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Analytical Methods (v.3, #12)

Front cover (pp. 2663-2664).

CNT/Ni hybrid nanostructured arrays (NSAs) are synthesized on a stainless steel substrate through a one-step chemical-vapor-deposition (CVD) method using nullaginite NSAs as starting materials. During the CVD process, the nullaginite NSAs are transformed into Ni NSAs, which can further act as the catalysts to initiate the simultaneous in situ growth of CNTs on their surface, leading to an intriguing three-dimensional (3D) hybrid nanostructure. The resulting ordered CNT/Ni NSAs are highly porous and conductive, which are believed to be quite favorable for electrochemical applications. As a proof-of-concept demonstration of the functions of such a well-designed architecture in energy storage, the CNT/Ni NSAs are tested as the working electrodes of electrochemical capacitors (ECs). After being activated, the composite electrode exhibits both well-defined pseudo-capacitive and electrical double-layer behavior with high areal capacitance (up to ∼0.901 F cm⁻²), excellent cyclability (nearly 100% capacitance retention after 5000 cycles), and outstanding rate capability. The unique interconnected hybrid structure and virtues inherited from the conductive CNT network and porous NSAs are believed to be responsible for the excellent performance.

Contents (pp. 2665-2680).

A simple gas-phase chemiluminescence (GPCL) technique has been developed for routine measurement of inorganic arsenic in water samples. The internal hydrogen pressure generated in the cell was used to reproducibly transfer arsine into a chemiluminescence (CL) reaction cell to react with ozone. This instrument setup reduces a major component from the system and reduces cost. The technique is optimized and calibrated from 0–300 μg L⁻¹ (ppb) of total inorganic arsenic with a limit of detection (LOD) of 0.4 μg L⁻¹ and a sample throughput of 20 samples per hour without sampling automation. The technique is validated against HGAFS, ICPAES, ASV, and arsenic kit using certified standards and extensively used for groundwater sample analysis. The response of the instrument was mathematically modeled for a better understanding of the analytical process.

Let there be chip—towards rapid prototyping of microfluidic devices: one-step manufacturing processes by Ansgar Waldbaur; Holger Rapp; Kerstin Länge; Bastian E. Rapp (pp. 2681-2716).

Microfluidics is an evolving scientific field with immense commercial potential: analytical applications, such as biochemical assay development, biochemical analysis and biosensors as well as chemical synthesis applications essentially require microfluidics for sample handling, treatment or readout. A number of techniques are available to create microfluidic structures today. On industrial scale replication techniques such as injection molding are the gold standard whereas academic research mostly focuses on replication by casting of soft elastomers such as polydimethylsiloxane (PDMS). Both of these techniques require the creation of a replication master thus creating the microfluidic structure only in the second process step—they can therefore be termed two-(or multi-)step manufacturing techniques. However, very often the number of pieces to be created of one specific microfluidic design is low, sometimes even as low as one. This raises the question if two-step manufacturing is an appropriate choice, particularly if short concept-to-chip times are required. In this case one-step manufacturing techniques that allow the direct creation of microfluidic structures from digital three-dimensional models are preferable. For these processes the number of parts per design is low (sometimes as low as one), but quick adaptation is possible by simply changing digital data. Suitable techniques include, among others, maskless or mask based stereolithography, fused deposition molding and 3D printing. This work intends to discuss the potential and application examples of such processes with a detailed view on applicable materials. It will also point out the advantages and the disadvantages of the respective technique. Furthermore this paper also includes a discussion about non-conventional manufacturing equipment and community projects that can be used in the production of microfluidic devices.

Thermally responsive polymer as a sieving matrix of proteins in capillary gel electrophoresis by Chun Yang; Chunyan Chang; Jun Wang; Qishu Qu; Xiaoya Hu; Yang Wang (pp. 2717-2720).

A thermally responsive polymer, termed as P(IPAAm-AM-BisAM), was prepared by the copolymerization of N-isopropyl acrylamide, acrylamide, and N,N′-methylenebisacrylamide. At room temperature this polymer was dissolved in water to form a low viscous solution so that it could be loaded in a capillary easily. When a high voltage was applied on the capillary, the polymer was stimulated by the Joule heat and transferred from a liquid state into a solid state, acting as a sieving matrix for the separation of proteins according to their molecular weights. The logarithm values of the molecular weights of the proteins correlated linearly with the migration times. This capillary gel electrophoresis of proteins was carried out using a conventional instrument. Using such a copolymer, we can easily realize high-speed, high-efficiency and reproducible capillary gel electrophoresis for proteins without any instrumental rebuilding or investment.

Introducing an orthogonal-triangular decomposition algorithm and its application in multivariate calibration by Mohammadreza Khanmohammadi; Mohammadhossein Ahmadi Azqhandi (pp. 2721-2725).

An accurate and stable algorithm, Orthogonal-Triangular Decomposition Algorithm (OTDA) is for the first time presented in the field of chemistry. The basic principle of OT Multivariate Calibration Algorithm (OTMCA) is investigated. Complexes of sodium tripolyphosphate (STTP), sodium sulfate (SS) and sodium carbonate (SC), which in IR spectrometry present serious overlapping absorption peaks, are analyzed by OTMCA. We report that OTDA avoids matrix inverting, reduces the orders of matrices and speeds up the operation of matrices. So, it offers bright prospects in chemometrics. OTDA is implemented by an orthogonal and an upper triangular matrix decomposition process which is robust and convenient. Here, it is applied to overcome the problem of overlapping spectra by the different components contained in detergent washing powders.

Process analytical chemistry in a nickel electroplating bath. Automated sequential injection for additive determination by M. Ostra; C. Ubide; M. Vidal; J. Zuriarrain (pp. 2726-2732).

Most of the useful parameters of a nickel electroplating bath can be monitored along the bath life. Process analytical chemistry (PAC) has been applied to follow parameters such as temperature, pH, chloride or nickel concentration. The monitoring of additives has special relevance because the final quality of finish depends on them. Two out of the four additives used in the commercial nickel bath used in this paper show UV absorption (A-5(2X) and SPB) and a sequential injection (SI) method has been developed to conduct and automatically dilute aliquots from the bath to a diode-array detector where UV spectra are acquired. Because the UV bands of the absorbing additives overlap, partial least squares (PLS) regression is used as a calibration method to resolve the mixture. A commercial software program has been used for the automated data acquisition. The program configuration and the SI manifold are given. The results obtained for additives are compared with those obtained from a manual method that is used as a reference. Mean random errors under 8% were always obtained. The limits of detection (LOD) found for A-5(2X) and SPB were 0.2 mL L⁻¹ and 0.09 mL L⁻¹ respectively. The SI methodology was applied with excellent results along a whole bath life and can be used to maintain the proper coating conditions.

Evaluation of label-free quantitative proteomics in a plant matrix: A case study of the night-to-day transition in corn leaf by Leah S. Riter; Pamela K. Jensen; Joan M. Ballam; Ewa Urbanczyk-Wochniak; Timothy Clough; Olga Vitek; Jennifer Sutton; Michael Athanas; Mary F. Lopez; Susan MacIsaac (pp. 2733-2739).

The application of a label-free, LC-MS/MS based proteomics method for analysis of plant tissues was evaluated using both a spike study and case study in corn (Zea mays) leaf tissue. The spike study was utilized to establish a label-free proteomics protocol for corn leaf tissue, with focus on the assessment of sensitivity and accuracy. The data from this spike study indicated that this protocol had quantitative accuracy within ±20% of the true values and was able to differentiate 1.5 fold changes in protein abundance in a corn leaf matrix. Furthermore, the applicability of this protocol as a useful tool for answering biologically relevant questions was tested in a case study of the response of the proteome to night-to-day transition in corn leaf tissue. The label-free proteomics approach detected 136 differentially abundant proteins (FDR = 0.01 with an absolute log fold change ≥ 0.8) and 313 proteins whose abundance did not change in response to the diurnal cycle using ANOVA fixed effects model analysis. Identified proteins were mapped to their Gene Ontology (GO) biological processes and compared with expected diurnal biology. Many observed changes, including an increase in photosynthetic processes, were consistent with anticipated biological responses to the night-to-day transition. The results from the spike and case studies show that the label-free method can reliably provide a means to detect changes in protein abundance in plant tissue.

Stereospecific redox reaction of ascorbic acid and isoascorbic acid based on chiral electropolymerized films by Juan Zhou; Qiao Chen; Yonghua Wang; Qian Han; Yingzi Fu (pp. 2740-2742).

A simple and fast strategy for stereospecific redox reaction is proposed using glutamic acid enantiomer electropolymerized films. The mechanism of enantioselectivity on the electropolymerized films has been explored.

Comprehensive 2D chromatography with mass spectrometry: a powerful tool for following the hydrotreatment of a Straight Run Gas Oil by Guy Toussaint; Chantal Lorentz; Michel Vrinat; Christophe Geantet (pp. 2743-2748).

Comprehensive two-dimensional gas chromatography (GC × GC) is a technique which is rapidly gaining importance for the analysis of complex samples, especially within petrochemical matrixes. Until recently GC × GC has been a technique used within analytical laboratories to characterize complex multi-component mixtures such as fuels, perfumes and organic aerosol extracts, which are difficult to analyze using conventional GC or GC-MS techniques. In the present study we will illustrate how GC × GC-qMS can be used as an effective tool to accurately monitor the conversion of a Straight Run Gas Oil (SRGO) on a Cobalt Molybdenum (CoMo) supported on an alumina sulfide catalyst. A SRGO was hydrotreated at various temperatures and liquid hourly space velocities (LHSV). The products were analyzed and attention was paid to the transformation of sulfur and aromatic compounds. Quantitative analyses using GC × GC-qMS were performed and compared to the “Simulated Distillation” and total sulfur analysis illustrating that this technique can provide a comprehensive view of the entire matrix, family of products and their distribution as well as single molecule evolution upon catalytic conversion.

Optimization of micellar LC conditions for separation of opium alkaloids and their determination in pharmaceutical preparations by Artem U. Kulikov; Alexander P. Boichenko; Aleksey G. Verushkin (pp. 2749-2757).

Micellar liquid chromatography (MLC) has been developed for the analysis of opium alkaloids. The composition of micellar mobile phase for the separation of morphine, codeine, papaverine and noscapine have been optimized by a chemometric tool taking into account the efficiency and asymmetry of chromatographic peaks, resolution between each pair of peaks and total time of separation. The optimized mobile phase composition (0.10 M sodium dodecylsulfate (SDS), 5% (v/v) 1-butanol; pH 2.5) allows to fully separate alkaloids within 15 min. The proposed MLC method was validated, compared with the RP-HPLC method and successfully applied for the analysis of the pharmaceutical preparation “Omnopon, solution for injection”.

PARAFAC based methods for the analysis of Diltiazem drug excitation emission matrices of fluorescence obtained by a derivatization reaction by João M. M. Leitão; Eliana F. C. Simões; Joaquim C. G. Esteves da Silva (pp. 2758-2769).

A fluorescent derivatization reaction for Diltiazem drug quantification based on the condensation reaction of citric or malonic acid with acetic anhydride, catalyzed by the tertiary amine group of Diltiazem, was developed. Excitation emission matrices (EEMs) of fluorescence of the pure solvent (ethanol), standard and sample solutions following a standard addition methodology were analysed by PARAFAC based methods (PARAFAC, PARAFAC2 and PARALIND) to obtain robust calibration methodologies. The quantification results of the sample were compared with the official US Pharmacopeia high performance liquid chromatography-ultraviolet method (USP HPLC-UV). Although the experimental sets of EEM show linearity deviations all the PARAFAC based methods allow correct robust estimation of Diltiazem concentration in pharmaceutical formulations. The closest results were: derivatization with citric acid and PARAFAC2 six components non-negativity constraint model with a detection limit of 0.088 ppm; and, derivatization with malonic acid and PARAFAC six components non-negativity constraint model with a detection limit of 0.066 ppm for the malonic acid was observed. The simultaneous utilization of the three PARAFAC methods gives further information about the intrinsic structure of the data sets under analysis, i.e., it works as an efficient diagnostic tool for the existence of non-linearity and colinearity.

Intracellular and extracellular sampling to monitor the neurotransmission process using a chromatographic method by Leena Parmar; Lindsay D. Morgan; Bhavik Anil Patel (pp. 2770-2776).

The neurotransmission process is essential for cellular communication and in a variety of disorders the mechanism is altered. At present, biological tissue sampling approaches utilise single sampling techniques where either neurochemicals present inside the cell or released from the cell are monitored, yet the neurotransmission mechanism involves both processes. We have utilised a sampling approach that allows for monitoring intracellular and extracellular neurochemicals, using image analysis of the tissue area to normalise neurochemicals levels for both methods. Both ratios and neurochemical levels were presented to explain alterations in neurotransmission mechanism between proximal and distal colon. The new parameters obtained from intracellular and extracellular sampling are more suited to explain neurotransmitter release and clearance compared to conventionally used parameters from single sampling studies.

Complex electrochemical and impedimetric evaluation of DNA damage by using DNA biosensor based on a carbon screen-printed electrode by Guzel Ziyatdinova; J. Labuda (pp. 2777-2782).

DNA biosensor (DNA/SWCNT-COOH-CHIT/SPCE) composed of dsDNA adsorptive layer on a carboxylated single-walled carbon nanotubes–chitosan composite deposited at a commercial carbon based screen-printed electrode has been prepared and applied to a complex investigation of damage to DNA by the Fenton type cleavage agent (hydroxyl radicals formed in the mixture of Cu²⁺, H2O2 and ascorbic acid) and copper(ii)–quercetin system in 0.1 M PBS pH 7.0 under aerobic conditions. The dsDNA damage detection is performed by using square-wave voltammetry (SWV), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in 1 × 10⁻⁷ M thioridazine and 1 × 10⁻³ M K4[Fe(CN)6]/K3Fe(CN)6 in the 0.1 M phosphate buffer solution, pH 7.0. Initial enhancement of the intrinsic guanine and adenine moieties SWV response over that of original dsDNA one indicates opening of the helix structure in the first stage of damage. At the same time, decrease in the intercalated thioridazine response confirms damage of the helix structure in parallel to deep degradation of the DNA chain and its removal from the electrode surface as indicated by the CV and EIS measurements in the presence of the [Fe(CN)6]^3−/4− redox indicator in solution.

Raman spectroscopy study of lichens using three spectrometers under different experimental conditions: analyses of the results with relevance for extraplanetary exploration by S. E. Jorge-Villar; I. Miralles; C. Capel Ferrón; V. Hernández (pp. 2783-2791).

We have carried out analyses on three extremophile lichens from the Tabernas Desert (Spain) under different experimental conditions: dry and wet samples in the laboratory and wet specimens in the field, using three spectrometers: one portable, one FT-Raman and one dispersive micro-Raman instruments. Apart from pigment characterization, the information obtained from the spectra is compared and the differences analysed. The fact that no results were achieved on dry lichens using the handheld spectrometer is of special relevance for those looking for life in hazardous environments. Since in some extreme habitats, life could be “dormant” and only activates under appropriate conditions, miniaturized instruments (such as those included for extraplanetary exploration missions) could not detect bio-markers and, then, life signals will not be noticed when, actually, life is there. Furthermore, we show in this work, using the miniaturized Raman spectrometer, that not only laser wavelength, spectral resolution and wavenumber region of the spectrum are important for the bio- or geo-marker recognition but also spot-size is of vital relevance for the unambiguous biomolecular characterization. In our opinion, mini-Raman instruments are useful for assessing in situ the eventual presence of bio-markers in complex natural samples, such as organisms, but are not accurate enough for precise molecular identification.

Synthesis of MgFe2O4 nanoparticles and MgFe2O4 nanoparticles/CPE for electrochemical investigation of dopamine by Sathish Reddy; B. E. Kumara Swamy; Umesh Chandra; K. R. Mahathesha; T. V. Sathisha; H. Jayadevappa (pp. 2792-2796).

Magnesium ferrite nanoparticles (MgFe2O4 NPs) were prepared by a solution based method using magnesium sulphate (MgSO4), ferrous sulphate (FeSO4), dl serine and NaOH as a precipitant and the obtained precipitation was calcinated under 500 °C for 4 h. The resulting material was characterized by using X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The MgFe2O4 NPs were used for preparation of MgFe2O4 NPs/carbon paste electrode (MgFe2O4 NPs/CPE) and applied for electrochemical investigation of dopamine (DA) which exhibits good electrocatalytic activity for investigation of DA at physiological pH 7.4. The effect of pH range from 5.5 to 8.0 was studied and the result shows that the redox peak current was maxima at pH 7.5 and the redox peak was pH dependent with a slope of 0.061 V/pH. The scan rate effect was found to be an adsorption-controlling electrode process. The electrocatalytic currents increased linearly with an increase in DA concentration in the range 0.1–1.2 μM and the detection limit was found to be 7.7 × 10⁻⁸ M. The proposed method was successfully applied to the determination of DA in injection samples.

Hapten synthesis and development of an indirect competitive enzyme-linked immunosorbent assay for chlorpromazine in pork, chicken and swine liver by Yu-Dong Shen; Ben Xiao; Zhen-Lin Xu; Hong-Tao Lei; Hong Wang; Jin-Yi Yang; Yuan-Ming Sun (pp. 2797-2803).

The use of chlorpromazine (CPZ) as a sedative for livestock has been prohibited in the European Union and many other countries. In this study, a new hapten 7-amino-chlorpromazine sulfoxide (hapten 1) against CPZ was synthesized and coupled to ovalbumin (OVA) as an immunogen to produce polyclonal antibody (PAb) specific for CPZ. An heterologous hapten 7-(4-carboxyl-phenylazo)-chlorpromazine (hapten 2) was synthesized and coupled to bovine serum albumin (BSA) as coating antigen to improve the assay sensitivity. The results showed that the hapten-heterologous systems exhibited 20 times higher sensitivity than the hapten-homologous one. Based on the hapten-heterologous system, an indirect competitive enzyme-linked immunosorbent assay (ELISA) for CPZ was developed, the IC50 value was 0.58 ng mL⁻¹ and the limit of detection was 0.03 ng mL⁻¹. The assay showed no cross-reaction with the CPZ analogues. The average recoveries of CPZ from spiked samples were estimated to range from 77.1% to 98.6%, with a coefficient of variation (CV) of less than 10.9%. Linear regression analysis showed a good correlation between the CPZ concentrations obtained from ELISA and HPLC analysis, which suggested that the ELISA is a convenient supplementary analytical tool for monitoring CPZ.

Batch injection analysis with amperometric detection: application for simultaneous analysis using a single working electrode by Rodrigo Amorim Bezerra da Silva; Denise Tofanello Gimenes; Thiago Faria Tormin; Rodrigo Alejandro Abarza Munoz; Eduardo Mathias Richter (pp. 2804-2808).

In this work, we describe for the first time the association of batch injection analysis (BIA) with dual pulse amperometric (DPA) detection for simultaneous determination of multi-analytes using a single working electrode. The sequence of pulses is selected in such a way that the analytes are detected individually and independently at the same working unmodified electrode (using a correction factor). BIA provides fast response (high-throughput analysis), elevated precision, reduction of sample volumes and minimization of waste. To illustrate the potential of this method, BIA-DPA was applied for the simultaneous determination of biodiesel preservatives (tert-butylhydroquinone and butylated hydroxyanisole) and pharmaceutical compounds (paracetamol and caffeine or dipyrone and caffeine).

Simple and effective method to measure the diffusion coefficient of organic vapors in porous media by Hongyang Li; Ali R. Zand; Yuri Sikorski; Bojan Markicevic; Jennifer Meyers; Carlos Rincon; Elizabeth Bowden; Travis Bethel; Matthew S. Sanders; Homayun K. Navaz; Montserrat Rabago Smith (pp. 2809-2814).

A quick and reliable method to measure a vapor concentration within porous substrate was developed. The technique consists of two steps, where a modified head space single drop microextraction (HS-SDME) sampling is used to entrap the vapor phase. In the second step, the entrapped vapor concentration is measured by gas chromatography (GC-FID). The technique is used to measure an effective diffusion coefficient of n-pentane in dry medium grain sand, with the sand partially saturated with water as an inert liquid. The measurements are carried out in a cylindrical sand holder on which the HS-SDME sampling ports are mounted. A linear vapor concentration profile along the bed thickness is found. From known concentration gradient and measuring the mass flux gravimetrically, the effective diffusion coefficient is determined. It turns out that the diffusion coefficient decreases from 8.49 × 10⁻⁶ for dry sand to 7.13 × 10⁻⁶ m² s⁻¹ as a function of water saturation. Additional hindrance to the vapor transport is observed from both the simple volumetric effect due to the porous medium void space reduction caused by the presence of water and increase of the tortuosity.

A kinetic spectrophotometric method for vanadium(v) determination in food samples using a Janus Green-bromate system by M. Reza Shishehbore; Roohollah Jokar (pp. 2815-2821).

This paper describes a new, simple, sensitive and selective catalytic kinetic spectrophotometric method for trace amount determination of vanadium(v) in food samples. The method is based upon the catalytic effect of vanadium(v) on the oxidation of Janus Green by bromate in sulfuric acid media. The reaction was followed spectrophotometrically by measuring the decrease in absorbance of Janus Green at 618 nm. The dependence of sensitivity on the reaction variables was studied and discussed. Under optimum experimental conditions, the fixed time procedure was used to obtain a calibration curve over the range of 0.5–150.0 ng mL⁻¹ of vanadium(v). The calculated detection limit (3Sb/m) was 0.11 ng mL⁻¹ for twelve replicate measurement of blank signal. The relative standard deviations for six replicate determinations of 10.0, 50.0 and 100.0 ng mL⁻¹ of vanadium(v) were 1.22, 0.96 and 0.80%, respectively. The effect of various species commonly associated with vanadium(v) in real samples was also investigated. The proposed method was successfully applied for the determination of vanadium(v) in food samples and the results were in excellent agreement with those of atomic absorption spectrometry.

Characterization of lysophosphatidic acid subspecies produced by autotaxin using a modified HPLC ESI-MS/MS method by Dayanjan S. Wijesinghe; Eric K. Mayton; Jennifer A. Mietla; Abir Mukherjee; Jinhua Wu; Xianjun Fang; Charles E. Chalfant (pp. 2822-2828).

Lysophosphatidic acid (LPA) is a bioactive lipid with a plethora of biological functions including roles in cell survival, proliferation, and migration. Although high-performance liquid chromatography electrospray ionization tandem mass spectrometry (HPLC ESI-MS/MS) technology has been used to measure the levels of LPA in human blood, serum and plasma, current methods cannot readily detect the minute levels of LPA from cell culture. In this study, a modified HPLC ESI-MS/MS method with enhanced sensitivity was developed, which allows accurate measurements of LPA levels with a limit of quantitation at approximately 10 femtomoles. The method was validated by quantitation of LPA levels in the media of previously characterized cell lines ectopically expressing autotaxin. Specifically, autotaxin overexpression induced an increase in the 16:0, 18:2, 18:1, 18:0, and 20:4 subspecies of LPA, but not the 22:6 LPA subspecies. Lastly, this HPLC ESI-MS/MS method was cross-validated via biological assays previously utilized to assay LPA levels. Hence, this HPLC ESI-MS/MS method will allow researchers to measure in vitro LPA levels and also distinguish between specific LPA subspecies for the delineation of individual biological mechanisms.

Enzymatic conversion of arginine to citrulline for improving fragmentation of N^α-tris(2,4,6-trimethoxyphenyl)phosphonium-acetylated peptides by tandem mass spectrometry by Hiroki Kuyama; Chihiro Nakajima; Takashi Nakazawa; Osamu Nishimura (pp. 2829-2835).

We present a technique for improving fragmentation in tandem mass spectrometry (MS/MS) of arginine-containing peptides by derivatising the N-termini with the tris(2,4,6-trimethoxyphenyl)phosphonium acetyl group (TMPP-Ac), followed by the conversion of arginine to citrulline with peptidyl arginine deiminase. Owing to the use of enzyme reaction, the deimination occurred specifically at arginine residues and proceeded under mild conditions (at 55 °C and pH 7.4, for 3 h). Although the TMPP-Ac-tagged arginine-containing peptides undergo fragmentation to give spectra not informative enough to obtain sequence data, the deimination to yield the corresponding citrulline-containing peptides has greatly enhanced the performance of matrix assisted laser desorption/ionization (MALDI) MS/MS by limiting the observation of fragment peaks to those of a-type ions. Additional information available to interpret the fragment patterns for sequencing includes the subsidiary but characteristic appearance of peaks due to the −17 Da and −43 Da neutral losses of ammonia and isocyanic acid, respectively, from a-type ions.

Fast analysis of flavonoids in apple juice on new generation halo column by SPE-HPLC by Imran Ali; Salma M. Z. Al-kindy; Fakhreldin O. Suliman; Syed Dilshad Alam (pp. 2836-2841).

A fast SPE-HPLC method is described for the analysis of flavonoids in apple juice. The mobile phase used was water-acetonitrile (60 : 40, v/v) at 0.80 mL min⁻¹ flow rate with UV detection at 252 nm. The column used was new generation Halo C18 (100 × 46 mm; shell particles; 2.7 μm). The capacity factors were in the range of 0.67 to 20.56, respectively. The separation and resolution factors ranged from 1.18–2.21 and 1.00–10.00, respectively. The values for LOD and LOQ for flavonoids ranged from 0.40–5.5 ng and 2.25–26.0 ng, respectively. The linearity was observed in the concentration ranges of 0.01 to 0.10 mg mL⁻¹ for all flavonoids. The concentrations of quercetin, apigenin, kaemferol and chrysin in apple juice were 4.00, 0.50, 0.40 and 0.25 mg kg⁻¹, respectively. Therefore, the reported method can be used for the quality control of apple juice in food industries. Besides, this method can also be used for the analyses of flavonoids in other fruits and vegetables.

Simultaneous voltammetric determination of Brilliant Blue and Tartrazine in real samples at the surface of a multi-walled carbon nanotube paste electrode by Sayed Mehdi Ghoreishi; Mohsen Behpour; Mahshid Golestaneh (pp. 2842-2847).

A carbon paste electrode (CPE) chemically modified with multi walled carbon nanotubes (MWCNTs) was used for the sensitive and selective determination of Brilliant Blue (BB) and Tartrazine (Tz) by voltammetric methods such as cyclic, differential pulse and square wave voltammetry (CV, DPV, and SWV), and chronoamperometry (CHA). The peak current increased linearly with the BB concentration within the concentration range of 0.05 to 22.0 μmol l⁻¹ for DPV and from 0.05 to 25.0 μmol l⁻¹ for SWV. The detection limits (S/N > 3) for BB by DPV and SWV were found to be 9.0 and 5.0 nmol l⁻¹, respectively. Results of CV showed two well-resolved anodic waves with the peak separation approximately 200 mV for the electrochemical oxidation of BB and Tz, which makes it possible for simultaneous determination of both compounds. The treatment of the CV data showed that the redox of BB and Tz was reversible diffusion-controlled and totally irreversible reactions, respectively. The diffusion coefficient (D/cm² s⁻¹ = 2.8 × 10⁻⁵) for BB was determined using chronoamperometry. DPV method was applied for the quantitative determination of BB and Tz. High sensitivity and selectivity, low detection limit (nanomolar), good reproducibility, easy preparation and regeneration of the electrode make it very suitable for the determination of BB and Tz in soft drinks.

Analysis of benzophenones in environmental water samples after topical skin application using dispersive liquid–liquid microextraction and micellar electrokinetic capillary chromatography by Zhenli Deng; Lijuan Han; Jing Zhang; Yiwei Wu (pp. 2848-2853).

Dispersive liquid–liquid microextraction (DLLME) was developed for MEKC determination of 2,4-dihydroxy-benzophenone (HBP) and 2-hydroxy-4-methoxy-benzophenone (HMBP) in environmental water samples after topical skin application. Parameters affecting the extraction efficiency were investigated in detail. Under the optimum conditions, enrichment factors (EFs) of 208.9 for HBP and 194.6 fold for HMBP were obtained. The detection limits are 0.52 μmol L⁻¹ HBP and 0.29 μmol L⁻¹ HMBP, and the precisions for eight replicate measurements of 5.0 μmol L⁻¹ of HBP and HMBP are 4.9% and 1.5%, respectively. Environmental water samples after topical skin application were successfully analyzed by the proposed method with satisfactory results.

A cost-effective acid digestion method using closed polypropylene tubes for inductively coupled plasma optical emission spectrometry (ICP-OES) analysis of plant essential elements by Matthew S. Wheal; Teresa O. Fowles; Lyndon T. Palmer (pp. 2854-2863).

A novel closed-tube nitric acid/hydrogen peroxide digestion method was developed for inductively coupled plasma optical emission spectrometry (ICP-OES) analysis of plant tissue and tested on six botanical reference materials. A suite of 18 mineral elements commonly found in plant tissues as either essential elements (B, Ca, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, S, Se, Zn), potentially toxic metals (Al, Cd, Cr), or soil contaminants (Ti) was analysed by radial view ICP-OES after digestion by the new method and two open-tube methods. Closed-tube method blanks showed less frequent and less severe contamination than the open tube blanks. The closed-tube method was as efficient as the open-tube digestions of reference materials, achieving recoveries of 94–113% of published concentrations for most essential elements, with variability of 2–6%RSD, while the open-tube digests yielded 93–115% recovery and 1–8% RSD. Boron was accurately recovered by the closed-tube method but some loss by volatilization was observed in perchloric acid digests. Concentrations of minor elements (Cd, Cr, Mo, Ni, Ti) in some reference materials were below method reporting limits. High concentrations of Ti (>1 mg kg⁻¹) detected in leafy reference materials was suspected to be derived from soil contamination, potentially also increasing Al and Fe concentrations. Recovery of Al was highly dependant on sample material and digestion method. The closed-tube method uses smaller masses, less reagent, lower digest temperatures and takes less time to complete digestion than existing methods.

Successful characterization of degradation products of drugs using LC-MS tools: Application to piroxicam and meloxicam by Dattatray T. Modhave; Tarun Handa; Ravi P. Shah; Saranjit Singh (pp. 2864-2872).

The degradation behavior of piroxicam and meloxicam was studied by subjecting the drugs individually to hydrolytic (acidic, basic and neutral), oxidative, photolytic and thermal stress. Both the drugs showed significant degradation in hydrolytic, oxidative and photo-neutral conditions, while they were stable under dry heat and on exposure to light in the solid state. In total, five and four degradation products were formed from piroxicam and meloxicam, respectively. For characterization of the degradation products, mass fragmentation pathways of both the drugs were established with the help of MS/TOF, MSⁿ and H/D exchange mass studies, followed by LC-MS/TOF and on-line H/D exchange experiments on the degradation products. The collected data helped to identify the degradation products of both the drugs. Eventually, degradation pathways were established, along with proposition of mechanisms for the formation of the degradation products.

Analysis of haloacetic acids in drinking water using post-column reaction-ion chromatography with on-line internal standardization by Patricia L. Ranaivo; Christina M. Henson; Paul S. Simone; Gary L. Emmert (pp. 2873-2880).

A post-column reaction-ion chromatography analyzer (PCR-IC) with automated internal standardization (IS) has been optimized to determine nine haloacetic acid (HAAs) species in drinking water while operating in near real-time with a one hour analysis time. The IS-PCR-IC method requires minimal sample preparation that consists of passing water samples through cartridges to remove anions and introducing the pretreated samples into the on-line channel of the automated instrumentation. Two sets of water samples have been analyzed and method detection limit (MDL), accuracy and precision measurements have been conducted prior to the water sample analysis. The experimental MDL values for the HAA species ranged from 1.4 to 7.8 μg L⁻¹; the accuracy ranged from 75.9 to 112%; and the precision ranged from 6.2 to 34.6%. The concentration of each HAA and the Total HAAs found in these water samples were determined using internal standardization and the results were compared to USEPA Method 552.3. The bias estimates between these two methods for Total HAA9 range from −8.3 to 12.5 μg L⁻¹.

Validation of a microwave-assisted extraction gas chromatography detection method for the determination of fungicides in grapes by L. Lagunas-Allué; J. Sanz-Asensio; M. T. Martínez-Soria (pp. 2881-2892).

A microwave assisted extraction (MAE) method was developed for the simultaneous extraction of eight pesticides, vinclozolin, dichlofluanid, penconazole, captan, quinoxyfen, fluquinconazole, boscalid and pyraclostrobin, in grapes. The different parameters affecting the MAE method, such as temperature, extraction time and nature and volume of the extraction solvent, were evaluated. The experimental procedure was optimized using a multivariate statistical approach and the final analyses were carried out by gas chromatography-mass spectrometry (GC-MS). These eight fungicides could be efficiently extracted from 2.0 g of grapes with 10 mL of hexane/acetone (1 : 1, v/v) mixture at 105 °C in 10 minutes with microwave power set at 100% (600 W). Using the optimized conditions, the method was validated in terms of accuracy and precision. A matrix effect study was also carried out using different grape samples. Recoveries from spiked grape samples ranged from 82 to 107% and relative standard deviations were less than 10%. Detection and quantification limits ranged from 0.7 to 1.7 μg kg⁻¹ and 2.2 to 5.8 μg kg⁻¹, respectively, which were lower than the maximum residue limits of the pesticides in grape samples established by the European Union. Uncertainty assessment of measurement obtained by applying the proposed analytical method was estimated according to EURACHEM/CITAC guide. The expanded uncertainties were below 26% and 7% at two concentration levels, 10 and 50 μg kg⁻¹, respectively.

A new capillary electrophoresis-direct chemiluminescence system for the determination of epinephrine and mechanism study by Yingying Su; Chen Chen; Xiaoling Hou; Jiyou Zhang (pp. 2893-2897).

Epinephrine can significantly enhance the intensity of chemiluminescence (CL) produced by the reaction between luminol and potassium hexacyanoferrate(iii) (K3[Fe(CN)6] under alkaline conditions, and the increased CL intensity is proportional to the concentration of epinephrine. Based on this phenomenon, a new, simple and rapid capillary electrophoresis (CE)-direct CL detection method was established for sensitive determination of epinephrine. Optimal separation and detection were obtained with an electrophoretic buffer of 20 mM sodium (pH = 9.00) borate containing 5 × 10⁻⁵ M luminol and a post-column solution of 1 × 10⁻⁴ M K3[Fe(CN)6] in 0.5 M NaOH. A limit of detection of 8.3 × 10⁻⁹ M was achieved. The relative standard derivations (RSD) of CL intensity and migration time were 3.5% and 0.8%, respectively. The applicability of the method for analysis of pharmaceutical and biological samples was examined. And the possible mechanism of the enhanced CL intensity was proposed via examining CL and UV-vis spectra.

Metabolomics analysis of major metabolites in medicinal herbs by Chin Chye Teo; Swee Ngin Tan; Jean Wan Hong Yong; Tenmoli Ra; Peiling Liew; Liya Ge (pp. 2898-2908).

A metabolomics approach with a platform consisting of GC-MS, ¹H NMR and HPLC-UV was used to investigate the regulatory mechanisms of metabolic pathways in Stevia rebaudiana and Coptidis rhizoma. The data suggested that glycolysis and the oxidative pentose phosphate pathway (OPPP) remained as the main components of plant respiration in these botanicals. However, the absence of citrate, succinic acids, glutamate and fumarate in Stevia suggested that the tricarboxylic acid (TCA) cycle was not required extensively to synthesize its bioactive diterpene glycosides. The results further suggested that the carbon flow was directed between the shikimic acid and methylerythritol 4-phosphate (MEP) pathway. For the Coptidis, the use of an alternative biosynthesis route with proline, phenylalanine, catechollactate and 2-mono-isobutyrin was proposed to synthesize its major bioactive alkaloids. It was observed that different fatty acids might be needed to modulate the biosynthesis of the bioactive secondary metabolites in the medicinal herbs. Concurrently, primary and secondary metabolite profiling was studied by unsupervised multivariate Principal Component Analysis (PCA) to discriminate and assign the different phenotypes under various cultivation conditions. Hence, the simultaneous profiling of primary and secondary metabolites could significantly aid the existing functional genomics approaches to study the biosynthesis function in medicinal herbs.

Application of magnetic material in the determination of polycyclic aromatic hydrocarbons in tree leaves by high performance liquid chromatography by Rui shen; Fei Yang; Jianping Wang; Yong Li; Shunji Xie; Chunyan Chen; Qingyun Cai; Shouzhuo Yao (pp. 2909-2914).

Carbon coated Fe3O4 magnetic particles (Fe3O4/C) were synthesized by hydrothermal reaction, and characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), vibrating sample magnetometry (VSM) and transmission electron microscopy (TEM). The material is applied to microwave-assisted extraction for clean-up and enrichment of polycyclic aromatic hydrocarbons (PAHs) from tree leaves. Magnetic solid-phase extraction (MSPE) parameters including elution solvents, amount of sorbents and enrichment time are optimized together with microwave extraction time, power, extraction solvents and the ratio of liquid to solid. Under the optimal conditions, the developed method provides spiked recoveries of 77.7–103.8% with RSDs of less than 4.0%, and limits of detection (LOD) of 0.5–2.0 ng g⁻¹. PAHs in tree leaves are successfully determined.

Combined cloud point extraction and Tween 20-stabilized gold nanoparticles for colorimetric assay of silver nanoparticles in environmental water by Zong-Han Wu; Wei-Lung Tseng (pp. 2915-2920).

This study investigated a simple, sensitive, and selective method for the colorimetric assay of silver nanoparticles (AgNPs) using Triton X-114-based cloud point extraction (CPE) as a preconcentration step and Tween 20-stabilized gold nanoparticles (Tween 20-AuNPs) as a colorimetric probe. After heating beyond the cloud point temperature of Triton X-114, a solution containing Triton X-114 micelles and AgNPs separated into a surfactant-rich phase (small volume) and a dilute aqueous phase. AgNPs partitioned into a Triton X-114-rich phase through a hydrophobic interaction between Triton X-114 micelles and AgNPs. After phase separation, the concentrated AgNPs oxidized to form Ag⁺ upon adding H2O2. The generated Ag⁺ triggered the aggregation of Tween 20-AuNPs in a high-ionic-strength solution because the reduction of Ag⁺ on the AuNP surface enabled Tween 20 (stabilizer) to be removed from the NP surface. The efficiency of Triton X-114-based CPE for the AgNPs was found to be insensitive to their coating type when the AgNPs were modified with a nonionic surfactant and a small ligand. Under optimal extraction and detection conditions, the selectivity of this method for AgNPs was greatly higher than for other nanomaterials. The limit of detection for 10 nm AgNPs was measured to be 1 ng mL⁻¹. This method was successfully applied to the analysis of 10 nm AgNPs in tap water and seawater.

Development of a gas phase chemiluminescence system for the measurement of arsenic in drinking water by Kirubel Assegid; Farhan Ahmed; Sad Ahamed; Abul Hussam (pp. 2921-2928).

Solid-phase microextraction with a novel graphene-coated fiber coupled with high-performance liquid chromatography for the determination of some carbamates in water samples by Guangying Zhao; Shuangju Song; Chun Wang; Qiuhua Wu; Zhi Wang (pp. 2929-2935).

In this study, a novel graphene nanocomposite was synthesized and used as a solid-phase microextraction fiber coating material. The application of the graphene-coated fiber was evaluated through the extraction and determination of the four carbamate pesticides (carbofuran, carbaryl, pirimicarb, diethofencarb) in water samples by high performance liquid chromatography-diode array detection. Parameters that affect the extraction efficiencies, such as the extraction time, stirring rate, extraction temperature, and salt addition, were investigated and optimized. Compared with the two commonly used commercial fibers (CW/TPR, 50 μm; PDMS/DVB, 60 μm), the graphene-coated fiber showed higher extraction efficiency. Under the optimum conditions, the limits of detection (LODs), based on a signal-to-noise ratio (S/N) of 3, were 0.1–0.8 ng mL⁻¹. The limits of quantification (LOQ, S/N = 9) were 0.3–2.4 ng mL⁻¹. The linearity was observed in the range from their corresponding LOQs to 400.0 ng mL⁻¹ with the correlation coefficients (r) ranging from 0.9994 to 0.9998. The recoveries of the carbamate pesticides from water samples at spiking levels of 10.0, 50.0 and 100 ng mL⁻¹ were in the range of 83.8%–95.4%, and the relative standard deviations were between 2.2% and 6.6%.

Simultaneous determination of aluminum, copper, iron and zinc in Oscillatoria, Juncus littoralis tissues and wetland water samples by ultrasound-assisted emulsification-microextraction combined with ICP-OES by Hassan Sereshti; Sadjad Bakhtiari; Vahid Khojeh (pp. 2936-2942).

Ultrasound-assisted emulsification microextraction (USAEME) followed by inductively coupled plasma-optical emission spectrometry (ICP-OES) for simultaneous extraction, preconcentration and determination of trace levels of aluminum, copper, iron and zinc in Oscillatoria, Juncus littoralis tissues and wetland water samples is presented. Sodium diethyldithiocarbamate trihydrate (Na-DDTC·3H2O) was used as a chelating agent and tetrachloroethylene was selected as an extraction solvent. The effective parameters of the USAEME method including volume of extraction solvent, ultrasonic time, salt concentration, temperature, concentration of ligand and pH were investigated by a fractional factorial design. The results showed that temperature had no considerable effect on the efficiency. A Box-Behnken design (BBD) was applied to optimize the effective parameters. The optimal conditions were obtained as 48 μL for volume of extraction solvent, 6 min for ultrasonic time, 16.6 (w/v %) for salt concentration, 1440 mg L⁻¹ for concentration of the ligand and 7 for pH. The linear dynamic range (LDR) was 1–1000 μg L⁻¹ with determination coefficient of 0.994–0.998. The limits of detection (LODs) and relative standard deviations (RSDs) were 0.64–0.91 μg L⁻¹ and 2.6–5.3%, respectively. The method was successfully applied to the determination of Al, Cu, Fe and Zn in real environmental samples and satisfactory relative recoveries (92–99%) were obtained.

Determination of seven commonly used organic UV filters in fresh and saline waters by liquid chromatography-tandem mass spectrometry by Stephanie Bratkovics; Yelena Sapozhnikova (pp. 2943-2950).

An analytical method for the simultaneous determination of seven of the most widely used organic UV filter compounds in tap and saline waters was developed and validated. Target compounds included oxybenzone, dioxybenzone, sulisobenzone, avobenzone, octocrylene, octinoxate, and padimate-O. Water samples were adjusted to pH 2 prior to solid-phase extraction (SPE) using Oasis HLB 500 mg cartridges. The detection and quantification were performed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) with positive electrospray ionization (ESI) using Multiple Reaction Monitoring mode (MRM). Calculated recoveries from fortified samples ranged from 74 to 109% with relative standard deviations of 6–25% for fortified tap water samples and from 71 to 111% with relative standard deviations 2–12% for fortified seawater samples, indicating acceptable method accuracy and precision (n = 5). Method reporting limits ranged from 0.5 to 25 ng L⁻¹ for the seven compounds. Oxybenzone, avobenzone, octocrylene, octinoxate, and padimate-O were detected in seawater samples collected from Folly Beach, South Carolina in the summer of 2010, at concentrations ranging from 10 to 2013 ng L⁻¹, demonstrating the ability of the developed method to measure target compounds in environmental samples. Oxybenzone and octocrylene were found in the highest concentrations, up to 2013 ng L⁻¹ and 1409 ng L⁻¹, respectively. Concentrations for avobenzone, octinoxate, and padimate-O ranged from 62–321 ng L⁻¹, 30–264 ng L⁻¹ and <1–111 ng L⁻¹, respectively, in surface seawater samples (n= 4). Dioxybenzone and sulisobenzone were not detected in any samples from the four sites (method reporting limits 1 ng L⁻¹). To our knowledge, this is the first study reporting sunscreen compounds in the coastal waters of the U.S.A.

Back matter (pp. 2951-2952).

A series of Gd2Ti2O7/GdCrO3 composites are prepared by solid state combustion method using Gd(NO3)3, TiO2, Cr2O3 as metal source and urea as a fuel. The composites are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible diffuse reflectance spectra (DRUV–vis), Brunauer–Emmett–Teller (BET) surface area measurements, photoluminescence spectra (PL), X-ray photoelectron spectroscopic (XPS) studies, photocurrent measurements etc. The photocatalytic activity of the composites is examined towards hydrogen production without using any co-catalyst under visible light illumination. The rate of formation of hydrogen is measured by the photocatalytic activity measurement device and gas chromatography (GC). The highest efficiency is observed over the composite GTC (Cr:Gd:Ti = 1 : 1 : 1). On the basis of photocurrent measurements and PL, a mechanism for the enhanced photocatalytic activity has been discussed.

Back cover (pp. 2953-2954).

We demonstrate a simple method for tuning the morphologies of as-spun micellar thin films by modifying the surface energy of silicon substrates. When a polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) copolymer dissolved in o-xylene was spin-coated onto a PS-modified surface, a dimple-type structure consisting of a thick PS shell and P2VP core was obtained. Subsequently, when the films were immersed in metal precursor solutions at certain periods of time and followed by plasma treatment, metal individual dots in a ring-shaped structure, metal nanoring, and metal corpuscle arrays were fabricated, depending on the loading amount of metal precursors. In contrast, when PS-b-P2VP films cast onto silicon substrates with a native oxide were used as templates, only metal dotted arrays were obtained. The combination of micellar thin film and surface energy modification offers an effective way to fabricate various nanostructured metal or metal oxide films.

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Analytical Methods (v.3, #12)

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Analytical Methods (v.3, #12)