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Analytica Chimica Acta (v.674, #2)

Editorial Board (pp. i).

A compact portable flow analysis system for the rapid determination of total phosphorus in estuarine and marine waters by Brady S. Gentle; Peter S. Ellis; Peter A. Faber; Michael R. Grace; Ian D. McKelvie (pp. 117-122).

The development and evaluation of a portable flow analysis system for the in situ determination of total phosphorus is described. The system has been designed with rapid underway monitoring in mind. The system employs an ultra-violet photo-reactor and thermal heating for peroxodisulfate digestion of total phosphorus to orthophosphate, followed by spectrophotometric detection with a multi-reflective flow cell and low-power light emitting diode using the molybdenum blue method. Reagents are stored under gas pressure and delivered using software controlled miniature solenoid valves. The fully automated system has a throughput of 115 measurements per hour, a detection limit of 1μgPL⁻¹, and gives a linear response over the calibration range of 0–200μgPL⁻¹ ( r²=0.9998), with a precision of 4.6% RSD at 100μgPL⁻¹ ( n=10). Field validation of the instrument and method was performed in Port Philip and Western Port Bays in Victoria, SE Australia, where 2499 analyses were performed over a 25h period, over a cruise path of 285km. Good agreement was observed between determinations of samples taken manually and analysed in the laboratory and those measured in situ with the flow analysis system.

Keywords: Flow analysis; Phosphorus; Nutrient monitoring; Natural waters

Tutorial on evaluation of type I and type II errors in chemical analyses: From the analytical detection to authentication of products and process control by M.C. Ortiz; L.A. Sarabia; M.S. Sánchez (pp. 123-142).

Uncertainty is inherent in all experimental determinations. Nevertheless, these measurements are used to make decisions including the performance of the own measurement systems. The link between the decision and the true implicit system that generates the data (measurement system, production process, category of samples, etc.) is a representation of this uncertainty as a probability distribution. This representation leads to the probabilistic formalization of the possibility of making errors. In the context of regulations established by official agencies, it is important to use these statistical decision methods in some cases because the own norm makes them mandatory and, in general, because this is the way of reasonably evaluating whether a working hypothesis is rejected on the basis of the experimental data.The aim of the present tutorial is to introduce some ideas and basic methods for the critical analysis of experimental data. With this goal, the basic elements of the Neyman–Pearson theory of hypothesis testing are formally introduced in connection with the common problems in chemical analysis and, if this is the case, their relation to the norms of regulatory agencies. The notion of decision with ‘enough quality’ is modelled when explicitly considering: (1) the null, H₀, and alternative, H₁, hypotheses. (2) The significance level of the test, which is the probability, α, of rejecting H₀ when it is true, and the power of the test, 1− β, β being the probability of accepting H₀ when it is false. (3) The difference between H₀ and H₁ that has to be detected with experimental data. (4) The needed sample size. These four concepts should be explicitly defined for each problem and, under the usual assumption of normal distribution of the data, the mathematical relations among these concepts are shown, which allow the analyst to design a decision rule with pre-set values of α and β.To illustrate the unifying character of this inferential methodology, several situations are exposed along the tutorial: the design of a hypothesis test to decide on the performance characteristics of analytical methods, the capability of detection of both quantitative and qualitative analytical methods (including its generalization to the case of multivariate and/or multiway signals), the analytical sensitivity with multivariate signals, the class-modelling and the process control.

Keywords: Capability of detection; Decision limit; Multivariate analytical sensitivity; False compliance/noncompliance; False positive/negative; Class-modeling; Shewhart control charts

Uranium determination using atomic spectrometric techniques: An overview by Juracir S. Santos; Leonardo S.G. Teixeira; Walter N.L. dos Santos; Valfredo A. Lemos; Jose M. Godoy; Sérgio L.C. Ferreira (pp. 143-156).

This review focuses on the determination of uranium using spectroanalytical techniques that are aimed at total determination such as flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ETAAS), inductively coupled plasma optical emission spectrometry (ICP-OES); and inductively coupled plasma mass spectrometry (ICP-MS) that also enables the determination of uranium isotopes. The advantages and shortcomings related to interferences, precision, accuracy, sample type and equipment employed in the analysis are taken into account, as well as the complexity and costs (i.e., acquisition, operation and maintenance) associated with each of the techniques. Strategies to improve their performance that employ separation and/or preconcentration steps are considered, with an emphasis given to solid-phase extraction because of its advantages compared to other preconcentration procedures.

Keywords: Uranium determination; Spectroanalytical techniques

Magnetic solids in analytical chemistry: A review by K. Aguilar-Arteaga; J.A. Rodriguez; E. Barrado (pp. 157-165).

Magnetic solids are widely used in detection and analytical systems because of the performance advantages they offer compared to similar solids that lack magnetic properties. These solids can be used to pre-concentrate analytes and for the magnetic separation and molecular identification of biomolecules, and organic and inorganic species. Magnetic solid separation techniques also offer benefits over centrifugation, filtration, and solid-phase extraction. In this review, we describe the synthesis, characterization and applications of a series of solids including silica supports, carbon nanotubes, alumina, organic polymers and other materials, mostly containing magnetite or paramagnetic metals. Also addressed are the future perspectives of magnetic solid applications.

Keywords: Magnetic solids; Synthesis; Characterization; Separation; Pre-concentration; Biomolecules; Organic; Inorganic

Quantification of organic acids in beer by nuclear magnetic resonance (NMR)-based methods by J.E.A. Rodrigues; G.L. Erny; A.S. Barros; V.I. Esteves; T. Brandão; A.A. Ferreira; E. Cabrita; A.M. Gil (pp. 166-175).

The organic acids present in beer provide important information on the product's quality and history, determining organoleptic properties and being useful indicators of fermentation performance. NMR spectroscopy may be used for rapid quantification of organic acids in beer and different NMR-based methodologies are hereby compared for the six main acids found in beer (acetic, citric, lactic, malic, pyruvic and succinic). The use of partial least squares (PLS) regression enables faster quantification, compared to traditional integration methods, and the performance of PLS models built using different reference methods (capillary electrophoresis (CE), both with direct and indirect UV detection, and enzymatic essays) was investigated. The best multivariate models were obtained using CE/indirect detection and enzymatic essays as reference and their response was compared with NMR integration, either using an internal reference or an electrical reference signal (Electronic REference To access In vivo Concentrations, ERETIC). NMR integration results generally agree with those obtained by PLS, with some overestimation for malic and pyruvic acids, probably due to peak overlap and subsequent integral errors, and an apparent relative underestimation for citric acid. Overall, these results make the PLS-NMR method an interesting choice for organic acid quantification in beer.

Keywords: Beer; Organic acids; Quantification; NMR; ERETIC; Partial least squares (PLS)

Development of a sensitive and selective Riboflavin sensor based on carbon ionic liquid electrode by Afsaneh Safavi; Norouz Maleki; Hamid Ershadifar; Fariba Tajabadi (pp. 176-181).

The electrochemical properties of Riboflavin adsorbed on carbon ionic liquid electrode (CILE) were studied by cyclic voltammetry. A film with a surface coverage of up to 3.3×10⁻⁹molcm⁻² was formed after 10min exposure time. Electron transfer coefficient and rate constant of electron transfer across the modified electrode were found to be 0.43 and 3.03s⁻¹, respectively. Differential pulse voltammetry was used for the determination of Riboflavin. Two linear working ranges of 0.8–110nM and 0.11–1.0μM were obtained with correlation coefficients of 0.998 and 0.996, respectively. The experimental detection limit was obtained as 0.1nM. The relative standard deviation for five replicate analyses was 4.7%. Other soluble vitamins had no significant interferences and the electrode was used for the determination of Riboflavin in pharmaceutical products, nutrition and beverages.

Keywords: Riboflavin; Sensor; Electrochemical determination; Carbon ionic liquid electrode

Ultra-sensitive voltammetric sensor for trace analysis of carbamazepine by Alfredina Veiga; Ana Dordio; A.J. Palace Carvalho; Dora Martins Teixeira; Jorge Ginja Teixeira (pp. 182-189).

A multi-walled carbon nanotubes (MWCNTs) film-coated glassy carbon electrode (GCE) was used for the voltammetric determination of carbamazepine (CBZ). The results showed that this simple modified electrode exhibited excellent electrocatalytic activity towards the oxidation of CBZ. The voltammetric response of CBZ at this film-modified electrode increased significantly when compared with that at a bare glassy carbon electrode and the sensor response was reproducible. The proposed method was applied to the quantification of CBZ in wastewater samples, collected in a municipal wastewater treatment plant, and in pharmaceutical formulations. The developed methodology yields results in accord with those obtained by chromatographic techniques commonly used in the quantification of pharmaceutical compounds in real samples. Good recoveries have been obtained and the limits of detection and quantification (40 and 140nM, respectively) are among the lowest that have been reported to date for this pharmaceutical compound using voltammetric techniques.

Keywords: Carbamazepine; Multi-walled carbon nanotubes (MWCNTs); Voltammetric determination; Environmental samples; Pharmaceutical formulations

Molecularly imprinted polymer layer-coated silica nanoparticles toward dispersive solid-phase extraction of trace sulfonylurea herbicides from soil and crop samples by Yan Peng; Ying Xie; Jing Luo; Li Nie; Yun Chen; Lina Chen; Shuhu Du; Zhongping Zhang (pp. 190-200).

This paper reports the preparation of metsulfuron-methyl (MSM) imprinted polymer layer-coated silica nanoparticles toward analysis of trace sulfonylurea herbicides in complicated matrices. To induce the selective occurrence of surface polymerization, the polymerizable double bonds were first grafted at the surface of silica nanoparticles by the silylation. Afterwards, the MSM templates were imprinted into the polymer-coating layer through the interaction with functional monomers. The programmed heating led to the formation of uniform MSM-imprinted polymer layer with controllable thickness, and further improved the reproducibility of rebinding capacity. After removal of templates, recognition sites of MSM were exposed in the polymer layers. As a result, the maximum rebinding capacity was achieved with the use of optimal grafting ratio. There was also evidence indicating that the MSM-imprinted polymer nanoparticles compared with nonimprinted polymer nanoparticles had a higher selectivity and affinity to four structure-like sulfonylurea herbicides. Moreover, using the imprinted particles as dispersive solid-phase extraction (DSPE) materials, the recoveries of four sulfonylurea herbicides determined by high-performance liquid chromatography (HPLC) were 80.2–99.5%, 83.8–102.4%, 77.8–93.3%, and 73.8–110.8% in the spiked soil, rice, soybean, and corn samples, respectively. These results show the possibility that the highly selective separation and enrichment of trace sulfonylurea herbicides from soil and crop samples can be achieved by the molecular imprinting modification at the surface of silica nanoparticles.

Keywords: Molecular imprinting; Dispersive solid-phase extraction; Programmed heating; Nanosilica; Sulfonylurea herbicides; Trace analysis

Dispersive liquid–liquid microextraction based on the solidification of floating organic droplet for the determination of polychlorinated biphenyls in aqueous samples by Liping Dai; Jing Cheng; Guzalnur Matsadiq; Lu Liu; Jun-Kai Li (pp. 201-205).

In the proposed method, an extraction solvent with a lower toxicity and density than the solvents typically used in dispersive liquid–liquid microextraction was used to extract seven polychlorinated biphenyls (PCBs) from aqueous samples. Due to the density and melting point of the extraction solvent, the extract which forms a layer on top of aqueous sample can be collected by solidifying it at low temperatures, which form a layer on top of the aqueous sample. Furthermore, the solidified phase can be easily removed from the aqueous phase. Based on preliminary studies, 1-undecanol was selected as the extraction solvent, and a series of parameters that affect the extraction efficiency were systematically investigated. Under the optimized conditions, enrichment factors for PCBs ranged between 494 and 606. Based on a signal-to-noise ratio of 3, the limit of detection for the method ranged between 3.3 and 5.4ngL⁻¹. Good linearity, reproducibility and recovery were also obtained.

Keywords: Polychlorinated biphenyls; Floating organic droplet; 1-Undecanol; Gas chromatography; Water analysis

Application of dispersive liquid–liquid microextraction and spectrophotometric detection to the rapid determination of rhodamine 6G in industrial effluents by Pourya Biparva; Elias Ranjbari; Mohammad Reza Hadjmohammadi (pp. 206-210).

A rapid and effective preconcentration method for extraction of rhodamine 6G was developed by using a dispersive liquid–liquid microextraction (DLLME) prior to UV–vis spectrophotometry. In this extraction method, a suitable mixture of acetone (disperser solvent) and chloroform (extractant solvent) was injected rapidly into a conical test tube containing aqueous solution of rhodamine 6G. Therefore, a cloudy solution was formed. After centrifugation of the cloudy solution, sedimented phase was evaporated, reconstituted with methanol and measured by UV–vis spectrophotometry. Different operating variables such as type and volume of extractant solvent, type and volume of disperser solvent, pH of the sample solution, salt concentration and extraction time were investigated. The optimized conditions (extractant solvent: 300μL of chloroform, disperser solvent: 3mL of acetone, pH: 8 and without salt addition) resulted in a linear calibration graph in the range of 5–900ngmL⁻¹ of rhodamine 6G in initial solution with R²=0.9988 ( n=5). The Limits of detection and quantification were 2.39 and 7.97ngmL⁻¹, respectively. The relative standard deviation for 50 and 250ngmL⁻¹ of rhodamine 6G in water were 2.88% and 1.47% ( n=5), respectively. Finally, the DLLME method was applied for determination of rhodamine 6G in different industrial waste waters.

Keywords: Dispersive liquid–liquid microextraction; Rhodamine 6G; Waste water samples; Spectrophotometry

Extraction and separation of a lysine-rich protein by formation of supramolecule between crown ether and protein in aqueous two-phase system by Tatsuya Oshima; Akinori Suetsugu; Yoshinari Baba (pp. 211-219).

The macrocyclic calixarenes and crown ethers have recently been found to form hydrophobic complexes with the cationic protein cytochrome c (Cyt- c), by recognizing lysine residues on the protein surface. In the present study, it was found that the distribution of cytochrome c in Li₂SO₄/PEG aqueous two-phase system (ATPS) can be controlled by complexation with the crown ether dicyclohexano-18-crown-6 (DCH18C6). The protein was quantitatively extracted into the PEG-rich phase in the presence of DCH18C6 and perchlorate ion. Of various crown ethers and their analogues that were investigated, only DCH18C6 was able to extract cytochrome c into the PEG-rich phase. Extraction of cytochrome c in the ATPS using DCH18C6 is complete within 5min. Cytochrome c complexed with DCH18C6 in the PEG-rich phase was quantitatively recovered into a salt-rich phase using K₂SO₄ by ion exchange of potassium ion and cationic protein in the cationic protein complex with DCH18C6. Selective extraction of cationic proteins was demonstrated in the ATPS. Under optimum conditions, the lysine-rich protein cytochrome c was selectively extracted over other cationic proteins using DCH18C6.

Keywords: Crown ether; Protein; Separation; Aqueous two-phase system; Molecular recognition; Cytochrome; c

Infrared chemical imaging: Spatial resolution evaluation and super-resolution concept by Marc Offroy; Yves Roggo; Peyman Milanfar; Ludovic Duponchel (pp. 220-226).

Chemical imaging systems help to solve many challenges in various scientific fields. Able to deliver rapid spatial and chemical information, modern infrared spectrometers using Focal Plane Array detectors (FPA) are of great interest. Considering conventional infrared spectrometers with a single element detector, we can consider that the diffraction-limited spatial resolution is more or less equal to the wavelength of the light (i.e. 2.5–25μm). Unfortunately, the spatial resolution of FPA spectroscopic setup is even lower due to the detector pixel size. This becomes a real constraint when micron-sized samples are analysed. New chemometrics methods are thus of great interest to overcome such resolution drawback, while keeping our far-field infrared imaging spectrometers. The aim of the present work is to evaluate the super-resolution concept in order to increase the spatial resolution of infrared imaging spectrometers using FPA detectors. The main idea of super-resolution is the fusion of several low-resolution images of the same sample to obtain a higher-resolution image. Applying the super-resolution concept on a relatively low number of FPA acquisitions, it was possible to observe a 30% decrease in spatial resolution.

Keywords: Super-resolution; Chemometrics; Infrared imaging; Focal plane array detector; Spatial resolution

Use of multiple colorimetric indicators for paper-based microfluidic devices by Wijitar Dungchai; Orawon Chailapakul; Charles S. Henry (pp. 227-233).

We report here the use of multiple indicators for a single analyte for paper-based microfluidic devices (μPAD) in an effort to improve the ability to visually discriminate between analyte concentrations. In existing μPADs, a single dye system is used for the measurement of a single analyte. In our approach, devices are designed to simultaneously quantify analytes using multiple indicators for each analyte improving the accuracy of the assay. The use of multiple indicators for a single analyte allows for different indicator colors to be generated at different analyte concentration ranges as well as increasing the ability to better visually discriminate colors. The principle of our devices is based on the oxidation of indicators by hydrogen peroxide produced by oxidase enzymes specific for each analyte. Each indicator reacts at different peroxide concentrations and therefore analyte concentrations, giving an extended range of operation. To demonstrate the utility of our approach, the mixture of 4-aminoantipyrine and 3,5-dichloro-2-hydroxy-benzenesulfonic acid, o-dianisidine dihydrochloride, potassium iodide, acid black, and acid yellow were chosen as the indicators for simultaneous semi-quantitative measurement of glucose, lactate, and uric acid on a μPAD. Our approach was successfully applied to quantify glucose (0.5–20mM), lactate (1–25mM), and uric acid (0.1–7mM) in clinically relevant ranges. The determination of glucose, lactate, and uric acid in control serum and urine samples was also performed to demonstrate the applicability of this device for biological sample analysis. Finally results for the multi-indicator and single indicator system were compared using untrained readers to demonstrate the improvements in accuracy achieved with the new system.

Keywords: Paper-based microfluidics devices; Colorimetric detection; Microfluidic paper analytical devices

A novel and specific fluorescence reaction for uracil by Takayuki Shibata; Shin-ya Kawasaki; Jun-ya Fujita; Tsutomu Kabashima; Masaaki Kai (pp. 234-238).

Facile and specific methods to quantify a nucleobase in biological samples are of great importance for diagnosing disorders in nucleic acid metabolism. In the present study, a novel fluorogenic reaction specific for uracil has been developed. The reaction was carried out in an alkaline medium containing benzamidoxime and K₃[Fe(CN)₆] which were heated for 2.0min. Under the optimum reaction conditions, strong fluorescence was produced only from uracil, not from other many biogenic compounds tested such as cytosine, thymine, adenine, guanine, nucleobases, nucleosides, nucleotides, amino acids, saccharides, creatine, creatinine and urea. The sensitivity of this method was compared with a known fluorogenic reaction using phenacylbromide which does not react with uracil but reacts with cytosine, adenine and their analogues. The proposed uracil-specific reaction showed approximately 400-fold higher sensitivity than the phenacylbromide reaction. The lower detection limit of uracil by the present method was 100pmolmL⁻¹, and a good linearity of the calibration curve was obtained up to 100nmolmL⁻¹ uracil. Due to its high sensitivity and specificity, the quantitative determination of uracil was possible by the proposed fluorimetric method.

Keywords: Fluorescence reaction; Benzamidoxime; Uracil specificity; High sensitivity; Pyrimidine metabolism

Determination of glutathione content in grape juice and wine by high-performance liquid chromatography with fluorescence detection by Lucija Janeš; Klemen Lisjak; Andreja Vanzo (pp. 239-242).

A modified preparation of sample was developed for the determination of glutathione content in grape juice and wine by high-performance liquid chromatography with fluorescence detection, using on-line pre-column derivatization. Ice-cold deoxygenated methanol was used to deactivate the oxidation enzymes in juices or wines and keep the glutathione stable. The optimum recovery of glutathione content in grape juice and wine was obtained when either the sample of grape juice or wine was mixed in ice-cold deoxygenated methanol in the ratio 10:90 (v:v) and further diluted in sodium acetate buffer in the ratio 1:1 (v:v). The optimized method was validated for linearity, limit of detection, limit of quantification, precision and uncertainty. According to the validation data the method is appropriate for the determination of glutathione content in grape juice and wine. Glutathione contents in grape juices made from White Muscat grapes and Sauvignon Blanc wines were analysed. The average glutathione content in 28 young Sauvignon Blanc wines was 12.5mgL⁻¹.

Keywords: Glutathione; High-performance liquid chromatography with fluorescence detection; Pre-column derivatization; Wine; Grape juice

Polymeric ionic liquid as a dynamic coating additive for separation of basic proteins by capillary electrophoresis by Jing Li; Haifeng Han; Qing Wang; Xia Liu; Shengxiang Jiang (pp. 243-248).

A simple and economical capillary electrophoresis method has been developed for the analysis of four model basic proteins by employing a polymeric ionic liquid (PIL), poly(1-vinyl-3-butylimidazolium) bromide, as the dynamic coating additive. When a small amount of PIL was present in the background electrolyte, a cationic coating on the inner surface of fused-silica capillary was established. These PIL modified capillaries not only generated a stable reversed electroosmotic flow, but also effectively eliminated the wall adsorption of proteins. Several important parameters such as the PIL concentration in the background electrolyte, pH values and concentrations of the background electrolyte were optimized to improve the separation of basic proteins. Consequently, under the optimum conditions, a satisfied separation of basic proteins with peak efficiencies ranging from 247,000 to 540,000 (platesm⁻¹) had been accomplished within 11min. The run-to-run RSDs ( n=3) of the migration times for the four basic proteins were all less than 0.37%.

Keywords: Capillary electrophoresis; Dynamic coating; Reversed electroosmotic flow; Polymeric ionic liquid; Proteins

Enantioselective analysis of ofloxacin and ornidazole in pharmaceutical formulations by capillary electrophoresis using single chiral selector and computational calculation of their inclusion complexes by Khaldun M. Al Azzam; Bahruddin Saad; Rohana Adnan; Hassan Y. Aboul-Enein (pp. 249-255).

A capillary electrophoretic method for the separation of the enantiomers of both ofloxacin and ornidazole is described. Several parameters affecting the separation were studied, including the type and concentration of chiral selector, buffer pH, voltage and temperature. Good chiral separation of the racemic mixtures was achieved in less than 16min with resolution factors Rs=5.45 and 6.28 for ofloxacin and ornidazole enantiomers, respectively. Separation was conducted using a bare fused-silica capillary and a background electrolyte (BGE) of 50mM H₃PO₄–1M tris solution; pH 1.85; containing 30mgmL⁻¹ of sulfated-β-cyclodextrin (S-β-CD). The separation was carried out in reversed polarity mode at 25°C, 18kV, detection wavelength at 230nm and using hydrodynamic injection for 15s. Acceptable validation criteria for selectivity, linearity, precision, and accuracy were studied. The limits of detection (LOD) and limits of quantitation (LOQ) of the enantiomers (ofloxacin enantiomer 1 (OF-E1), ofloxacin enantiomer 2 (OF-E2), ornidazole enantiomer 1 (OR-E1) and ornidazole enantiomer 2 (OR-E2)) were (0.52, 0.46, 0.54, 0.89) and (1.59, 1.40, 3.07, 2.70) μgmL⁻¹, respectively. The proposed method was successfully applied to the assay of enantiomers of both ofloxacin and ornidazole in pharmaceutical formulations. The computational calculations for the enantiomeric inclusion complexes rationalized the reasons for the different migration times between the ofloxacin and ornidazole enantiomers.

Keywords: Capillary electrophoresis; Ofloxacin; Ornidazole; Enantiomers; Pharmaceutical formulations; Computational calculations

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Analytica Chimica Acta (v.674, #2)