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Analytica Chimica Acta (v.729, #)

Editorial Board (pp. iii).

Using a photochemical method and chitosan to prepare surface-enhanced Raman scattering–active silver nanoparticles by Kuang-Hsuan Yang; Chia-Ming Chang (pp. 1-6).

SEM images of Ag NPs obtained after reducing Ag⁺-containing complexes in solutions of 0.1M HNO₃ containing 1gL⁻¹ Ch (pH 6.9, adjusted with 1M NaOH) under irradiation with UV light of wavelength of 310nm for 30min.Display Omitted► Prepare SERS-active Ag nanoparticles by using green process with aid of chitosan. ► The Ag-containing complex was irradiated with UV light to yield SERS activity. ► pH of the solution and the presence of Ch both affect the resulting SERS activities.In this paper, we report a new strategy for the preparation of surface-enhanced Raman scattering (SERS)-active silver nanoparticles (Ag NPs), using a photochemical method and the presence of chitosan (Ch). First, Ag substrates were subjected to electrochemical oxidation/reduction cycles (ORCs) in deoxygenated aqueous solutions containing 0.1M HNO₃ and 1gL⁻¹ Ch (pH 6.9, adjusted by adding 1M NaOH), resulting in Ag⁺–Ch complexes. These substrates were then irradiated with UV light at various wavelengths to yield the SERS-active Ag NPs. A stronger SERS effect was observed on the SERS-active Ag NPs prepared by using UV irradiation at 310nm. The pH of the solution and the presence of Ch during the preparation process both affected the resulting SERS activities.

Keywords: Silver nanoparticles; Chitosan; Photochemical method; Surface-enhanced Raman scattering

Determination of inorganic phosphate by electroanalytical methods: A review by Sheela Berchmans; Touma B. Issa; Pritam Singh (pp. 7-20).

Display Omitted► Advantages of electrochemical sensing of phosphate. ► Classification of electrochemical methods of sensing. ► Ionophores for potentiometric sensing of phosphate. ► Supramolecular based sensing of phosphate: voltammetry and amperometry. ► Unconventional and indirect methods of sensing phosphate.Determination of inorganic phosphate is of very high importance in environmental and health care applications. Hence knowledge of suitable analytical techniques available for phosphate sensing for different applications becomes essential. Electrochemical methods for determining inorganic phosphate have several advantages over other common techniques, including detection selectivity, stability and relative environmental insensitivity of electroactive labels. The different electrochemical sensing strategies adopted for the determination of phosphate using selective ionophores are discussed in this review. The various sensing strategies are classified based on the electrochemical detection techniques used viz., potentiometry, voltammetry, amperometry, unconventional electrochemical methods etc., The enzymatic sensing of phosphate coupled with electrochemical detection is also included. Various electroanalytical methods available in the literature are assessed for their merits in terms of selectivity, simplicity, miniaturisation, adaptability and suitability for field measurements.

Keywords: Electroanalysis of phosphate; Review; Potentiometry; Amperometry; Bioelectroanalytical methods

Direct rapid analysis of trace bioavailable soil macronutrients by chemometrics-assisted energy dispersive X-ray fluorescence and scattering spectrometry by M.I. Kaniu; K.H. Angeyo; A.K. Mwala; M.J. Mangala (pp. 21-25).

Display Omitted► Chemometrics-assisted EDXRFS spectroscopy realizes direct, rapid and accurate analysis of trace bioavailable macronutrients in soils. ► The method is minimally invasive, involves little sample preparation, short analysis times and is relatively insensitive to matrix effects. ► This opens up the ability to rapidly characterize large number of samples/matrices with this method.Precision agriculture depends on the knowledge and management of soil quality (SQ), which calls for affordable, simple and rapid but accurate analysis of bioavailable soil nutrients. Conventional SQ analysis methods are tedious and expensive. We demonstrate the utility of a new chemometrics-assisted energy dispersive X-ray fluorescence and scattering (EDXRFS) spectroscopy method we have developed for direct rapid analysis of trace ‘bioavailable’ macronutrients (i.e. C, N, Na, Mg, P) in soils. The method exploits, in addition to X-ray fluorescence, the scatter peaks detected from soil pellets to develop a model for SQ analysis. Spectra were acquired from soil samples held in a Teflon holder analyzed using¹⁰⁹Cd isotope source EDXRF spectrometer for 200s. Chemometric techniques namely principal component analysis (PCA), partial least squares (PLS) and artificial neural networks (ANNs) were utilized for pattern recognition based on fluorescence and Compton scatter peaks regions, and to develop multivariate quantitative calibration models based on Compton scatter peak respectively. SQ analyses were realized with high CMD ( R²>0.9) and low SEP (0.01% for N and Na, 0.05% for C, 0.08% for Mg and 1.98μgg⁻¹ for P). Comparison of predicted macronutrients with reference standards using a one-way ANOVA test showed no statistical difference at 95% confidence level. To the best of the authors’ knowledge, this is the first time that an XRF method has demonstrated utility in trace analysis of macronutrients in soil or related matrices.

Keywords: Chemometrics; Energy dispersive X-ray fluorescence and scattering; Bio-available soil nutrients; Spectroanalysis

Mesoporous TiO₂ aerogel for selective enrichment of phosphopeptides in rat liver mitochondria by Liyuan Zhang; Zhen Liang; Kaiguang Yang; Simin Xia; Qi Wu; Lihua Zhang; Yukui Zhang (pp. 26-35).

Display Omitted► The specific surface area of TiO₂ aerogel is 10 times larger than TiO₂ nanoparticle. ► The limit of detection for phosphopeptides was down to 30amol by TiO₂ aerogel. ► The loading capacity for phosphopeptides was 6-fold larger than TiO₂ microparticle.The enrichment of low abundance phosphopeptides before MS analysis is a critical step for in-depth phosphoproteome research. In this study, mesoporous titanium dioxide (TiO₂) aerogel was prepared by precipitation and supercritical drying. The specific surface area up to 490.7m²g⁻¹ is achieved by TiO₂ aerogel, much higher than those obtained by commercial TiO₂ nanoparticles and by the latest reported mesoporous TiO₂ spheres. Due to the large specific surface area and the mesoporous structure of the aerogel, the binding capacity for phosphopeptides is six times higher than that of conventional TiO₂ microparticles (173 vs 28μmolg⁻¹). Because of the good compatibility of enrichment procedure with MALDI-TOF-MS and the large binding capacity of TiO₂ aerogel, a detection limit as low as 30amol for analyzing phosphopeptides in β-casein digest was achieved. TiO₂ aerogel was further applied to enrich phosphopeptides from rat liver mitochondria, and 266 unique phosphopeptides with 340 phosphorylation sites, corresponding to 216 phosphoprotein groups, were identified by triplicate nanoRPLC-ESI-MS/MS runs, with false-positive rate less than 1% at the peptide level. These results demonstrate that TiO₂ aerogel is a kind of promising material for sample pretreatment in the large-scale phosphoproteome study.

Keywords: TiO; ₂; aerogel; Phosphoproteome; Mass spectrometry; Nano-Reversed phase liquid chromatography-electrospray ionization tandem mass spectrometry; Rat liver mitochondria

Selective trace analysis of chloroacetamide herbicides in food samples using dummy molecularly imprinted solid phase extraction based on chemometrics and quantum chemistry by Lei Zhang; Fang Han; Yanyun Hu; Ping Zheng; Xuan Sheng; Hao Sun; Wei Song; Yaning Lv (pp. 36-44).

Display Omitted► Hyperchem was used to simulate chloroacetamide herbicides and their metabolites. ► Clustering analysis was conducted to analyze the structural data. ► Metolachlor deschloro was selected as the dummy template to synthesize DMIPs. ► The elution order of herbicides on DMIPs was predicted using clustering analysis. ► Compared with other SPE columns, the matrix effect was decreased using DMISPE.A methodology based on chemometrics and quantum chemistry was proposed to design and synthesize dummy molecularly imprinted polymers (DMIPs) capable of extracting chloroacetamide herbicides from food samples. Molecular modeling approach in conjunction with clustering analysis was used to predict the most suitable dummy template. Metolachlor deschloro was selected as the template to synthesize DMIPs, which were used as the solid phase extraction (SPE) materials. The selective adsorption of DMIPs was evaluated by high performance liquid chromatography (HPLC). The retention property of six chloroacetamide herbicides on DMIPs was also predicted using clustering analysis. The optimum loading, washing and eluting conditions for dummy molecularly imprinted solid phase extraction (DMISPE) were established to obtain high selectivity and sensitivity. Water, dichloromethane and methanol were chosen as loading, washing and elution solvent, respectively. Under optimized DMISPE conditions, recoveries of analytes were in the range of 83.4–106.7% with satisfactory precision (RSD% lower than 13%). Compared with other commercial SPE columns, DMISPE exhibited selective binding properties for chloroacetamide herbicides and the matrix effect was significantly decreased.

Keywords: Dummy template; Dummy molecularly imprinted solid phase extraction; Molecule modeling; Clustering analysis; Chloroacetamide herbicides

Measurement of laser activated electron tunneling from semiconductor zinc oxide to adsorbed organic molecules by a matrix assisted laser desorption ionization mass spectrometer by Hongying Zhong; Jieying Fu; Xiaoli Wang; Shi Zheng (pp. 45-53).

Display Omitted► Irradiation of photons with energies more than the band gap generates electron–hole pairs. ► Electron tunneling probability is dependent on the electron mobility. ► Tunneling electrons are captured by charge deficient atoms. ► Unpaired electrons induce cleavages of chemical bonds.Measurement of light induced heterogeneous electron transfer is important for understanding of fundamental processes involved in chemistry, physics and biology, which is still challenging by current techniques. Laser activated electron tunneling (LAET) from semiconductor metal oxides was observed and characterized by a MALDI (matrix assisted laser desorption ionization) mass spectrometer in this work. Nanoparticles of ZnO were placed on a MALDI sample plate. Free fatty acids and derivatives were used as models of organic compounds and directly deposited on the surface of ZnO nanoparticles. Irradiation of UV laser ( λ=355nm) with energy more than the band gap of ZnO produces ions that can be detected in negative mode. When TiO₂ nanoparticles with similar band gap but much lower electron mobility were used, these ions were not observed unless the voltage on the sample plate was increased. The experimental results indicate that laser induced electron tunneling is dependent on the electron mobility and the strength of the electric field. Capture of low energy electrons by charge-deficient atoms of adsorbed organic molecules causes unpaired electron-directed cleavages of chemical bonds in a nonergodic pathway. In positive detection mode, electron tunneling cannot be observed due to the reverse moving direction of electrons. It should be able to expect that laser desorption ionization mass spectrometry is a new technique capable of probing the dynamics of electron tunneling. LAET offers advantages as a new ionization dissociation method for mass spectrometry.

Keywords: Laser; Electron tunneling; Semiconductor; Ionization; Mass spectrometry

Small molecule analysis using laser desorption/ionization mass spectrometry on nano-coated silicon with self-assembled monolayers by Ömür Çelikbıçak; Gökhan Demirel; Erhan Pişkin; Bekir Salih (pp. 54-61).

Display Omitted► A new substrate using controllable nano-structured silicon surfaces based on the self-assembly of silane molecules (OTS and TPDA) was proposed. ► A matrix-free approach for use in laser desorption/ionization mass spectrometry (LDI-MS) for the analysis of small target molecules was demonstrated. ► The modified surfaces with nano-overlayers should be seriously considered to improve LDI-MS analysis. ► The detection of small molecules by eliminating the need for matrix provides a number of important advantages.Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is an emerging technique for the determination of the molecular weight of biomolecules and their non-covalent complexes without fragmentation. One problem with this technique is the use of excess amounts of matrices, which may produce intense fragment ions and/or clusters at low mass ranges between 1 and 800Da. These fragments lead to interference, especially concerning the signals of small target molecules. Here, a simple, reusable, and quite inexpensive approach was demonstrated to improve the effectiveness of laser desorption/ionization mass spectrometry (LDI-MS) analysis, especially for small molecules, without using matrix molecules. In this study, substrates with controllable morphologies and thicknesses were developed based on the self-assembly of silane molecules on silicon surfaces using N-(3-trimethoxysilylpropyl)diethylenetriamine (TPDA) and octadecyltrichlorosilane (OTS) molecules. Prepared substrates with nano-overlayers were successfully used in the analysis of different types of small target molecules, namely acrivastine,l-histidine,l-valine,l-phenylalanine,l-arginine,l-methionine and angiotensin I. Our substrates exhibited clear peaks almost without fragmentation for all target molecules, suggesting that these surfaces provide a number of important advantages for LDI-MS analysis, such as ease of preparation, costs, reusability, robustness, easy handling and preventing fragmentation.

Keywords: LDI; SAMs; Matrix-free target; Desorption/ionization; Small molecule analysis; Mass spectrometry

Dual lifetime referenced fluorometry for the determination of doxorubicin in urine by Fernando Martínez Ferreras; Otto S. Wolfbeis; Hans H. Gorris (pp. 62-66).

Display Omitted► Self-referenced determination of fluorescent analytes in solution by dual lifetime referencing. ► Comparison of frequency-domain DLR and time-domain DLR. ► DLR has a detection limit of 400nM doxorubicin.Dual lifetime referencing (DLR) is introduced as a rapid and self-referenced method for measuring the concentration of a fluorescent analyte in solution. The fluorescent cancer chemotherapeutic doxorubicin was chosen as a medically relevant analyte and blended with a reference dye (Ru(dpp)₃) that displays overlapping excitation and emission spectra. The relative contributions of the short-lived (nanoseconds) fluorescent analyte and the long-lived (microseconds) reference dye define the observed lifetime. Measuring this lifetime by both frequency-domain DLR and time-domain DLR yields similar analytical ranges and limits of detection (0.4μM). To assess the matrix effect of medical samples, the standard addition method was employed to both modes of DLR. Urine was spiked with doxorubicin and recovery rates of ≥97% were obtained.

Keywords: Doxorubicin; Fluorescence lifetime; Self-referenced measurementsAbbreviations; DLR; dual lifetime referencing; LOD; limit of detection; PAN; polyacrylonitrile; Ru(dpp); ₃; ruthenium(II)tris-(4,7-diphenyl-1,10-phenanthroline)

Sequence-specific detection of nucleic acids utilizing isothermal enrichment of G-quadruplex DNAzymes by Hao-Jie Xiao; Ho Chol Hak; De-Ming Kong; Han-Xi Shen (pp. 67-72).

A novel, specific nucleic acid detection method was reported based on an isothermal amplification strategy of G-quadruplex DNAzymes. Using this method, simple, rapid and cost-effective nucleic acid detection could be achieved. This method displayed high target length tolerance and good detection specificity, one-base mismatch could be easily judged, even by visually. This method may be used as an auxiliary tool for amplified detection of specific DNA targets in some situations, in which isothermal detection is desirable.Display Omitted► A novel, specific nucleic acid detection method was designed. ► This method utilized a target-mediated isothermal amplification of G-quadruplex DNAzymes. ► This method provides a new way for single-nucleotide polymorphism detection. ► This nucleic acid detection method displayed high target length tolerance. ► This method needs no labeled oligonucleotides, and only simple colorimetric detection was required.G-quadruplex DNAzymes are peroxidase-like complexes formed by nucleic acid G-quadruplexes and hemin. Various chemical sensors and biosensors have been developed, based on such DNAzymes. Here we report a novel, specific nucleic acid detection method utilizing the isothermal amplification strategy of G-quadruplex DNAzymes. In this method, an unlabeled oligonucleotide probe was used. The probing sequence of the oligonucleotide was in the form of a stem-loop structure. A G-rich sequence, containing three GGG repeats, was linked to the 5′-end of the stem-loop structure. In the presence of target, the probing sequence hybridized to the target, and a G_n ( n≥2) repeat was extended from its 3′-end. This G_n repeat, together with the three GGG repeats at the 5′-end, folded into a G-quadruplex, and displayed enhanced peroxidase acitivity upon hemin binding. Utilizing the dynamic binding interaction between the probe and its target, the enrichment of G-quadruplex DNAzymes was achieved. Using this method, simple, rapid and cost-effective nucleic acid detection could be achieved. This method displayed high target-length tolerance and good detection specificity; one-base mismatch could be judged easily, even by visual inspection. This method may be used as an auxiliary tool for amplified detection of specific DNA targets in some situations, in which isothermal detection is desirable.

Keywords: Nucleic acid detection; Isothermal enrichment, G-quadruplex; DNAzyme; Colorimetric

A new cleanup method of dioxins in sediment using large volume injection gas chromatography online coupled with liquid chromatography by Fengmei Tang; Yuwen Ni; Haijun Zhang; Yun Li; Jing Jin; Longxing Wang; Jiping Chen (pp. 73-79).

The sample extract could be purified by the LVI-GC-LC cleanup method, and satisfying cleanup efficiency was obtained.Display Omitted► A new cleanup method for the determination of dioxins in sediment was developed. ► The new method is simpler, less labor-intensive, and more economical. ► The new method showed satisfactory precision, accuracy and cleanup efficiency. ► The new method can be amenable to automation.A new cleanup method was developed and validated for the determination of polychlorinated dibenzo- p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in sediment. The sample extract was first treated with sulfuric acid and then cleaned up by a large volume injection gas chromatography online coupled with liquid chromatography (LVI-GC-LC) system. PCDD/Fs in the extract were separated by a GC column (DB-5), selected cut, cool trapped and transferred to a LC column (alumina). The fraction of PCDD/Fs eluted from the alumina column was collected and concentrated for the instrumental analysis. Under the optimized conditions, LVI-GC-LC method achieved the recoveries of 57–102% for 2,3,7,8-substituted PCDD/Fs, which met the requirements of US Environmental Protection Agency (EPA) Method 1613 and were better than those obtained using the conventional multistep column cleanup method. Meanwhile, compared with the conventional method, the limit of detection (LOD) values of 2,3,7,8-substituted PCDD/Fs cleaned up by LVI-GC-LC method were decreased due to the high-efficiency removal of interferents. These results suggested that the LVI-GC-LC cleanup method was a promising alternative to the multistep cleanup procedure for the determination of dioxins in environmental samples.

Keywords: Abbreviations; EPA; environmental protection agency; GC; gas chromatography; HPLC; high performance liquid chromatography; HRGC/HRMS; high resolution gas chromatography/high resolution mass spectrometer; I-TEF; international-toxic equivalency factor; I-TEQ; international-toxic equivalent quantity; LC; liquid chromatography; LOD; limit of detection; LVI; large volume injection; OCI; on-column injection; PCBs; polychlorinated biphenyls; PCDD/Fs; polychlorinated dibenzo-; p; -dioxins and polychlorinated dibenzofurans; pcGC; preparative capillary gas chromatography; POPs; persistent organic pollutants; RSD; relative standard deviations; SVE; solvent vapor exitDioxins; Online cleanup; Gas chromatography; Liquid chromatography; Large volume injection

Separation and determination of trace uranium using a double-receptor sandwich supramolecule method based on immobilized salophen and fluorescence labeled oligonucleotide by Minlong Wu; Lifu Liao; Minmin Zhao; Yingwu Lin; Xilin Xiao; Changming Nie (pp. 80-84).

Display Omitted► We report a double-receptor sandwich method for separating and determining uranium. ► One receptor used for separating uranium is an immobilized salophen. ► Another used for determining uranium is a fluorescence labeled oligonucleotide. ► The method utilizes the formation of supramolecule oligonucleotide-uranyl-salophen. ► It has the advantages of high selectivity, high sensitivity and good stability.A double-receptor sandwich supramolecule method for the separation and determination of trace uranium was proposed in this paper. One receptor is a salophen which can react with uranyl to form a uranyl-salophen complex, and another receptor is an oligonucleotide which can bind uranyl to form oligonucleotide-uranyl-salophen supramolecule. The salophen was immobilized on the surface of silica gel particles and used as the solid phase receptor for separating uranium from solution. The oligonucleotide was labeled with a fluorescent group and used as the labeled receptor for quantitatively analyzing uranium. In the procedure of separation and determination, uranyl ion was first combined with the solid phase receptor and then conjugated with the labeled receptor to form the sandwich-type supramolecule. The labeled receptor in the sandwich supramolecule was then eluted and determined by fluorescence analysis. The experimental results demonstrate that this method has a number of advantages such as high selectivity, excellent pre-concentration capability, high sensitivity, good stability and low cost. Under optimal conditions, the linear range for the detection of uranium is 0.5–30.0ngmL⁻¹ with a detection limit of 0.2ngmL⁻¹. The proposed method was successfully applied for the separation and determination of uranium in real samples with the recoveries of 95.0–105.5%.

Keywords: Uranium; Double-receptor; Sandwich supramolecule; Salophen; Oligonucleotide; Fluorescence

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Analytica Chimica Acta (v.729, #)

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Analytica Chimica Acta (v.729, #)