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Analytica Chimica Acta (v.662, #1)

Editorial Board (pp. iii).

Arsenic speciation in natural waters by cathodic stripping voltammetry by Kristoff Gibbon-Walsh; Pascal Salaün; Constant M.G. van den Berg (pp. 1-8).

Contamination of groundwater with arsenic (As) is a major health risk through contamination of drinking and irrigation water supplies. In geochemically reducing conditions As is mostly present as As(III), its most toxic species. Various methods exist to determine As in water but these are not suitable for monitoring arsenic speciation at its original pH and without preparation. We present a method that uses cathodic stripping voltammetry (CSV) to determine reactive As(III) at a vibrating, gold, microwire electrode. The As(III) is detected after adsorptive deposition of As(OH)₃⁰, followed by a potential scan to measure the reduction current from As(III) to As(0). The method is suitable for waters of pH 7–12, has an analytical range of 1nM to 100μM As (0.07–7500ppb) and a limit of detection of 0.5nM with a 60s deposition time. The As speciation protocol involves measuring reactive As(III) by CSV at the original pH and acidification to pH 1 to determine inorganic As(III)+As(V) by anodic stripping voltammetry (ASV) using the same electrode. Total dissolved As is determined by ASV after UV-digestion at pH 1. The method was successfully tested on various raw groundwater samples from boreholes in the UK and West Bengal.

Keywords: Cathodic stripping voltammetry; Arsenic; Arsenic speciation; Groundwater; Vibrating electrode

Micellar extraction and high performance liquid chromatography-ultra violet determination of some explosives in water samples by Saeed Babaee; Asadollah Beiraghi (pp. 9-13).

An analytical method based on the cloud point extraction combined with high performance liquid chromatography is used for the extraction, separation and determination of four explosives; octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazine (HMX), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 2,4,6-trinitrotoluene (TNT) and pentaerythritol tetranitrate (PETN). These compounds are extracted by using of Triton X-114 and cetyl-trimethyl ammonium bromide (CTAB). After extraction, the samples were analyzed using a HPLC-UV system. The parameters affecting extraction efficiency (such as Triton X-114 and CTAB concentrations, amount of Na₂SO₄, temperature, incubation and centrifuge times) were evaluated and optimized. Under the optimum conditions, the preconcentration factor was 40 and the improvement factors of 34, 29, 61 and 42 with detection limits of 0.09, 0.14, 0.08 and 0.40 (μgL⁻¹) were obtained for HMX, RDX, TNT and PETN, respectively. The proposed method was successfully applied to the determination of these compounds in water samples and showed recovery percentages of 97–102% with RSD values of 2.13–4.92%.

Keywords: Cloud point extraction; Explosives; High performance liquid chromatography; Surfactants

Development of a highly sensitive and selective hyphenated technique (molecularly imprinted micro-solid phase extraction fiber–molecularly imprinted polymer fiber sensor) for ultratrace analysis of folic acid by Bhim Bali Prasad; Mahavir Prasad Tiwari; Rashmi Madhuri; Piyush Sindhu Sharma (pp. 14-22).

A simple polymerization strategy is reported in this work which allows molecularly imprinted polymeric fiber (monolith) fabrication for direct use in sensing devices. This is advantageous for achieving higher degree of enrichment of target analyte (folic acid) from the complex matrices of real samples, without any surface fouling, cross-reactivity, and non-specific (false-positive) contributions. In order to measure serum folic acid at ultratrace level to detect spina bifida, a neural tube defect in mother, and other acute cases of proteomic diseases, the hyphenation between molecularly imprinted micro-solid phase extraction fiber and a complementary molecularly imprinted polymer–carbon composite fiber sensor has been found quite efficient. The primitive diagnosis of many chronic diseases is feasible by estimating folic acid as biomarker, with the detection limit as low as 0.0036ngmL⁻¹ (relative standard deviation=0.13%, signal/noise=3) in human blood serum.

Keywords: Molecularly imprinted micro-solid phase extraction fiber; Molecularly imprinted polymer–carbon composite fiber sensor; Folic acid; Differential pulse; Cathodic stripping voltammetry; Real sample analysis

New method for determination of trihalomethanes in exhaled breath: Applications to swimming pool and bath environments by Carolina Lourencetti; Clara Ballester; Pilar Fernández; Esther Marco; Celia Prado; Juan F. Periago; Joan O. Grimalt (pp. 23-30).

A method for the estimation of the human intake of trihalomethanes (THMs), namely chloroform, bromodichloromethane, dibromochloromethane and bromoform, during showering and bathing is reported. The method is based on the determination of these compounds in exhaled breath that is collected by solid adsorption on Tenax using a device specifically designed for this purpose. Instrumental measurements were performed by automatic thermal desorption coupled to gas chromatography with electron capture detection. THMs in exhaled breath samples were determined during showering and swimming pool attendance. The levels of these compounds in indoor air and water were also determined as reference for interpretation of the exhaled breath results. The THM concentrations in exhaled breath of the volunteers measured before the exposure experiments showed a close correspondence with the THMs levels in indoor air where the sampler was located. Limits of detection in exhaled breath were dependent on THM analytes and experimental sites. They ranged between 170 and 710ngm⁻³ in the swimming pool studies and between 97 and 460ngm⁻³ in the showering studies. Application of this method to THMs determination during showering and swimming pool activities revealed statistically significant increases in THMs concentrations when comparing exhaled breath before and after exposure.

Keywords: Trihalomethanes; Exhaled breath; Exposure studies; Swimming pool contamination; Showering; Bathing

Determination of fluoroquinolone antibiotics in environmental water samples based on magnetic molecularly imprinted polymer extraction followed by liquid chromatography–tandem mass spectrometry by Ligang Chen; Xiaopan Zhang; Yang Xu; Xiaobo Du; Xin Sun; Lei Sun; Hui Wang; Qi Zhao; Aimin Yu; Hanqi Zhang; Lan Ding (pp. 31-38).

A simple method based on magnetic separation for selective extraction of fluoroquinolones (FQs) from environmental water samples has been developed using magnetic molecularly imprinted polymer (MMIP) as sorbent. The MMIP has been prepared using ciprofloxacin as template molecule, methacrylic acid as functional monomer, ethylene glycol dimethacrylate as cross-linking agent and Fe₃O₄ magnetite as magnetic component. The polymer has been characterized by scanning electron microscopy, Fourier-transform infrared spectrometry and vibrating sample magnetometry. Various parameters affecting the extraction efficiency were evaluated in order to achieve optimal concentration and reduce non-specific interactions. The analytes desorbed from the polymers were determined by liquid chromatography–tandem mass spectrometry. The matrix effect was evaluated by using different washing solvents for removing interfering compounds from the MMIPs after sample loading. Under the optimal conditions, the linearity of the method obtained is in the range of 20–2000ngL⁻¹. The detection limits of FQs are in the range of 3.2–6.2ngL⁻¹. The relative standard deviations of intra- and inter-day tests ranging from 2.5 to 7.2% and from 3.6 to 9.1% are obtained. In all three spiked levels (20, 100 and 200ngL⁻¹), the recoveries of FQs are in the range of 76.3–94.2%. The proposed method was successfully applied to determine FQs including ciprofloxacin, enrofloxacin, lomefloxacin, levofloxacin, fleroxacin and sparfloxacin in different water samples, such as lake water, river water, primary and final sewage effluent. Ciprofloxacin and fleroxacin were found in primary and final sewage effluent samples with the contents in the range of 26–87ngL⁻¹.

Keywords: Magnetic molecularly imprinted polymer; Fluoroquinolone antibiotics; Environmental water; Liquid chromatography–tandem mass spectrometry

Determination of the steroid hormone levels in water samples by dispersive liquid–liquid microextraction with solidification of a floating organic drop followed by high-performance liquid chromatography by Chu-Chi Chang; Shang-Da Huang (pp. 39-43).

In this study, the steroid hormone levels in river and tap water samples were determined by using a novel dispersive liquid–liquid microextraction method based on the solidification of a floating organic drop (DLLME-SFO). Several parameters were optimized, including the type and volume of the extraction and dispersive solvents, extraction time, and salt effect. DLLME-SFO is a fast, cheap, and easy-to-use method for detecting trace levels of samples. Most importantly, this method uses less-toxic solvent. The correlation coefficient of the calibration curve was higher than 0.9991. The linear range was from 5 to 1000μgL⁻¹. The spiked environmental water samples were analyzed using DLLME-SFO. The relative recoveries ranged from 87% to 116% for river water (which was spiked with 4μgL⁻¹ for E1, 3μgL⁻¹ for E2, 4μgL⁻¹ for EE2 and 9μgL⁻¹ for E3) and 89% to 102% for tap water (which was spiked with 6μgL⁻¹ for E1, 5μgL⁻¹ for E2, 6μgL⁻¹ for EE2 and 10μgL⁻¹ for E3). The detection limits of the method ranged from 0.8 to 2.7μgL⁻¹ for spiked river water and 1.4 to 3.1μgL⁻¹ for spiked tap water. The methods precision ranged from 8% to 14% for spiked river water and 7% to 14% for spiked tap water.

Keywords: Dispersive liquid–liquid microextraction; Water sample analysis; Steroid hormone; High-performance liquid chromatography

Direct colorimetric detection of copper(II) ions in sampling using diffusive gradients in thin-films by Russell W. McGifford; Andrew J. Seen; Paul R. Haddad (pp. 44-50).

A novel binding phase was developed for use in diffusive gradients in thin-film (DGT) sampling for Cu(II) by employing methylthymol blue as a chelating and chromogenic agent. Methylthymol blue was adsorbed onto beads of Dowex 1×8 resin (200–400 mesh) and the resin beads were then immobilised onto an adhesive disc. Analysis of exposed binding discs by either UV–vis spectrophotometry or computer imaging densitometry provided robust quantification of adsorbed Cu(II) in the 0.2–1μgcm⁻² range, allowing detection at μgL⁻¹ concentrations in the test solution (ca. 17μgL⁻¹ for a 24h deployment), and in good agreement with established DGT theory. The method was shown to be a potential replacement for binding phases based on Chelex 100 where a colorimetric response to a specific metal is desired.

Keywords: Passive sampling; Binding phase; Colorimetry; Computer imaging densitometry; Copper; Methylthymol blue

Novel approaches in analysis of Fusarium mycotoxins in cereals employing ultra performance liquid chromatography coupled with high resolution mass spectrometry by M. Zachariasova; O. Lacina; A. Malachova; M. Kostelanska; J. Poustka; M. Godula; J. Hajslova (pp. 51-61).

Rapid, simple and cost-effective analytical methods with performance characteristics matching regulatory requirements are needed for effective control of occurrence of Fusarium toxins in cereals and cereal-based products to which they might be transferred during processing. Within this study, two alternative approaches enabling retrospective data analysis and identification of unknown signals in sample extracts have been implemented and validated for determination of 11 major Fusarium toxins. In both cases, ultra-high performance liquid chromatography (U-HPLC) coupled with high resolution mass spectrometry (HR MS) was employed.¹³C isotopically labeled surrogates as well as matrix-matched standards were employed for quantification. As far as time of flight mass analyzer (TOF-MS) was a detection tool, the use of modified QuEChERS (quick easy cheap effective rugged and safe) sample preparation procedure, widely employed in multi-pesticides residue analysis, was shown as an optimal approach to obtain low detection limits. The second challenging alternative, enabling direct analysis of crude extract, was the use of mass analyzer based on Orbitrap technology. In addition to demonstration of full compliance of the new methods with Commission Regulation (EC) No. 401/2006, also their potential to be used for confirmatory purposes according to Commission Decision 2002/657/EC has been critically assessed.

Keywords: Fusarium; mycotoxins; Quick easy cheap effective rugged and safe; Ultra-high performance liquid chromatography; Time of flight mass spectrometry; Orbitrap mass spectrometry

Simultaneous determination of aflatoxins B1, B2, G1, G2, M1 and M2 in peanuts and their derivative products by ultra-high-performance liquid chromatography–tandem mass spectrometry by Baifen Huang; Zheng Han; Zengxuan Cai; Yongjiang Wu; Yiping Ren (pp. 62-68).

A reliable ultra-high-performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) method for simultaneous determination of aflatoxins B1, B2, G1, G2, M1 and M2 in peanuts and their derivative products was developed. The sample was extracted by 84% of acetonitrile aqueous solution and the extract was purified by a reliable solid phase extraction-based clean-up method. Then, the analytes were separated on Acquity UPLC HSS T3 column (100mm×2.1mm, 1.8μm particle size), and eluted with a mobile phase consisting of (A) water containing 0.1% formic acid and (B) acetonitrile/methanol (50/50, v/v). The separated compounds were detected with a Waters Micromass Quattro Ultima Pt tandem quadrupole mass spectrometer operating in positive electro-spray ionization using multiple reaction monitoring mode. The established method was extensively validated by determining the linearity ( R²≥0.9990), average recovery (74.7–86.8%) and precision (relative standard deviation≤10.9%). It was shown to be a suitable method for simultaneous determination of the six aflatoxins in peanuts and their derivative products. Finally, a total of 73 samples randomly collected from different areas in Zhejiang province were screened for aflatoxins with the proposed method. The results showed that 31 samples of peanut butter, 14 samples of fresh peanut and 5 samples of musty peanut were contaminated with aflatoxins. Meanwhile, this was the first report on aflatoxins M1 and M2, which were found in unprocessed peanuts and their derivative products.

Keywords: Ultra-high-performance liquid chromatography–tandem mass spectrometry; Aflatoxins; Peanuts

Screening and determination of melamine residues in tissue and body fluid samples by Zongyi Wang; Xi Ma; Liying Zhang; Wenjun Yang; Limin Gong; Pingli He; Zhen Li (pp. 69-75).

Melamine is a chemical product that was sporadically mixed into animal feeds to boost protein content. Excessive melamine in animal feed can induce renal failure and even death in animals. The residue of melamine in edible animal products also threatens human health. Currently, there is no real-time and high throughput method to detect residual melamine in animal tissues. Successful development of such methods is very important for fast and on-site screening of melamine residue in animal tissues to eliminate the potential threat to human health. Here we demonstrate the detection of residual melamine from swine and chicken tissues and body fluids using indirect competitive enzyme-linked immunosorbent assay (ELISA) method. A detection sensitivity of 0.5μgmL⁻¹ and a limit of detection of 0.05μgmL⁻¹ were achieved with this method. A gas chromatography–mass spectrometry (GC–MS) method was also developed to act as a confirmatory and quantitative procedure for the ELISA results. The limits of quantitation (LOQ) of were 0.01μgg⁻¹ and 0.005μgmL⁻¹ for tissues and body fluids, respectively. The two methods showed good agreement ( r²>0.992). The method developed was performed on samples of tissues from chickens fed with melamine-spiked feed.

Keywords: Melamine; Enzyme-linked immunosorbent assay; Gas chromatography–mass spectrometry; Quantification

A selective and sensitive carbon composite coated platinum electrode for aluminium determination in pharmaceutical and mineral water samples by A. Abbaspour; M. Refahi; A. Khalafi-nezhad; M.N. Soltani Rad; S. Behrouz (pp. 76-81).

A novel coated wire electrode (CWE) for Al(III) ions is described based on 2-(1 H-benzo[d]imidazole-1-yl)-1-phenylethanoneoxime as a new ionophore in carbon–PVC composite. The sensor exhibits significantly enhanced selectivity toward Al³⁺ ions over the concentration range 4.3×10⁻⁷ to 5.0×10⁻²M with a lower detection limit of 2.5×10⁻⁷M and a Nernstian slope of 19.41±0.52mVdecade⁻¹ of aluminium activity. This sensor has a short response time of about 10s and is reproducible and stable for at least forty-five days. This proposed CWE which is designed for the first time revealed good selectivity for Al(III) over a wide variety of other cations. The performance of the sensor is best in the pH range of 3.1–5.5 and it also works well in partially non-aqueous medium. Moreover, the assembly has been successfully used as an indicator electrode in the potentiometric titration of aluminium (III) against EDTA and also in determining Al(III) quantitatively in pharmaceutical and mineral water samples.

Keywords: Coated platinum electrode; Carbon composite; Aluminium (III); Coated wire electrode; Phenylethanoneoxime

Evaluation of the feasibility of the electronic tongue as a rapid analytical tool for wine age prediction and quantification of the organic acids and phenolic compounds. The case-study of Madeira wine by A. Rudnitskaya; S.M. Rocha; A. Legin; V. Pereira; J.C. Marques (pp. 82-89).

A set of fourteen Madeira wines comprising wines produced from four Vitis vinifera L. varieties (Bual, Malvasia, Verdelho and Tinta Negra Mole) that were 3, 6, 10 and 17 years old was analysed using HPLC and an electronic tongue (ET) multisensor system. Concentrations of 24 organic acids, phenolic and furanic compounds were determined by HPLC. The ET consisting of 26 potentiometric chemical sensors with plasticized PVC and chalcogenide glass membranes was used. Significance of the effects of age and variety on the ET response and wine composition with respect to the organic acids, phenolics and furanic derivatives were evaluated using ANOVA—Simultaneous Component Analysis (ASCA). Significance of the effects was estimated using a permutation test (1000 permutations). It was found that effects of age, grape variety and their interaction were significant for the HPLC data set and only the effect of age was significant for the ET data. Calibration models of the HPLC and ET data with respect to the wine age and of the ET data with respect to the concentration of the organic acids and phenolics were calculated using PLS1 regression. Models were validated using cross-validation. It was possible to predict wine age from HPLC and ET data with the accuracy in cross-validation of 2.6 and 1.8 years respectively. The ET was capable of detecting the following components (mean relative error in cross-validation is shown in the parentheses): tartaric (8%), citric (5%), formic (12%), protocatehuic (5%), vanillic (18%) and sinapic (14%) acids, catechin (6%), vanillin (12%) and trans-resveratrol (5%). The ET capability of predicting Madeira wine age with good accuracy (1.8 years) as well as quantify of some organic acids and phenolic compounds was demonstrated.

Keywords: Electronic tongue; Potentiometric sensors; Organic acids; Phenolics; Madeira wine; Wine age

Single-walled carbon nanotubes as solid-phase microextraction adsorbent for the determination of low-level concentrations of butyltin compounds in seawater by Noushin Rastkari; Reza Ahmadkhaniha; Nasrin Samadi; Abbas Shafiee; Masud Yunesian (pp. 90-96).

Carbon nanotubes are a kind of new carbon-based nanomaterials, which have drawn great attention in many application fields. The potential of single-walled carbon nanotubes (SWCNTs) as solid-phase microextraction (SPME) adsorbent for the preconcentration of environmental pollutants has been investigated in recent years. In the present study, the feasibility of SWCNTs as SPME adsorbent for the determination of monobutyltin, dibutyltin and tributyltin in seawater samples was studied. To achieve this aim, the potential factors affecting the SPME efficiency, including extraction time, extraction temperature, desorption time, desorption temperature, and salinity were optimized. The developed method showed good performance according to the ICH (International Conference on Harmonization of Technical Requirements for Analytical Methods) criteria. The acquired calibration curves were linear ( r≥0.992) over the concentration range from ≤12 to 2000ngL⁻¹. For all of the analytes, the limit of detection at signal-to-noise ratio of 3 was below 5ngL⁻¹. Furthermore, in comparison with the commercial carboxen/polydimethylsiloxane fiber, the developed SWCNT fiber showed better thermal stability (over 350°C) and longer life span (over 150 times). The application of the proposed method in environmental analyses was shown by analyzing seawater samples from the harbors on the Persian Gulf for butyltin residues. Some of the butyltins were detected in the analyzed samples. Results of the present study demonstrate the feasibility of the SWCNTs as SPME adsorbent for the determination of butyltins in seawater samples.

Keywords: Butyltin compounds; Single-walled carbon nanotubes; Headspace solid-phase microextraction; Seawater; Environmental analyses

A simple and sensitive HPLC method for the simultaneous determination of eight bioactive components and fingerprint analysis of Schisandra sphenanthera by Hua Wei; Lianna Sun; Zongguang Tai; Shouhong Gao; Wen Xu; Wansheng Chen (pp. 97-104).

A simple and sensitive high performance liquid chromatography method with photodiode array detection (HPLC-DAD) was developed for simultaneous determination of eight bioactive constituents (schisandrin, schisandrol B, schisantherin A, schisanhenol, anwulignan, deoxyshisandrin, schisandrin B and schisandrin C) in the ripe fruit of Schisandra sphenanthera and its traditional Chinese herbal preparations Wuzhi-capsule by optimizing the extraction, separation and analytical conditions of HPLC-DAD. The chemical fingerprint of S. sphenanthera was established using raw materials of 15 different origins in China. The chromatographic separations were obtained by an Agilent Eclipse XDB-C18 reserved-phase column (250mm×4.6mm i.d., 5μm) using gradient elution with water–formic acid (100:0.1, v/v) and acetonitrile, at a flow rate of 1.0mLmin⁻¹, an operating temperature of 35°C, and a wavelength of 230nm. The constituents were confirmed by (+) electrospray ionization LC–MS. The new method was validated and was successfully applied to simultaneous determination of components in 13 batches of Wuzhi-capsule. The results indicate that this multi-component determination method in combination with chromatographic fingerprint analysis is suitable for quantitative analysis and quality control of S. sphenanthera.

Keywords: Schisandra sphenanthera; Chromatographic fingerprint; Quality evaluation; High performance liquid chromatography method with photodiode array detection; Liquid chromatography-mass spectrometry

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Analytica Chimica Acta (v.662, #1)

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Analytica Chimica Acta (v.662, #1)