies.

Back cover (4067-4068).