Analytical Methods (v.8, #27)

Front cover (5313-5314).

Contents list (5315-5322).

FRET spectroscopy—towards effective biomolecular probing by Eugene M. Obeng; Elvina C. Dullah; Michael K. Danquah; Cahyo Budiman; Clarence M. Ongkudon (5323-5337).
The advent of super-resolution microscopy has been a major breakthrough in bioscience research, allowing accurate molecular signaling analysis of cellular and biological materials. Förster resonance energy transfer (FRET) spectroscopy, for instance, has emerged to be significant over the past few decades, owing to its non-invasive spatiotemporal cellular and subcellular probing abilities. The success of FRET has been the resurgence of fluorescent proteins (FPs) and sophisticated imaging techniques. The developments in FP and FRET-based techniques have made FRET investigations possible in diverse biotechnological fields. However, the current literature suffers a dearth in terms of a review that explains the fundamental principles (with examples) of the major areas of FRET application. This article presents a retrospective overview of the salient exploits and advancements of FRET spectroscopy and discusses the current challenges with some options. Moreover, some of the much anticipated future applications have been highlighted.

Detection and characterization of fluoride is an important part of understanding the benefits as well as the potential toxicity of fluoride in biotic and abiotic natural sources. Fluoride can have a detrimental effect on human health at high concentrations (>1.5 mg L−1), thus, it must be detected and quantitated. For this analytical methods play an important role. This review underlines the role of analytical methods in the detection and quantitation of fluoride. The review highlights a variety of analytical methods, for instance, inductively coupled plasma mass spectrometry (ICP-MS), atomic absorption spectrometry (AAS) and molecular absorption spectrometry (MAS), and electrochemical methods that have been applied in the determination of fluoride. The principles of these techniques in conjunction with their pros and cons, and their applications regarding the determination and detection of fluoride are discussed. The commonly used fluoride sensing methods, including fluorescence and colorimetric methods have also been discussed. We hope this review will promote the next generation approaches and application of innovative analytical methods for fluoride detection and quantification.

Alpha spectrometry (AS) is an important and useful radiometric analytical technique for the qualitative identification and quantitative determination of α-emitting radionuclides in environmental, biological and nuclear technology related samples. Isotope dilution alpha spectrometry (IDAS), using a suitable tracer (spike), along with a suitable method of alpha spectrum evaluation to account for the tail contribution due to energy degradation, provides accurate data on the concentration because this approach eliminates uncertainties in chemical yield in the elaborate sample preparation and purification steps. Non-isotopic tracers (N-IDAS) can also be used for the simultaneous determination of actinide isotopes. High resolution alpha spectrometry with deconvolution algorithms can now resolve close lying α-energies of radionuclide pairs e.g. (239Pu, 240Pu; 233U, 234U; 238Pu, 241Am, etc.). Nuclear decay data on the emission probabilities of different α-energies emitted by an α-emitter, and half-lives are being constantly improved by detailed critical studies at various international laboratories. Nuclear technology depends strongly on alpha spectrometry for precise and accurate data on 232U, 236Pu, 238Pu and 241Am in different fuel samples. Alpha spectrometry is poised to play an important role in the future decommissioning of aged reactors and nuclear waste disposal programs, to determine long-lived radioactive nuclides. Fast and better source preparation methods are in great demand to minimize the time to provide data on various nuclear forensic samples and in emergency contamination situations. Semiconductor passivated and implanted planar silicon (PIPS) detectors with active surface areas that range from 20 mm2 to about 2000 mm2 are used for high and low-activity samples, respectively. Exotic detectors based on cryogenic micro-calorimetry, magnetic calorimetry, and Q-value spectroscopy (using a super-conducting transition edge sensor) capable of giving an energy resolution of 1–3 keV at 5.5 MeV are being developed. Enriched isotopes of actinides and reference materials of known activity ratios are required by researchers world-wide. This review discusses recent advances that have taken place in the last decade in the important metrological radiometric technique of alpha spectrometry.

Ultrasensitive detection of site-specific DNA methylation by loop-mediated isothermal amplification by Hui Wen; Hui Wang; Honghong Wang; Jingli Yan; Hui Tian; Zhengping Li (5372-5377).
A novel loop-mediated isothermal amplification (LAMP)-based methylation assay for simple, robust and cost-effective detection of site-specific DNA methylation has been developed. DNA targets are first treated with methylation-sensitive restriction endonuclease (HpaII), where the DNA targets will be cleaved at specific unmethylated-cytosine residues while leaving the methylated DNA intact. Subsequently, the methylated DNA targets can serve as templates to perform LAMP for the detection of DNA methylation with real-time fluorescence measurements by using a common fluorescent dye (SYBR Green I). Taking advantage of the simplicity and high specificity of HpaII digestion and the isothermal nature and high sensitivity of LAMP, the proposed assay can greatly simplify the detection of DNA methylation and achieve ultrahigh sensitivity and specificity. With this assay, as low as 10 aM methylated DNA can be detected and 0.1% methylated DNA can be determined in the presence of a large excess of unmethylated DNA.

Solvent-saving approaches for the extraction of siloxanes from pine needles, soils and passive air samplers by S. Ramos; J. A. Silva; V. Homem; A. Cincinelli; L. Santos; A. Alves; N. Ratola (5378-5387).
In this study, a solvent-saving analytical strategy was validated to quantify the levels of 8 volatile methyl siloxanes (VMSs) in pine needles, soils and air (measured by sorbent-impregnated polyurethane foam passive samplers, SIPs). Different extraction solvents and sample handling procedures were tested and the protocol that reached the highest recoveries employed QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) and was adapted to pine needles and soils. For SIPs, another method was developed in parallel, as QuEChERS could not be applied to this matrix due to logistic and operative constraints. Thus, extraction was performed using classic Soxhlet extractors and a short clean-up step, limited to the removal of water by a solid-phase extraction (SPE) column containing sodium sulphate. The quantification of the target compounds was performed by gas chromatography/mass spectroscopy (GC/MS), with identical set-ups for the three matrices. Similar validation protocols were applied and yielded limits of detection (LODs) from 1.8 to 10.8 ng kg−1 (dry weight) for pine needles, from 3.4 to 19.8 ng kg−1 (dw) for soils and from 4.7 to 10.2 ngSIP−1 (dw) for SIPs. The overall mean recoveries were 75 ± 11%, 69 ± 17% and 87 ± 8%, respectively. The application of the methodologies to naturally contaminated samples collected in an urban and a remote site revealed siloxane levels comparable to other studies in the literature and a predominance of the cyclic siloxanes over the linear ones, which were frequently not detected.

Ion mobility spectrometry (IMS) provides quick and reliable responses when applied in the environmental field. However, when headspace (HS) is used as the sample introduction system, in some cases there may be a need to preconcentrate analyte if it is presented at low concentrations due to the low efficiency of HS. Herein, we discuss the parameters that affect the HS and the potential of combining solid phase extraction (SPE) and HS-IMS to improve the sensitivity of the method. The determination of phenol when it is presented in water or soil samples was selected as a case study and a limit of detection of 0.94 μg mL−1 and 0.14 μg mL−1 was obtained when direct analysis by HS-IMS was used. This methodology, which was developed based on SPE prior to HS-IMS analysis, was suitable for the detection of phenol at 0.05 μg mL−1 when 15 mL of water sample was passed through an HLB 60 mg SPE cartridge and eluted with 1 mL of dichloromethane. The HS-IMS analysis of the eluent in which phenol was present was carried out without any interference from the solvent.

A novel ratiometric fluorescent immunoassay for human α-fetoprotein based on carbon nanodot-doped silica nanoparticles and FITC by Yuanyuan Wu; Peng Wei; Sumate Pengpumkiat; Emily A. Schumacher; Vincent T. Remcho (5398-5406).
The application of fluorescent carbon nanodots (C-dots or CD), non-toxic particulate organic labels, to disease biomarker detection is still in its earliest stage of development. In the effort described here, a novel ratiometric immunoassay was developed to target a model protein disease biomarker, alpha-fetoprotein (AFP), using C-dot doped silica nanoparticles (CD-SNPs) and fluorescein isothiocyanate (FITC) as signaling agents. Highly fluorescent C-dots were hydrothermally synthesized from citric acid and ethylene diamine. The C-dots were then encapsulated in silicate shells to yield 45 nm nanoparticles using a novel reverse microemulsion method, enabling convenient handling (centrifugation and washing) and straightforward surface chemistry modification to facilitate development of bioassays. Capture antibody capped CD-SNPs (Ab1-CD-SNPs), together with FITC labeled antibodies (Ab2-FITC) constituted a new ratiometric immunosensor for AFP, in which CD-SNPs functioned as both solid supports for washing and separation and as built-in reference signaling agents to correct for inconsistent environmental effects. A calibration curve was established between the ratiometric signal (the ratio of fluorescence signals of FITC and C-dots, F/C) and AFP concentration in the broad range of 0.317–280 μg dL−1, exhibiting a useful linear range (0.317–35 μg dL−1, R2 = 0.9977), low detection limit (0.317 μg dL−1) and acceptable recovery (105–120%). This assay format can be applied to a wide range of immunoassay targets. Our demonstration of encapsulating low-cost, easily synthesized, highly-fluorescent C-dots into silica nanoparticles for use in immunoassays will be useful in expanding future applications of these carbon nanomaterials to areas such as in vivo cellular imaging, drug delivery, and in vitro cell labeling and biomolecule sensing.

Current clinical tests employed to diagnose asthma are inaccurate and limited by their invasive nature. New metabolite profiling technologies offer an opportunity to improve asthma diagnosis using non-invasive sampling. A rapid analytical method for metabolite profiling of saliva is reported using ultra-high performance liquid chromatography combined with high resolution time-of-flight mass spectrometry (UHPLC-MS). The only sample pre-treatment required was protein precipitation with acetonitrile. The method has been applied to a pilot study of saliva samples obtained by passive drool from well phenotyped patients with asthma and healthy controls. Stepwise data reduction and multivariate statistical analysis was performed on the complex dataset obtained from the UHPLC-MS analysis to identify potential metabolomic biomarkers of asthma in saliva. Ten discriminant features were identified that distinguished between moderate asthma and healthy control samples with an overall recognition ability of 80% during training of the model and 97% for model cross-validation. The reported method demonstrates the potential for a non-invasive approach to the clinical diagnosis of asthma using mass spectrometry-based metabolic profiling of saliva.

A miniaturized detection system for chemiluminescence that is generated on a microfluidic paper-based analytical device (μPAD) was developed using optical fibers and was applied to the determination of Cr(iii). The μPAD was fabricated by wax printing and consisted of 6 separate channels in a parallel alignment. Each channel was composed of an injection zone for a reagent solution, a reaction zone, and a waste zone. The μPAD was placed on a plastic holder equipped with 6 optical fibers to collect chemiluminescence (CL). The other ends of the optical fibers were bundled and introduced into a small photomultiplier tube module to obtain the CL signals. The CL reaction was based on luminol oxidation by hydrogen peroxide in the presence of Cr(iii), which catalyzed the reaction in an alkaline medium. The reaction conditions, including the use of an enhancer and a masking agent, were optimized to obtain high sensitivity and selectivity. Under the optimal conditions, a linear range was obtained at 0.05 to 1.00 ppm with a detection limit of 0.02 ppm. The analysis time was less than 1 min per one μPAD in order to obtain 6 measurements of differing concentrations with a precision of <6.5%. This method was successfully applied to the determination of Cr(iii) spiked into natural water samples at the sub-ppm range.

Multi-metal element analysis for the identification of foodborne pathogenic bacteria by Xingxing Zhang; Xueling Li; Yadi Wang; Qilong Xu; Jun Hu; Junhong Lü (5421-5426).
Mineral element contents, combined with multivariate analysis, were used for the identification and classification of foodborne pathogens from a common genus (Rhodococcus equi, Staphylococcus spp., Listeria spp., Salmonella spp., Shigella spp., Escherichia coli, Enterobacter sakazakii, Yersinia enterocolitica and Vibrio spp.). 45 macro- and trace mineral elements of 30 foodborne pathogens were determined by a semiquantitative inductively coupled plasma mass spectrometry (SQ-ICP-MS) technique. The elemental analysis identified 10 significant elements (28Si, 43Ca, 57Fe, 47Ti, 52Cr, 55Mn, 66Zn, 88Sr, 137Ba and 208Pb) by ANOVA in different types of pathogens. Principal component analysis (PCA) reduced the 10 variables to 6 principal components which could explain 98.40% of the total variance. The classification models constructed by the Fisher linear discriminant analysis (Fisher LDA) and back-propagation artificial neural network (BP-ANN) achieved correctly classified rates of 86.9% and 91.3%, respectively. The results indicated that the combination of multi-metal element composition determination and multivariate analysis can be used as fingerprint to quickly identify and classify foodborne pathogens.

Determination of residual automotive lubricant oil and residual solvent used in a dry wash as adulterants in Brazilian S-10 diesel (B7) using mid-infrared spectroscopy data and chemometric methods by Sarmento Júnior Mazivila; Letícia Maria de Souza; Ibrahim Muhammad Abubakar; Elisa Langa Mavulula; Waldomiro Borges Neto (5427-5434).
This paper presents methodologies for safe discrimination between adulterated and unadulterated samples of Brazilian S-10 diesel using mid-infrared (MIR) spectroscopy and partial least squares discriminant analysis (PLS-DA). The samples of unadulterated and adulterated Brazilian S-10 diesel were classified correctly into their respective groups, that is, the PLS-DA models showed 100% correct classification for samples of a test set with high levels of sensitivity and specificity to discriminate between unadulterated and adulterated samples with residual automotive lubricant oil (RAL) and residual solvent used in a dry wash (RSUDW). In order to extend the work, the adulterant content was predicted using partial least squares (PLS), which showed a good correlation between the reference values with R = 0.9999 for RAL and RSUDW in Brazilian S-10 diesel. The methodologies were validated, estimating specific figures of merit for the qualitative and quantitative multivariate analysis and were able to detect and quantify RAL and RSUDW in Brazilian S-10 diesel. The results from both methods were satisfactory for both qualitative and quantitative detection of RAL and RSUDW, as adulterants in Brazilian S-10 diesel (B7), commonly used in Brazil. Therefore, the proposed methodologies for the quantification of adulterants and discrimination between adulterated and unadulterated samples of Brazilian S-10 diesel are fast, practical, economical and efficient and can be used by industries and fuel distributors.

Nonenzymatic electrochemical detection of rutin on Pt nanoparticles/graphene nanocomposite modified glassy carbon electrode by Shumin Li; Beibei Yang; Jin Wang; Duan Bin; Caiqin Wang; Ke Zhang; Yukou Du (5435-5440).
In this article, a nonenzymatic electrochemical sensor based on chemically reduced graphene oxide (RGO) and a Pt nanoparticles (PtNPs) modified glassy carbon electrode has been fabricated and used to determine rutin. The nanocomposites of PtNPs/RGO were characterized by transmission electron microscopy and X-ray diffraction, and the electrochemical behaviors of rutin on PtNPs/RGO were demonstrated by cyclic voltammetry and differential pulse voltammetry. The as-fabricated electrochemical sensor for rutin exhibited a wide linear range from 0.057 to 102.59 μM with a detection limit of 0.02 μM (S/N = 3). Additionally, the as-prepared electrode displayed a good reproducibility, stability and anti-interference ability for the detection of rutin. Finally, the electrode was successfully applied for the determination of rutin in pharmaceutical tablets.

Determination of ascorbic acid in the retina during chicken embryo development using high performance liquid chromatography and UV detection by Débora R. S. Lima; Marcelo Cossenza; Carlos Gustavo Garcia; Camila C. Portugal; Flávia F. de C. Marques; Roberto Paes-de-Carvalho; Annibal D. Pereira Netto (5441-5447).
The retina is a specialized tissue of the central nervous system (CNS) and it is the only part of the CNS that can be visualized non-invasively. During vertebrate development, the retina originates together with the optic nerve as outgrowths of the developing brain, and in this respect, the avian retina is a very convenient model for neurochemical studies of the CNS. In this study, a HPLC-UV method was developed and validated for the determination of ascorbic acid (AA) in the chicken embryo retina. AA has an important role in the retina because of its antioxidant properties. The developed method showed very good figures of merit (recovery = 91 ± 2%; repeatability and intermediate precision better than 1.67% and 2.53% and a limit of quantification of 0.03 mg L−1). Retinas of two embryo ages (12 days and 18 days) showed AA concentrations of 0.0107 ± 0.0010 and 0.0055 ± 0.0005 μg of AA per μg of protein, respectively, and the statistical comparison of results confirmed the decrease of the AA level. These results seem to correlate well with oxidative stress protection, but this fact is still under investigation. As far as we are aware, this is the first study that demonstrates the HPLC-UV determination of ascorbic acid in the chicken embryo retina and its variation along embryo development.

Determination of Sudan I in duck feed by microscopic image processing and confocal Raman spectroscopy by Qingbo Li; Jialin Zhang; Dongdong Shi; Xiang Li; Qingsheng Liu (5448-5456).
Duck feed is a globally traded agricultural product that is sometimes adulterated illegally with Sudan I for colour enhancement. This paper proposes a novel method combining microscopic image processing and confocal Raman spectroscopy to detect qualitatively the adulteration of duck feed. Image analysis of duck feed samples adulterated with Sudan I can rapidly and objectively locate highly suspicious areas to improve detection accuracy and speed. Confocal Raman spectroscopy is a valuable analytical tool in trace detection of Sudan I due to its high spatial resolution (below 1 μm) and non-invasive nature. In this study, the microscopic images of Sudan I-spiked duck feed tablets (spiking levels: 0.0001–2%) are used to locate suspicious pixels that may contain the adulterant. The spectra of detected pixels were recorded using a confocal Raman spectrometer. An improved spectral angle measurement algorithm, feature-enhanced spectral angle measurement (FESAM), was used to enhance Raman spectral characteristics. Very good calibration statistic results were obtained to distinguish Sudan I from duck feed. In addition, model reliability was verified by other common additives that have similar colour to Sudan I. Results showed that an extension of the Sudan I adulterated calibration range increased the robustness of the model. FESAM effectively extracted and enhanced the characteristic peaks of low concentration Sudan I in duck feed, which decreased the limits of detection to 2.5 ppm. The whole detection process was completed very quickly (several minutes) without requiring sample pre-treatment. Therefore, Raman technology combined with image analysis data is a promising technique for detecting Sudan I adulteration in feed. The proposed method may be used to analyse other adulterated feeds with low concentrations of contaminants.

Development of a low pressure chromatographic flow system for monitoring the biodegradation of ofloxacin and ciprofloxacin by Inês C. Santos; Raquel B. R. Mesquita; Catarina L. Amorim; Paula M. L. Castro; António O. S. S. Rangel (5457-5465).
In this work, we propose a simple low pressure chromatography method with a high throughput for monitoring the biodegradation of fluoroquinolones. Fluoroquinolones are a class of antibiotics that have been accumulating in the environment as a consequence of their release from different sources, namely hospital waste. It has been found that wastewater treatment plants are not able to completely remove this type of micro-pollutants and so, alternative solutions are necessary. Some biodegradation studies have been done but the HPLC-based methodologies used to monitor the degradation process usually require high cost instrumentation such as analytical columns and detectors. For this reason, a 1 cm monolithic column was coupled to a flow injection system and used for the simultaneous quantification of ofloxacin and ciprofloxacin with UV detection at 295 and 275 nm, respectively. LODs of 0.5 and 0.29 mg L−1 for ofloxacin and ciprofloxacin were obtained, respectively, with repeatability within the range of 2–10%. The developed method was successfully applied to monitor the biodegradation of ofloxacin and ciprofloxacin by the strain Labrys portucalensis F11. The results proved that the low pressure chromatography method is a simpler, cheaper, and faster alternative to monitor biodegradation studies.

The simplified bioaccessibility extraction test (SBET) and the stomach phase of the unified bioaccessibility method (UBM) have been modified for use in assessing the bioaccessibility of potentially toxic elements in samples of PM10 collected during routine air quality monitoring. Arsenic, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn were measured by inductively coupled plasma mass spectrometry in extracts of synthetic PM samples prepared by loading candidate soil reference material BGS102 onto TX40 (Teflon-coated borosilicate) filters widely used in standard commercial tapered element oscillating microbalance/filter dynamics measurement system (FDMS) ambient particulate monitors. Analysis of blanks revealed two important sources of contamination that had to be controlled in order to achieve reproducible results. The syringe filters used in the SBET released Cu and Zn into sample extracts during filtration and had to be washed with 80 mL of 0.4 M glycine at pH 1.5 immediately prior to use, whilst the FDMS filters used to collect PM10 were found to contain sufficient extractable Zn (ca. 3 μg per filter) to almost double the concentration released by the soil. The latter is a consequence of the use of Zn in filter manufacture and so could not be eliminated, but was successfully overcome by means of blank-subtraction. A ten-fold miniaturisation of the SBET and six-fold miniaturisation of the UBM allowed 0.1 g samples to be processed, with analyte recoveries generally within ±10% of those obtained when the conventional procedures were used. Comparison between results obtained when the modified procedures were applied to soil alone, and when soil was loaded onto FDMS filters, indicated that the presence of the filter had no effect on extraction efficiency, except for Fe, provided blank-correction was performed. Results obtained for As, Cd and Pb when the modified UBM was applied to BGS102 on FDMS filters were 4.40 ± 0.04, 0.224 ± 0.002 and 17.3 ± 0.8 mg kg−1, respectively (n = 3), all within recommended ranges.

Simultaneous determination of lead and tin at the bismuth film electrode by square wave stripping voltammetry and chemometric methods by Wenxian Tang; Jun Bin; Wei Fan; Zhiming Zhang; Yonghuan Yun; Yizeng Liang (5475-5486).
The voltammograms of lead and tin are strongly overlapped due to their similar properties in electroanalysis, making it difficult for the individual quantification of each analyte. A square wave anodic stripping voltammetry (SWASV) method for the simultaneous determination of the two metals at the bismuth film electrode (BiFE) was proposed. The experimental conditions were investigated and optimized. The linear dynamic ranges and limits of detection (LODs) were determined to be 4–150 μg L−1 and 1.13 μg L−1 for lead, and 4–110 μg L−1 and 0.74 μg L−1 for tin. Radial basis function artificial neural network (RBF-ANN) was introduced to solve the resolution problem, and its performance was compared with the conventional chemometric methods including principal component regression (PCR), partial least squares (PLS) and least-squares support vector machines (LS-SVM). By analyzing a set of synthetic mixtures of the two metals with the proposed methods, the lowest root-mean-square error of calibration (RMSEC) and root-mean-square error of prediction (RMSEP) were achieved with RBF-ANN and the method was applied to real tap water samples spiked with known amounts of lead and tin with satisfactory recoveries of 105% and 102%, respectively. Therefore, it is concluded that SWASV coupled with RBF-ANN is an effective alternative for the simultaneous determination of lead and tin.

We report a rapid, efficient analytical method for detecting Brominated Flame Retardants (BFRs) in plastic materials using direct insertion probe with double focusing magnetic sector high resolution mass spectrometry. We acquired the total ion spectrum (30 to 1000 m/z) and observed 959 and 799 m/z ions respectively for quantification and evaluation of the fragmentation reproducibility of decabromodiphenyl ether (BDE209, MW 959 amu). Ad hoc prepared Acrylonitrile Butadiene Styrene (ABS) solid reference materials (RMs) containing different concentrations of BDE209 were used to develop a 5-point calibration curve that showed linearity (R2 > 0.999) over a concentration range of 0.1–2% w/w BDE209. Relative standard deviation between triplicate determinations of BDE209 ranged from 0.32% to 0.42%. The limit of detection (LOD) obtained for BDE209 was 0.112 mg kg−1, 4 orders of magnitude lower than the EU's maximum allowed concentration (MAC) in plastic. To our knowledge, this is the first method for compound specific quantification of BDE209 that does not require any sample preparation, reducing the analysis time from roughly 14 hours to 12 minutes with comparable quality of results.

An anodically pretreated screen-printed ring disk carbon electrode (SPRDCE*) coupled with a flow injection analysis system was developed as a simple, rapid, sensitive, and self-validated hydroquinone (HQ) sensor. HQ was electrocatalytically oxidized at the preanodized disk electrode and the oxidized product para-benzoquinone was then electrocatalytically reduced to HQ at the preanodized ring electrode. A well-defined and quasireversible redox peak couple was observed. The amount of HQ could be determined by using the catalytic current from the SPRDCE*. Besides, it is also worth noting that the performance of this system could be validated directly by using the redox current ratio (the reduction current at the ring electrode divided by the oxidation current at the disk electrode). Under optimized conditions, a linear range for HQ at the disk electrode was in the range of 0.25–160 ppm with 0.999 and 0.024 ppm for the correlation coefficient and the detection limit (S/N = 3), respectively. Using this method, HQ in cosmetic products was successfully quantified without any pre-treatment with recoveries between 97.76% and 103.74%.

Application of a robust solid-phase microextraction fiber consisting of NiTi wires coated with polypyrrole for the determination of haloanisoles in water and wine by Kalya Cravo Di Pietro Roux; Éverton Fabian Jasinski; Josias Merib; Maria Luísa Sartorelli; Eduardo Carasek (5503-5510).
In this study, the application of a solid-phase microextraction (SPME) fiber which was fabricated by electrolytically depositing polypyrrole (PPy) on a NiTi alloy support was investigated. The NiTi alloy was used as the support due to its superelasticity and shape memory properties and PPy is a suitable coating material since it offers facile synthesis and is a polar compound. Some parameters related to fiber fabrication, including the potential used for the electrodeposition, amount of electric charge and type of counterion, were subjected to multivariate optimization taking into account the uniformity, porosity and the adhesion of the fiber and, also the coating thickness on the support. In relation to method development for the determination of haloanisoles, the factors that affect the analyte uptake were also subjected to multivariate optimization using full factorial and response surface designs. The developed method exhibited correlation coefficients higher than 0.996, relative standard deviations lower than 16% and limits of detection ranging from 1 to 6 ng L−1. The matrix effect caused by complex samples was overcome with the use of acetylated-halophenols as the internal standards, allowing the use of standard aqueous solutions for calibration. The proposed NiTi–PPy fiber exhibited equal or superior performance compared to some commercially available SPME fibers. Therefore, the presented fiber is an attractive alternative due to its high robustness and ease of preparation.

In this study, a method combining molecularly imprinted polymer-solid phase extraction (MIP-SPE) and high performance liquid chromatography was developed to determine the residues of fluoroquinolone drugs in milk. During the experiments, different templates, functional monomers, porogens and template/monomer ratios were evaluated. The norfloxacin based MIP capable of recognizing four fluoroquinolones (ciprofloxacin, norfloxacin, enrofloxacin and lomefloxacin) was used to prepare the SPE cartridge. The MIP-SPE cartridge showed high adsorption capacities (≥4520 ng) and high recoveries (≥96%) to the four drugs, and could be reused for at least fifty times. Then the four drugs were fortified into blank milk samples respectively to be analyzed. The limits of detection were in the range of 10–20 ng mL−1 and the recoveries were in the range of 76.8–97.7% with coefficients of variation lower than 8.3%. Furthermore, the MIP-SPE cartridge showed a better purification effect than three commercial SPE cartridges. This is the first study reporting the use of norfloxacin based MIP-SPE for determination of fluoroquinolones in milk.

Zinc metal is an essential micronutrient which is required for different biological and physiological processes in humans, animals and plants. Here, a simple, rapid and sensitive method for the determination of zinc in environmental water samples using surfactant-assisted dispersive liquid–liquid micro-extraction (SA-DLLME) prior to flame atomic absorption spectrometry (FAAS) analysis has been reported. This method involved the formation of a zinc complex with 4-(2-pyridylazo) resorcinol (PAR) and subsequently SA-DLLME was applied to extract the Zn(ii)–(PAR)2·CPC complex into chloroform in the presence of a cationic surfactant. Optimum extraction of the complex was observed when the concentration of cetylpyridinium chloride (CPC) and PAR was 0.1% for both at pH 9.0 and with an extraction time of 10 min. The calibration curve was found to be linear over the range of 1.5–60 μg L−1 with a correlation of estimation (r2) of 0.997. This optimized method has been successfully applied for the determination of zinc in environmental water (tap, river and well) samples.

Colorimetric sensing of chromium(vi) ions in aqueous solution based on the leaching of protein-stabled gold nanoparticles by Guo Jian-feng; Hou Chang-jun; Yang Mei; Huo Dan-qun; Li Jun-jie; Fa Huan-bao; Luo Hui-bo; Yang Ping (5526-5532).
Herein, we developed a simple, sensitive and non-aggregation-based method for the selective colorimetric detection of chromium(vi) ions (Cr(vi)) in an aqueous solution. In the presence of hydrobromic acid (HBr), bovine serum albumin stable gold nanoparticles (BSA-Au NPs) were gradually dissolved by Cr(vi) in the etching process of gold. The leaching of the BSA-Au NPs results in a rapid and remarkable damping of the surface plasmon resonance (SPR) and hence induces a visible color change. This colorimetric strategy based on the etching process of gold provided a highly sensitive and selective detection method toward Cr(vi). Under optimal conditions, the amount-dependent colorimetric response was linearly correlated with Cr(vi) concentrations ranging from 0.15 μM to 50.0 μM, with a detection limit down to 120 nM measured as 3δ. Moreover, the developed cost-effective probe was successfully applied to real river samples, which demonstrated its potential for field applications.

Application of supramolecular solvent-based dispersive liquid–liquid microextraction for trace monitoring of lead in food samples by Ayoob Rastegar; Ahmad Alahabadi; Ali Esrafili; Zahra Rezai; Ahmad Hosseini-Bandegharaei; Shahram Nazari (5533-5539).
In this study, an efficient sample treatment method based on supramolecular solvent-based dispersive liquid–liquid microextraction (SM-DLLME) was applied for trace monitoring of lead by flow injection flame atomic absorption spectrometry. A supramolecular solvent comprising reverse micelles of 1-decanol in tetrahydrofuran (THF) was created by injection of these solvents into the aqueous sample solution. After injection of 1-decanol : THF mixtures into the sample solution, nanomicelles were produced in an ultrasonic bath and the lead–dithizone complex was extracted to the supramolecular phase at optimized pH. The solution was centrifuged and the metal complex formed was extracted into the supramolecular solvent phase. The detection limit for lead ions was 0.4 μg L−1 under the optimized separation conditions. The relative standard deviations for six extraction analysis of 3, 10 and 100 μg L−1 of lead ions were 4.8%, 4.5% and 4.1%. Finally, SM-DLLME was successfully applied for trace monitoring of lead ions in agricultural and food samples.

Back cover (5541-5542).