Analytical Methods (v.8, #28)

Front cover (5543-5544).

Contents list (5545-5552).

z-Scores were devised to provide a transparent but widely-applicable scoring system for participants in proficiency tests for analytical laboratories. The essential idea is to provide an appropriate scaling of the difference between a participant’s result and the ‘assigned value’ for the concentration of the analyte. Interpretation of a z-score is straightforward but some aspects need careful attention to avoid misconception. Over time several related scores have been devised to cope with a diversified range of applications. The main types of score have recently been codified in ISO 13528 (2015).

Recent advancements in analytical methods for the determination of steroidal estrogen residues in environmental and food matrices by Sameera R. Gunatilake; Vihanga K. Munasinghe; Ruchiranga Ranaweera; Todd E. Mlsna; Kang Xia (5556-5568).
Residual steroidal estrogens in environmental and food samples have become a cause for concern as they can affect organisms at low ppt concentrations. Analytical method development plays a key role in trace estrogen analysis due to the combination of low concentrations and complicated sample matrices. Reliable quantification of these trace level steroidal estrogens has become a major concern during the past decade. This mini review focuses on advancements in analytical methods developed for estrogen detection and quantification in environmental and food samples from 2014–2016. A comprehensive overview of the novelties and the advantages of the recently developed sample pre-concentration, clean-up, and detection methods is discussed. During the past three years, a wide variety of sample extraction methods including the utilization of innovative imprinted magnetic sorbents, QuEChERS (quick, easy, cheap, effective, rugged and safe) method and various microextraction methods such as dispersive liquid–liquid microextraction (DLLME), thin film microextraction (TFME), solid phase microextraction (SPME), and vortex assisted hollow fiber liquid-phase microextraction (VA-HF-LPME) have been published. Further, novel detection methods including electrochemical methods and bio-assays that have been developed for estrogen analysis have also been reported in the recent literature. Further, conventional Solid Phase Extraction (SPE) based methods that have been improved to minimize time, complexity, and cost have been described. These new approaches have resulted in recent significant progress in the analytical chemistry of endocrine disrupting compounds (EDCs) in environmental samples.

Evaluation of procedures for assessing anti- and pro-oxidants in plant samples by P. Majer; M. Vidović; Gy. Czégény; S. Veljović Jovanović; Å. Strid; É. Hideg (5569-5580).
Plants as well as other aerobic organisms constantly produce reactive oxygen species (ROS). At regulated low concentrations ROS may serve as signal molecules, while in excessive amounts these may cause oxidative damage to biomolecules. Actual cellular concentrations are controlled by a network of various antioxidants, and acclimation to stress conditions is achieved by a dynamic balance of ROS production and neutralization. Accordingly, plant stress physiology studies generally include an array of methods testing the occurrence of ROS as well as evaluating antioxidant capacities. The aim of the present work is to provide an overview of these methods, with special emphasis on avoiding errors that can possibly lead to either inaccurate data or misinterpretations of otherwise correct measurements.

Rapid, high-throughput, and quantitative determination of orange juice adulteration by Fourier-transform infrared spectroscopy by David I. Ellis; Joanne Ellis; Howbeer Muhamadali; Yun Xu; Andrew B. Horn; Royston Goodacre (5581-5586).
Orange juice is a hugely popular, widely consumed, and high price commodity typically traded in a concentrate form making it highly susceptible to adulteration. It has been consistently shown to be one of the leading food categories of reported cases of food fraud. One of the many forms of adulteration is dilution which can then be disguised with sugar solutions, or juices from other fruits or vegetables, which mimic the natural fruit sugars in this juice. Here, we demonstrate Fourier transform infrared (FT-IR) spectroscopy as a rapid, high-throughput and quantitative method for the determination of orange juice adulteration. Initial experiments involved the simple adulteration of pure orange juice with 0.5–20.0% water disguised with glucose, fructose or sucrose individually. This was followed by more complex mixtures of these three sugars at appropriate concentrations found in freshly prepared orange juice established using GC-MS; a total of 41 samples were prepared and all experiments undertaken in triplicate. Principal components-discriminant function analysis (PC-DFA) was undertaken on raw spectral data followed by partial least squares regression (PLSR) for quantification of the level of adulteration. Results from these chemometric analyses showed that infrared spectra contained information allowing for the discrimination and quantification between the three naturally occurring sugars in orange juice to disguise adulteration via dilution. Furthermore, it was clearly demonstrated that FT-IR in combination with PLSR is able to predict the levels of adulteration with excellent accuracy; the typical error on these predictions for test samples was 1.7%. We believe that the further development of these and other rapid methods could have an important role to play in the area of food authenticity and integrity, and food analysis in general.

A new ion chromatographic method for the speciation of iodine in aquacultural seawater samples has been developed. This simple, isocratic, non-suppressed ion chromatographic method, which uses an electrolytically generated potassium hydroxide eluent with a high capacity anion exchange column (Dionex IonPac AS20, 250 × 4 mm ID, 7.5 μm), allows the direct injection of undiluted seawater samples, with detection based upon standard ultraviolet absorbance (226 nm). Using a sample injection volume of 125 μL, a method limit of detection for iodide of 9.45 nM in seawater was achieved, with an absolute detection limit of 0.15 ng. Speciation (iodide/iodate) was accomplished via off-line sample reduction using ascorbic acid (0.2 M) and HCl (6 M). The new method was applied to the study of iodine speciation in raw, ultraviolet- and ozone-treated aquacultural seawater samples.

Development of a novel method for the bioanalysis of benfotiamine and sulbutiamine in cancer cells by Jaeah Kim; Christopher P. Hopper; Kelsey H. Connell; Parisa Darkhal; Jason A. Zastre; Michael G. Bartlett (5596-5603).
Quantification of benfotiamine and sulbutiamine, synthetic thiamine analogs, in biological samples is an essential step toward understanding the role of these thiamine analogs on cancer cell proliferation. A sensitive method to quantitate benfotiamine and sulbutiamine in cells and media was successfully developed using reversed-phase HPLC. Accuracy, precision, specificity and robustness were evaluated to assess the reliability of this method in accordance with U.S. FDA guidelines. The method provided a linear range from 100–50 000 nM for benfotiamine and from 500–30 000 nM for sulbutiamine in both cells and media. The method was validated and the precision was found to be within 15% relative standard deviation (RSD), and the accuracy to be within 15% relative error (RE). Benfotiamine and sulbutiamine were used as internal standards for each other to achieve a high level of reproducibility. This method has been successfully applied to the study of benfotiamine and sulbutiamine to determine their uptake and disposition between mammalian cells and cell media. The method can contribute to future studies to determine the effect of benfotiamine and sulbutiamine as novel thiamine analogs on cancer cell proliferation.

Cysteamine (CA) is a high performance drug with a radiation protection effect on guanine (GA) and adenine (AD). Therefore, we focus on the preparation of a highly sensitive electrochemical sensor for determination of CA in the presence of GA and AD in biological samples. For this goal, a carbon paste electrode modified with magnesium oxide nanoparticles (MgO/NPs) and N-(4-hydroxyphenyl)-3,5-dinitrobenzamide (N-4-HP-DNBA) was fabricated. The efficiency of the proposed sensor was investigated for the electrocatalytic oxidation of CA in the presence of GA and AD for the first time. The mediated oxidation of CA at the N-4-HP-DNBA/MgO/NPs/CPE was investigated using an electrochemical approach. The electro-oxidation peak currents for CA, GA and AD were found to vary linearly with their concentrations in the range of 0.03–600 μM; 0.8–400 μM and 5.0–500 μM with detection limits of 0.009 μM, 0.4 μM and 1.0 μM, respectively. The N-4-HP-DNBA/MgO/NPs/CPE was used for the determination of CA, GA, and AD in capsule and pharmaceutical serum samples.

Detection and identification of sugar alcohol sweeteners by ion mobility spectrometry by Christopher A. Browne; Thomas P. Forbes; Edward Sisco (5611-5618).
The rapid and sensitive detection of sugar alcohol sweeteners was demonstrated using ion mobility spectrometry (IMS). IMS provides a valuable alternative in sensitivity, cost, and analysis speed between the lengthy gold-standard liquid chromatography-mass spectrometry (LC-MS) technique and rapid point-of-measurement disposable colorimetric sensors, for the Food and Nutrition industry's quality control and other “foodomics” area needs. The IMS response, characteristic signatures, and limits of detection for erythritol, pentaerythritol, xylitol, inositol, sorbitol, mannitol, and maltitol were evaluated using precise inkjet printed samples. IMS system parameters including desorption temperature, scan time, and swipe substrate material were examined and optimized, demonstrating a strong dependence on the physicochemical properties of the respective sugar alcohol. The desorption characteristics of each compound were found to dominate the system response and overall sensitivity. Sensitivities for these compounds ranged from single nanograms to hundreds of picograms with optimal desorption temperatures ranging from 125 °C to 200 °C. Sugar alcohol components of commercial products – chewing gum and a sweetener packet – were detected and identified using IMS. IMS is demonstrated to be an advantageous field deployable instrument, easily operated by non-technical personnel, and enabling sensitive point-of-measurement quality assurance for sugar alcohols.

Density, refractive index and viscosity as content monitoring tool of acylglycerols and fatty acid methyl esters in the transesterification of soybean oil by Luis R. S. Kanda; Carlos I. Yamamoto; André R. Lopes; Fernando A. P. Voll; Marcos L. Corazza; Fernando Wypych (5619-5627).
The growing interest in research and development for alternative biofuels has drawn special attention to biodiesel, a mixture of fatty acid methyl esters (FAMEs) that can be obtained by the transesterification reaction of triacylglycerols (TAGs) with a short chain alcohol. During transesterification reaction kinetic studies, it is important to monitor the levels of diacylglycerols (DAGs) and monoacylglycerols (MAGs), as well as those of TAGs and FAMEs. These contents are generally determined according to reference methods by GC-FID analysis. This technique is expensive and time consuming, not to mention that samples with higher TAG contents can be harmful to the chromatography column and accessories. In this context, this study aims to determine the composition of a quaternary system, in which virtually only the four compounds cited previously are present, using a single-step chemometrics analysis that uses mathematical modelling to correlate the composition with three physical properties (density, refractive index and viscosity) of the same sample, one at a time. Subsequently, a sample with an unknown composition has the same properties determined and then a system of equations composed of three equations (one for each physical property) with three unknowns are solved to determine the unknown sample's composition. This method can be used as an initial screening method to determine both the TAG and FAME content in a sample, to be implemented prior to the performance of the GC analysis, because the results obtained in this study have shown that the approach proposed was able to determine mass fractions of quaternary systems with both a Mean Absolute Error (MAE) and Root Mean Square Deviation (RMSD) of less than 0.03.

A rapid ultra-high performance liquid chromatography with a linear ion trap-orbitrap high resolution mass spectrometer (UHPLC-LTQ-Orbitrap HRMS) method for the determination of 21 nutrients in rice was developed. A simultaneous separation of tocopherols (α-, β-, γ-, δ-), tocotrienols (α-, β-, γ-, δ-), phospholipids, γ-oryzanols and β-carotene was achieved in less than 13 min. The detection was performed using a LTQ-Orbitrap MS detector using full scan in positive ion mode. This method was validated according to linearity, limits of detection and quantitation, reproducibility and recoveries. A regression coefficient (r2 > 0.99) was obtained within a range of 0.05–10 μg mL−1 for tocopherols, tocotrienols and β-carotene, 0.1–50 μg mL−1 for phospholipids and 0.001–10 μg mL−1 for γ-oryzanols. The method gave detection limits (S/N, 3) of 0.2 to 1.9 ng mL−1 and quantitation limits (S/N, 10) of 0.7 to 6.3 ng mL−1. Relative standard deviations, which were applied to estimate repeatability, ranged from 2.3 to 9.6%. Recoveries within a range of 80.6–109.6% for all the analytes were obtained. The mass accuracy for 21 validated compounds was ≤3 ppm. Furthermore, quantitative determination showed that rice processing could cause content changes of nutritional composition between brown and white rice. The total ion current fingerprint profile (TICFP) could reveal the significant differences between the two types of rice samples (brown and white rice) from different regions. This method allowed fast and convenient analysis for the determination of nutrients in rice, which indicated that the Orbitrap technology is beneficial for food testing.

An improved TEAC (Trolox Equivalent Antioxidant Capacity) analytical procedure to evaluate the in vitro antioxidant capacity of some radical scavengers, including copper proteins (i.e. hemocyanin, ceruloplasmin or diamine oxidase) and some copper complexes (i.e. serine2–copper), is described. The TEAC method consists in measuring the reduction of the 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt radical monocation (ABTS˙+) with a decoloration induced by the scavenger to be analyzed. Several disadvantages, such as a particularly long time (about 16 h) for the activation of ABTS with potassium persulfate (free radical initiator), justify the need to improve this operatory mode. Consequently, we propose a new procedure consisting in a rapid activation of ABTS by electrolysis in about 20 s instead of 16 hours as required by the activation with potassium persulfate. Furthermore, the ABTS activation by electrolysis provides an improved reagent stability for 7–8 days whereas the stability in the case of the classical method is limited to 3 days. The fast assay was compared with the classical activation with potassium persulfate as a method of reference to activate ABTS and the results were expressed in equivalents of Trolox (standard reference scavenger). A good linearity of the answer in terms of Trolox amounts has been obtained with the fast assay, as with the classical method. Therefore, the fast assay seems compatible with the classical method, with the only difference and advantage that it is much faster and easier to operate.

A rapid quantitative 1H NMR analysis of kinsenoside and other bioactive principles from Anoectochilus formosanus by Li-Ying Hsieh; Hsiu-Hui Chan; Hsin-Yi Hung; Chao-Lin Kuo; Jin-Bin Wu; I-Wen Sun; Ping-Chung Kuo; Tian-Shung Wu (5645-5650).
Anoectochilus formosanus is a famous traditional Taiwanese folk medicine. Kinsenoside (1), one of the major active components in A. formosanus, exhibits hepatoprotective, antihyperliposis and antiflammatory activities. In this study, a proton nuclear magnetic resonance (1H NMR) method was developed for rapid quantitative analysis of several bioactive major constituents, including kinsenoside (1), 3-(R)-3-β-d-gluco-pyranosyloxy-4-hydroxybutanoic acid (2), 1-O-isopropyl-β-d-gluco-pyranoside (3), 4-(β-d-gluco-pyranosyloxy)benzyl alcohol (4) and benzoic acid (5) in plant samples and commercial products of A. formosanus. Interferences were removed by a simple Diaion HP-20 column chromatography. In the 1H NMR spectrum, the signals of compounds 1 (δ 2.88), 2 (δ 2.47), 3 (δ 1.12), 4 (δ 7.05) and 5 (δ 7.84) were selected and integrated as the target peaks, separated well from other signals in D2O. The developed 1H NMR method provides a rapid and simple quantitative method without any derivatization, pH control or addition of NMR shift reagent, and the analytical solvent system is very safe, convenient and simple.

Preparation and evaluation of molecularly imprinted composite membranes for inducing crystallization of oleanolic acid in supercritical CO2 by Wencheng Zhang; Qing Zhang; Xingyuan Zhang; Zeyu Wu; Bing Li; Xiuli Dong; Bingsong Wang (5651-5657).
In this study, novel molecularly imprinted composite membranes (MICMs) for inducing crystallization of oleanolic acid (OA) in supercritical CO2 (ScCO2) have been described. The MICMs were synthesized by the UV initiated photo-copolymerization, with OA as a template molecule, copolymerization of methacrylic acid (MAA) as a functional monomer, ethylene glycol dimethacrylate (EGDMA) as a cross-linker and polysulfone (PSF) ultrafiltration membranes as porous supports. The preparation conditions of OA–MICMs were optimized as follows: the molar ratio of OA, MAA and EGDMA 1 : 4 : 12, the amount of photoinitiator 1.5%, the concentration of OA 1 mmol L−1 and the elution time 6 h. Scanning electron microscopy (SEM) was used for the characterization of MICMs. The MICMs were used for inducing crystallization of OA in ScCO2. The purity and the crystallization rate of OA were 98.3% and 45.3%, respectively. Our work presents a new method to induce crystallization of OA in ScCO2 by using MICMs, with specific adsorption properties and capacities.

Determination of the geographical origin and ethanol content of Brazilian sugarcane spirit using near-infrared spectroscopy coupled with discriminant analysis by Lívia Cirino de Carvalho; Camilo de Lelis Medeiros de Morais; Kássio Miguel Gomes de Lima; Luis Carlos Cunha Júnior; Paloma Andrade Martins Nascimento; João Bosco de Faria; Gustavo Henrique de Almeida Teixeira (5658-5666).
Aguardente is a typical Brazilian spirit produced by the distillation of sugarcane. The valorisation of this spirit can be attributed to its notoriety, related to its production origin which can influence its quality. Therefore, the objective of this study was to use NIR spectroscopy coupled with discriminant analysis as a non-destructive method to validate the authenticity of aguardentes produced in two geographic regions and to predict their ethanol content. Some chemometric methods were used to discriminate the sugarcane aguardente, namely partial least squares-linear discriminant analysis (PLS-LDA), principal component analysis-linear discriminant analysis (PCA-LDA), and variable selection techniques such as successive projection algorithm (SPA-LDA) and genetic algorithm (GA-LDA). NIR spectra were collected using a FT-NIR spectrometer (4000–10 000 cm−1) with a spectral resolution of 16 cm−1, 8 cm−1 intervals, and 64 scans. The PCA results were not effective in classifying the aguardente samples, but with PLS-DA, PCA-LDA, SPA-LDA, GA-LDA and LDA it was possible to obtain an 87.2% prediction accuracy. Better results were obtained using PLS-DA on raw spectra and GA-LDA using only six wavelengths (namely 1025 nm, 1181 nm, 1596 nm, 1610 nm, 1653 nm, 2125 nm) which gave a relatively good accuracy rate (up to 87.2%). NIR spectroscopy and chemometrics can be used as a non-destructive method to validate authenticity, and PLSR combined with NIR was a good non-destructive method to predict ethanol content in sugarcane aguardente.

Potentiometry for the determination of oxidant activity by Kh. Z. Brainina; A. S. Zaharov; M. B. Vidrevich (5667-5675).
This paper aims to describe a new approach to using potentiometry for determining oxidants in liquids and ozonized and chlorinated water, in particular. The source of information is the electrode potential shift of the mediator system observed when an analyzed sample, containing oxidants, is inserted into an electrochemical cell. Criteria for the selection of the mediator system for oxidant determination are proposed. Potassium ferri/ferrocyanides serve as the mediator system in the proposed method. K3[Fe(CN)6] is chosen as the model oxidant. Special attention is focused on the role of the state of an indicator electrode surface and ways of its regeneration in generating an analytical signal. The information is essential for obtaining correct results in different areas of electrochemical analysis. As a result, a simple, fast, sensitive, and reliable method that does not require the use of reference solution is proposed, which ensures its advantages over other methods. The accuracy and reliability of the data obtained are confirmed by the analysis results received by using the standard method.

In this study, a simple and rapid sample pretreatment technique named pH-dependent continuous homogenous liquid–liquid extraction followed by gas chromatography-flame ionization detection has been developed for the extraction, preconcentration, and determination of four pesticides including diazinon, oxadiazon, bromopropylate, and fenazaquin in fruit juice and vegetable samples. In this method, two parallel glass tubes with different diameters and lengths are connected with a Teflon stopcock and used as an extraction device. Initially a basic organic solvent with low solubility in water (amine) as an extraction solvent is mixed with acidified deionized water containing the analytes and a homogenous solution is obtained. The homogenous solution is filled into one side (wide and short tube) of the extraction device. The other side (narrow and long tube) is filled with an ammonia solution. Then, the stopcock is slowly opened and the solution of ammonia is flowed into the other tube containing the homogenous solution under hydrodynamic pressure. By this action, an acid–base reaction occurs, so the homogenous solution is broken and the target analytes are extracted into the produced fine droplets of the organic solvent. The droplets move up through the aqueous phase to the top of the wide tube and form a separated layer owing to the low density of the organic phase compared to water. Several important parameters affecting the performance of the proposed method such as the type and amount of extraction solvent, ionic strength, and extraction time were investigated and optimized. Under the optimum extraction conditions, high enrichment factors (1220–1740, 407–580, and 244–348 for deionized water, fruit juices, and vegetable samples, respectively) and good extraction recoveries (61–87%) were obtained. Also, the method showed low limits of detection within the range of 0.12–0.32 μg L−1. The repeatability of the method was investigated at two concentrations of 20 and 50 μg L−1 of each analyte and relative standard deviations were obtained between 4 and 6% for six repeated determinations. Finally fruit juice and vegetable samples were successfully analyzed using the proposed method.

Polyethyleneimine protected silver nanoclusters (AgNCs@PEI) were prepared and used as high sensitive fluorescence probes for detecting Cr(vi). The mechanism worked by combining Cr(vi) with a primary amine of AgNCs@PEI causing electrostatic interaction, which led to the aggregation of AgNCs, as well as fluorescence quenching. Compared with other fluorescence sensors of Cr(vi) detection, this probe shows excellent performances: (i) The fluorescence probe responds immediately after adding Cr(vi). (ii) The fluorescence quenching efficiency of AgNCs@PEI was linearly related to the concentration of Cr(vi) over the range from 0.5 nM to 25 μM. (iii) The limit of detection is as low as 0.05 nM. (iv) High selectivity for Cr(vi) in 14 types of normal metal ions were obtained and especially the probe can be applied in both acidic and alkaline conditions (pH 2.0–11.0). (v) The probe can be used for the determination of Cr(vi) in real samples with satisfactory results. Therefore, the fluorescence probe is of practical significance and application prospects.

An electrochemical sensor based on fullerene nanorods for the detection of paraben, an endocrine disruptor by Jahangir Ahmad Rather; Abir Jumaa Al Harthi; Emad A. Khudaish; Ahsanulhaq Qurashi; Abdul Munam; Palanisamy Kannan (5690-5700).
In the present work, fullerene nanorods (C60NRs) were synthesized by liquid–liquid interface and characterized using Fourier transform infrared (FTIR) spectroscopy, field emission electron microscopy (FESEM) and X-ray diffraction (XRD) techniques. The C60NRs were covalently immobilized on the surface of a glassy carbon electrode (GCE) using surface bound diazonium salts as an interface. This method involves electrografting of the p-nitrophenyl diazonium salt at the GCE to give the nitrophenyl-modified electrode (GCE–Ph–NO2). The nitrophenyl groups of the GCE–Ph–NO2 modified electrode were reduced to phenylamine groups (GCE–Ph–NH2) using an aqueous solution of the sodium borohydride/gold–polyaniline (NaBH4/Au–PANI) system. The C60NRs were covalently immobilized on the surface of GCE–Ph–NH2via an N–H addition reaction across the π-bond of C60. The functionalized fullerene nanorod (C60NRs–NH–Ph–GCE) modified electrode was electrochemically reduced in 1.0 M potassium hydroxide (KOH) to produce a highly conductive electrochemically reduced fullerene nanorod (ERC60NRs–NH–Ph–GCE) sensor. The developed sensor shows high electrocatalytic activity for the detection of ethylparaben (EP) over a concentration range from 0.01–0.52 μM with a detection limit (LOD) of 3.8 nM (0.0038 μM). In addition, the ERC60NRs–NH–Ph–GCE sensor was also tested for EP in real sample analysis using the standard addition method where the total concentration of EP was found to be 0.011 μM (0.12%) within the permissible limit of 0.19%.

A silicon nanoparticle based turn off fluorescent sensor for sudan I by Ammu Rosin Jose; Unni Sivasankaran; Shalini Menon; Krishnapillai Girish Kumar (5701-5706).
Sudan dyes are synthetic colorants which were extensively used in food products before being banned due to their carcinogenic effect on living systems. To regulate their use and to ensure food quality, simple and cost effective methods need to be developed for their determination. A turn off fluorescence sensor based on hexadecylamine capped silicon nanoparticles (Si NPs) has been developed for the quantification of sudan I. The fluorescence of Si NPs was effectively quenched by sudan I via an inner filter effect (IFE). Under optimum conditions, this method can be used for the quantification of sudan I within the concentration range of 2.91 × 10−5 to 4.97 × 10−7 M with a detection limit of 3.90 × 10−8 M. The developed sensor was successfully applied for the determination of sudan I in chilli powder samples.

Quantitative analysis of vitamin K1 in fruits and vegetables by isotope dilution LC-MS/MS by Baifen Huang; Zhu Wang; Jianhua Yao; Xing Ke; Jiaojiao Xu; Xiao-Dong Pan; Xiaomin Xu; Meiling Lu; Yiping Ren (5707-5711).
A method has been developed for quantitative analysis of vitamin K1 in vegetables and fruits by LC-MS/MS. The method employed a neutral aluminum oxide column for sample clean-up. Considering matrix effects, an isotope standard (vitamin K1-D7) was added to correct matrix interferences, as well as pretreatment losses and instrument variability. Spiked recoveries in model matrices were 88.3–90.1% for spinach, 84–110% for lotus roots, and 108–115.6% for grapes. The relative standard deviations (RSDs) were 1.0–7.1% for intra-day and 2.8–8.8% for inter-day. The limit of detection (LOD) and limit of quantification (LOQ) were 0.001 mg kg−1 and 0.004 mg kg−1, respectively. The method is sensitive and reliable, which is successfully applied to different vegetable and fruit matrices. Vitamin K1 in fruit samples ranged from 0.008 mg kg−1 to 0.401 mg kg−1, and in vegetable samples from 0.0032 mg kg−1 to 3.973 mg kg−1.

Fabrication of a composite modified glassy carbon electrode: a highly selective, sensitive and rapid electrochemical sensor for silver ion detection in river water samples by Syaza Azhari; Palanivel Sathishkumar; Rahmalan Ahamad; Farediah Ahmad; Abdull Rahim Mohd Yusoff (5712-5721).
In this study, a glassy carbon electrode (GCE) was modified with multi-walled carbon nanotubes (MWCNTs), 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF6), N,N′-bis(2-hydroxyacetophenone)ethylenediamine (BZE) and Nafion to form a MWCNT-BZE-[bmim]PF6-Nafion-GCE. The electrochemical behaviour of the modified electrode with respect to silver (Ag(i)) ion detection was studied by cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV). Furthermore, the experimental parameters including the pH value of Britton–Robinson Buffer (BRB), Nafion, MWCNTs, BZE and ([bmim]PF6) concentrations and the deposition potential and time were optimized. The detection limit of the modified electrode for the Ag(i) ion was found to be 70 ng L−1 (6.49 × 10−10 mol L−1). Repetitive measurements revealed good reproducibility with a relative standard deviation (RSD) value of 0.4%. The system performance of the modified electrode was highly satisfactory and the recoveries for river water samples were found to be 96–121%. This study proved that the MWCNT-BZE-[bmim]PF6-Nafion-GCE is a highly selective and sensitive modified electrode for the detection of the Ag(i) ion in river water samples with good recovery value.

Raman microspectroscopic analysis of fibers in beverages by Alexandra C. Wiesheu; Philipp M. Anger; Thomas Baumann; Reinhard Niessner; Natalia P. Ivleva (5722-5725).
This technical note illustrates the applicability of Raman microspectroscopy (RM) for the analysis of the synthetic fiber content in different beverages (beer and mineral water). The particles and fibers were collected by filtration on a cellulose nitrate membrane filter (pore size = 0.45 μm) and subsequently identified and quantified by RM. Our results show no significant differences (p = 0.95) in the statistical distribution of fibers in beverage and blank samples, which suggests external contamination sources. Moreover, most of the identified fibers consisted of cellulose, which is a natural fiber and harmless compared to synthetic fibers. The other fibers identified were mainly made of polyethylene, which is used as a packaging material for the cellulose nitrate filter. Our study highlights the need for spectroscopic analysis as well as the use of adequate blank samples and an almost particle-free lab environment. Spectroscopic identification is crucial for the discrimination between cellulose and synthetic fibers; otherwise artefacts cannot be recognized and the interpretation will be misleading. The qualitative and quantitative analysis performed in our laboratory could not confirm the contamination of beverages with synthetic fibers reported by previous studies which relied on optical identification alone.

Correction: Simplifying microfluidic separation devices towards field-detection of blood parasites by S. H. Holm; J. P. Beech; M. P. Barrett; J. O. Tegenfeldt (5726-5726).
Correction for ‘Simplifying microfluidic separation devices towards field-detection of blood parasites’ by S. H. Holm et al., Anal. Methods, 2016, 8, 3291–3300.

Back cover (5727-5728).